ECSS E HB 32 22A Insert Design Handbook
ECSS E HB 32 22A Insert Design Handbook
ECSS E HB 32 22A Insert Design Handbook
20 March 2011
Space engineering
Insert design handbook
ECSS Secretariat
ESA-ESTEC
Requirements & Standards Division
Noordwijk, The Netherlands
ECSSEHB3222A
20March2011
Foreword
ThisHandbookisonedocumentoftheseriesofECSSDocumentsintendedtobeusedassupporting
material for ECSS Standards in space projects and applications. ECSS is a cooperative effort of the
EuropeanSpaceAgency,nationalspaceagenciesandEuropeanindustryassociationsforthepurpose
ofdevelopingandmaintainingcommonstandards.
This handbook has been prepared by the ECSSEHB3222 Working Group, reviewed by the ECSS
ExecutiveSecretariatandapprovedbytheECSSTechnicalAuthority.
Disclaimer
ECSSdoesnotprovideanywarrantywhatsoever,whetherexpressed,implied,orstatutory,including,
butnotlimitedto,anywarrantyofmerchantabilityorfitnessforaparticularpurposeoranywarranty
that the contents of the item are errorfree. In no respect shall ECSS incur any liability for any
damages,including,butnotlimitedto,direct,indirect,special,orconsequentialdamagesarisingout
of,resultingfrom,orinanywayconnectedtotheuseofthisdocument,whetherornotbasedupon
warranty,businessagreement,tort,orotherwise;whetherornotinjurywassustainedbypersonsor
propertyorotherwise;andwhetherornotlosswassustainedfrom,oraroseoutof,theresultsof,the
item,oranyservicesthatmaybeprovidedbyECSS.
Publishedby: ESARequirementsandStandardsDivision
ESTEC,P.O.Box299,
2200AGNoordwijk
TheNetherlands
Copyright: 2011bytheEuropeanSpaceAgencyforthemembersofECSS
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Change log
ECSSEHB3222A Firstissue.
20March2011
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Table of contents
1 Scope.....................................................................................................................27
2 References ............................................................................................................28
5 Insert......................................................................................................................70
5.1 General..................................................................................................................... 70
5.2 Types........................................................................................................................ 70
5.2.1 General....................................................................................................... 70
5.2.2 Group A ...................................................................................................... 70
5.2.3 Group B ...................................................................................................... 72
5.2.4 Group C ...................................................................................................... 72
5.2.5 Potting methods.......................................................................................... 73
5.2.6 Injection ...................................................................................................... 73
5.3 Sizes......................................................................................................................... 74
5.3.1 General....................................................................................................... 74
5.3.2 Standards ................................................................................................... 74
5.3.3 Strength ...................................................................................................... 75
5.3.4 Standardised diameters.............................................................................. 76
5.3.5 Standardised heights.................................................................................. 77
5.4 Materials................................................................................................................... 78
5.4.1 General....................................................................................................... 78
5.4.2 Aluminium alloys......................................................................................... 79
5.4.3 Titanium alloys............................................................................................ 79
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5.4.4 Steels.......................................................................................................... 80
5.4.5 Material selection........................................................................................ 80
5.5 Surface protection .................................................................................................... 80
5.5.1 General....................................................................................................... 80
5.5.2 Aluminium alloy .......................................................................................... 81
5.6 References ............................................................................................................... 82
5.6.1 General....................................................................................................... 82
5.6.2 ECSS standards ......................................................................................... 82
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7.3 Effective potting radius, or equivalent dimension ................................................... 100
7.3.1 Minimum value ......................................................................................... 101
7.3.2 Average value........................................................................................... 101
7.3.3 Relationship of minimum and average values.......................................... 102
7.4 Real potting radius, or equivalent dimension.......................................................... 103
7.4.1 Minimum value ......................................................................................... 103
7.4.2 Average value........................................................................................... 103
7.4.3 Relationship between minimum and average values ............................... 103
7.5 Potting height ......................................................................................................... 104
7.5.1 Full potting ................................................................................................ 104
7.5.2 Partial potting............................................................................................ 105
7.5.3 Minimum value ......................................................................................... 105
7.5.4 Average value........................................................................................... 105
7.5.5 Relationship of minimum and average values.......................................... 105
7.6 Potting mass........................................................................................................... 107
7.6.1 Effect of core and insert characteristics.................................................... 107
7.6.2 Total mass of insert system...................................................................... 109
7.7 References ............................................................................................................. 109
7.7.1 General..................................................................................................... 109
7.7.2 ECSS standards ....................................................................................... 109
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8.4.2 Load transfer ............................................................................................ 121
8.4.3 External load cases .................................................................................. 121
8.4.4 Example.................................................................................................... 123
8.4.5 Purpose of the potting compound............................................................. 128
8.4.6 Design guidelines ..................................................................................... 128
8.5 Remarks ................................................................................................................. 129
8.5.1 General..................................................................................................... 129
8.5.2 Antiplane theories..................................................................................... 129
8.5.3 Higher-order theories................................................................................ 130
8.5.4 ESAComp ............................................................................................... 130
8.6 References ............................................................................................................. 131
8.6.1 General..................................................................................................... 131
8.6.2 ECSS standards ....................................................................................... 133
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10.4.2 Minimum value ......................................................................................... 150
10.5 Adequate insert design........................................................................................... 151
10.5.1 Insert arrangement ................................................................................... 151
10.5.2 Typical spacecraft design ......................................................................... 151
10.5.3 Examples.................................................................................................. 152
10.6 Selection of inserts ................................................................................................. 152
10.6.1 General..................................................................................................... 152
10.6.2 Sufficient static strength ........................................................................... 153
10.6.3 Safety factor ............................................................................................. 154
10.7 Minimum and average insert capability .................................................................. 154
10.7.1 Minimum ................................................................................................... 154
10.7.2 Average .................................................................................................... 155
10.8 Pre-design .............................................................................................................. 155
10.8.1 Load path for in-plane forces.................................................................... 156
10.8.2 Load path for transverse forces................................................................ 158
10.8.3 Transverse and in-plane load interaction ................................................. 159
10.8.4 Proximity and edge effects ....................................................................... 159
10.9 Failure modes......................................................................................................... 159
10.9.1 General..................................................................................................... 159
10.9.2 Failures under out-of-plane loads............................................................. 160
10.9.3 Failures under in-plane loads ................................................................... 165
10.10 References ............................................................................................................. 167
10.10.1 General..................................................................................................... 167
12 Tensile strength................................................................................................172
12.1 Normal tensile load................................................................................................. 172
12.1.1 General..................................................................................................... 172
12.1.2 Failure modes........................................................................................... 172
12.1.3 Shear rupture: core surrounding the potting............................................. 173
12.1.4 Tensile rupture: core underneath the potting............................................ 174
12.1.5 Tensile rupture: potting underneath the insert.......................................... 175
12.2 Basic parameters ................................................................................................... 175
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12.2.1 Out-of-plane loads: Insert strength ........................................................... 178
12.3 Minimum and average design values ..................................................................... 180
12.3.1 Overview................................................................................................... 180
12.3.2 Minimum insert design values .................................................................. 180
12.3.3 Average insert values ............................................................................... 181
12.4 Safety factors ......................................................................................................... 182
12.4.1 Load capability.......................................................................................... 182
12.4.2 Failure modes........................................................................................... 183
12.5 Permissible tensile loads ........................................................................................ 183
12.5.1 General..................................................................................................... 183
12.5.2 Insert capability graphs............................................................................. 183
12.5.3 Design values ........................................................................................... 183
12.6 Influence of insert height ........................................................................................ 184
12.6.1 Insert capability graphs............................................................................. 184
12.6.2 Different insert heights.............................................................................. 184
12.7 Composite face sheet............................................................................................. 186
12.7.1 Effect of anisotropy................................................................................... 186
12.7.2 Loading by moments ................................................................................ 186
12.8 References ............................................................................................................. 186
12.8.1 General..................................................................................................... 186
13 Compressive strength......................................................................................187
13.1 Normal compressive load ....................................................................................... 187
13.1.1 General..................................................................................................... 187
13.1.2 Partially-potted inserts .............................................................................. 187
13.1.3 Potting strength ........................................................................................ 187
13.1.4 Increased face sheet thickness ................................................................ 187
13.1.5 Insert capabilities...................................................................................... 188
13.2 Permissible compressive loads .............................................................................. 188
13.2.1 Graphs of permissible static insert loads.................................................. 188
13.3 Composite face sheet............................................................................................. 188
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14.3.1 Strength .................................................................................................... 192
14.3.2 Face sheets .............................................................................................. 195
14.3.3 CFRP face sheets .................................................................................... 195
14.3.4 Effect of panel layout ................................................................................ 200
14.3.5 Sensitivity of insert strength in face sheets .............................................. 201
14.3.6 Effect of thin CFRP face sheet ................................................................. 202
14.4 References ............................................................................................................. 203
14.4.1 General..................................................................................................... 203
15 Bending strength..............................................................................................204
15.1 Bending load .......................................................................................................... 204
15.2 Permissible bending load ....................................................................................... 205
15.3 Composite face sheet............................................................................................. 206
15.4 References ............................................................................................................. 207
15.4.1 General..................................................................................................... 207
17 Combined loads................................................................................................211
17.1 Inclined load ........................................................................................................... 211
17.2 General load combinations..................................................................................... 212
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18.4.1 General..................................................................................................... 217
19 Insert groups.....................................................................................................218
19.1 Two inserts: Loaded in same direction ................................................................... 218
19.1.1 General..................................................................................................... 218
19.1.2 Close inserts............................................................................................. 218
19.1.3 Distant inserts........................................................................................... 219
19.1.4 Effect of load............................................................................................. 219
19.2 Two inserts: Loaded in opposite directions ............................................................ 220
19.2.1 General..................................................................................................... 220
19.2.2 Close inserts............................................................................................. 221
19.2.3 Distant inserts........................................................................................... 221
19.3 Series of inserts: Loaded in same direction ........................................................... 221
19.3.1 Overview................................................................................................... 221
19.3.2 First and last inserts ................................................................................. 221
19.3.3 Intermediate inserts .................................................................................. 222
19.3.4 Example.................................................................................................... 222
19.4 Series of inserts: Loaded in opposite directions ..................................................... 223
19.4.1 Overview................................................................................................... 223
19.4.2 First and last insert ................................................................................... 224
19.4.3 Intermediate inserts .................................................................................. 224
19.5 Insert groups: Loaded in same direction ................................................................ 224
19.5.1 General..................................................................................................... 224
19.5.2 Equal and equidistant inserts ................................................................... 224
19.6 Composite face sheets........................................................................................... 226
19.6.1 Out-of-plane loading ................................................................................. 226
19.6.2 In-plane loaded inserts ............................................................................. 226
19.7 References ............................................................................................................. 226
19.7.1 General..................................................................................................... 226
20 Stiffness ............................................................................................................228
20.1 Introduction............................................................................................................. 228
20.1.1 Overview................................................................................................... 228
20.1.2 Rotational stiffness ................................................................................... 228
20.1.3 In-plane stiffness ...................................................................................... 228
20.1.4 Out-of-plane stiffness ............................................................................... 228
20.2 Analysis and test .................................................................................................... 229
20.2.1 General..................................................................................................... 229
20.2.2 Analysis .................................................................................................... 229
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20.2.3 Testing...................................................................................................... 229
20.2.4 Comparison of analysis and test values ................................................... 229
20.2.5 Composite face sheets ............................................................................. 230
20.3 References ............................................................................................................. 230
20.3.1 General..................................................................................................... 230
21 Fatigue...............................................................................................................231
21.1 Insert fatigue life ..................................................................................................... 231
21.1.1 General..................................................................................................... 231
21.1.2 Potting ...................................................................................................... 231
21.1.3 Honeycomb core ...................................................................................... 231
21.2 Core local stress: Normal loads to plane................................................................ 232
21.2.1 General..................................................................................................... 232
21.2.2 Core circular stress................................................................................... 232
21.2.3 Example.................................................................................................... 233
21.3 Load-stress sequence: Constant amplitude ........................................................... 236
21.3.1 General..................................................................................................... 236
21.3.2 Mean stress ratio ...................................................................................... 236
21.3.3 Maximum peak load ................................................................................. 237
21.4 Load-stress sequence: Spectra of constant amplitude........................................... 237
21.4.1 General..................................................................................................... 237
21.4.2 Example.................................................................................................... 237
21.5 Fatigue life: Constant load amplitude ..................................................................... 237
21.5.1 Fatigue damage........................................................................................ 237
21.5.2 Fatigue life ................................................................................................ 238
21.5.3 Re-evaluation of core strength variation................................................... 239
21.5.4 Insert fatigue life: Metallic cores ............................................................... 240
21.5.5 Insert fatigue life: Non-metallic cores ....................................................... 251
21.6 Fatigue damage accumulation ............................................................................... 252
21.7 Non-metallic core ................................................................................................... 252
21.8 Composite face sheets........................................................................................... 254
21.9 References ............................................................................................................. 254
21.9.1 General..................................................................................................... 254
21.9.2 ECSS standards ....................................................................................... 255
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22.1.3 Mechanical loading after exposure to a thermal environment .................. 256
22.1.4 Mechanical loading after thermal cycling.................................................. 256
22.2 Thermal: Reduction of permissible load ................................................................. 258
22.2.1 Effect on permissible loads....................................................................... 258
22.2.2 Coefficient of thermal degradation............................................................ 258
22.3 Other conditions ..................................................................................................... 259
22.4 Composite face sheets........................................................................................... 260
22.4.1 In-plane load under thermal conditions .................................................... 260
22.5 References ............................................................................................................. 260
22.5.1 General..................................................................................................... 260
22.5.2 ECSS standards ....................................................................................... 260
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23.6.5 Pull-out strength test................................................................................. 269
23.7 Proof load ............................................................................................................... 270
23.8 Inspection ............................................................................................................... 270
23.9 Repair..................................................................................................................... 271
23.9.1 General..................................................................................................... 271
23.9.2 Undamaged core or face-sheet ................................................................ 271
23.9.3 Damaged core and face sheet ................................................................. 272
23.9.4 Replace or reposition inserts .................................................................... 272
23.10 Defects ................................................................................................................... 273
23.10.1 Poor storage of potting compound ........................................................... 273
23.10.2 Poor potting compound distribution .......................................................... 274
23.10.3 Poor positioning of insert .......................................................................... 275
23.10.4 Oversized bore hole size .......................................................................... 276
23.11 References ............................................................................................................. 276
23.11.1 General..................................................................................................... 276
23.11.2 ECSS standards ....................................................................................... 277
25 Potting ...............................................................................................................284
25.1 General................................................................................................................... 284
25.1.1 Environmental conditions ......................................................................... 284
25.1.2 Face sheet protection ............................................................................... 284
25.1.3 Degreasing of inserts................................................................................ 284
25.2 Manufacturing process ........................................................................................... 284
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25.3 Potting compounds................................................................................................. 285
25.3.1 Flow characteristics .................................................................................. 285
25.3.2 Resin system: Shur-Lok SLE 3010........................................................... 286
25.3.3 Potting foam: Lekutherm X227+T3........................................................... 286
25.3.4 Other potting materials ............................................................................. 286
25.4 References ............................................................................................................. 287
25.4.1 General..................................................................................................... 287
25.4.2 ECSS standards ....................................................................................... 288
26 Incoming inspection.........................................................................................289
26.1 Tests....................................................................................................................... 289
26.1.1 Material specifications .............................................................................. 289
26.1.2 Additional tests ......................................................................................... 289
26.2 Honeycomb core .................................................................................................... 289
26.2.1 Core properties......................................................................................... 289
26.2.2 Insert strength........................................................................................... 290
26.3 Potting resin ........................................................................................................... 290
26.3.1 Strength .................................................................................................... 290
26.3.2 Hardness .................................................................................................. 291
26.4 Composite face sheets........................................................................................... 291
26.4.1 Material characteristics............................................................................. 291
26.4.2 Composite laminate properties................................................................. 291
26.4.3 Consumables............................................................................................ 292
26.5 References ............................................................................................................. 292
26.5.1 General..................................................................................................... 292
26.5.2 ECSS standards ....................................................................................... 292
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27.4.1 Radiography ............................................................................................. 299
27.5 Composite face sheets........................................................................................... 299
27.6 References ............................................................................................................. 300
27.6.1 General..................................................................................................... 300
27.6.2 ECSS standards ....................................................................................... 300
29 Testing...............................................................................................................310
29.1 General................................................................................................................... 310
29.2 Insert static strength tests ...................................................................................... 310
29.2.1 Out-of-plane tests ..................................................................................... 310
29.2.2 In-plane tests ............................................................................................ 311
29.2.3 Bending tests............................................................................................ 314
29.2.4 Torsion tests ............................................................................................. 314
29.3 Geometric effects: Insert static strength tests ........................................................ 315
29.3.1 Edge distance........................................................................................... 315
29.3.2 Insert proximity ......................................................................................... 315
29.4 Dynamic tests......................................................................................................... 317
29.4.1 Sinusoidal loads ....................................................................................... 317
29.4.2 Static residual strength test ...................................................................... 317
29.5 References ............................................................................................................. 318
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29.5.1 General..................................................................................................... 318
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Annex F Case studies ...........................................................................................374
F.1 Introduction............................................................................................................. 374
F.2 ARIANE 1 Equipment Bay...................................................................................... 376
F.3 ARIANE 4 Equipment Bay...................................................................................... 377
F.4 ASAP 4................................................................................................................... 383
F.5 ASAP 5................................................................................................................... 388
F.6 ROSETTA Lander .................................................................................................. 392
F.7 SPOT 5................................................................................................................... 398
F.8 UMS ....................................................................................................................... 401
F.9 SILEX ..................................................................................................................... 403
F.10 HRG ....................................................................................................................... 410
F.11 NILESAT ................................................................................................................ 413
F.12 EXAMPLE: Insert verification ................................................................................. 417
F.13 References ............................................................................................................. 421
Annex G Formulae.................................................................................................422
G.1 Introduction............................................................................................................. 422
G.2 Nomenclature ......................................................................................................... 422
G.3 List of mathematical formulae ................................................................................ 425
Figures
Figure 4-1: Insert system: Components ................................................................................. 67
Figure 4-2: Insert system: Summary of loading modes.......................................................... 69
Figure 5-1: Typical insert........................................................................................................ 72
Figure 5-2: Standardised insert diameter ............................................................................... 76
Figure 5-3: Standardised insert height ................................................................................... 77
Figure 5-4 Preferred set of insert heights............................................................................... 78
Figure 6-1: Sandwich and core: designation .......................................................................... 84
Figure 6-2: Face sheet properties: Isotropic, anisotropic and quasi-isotropic
characteristics...................................................................................................... 85
Figure 6-3: Possible failures modes: Anisotropic face sheets under shear-loading............... 87
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Figure 6-4: Core strength: Deviation (%) of actual strength from guaranteed values ............ 90
Figure 7-1: Potting geometry.................................................................................................. 99
Figure 7-2: Effective potting radius as a function of insert diameter .................................... 102
Figure 7-3: Real potting radius as a function of insert diameter........................................... 104
Figure 7-4: Potting height as a function of the honeycomb core height ............................... 106
Figure 7-5: Mean weight of potting masses versus core height and insert diameter ........... 107
Figure 7-6: Correction coefficient for weight of insert heights .............................................. 108
Figure 8-1: Schematic of structural sandwich panel subjected to both in-plane and out-
of-plane external loading ................................................................................... 110
Figure 8-2: Sign conventions for sandwich beam element................................................... 112
Figure 8-3: Deformed sandwich beam element: deflection contributions from both
bending and shearing ........................................................................................ 113
Figure 8-4 Shearing deformation of sandwich beam element.............................................. 114
Figure 8-5: Failure modes: Honeycomb core sandwich panels ........................................... 116
Figure 8-6: Schematic of 'local bending effects in sandwich beam subjected to 3-point
bending .............................................................................................................. 118
Figure 8-7: Schematic of potted insert types for sandwich panels used for spacecraft
applications........................................................................................................ 121
Figure 8-8: Model definition of sandwich plate with through-the-thickness insert............... 122
Figure 8-9: Example: Lateral displacements of a symmetric sandwich plate with insert
subjected to compressive out-of-plane load ...................................................... 124
Figure 8-10: Example: Core stress components of symmetric sandwich plate with insert
subjected to out-of-plane compressive force ..................................................... 125
Figure 8-11: Example: Radial bending moment resultants in face sheets of symmetric
sandwich plate with insert subjected to out-of-plane compressive force ........... 127
Figure 9-1: Basic aspects of insert design, analysis and testing.......................................... 136
Figure 9-2: Insert load cases................................................................................................ 137
Figure 9-3: Insert out-of-plane load ...................................................................................... 137
Figure 9-4: Insert in-plane load ............................................................................................ 138
Figure 10-1: Typical insert arrangements............................................................................. 140
Figure 10-2: Insert load conditions ....................................................................................... 142
Figure 10-3: Sandwich panel with metallic face sheets: General design rules .................... 144
Figure 10-4: Insert design under in-plane load..................................................................... 145
Figure 10-5: Insert design loaded by moments .................................................................... 145
Figure 10-6: CFRP face sheets: Effect of small chamfer on insert flange on load
transfer to face sheet ......................................................................................... 146
Figure 10-7: Insert mounting modes .................................................................................... 148
Figure 10-8: Connections ..................................................................................................... 150
Figure 10-9: Selection of inserts: Partially potted................................................................. 153
Figure 10-10: Selection of inserts: Through-the-thickness................................................... 153
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Figure 10-11: Pre-design: Through-the-thickness insert under bending .............................. 157
Figure 10-12: Pre-design: Face sheet shear-out failure mode............................................. 158
Figure 10-13: Pre-design: Through-the-thickness insert under transverse force ................. 159
Figure 10-14: Failure modes: Moment load ......................................................................... 160
Figure 10-15: Failure modes: Load transfer in out-of-plane case ........................................ 161
Figure 10-16: Failure modes: Insert as a function of core height ......................................... 162
Figure 10-17: Failure modes: Non-correlation between number of the filled cells and
number of the failing cell walls........................................................................... 163
Figure 10-18: Failure modes: Unsymmetrical potting and crossed cell................................ 164
Figure 10-19: Failure modes: In-plane and torsion loads..................................................... 165
Figure 10-20: Failure modes: CFRP face sheets ................................................................. 166
Figure 11-1: Flow chart: Predefined sandwich and loads .................................................... 169
Figure 11-2: Flow chart: Variable main parameters ............................................................. 170
Figure 12-1: Failure modes in relation to the core height..................................................... 173
Figure 12-2: Out-of-plane capability: Contributions of the main components on
improved core shear .......................................................................................... 179
Figure 12-3: Out-of-plane capability: Contributions of the main components on
improved core tension ....................................................................................... 180
Figure 12-4: Influence of insert height on insert capability ................................................... 185
Figure 13-1: Compressive strength: Protruding insert.......................................................... 189
Figure 14-1: Shear-loaded inserts: Clamping conditions ..................................................... 190
Figure 14-2: Correlation between calculated and tested in-plane capabilities with fibre
orientation .......................................................................................................... 193
Figure 14-3: Correlation between calculated and tested in-plane capabilities with fibre
strength.............................................................................................................. 194
Figure 14-4: Nomenclature: Ultimate in-plane load against failure in tension ...................... 196
Figure 14-5: Shear strength: Stress concentration factor..................................................... 197
Figure 14-6: Shear strength: Failure angle........................................................................... 198
Figure 14-7: Shear strength: Critical stresses for intracellular buckling (dimpling) under
uniaxial compression ......................................................................................... 199
Figure 14-8: Shear strength: Influence of edge distance ..................................................... 201
Figure 14-9: In-plane capability: Contributions of the main components on improved
core shear.......................................................................................................... 202
Figure 15-1: Inserts loaded in bending: Clamping conditions .............................................. 205
Figure 15-2: Bending load: Schematic of load-transfer ........................................................ 206
Figure 15-3:Bending load: Insert footprint on moment loading ............................................ 207
Figure 16-1: Torsional load: Nomenclature .......................................................................... 209
Figure 17-1: Insert submitted to an inclined load ................................................................. 211
Figure 18-1: Edge distance: Effect on insert static strength capability................................. 215
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Figure 19-1: Insert groups: Reduced insert capability - two adjacent inserts loaded in
the same direction ............................................................................................. 220
Figure 19-2: Insert groups: Series of inserts loaded in same direction ................................ 222
Figure 19-3 Insert groups: series of inserts loaded in opposite directions ........................... 223
Figure 19-4: Insert groups: Interference coefficient for a group of equal and equidistant
inserts ................................................................................................................ 225
Figure 21-1: Static strength values with core height ............................................................ 233
Figure 21-2: Schematic: Design load spectrum ................................................................... 236
Figure 21-3: Insert fatique life: Insert diameter 9 mm........................................................... 243
Figure 21-4: Insert fatique life: Insert diameter 11 mm......................................................... 245
Figure 21-5: Insert fatique life: Insert diameter 14 mm......................................................... 247
Figure 21-6: Insert fatique life: Insert diameter 17.5 mm...................................................... 249
Figure 21-7: Insert fatique life: Insert diameter 22.5 mm...................................................... 251
Figure 21-8: Fatigue life: Non-metallic GFRP core .............................................................. 253
Figure 21-9: Fatigue life: Non-metallic Nomex core ........................................................... 254
Figure 22-1: Thermal effects: Reduction of insert capability ................................................ 257
Figure 22-2: Thermal effects: Reduction of potting resin strength ....................................... 258
Figure 22-3: Thermal effects: Coefficient of thermal degradation ........................................ 259
Figure 23-1: Basic manufacturing sequence........................................................................ 263
Figure 23-2: Inserts with connected potting mass................................................................ 264
Figure 23-3: Venting of non-perforated core ........................................................................ 265
Figure 23-4: Reference sample: Pull-out strength test specimen ........................................ 270
Figure 23-5: Insert repair: Geometry .................................................................................... 272
Figure 24-1: Sandwich panel machining: Combined drill and punch tool............................. 279
Figure 24-2 Sandwich panel machining: Series of single tools and their uses .................... 280
Figure 27-1: Manufacture control: Out-of-plane test fixture for tension (pull-out) tests ........ 295
Figure 27-2: Manufacture control: Out-of-plane test fixture for compression or fatigue
tests ................................................................................................................... 296
Figure 27-3: Manufacture control: In-plane test fixture for shear Bending test .................... 297
Figure 27-4: Manufacture control: Bending test fixture ........................................................ 298
Figure 27-5: Manufacture control: Torsion test fixture.......................................................... 298
Figure 28-1: QA: Poor potting causing strength degradation ............................................... 304
Figure 28-2: QA: Honeycomb core - incoming inspection.................................................... 307
Figure 28-3: QA: Core density correction factor for degree of expansion ............................ 308
Figure 29-1: Testing: Insert static out-of-plane strength fixture............................................ 311
Figure 29-2: Testing: Insert static in-plane strength fixture .................................................. 312
Figure 29-3: Testing: ASTM insert static in-plane strength fixture ....................................... 313
Figure 29-4: Testing: Bending fixture ................................................................................... 314
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Figure 29-5: Testing: Edge distance fixture.......................................................................... 315
Figure 29-6: Testing: Insert proximity tensile fixture............................................................. 316
Figure 29-7: Testing: Insert proximity tensile-compression fixture ....................................... 316
Figure 29-8: Testing: Determination of points for residual strength test............................... 318
Figure A-1 : Carbon fibre tube inserts: Comparison of design principles ............................. 323
Figure A-2 : Carbon fibre tube inserts: Fitting of spreadable CFRP tube............................. 324
Figure A-3 : Carbon fibre tube insert: Type 1 cap ................................................................ 325
Figure A-4 : Carbon fibre tube insert: Type 2 cap ................................................................ 325
Figure A-5 : Carbon fibre tube insert: Type 2 insert cap and carbon fibre sleeve ................ 326
Figure C-1 : Fully potted insert ............................................................................................. 333
Figure C-2 : Partially potted insert........................................................................................ 336
Figure D-1 Out-of-plane loading: Circular sandwich plate with through-the-thickness
insert .................................................................................................................. 346
Figure D-2 : Partially potted insert: out-of-plane loading ...................................................... 349
Figure E-1 : Manufacture control: Insert tensile pull-out test fixture ..................................... 364
Figure F-1 : Case study: ARIANE 1 equipment bay / ASAP 4 - tensile (pull-out) test
method............................................................................................................... 376
Figure F-2 : Case study: ARIANE 4 Case 1 ......................................................................... 378
Figure F-3 : Case study: ARIANE 4 Case 2 ......................................................................... 379
Figure F-4 : Case study: ARIANE 4 - tensile (pull-out) test method..................................... 380
Figure F-5 : Case study: ARIANE 4 - shear test method ..................................................... 380
Figure F-6 : Case study: ASAP 4 (AR4) 1............................................................................ 384
Figure F-7 : Case study: ASAP 4 (AR4) 2............................................................................ 384
Figure F-8 : Case study: ASAP 4 (AR4) - tensile (pull-out) method A.................................. 385
Figure F-9 : Case study: ASAP 4 (AR4) - tensile (pull-out) method B.................................. 386
Figure F-10 : Case study: ASAP 5 ....................................................................................... 389
Figure F-11 : ROSETTA Lander: Two structural components ............................................. 392
Figure F-12 : ROSETTA Lander: Tension-compression, shear, bending and torsion
tests ................................................................................................................... 393
Figure F-13 : Carbon fibre tube insert (type 2): With cap for unilateral fixing....................... 396
Figure F-14 : Carbon fibre tube inserts: Definition of the critical insert failure load, Fc......... 397
Figure F-15 : Case study: SPOT 5 - Case ........................................................................... 399
Figure F-16 : Case study: SPOT 5 - Structure I/F platform .................................................. 400
Figure F-17 : Case study: UMS - SST 1............................................................................... 402
Figure F-18 : Case study: UMS - SST 2............................................................................... 402
Figure F-19 : Case study: SILEX - insert.............................................................................. 404
Figure F-20 : Case study: SILEX GEO MPCS insert ........................................................ 405
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Figure F-21 : Case study: HRG - Insert................................................................................ 411
Figure F-22 : Case study: HRG - Test method..................................................................... 413
Figure F-23 : Case study: NILESAT battery 1...................................................................... 415
Figure F-24 : Case study: NILESAT battery 2...................................................................... 416
Figure F-25 : Example: Insert verification dimensions ...................................................... 417
Figure H-1 : Test fixture: Tension-compression load master drawing............................... 438
Figure H-2 : Test fixture: Tension-compression load part 1 .............................................. 439
Figure H-3 : Test fixture: Tension-compression load part 2 .............................................. 440
Figure H-4 : Test fixture: Tension-compression load part 3 .............................................. 441
Figure H-5 : Test fixture: Tension-compression load part 4 .............................................. 442
Figure H-6 : Test fixture: Tension-compression load part 5 .............................................. 443
Figure H-7 : Test fixture: Tension-compression load part 6 .............................................. 444
Figure H-8 : Test fixture: Tension-compression load part 7 .............................................. 445
Figure H-9 : Test fixture: In-plane shear load master drawing .......................................... 446
Figure H-10 : Test fixture: In-plane shear load part 1........................................................ 447
Figure H-11 : Test fixture: In-plane shear load part 2........................................................ 448
Figure H-12 : Test fixture: In-plane shear load part 3........................................................ 449
Figure H-13 : Test fixture: In-plane shear load part 4........................................................ 450
Figure H-14 : Test fixture: In-plane shear load part 5........................................................ 451
Figure H-15 : Test fixture: In-plane shear load part 6........................................................ 452
Figure H-16 : Test fixture: In-plane shear load part 7........................................................ 453
Figure H-17 : Test fixture: In-plane shear load part 8........................................................ 454
Figure H-18 : Test fixture: Bending master drawing.......................................................... 456
Figure H-19 : Test fixture: Bending part 1 ......................................................................... 457
Figure H-20 : Test fixture: Bending part 2 ......................................................................... 458
Figure H-21 : Test fixture: Bending part 3 ......................................................................... 459
Figure H-22 : Test fixture: Bending part 4 ......................................................................... 460
Figure H-23 : Test fixture: Bending part 5 ......................................................................... 461
Figure H-24 : Test fixture: Bending part 6 ......................................................................... 462
Figure H-25 : Test fixture: Bending part 7 ......................................................................... 463
Figure H-26 : Test fixture: Bending part 8 ......................................................................... 464
Figure H-27 : Test fixture: Bending part 9 ......................................................................... 465
Figure H-28 : Test fixture: Bending part 10 ....................................................................... 466
Figure H-29 : Test fixture: Bending parts 11, 12 and 13 ................................................... 467
Figure H-30 : Test fixture: Bending part 14 ....................................................................... 468
Figure H-31 : Test fixture: Torsion master drawing ........................................................... 470
Figure H-32 : Test fixture: Torsion part 1 .......................................................................... 471
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Figure H-33 : Test fixture: Torsion part 2 .......................................................................... 472
Figure H-34 : Test fixture: Torsion part 3 .......................................................................... 473
Figure H-35 : Test fixture: Torsion part 4 .......................................................................... 474
Figure H-36 : Test fixture: Torsion part 5 .......................................................................... 475
Figure H-37 : Test fixture: Torsion part 6 .......................................................................... 476
Figure H-38 : Test fixture: Torsion part 7 .......................................................................... 477
Figure H-39 : Test fixture: Torsion part 8 .......................................................................... 478
Figure H-40 : Test fixture: Torsion part 9 .......................................................................... 479
Figure H-41 : Test fixture: Torsion part 10 ........................................................................ 480
Figure H-42 : Test fixture: Torsion part 11 ........................................................................ 481
Figure H-43 : Test fixture: Torsion part 12 ........................................................................ 482
Figure H-44 : Test fixture: Torsion part 13 ........................................................................ 483
Figure H-45 : Test fixture: Torsion part 14 ........................................................................ 484
Figure H-46 : Test fixture: Torsion part 15 ........................................................................ 485
Figure H-47 : Test fixture: Torsion part 16 ........................................................................ 486
Figure H-48 : Test fixture: Torsion part 17 ........................................................................ 487
Tables
Table 4-1: Insert system: General definition........................................................................... 68
Table 5-1: Types of inserts..................................................................................................... 71
Table 5-2: Potting methods .................................................................................................... 73
Table 5-3: List of insert standards .......................................................................................... 75
Table 5-4: Inserts: Aluminium alloy 'equivalents'.................................................................... 79
Table 5-5: Typical insert materials and surface protection..................................................... 81
Table 6-1: Effect of sandwich components on insert load-bearing capability......................... 83
Table 6-2: Failure mode and shear-load capability of tested CFRP face sheets ................... 88
Table 6-3: Mechanical properties of common aluminium alloy hexagonal-type cores ........... 91
Table 6-4: Mechanical properties of common non-metallic hexagonal-type cores ................ 92
Table 7-1: Example: Insert potting compounds for space applications .................................. 97
Table 7-2: Example: Effect of increased potting radius on insert tensile capability.............. 100
Table 9-1: Summary of the basic insert design parameters................................................. 135
Table 10-1: Failure modes of insert joint .............................................................................. 160
Table 12-1: Properties for determining potted insert capability: Tensile load....................... 176
Table 12-2: Perforated cores: Effective and real potting radius versus insert diameter....... 177
Table 12-3: Non-perforated cores: Effective and real potting radius versus insert
diameter............................................................................................................. 177
Table 12-4: Out-of-plane capability: Effect of components on core shear ........................... 179
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Table 12-5: Out-of-plane capability: Effect of components on core tension......................... 179
Table 14-1: In-plane capability: Effect of components on core shear .................................. 201
Table 20-1: Insert stiffness: SILEX test configuration .......................................................... 229
Table 20-2: Insert stiffness: Comparison of analysis and test.............................................. 230
Table 21-1: Fatigue: Stress concentration factors for local stress ....................................... 235
Table 21-2: Fatigue: Coefficients to determine peak load.................................................... 240
Table 21-3: Links to fatigue life data .................................................................................... 241
Table 21-4: Insert diameter 9 mm: Fatigue correction factors.............................................. 242
Table 21-5: Insert diameter 11 mm: Fatigue correction factors............................................ 244
Table 21-6: Insert diameter 14 mm: Fatigue correction factors............................................ 246
Table 21-7: Insert diameter 17.5 mm: Fatigue correction factors......................................... 248
Table 21-8: Insert diameter 22.5 mm: Fatigue correction factors......................................... 250
Table 23-1: Insert capability: Effect of poor storage of potting compound ........................... 273
Table 23-2: Insert capability: Effect of poor distribution of potting compound...................... 275
Table 23-3: Insert capability: Effect of poor positioning of insert.......................................... 275
Table 23-4: Insert capability: Effect of oversized bore hole.................................................. 276
Table 26-1: Incoming inspection: Potting resin strength tests.............................................. 291
Table 28-1: QA: Potting failure and detectability .................................................................. 304
Table 29-1: Testing: Dynamic test load levels and number of cycles .................................. 317
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Table F-2 : Case study: ARIANE 4 materials and configuration ....................................... 377
Table F-3 : Case study: ARIANE 4 equipment bay - Allowable tensile load ........................ 381
Table F-4 : Case study: ARIANE 4 equipment bay - Allowable shear load.......................... 382
Table F-5 : Case study: ASAP 4 materials and configuration ........................................... 383
Table F-6 : Case study: ASAP 4 - interference and edge effects......................................... 387
Table F-7 : Case study: ASAP 5 materials and configuration ........................................... 388
Table F-8 : Case study: ASAP 5 - Allowable tensile load..................................................... 390
Table F-9 : Case study: ASAP 5 - interference and edge effects......................................... 391
Table F-10 : Carbon fibre tube inserts: Out-of-plane tension ............................................... 395
Table F-11 : Carbon fibre tube inserts: Out-of-plane compression ...................................... 395
Table F-12 : Carbon fibre tube inserts: In-plane shear load................................................. 396
Table F-13 : Carbon fibre inserts: Weibull analysis criteria .................................................. 397
Table F-14 : Case study: SPOT 5 materials and configuration ......................................... 398
Table F-15 : No details given, [29-29]. Case study: UMS Materials and configuration ..... 401
Table F-16 : Case study: SILEX Materials and configuration............................................ 403
Table F-17 :Case study: SILEX - Allowable tensile load ...................................................... 406
Table F-18 : Case study: SILEX - Allowable shear load ...................................................... 407
Table F-19 : Case study: SILEX - Allowable bending moment ............................................ 408
Table F-20 : Case study: SILEX - Allowable torsion moment .............................................. 409
Table F-21 : Case study: HRG Materials and configuration.............................................. 410
Table F-22 : Case study: HRG - Tensile load ...................................................................... 412
Table F-23 : Case study: NILESAT materials and configuration....................................... 414
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1
Scope
The ECSSHB3222A recommends engineering inserts and practices for European programs and
projects. It may be cited in contracts and program documents as a reference for guidance to meet
specificprogram/projectneeds.
The target users of this handbook are engineers involved in the design, analysis and verification of
launchers and spacecraft in relation to insert usage. The current knowhow is documented in this
handbookinordertomakeexpertisetoallEuropeandevelopersofspacesystems.
Itisaguidelinesdocument,thereforeitincludesadvisoryinformationratherthanrequirements.
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2
References
Duetothestructureofthedocument,eachclauseatitsendcontainsthelistofreferencecalledupon.
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3
Terms, definitions and abbreviated terms
The following provides an explanation of the terms, acronyms and abbreviations used in this ECSS
handbook; they are not definitions. Terms are listed in alphabetical order and interposed with
explanationsoftheacronymsandabbreviationsusedinthehandbook.
A
AA
AluminiumAssociation,USA
ABASISDESIGNALLOWABLE(Avalue)
mechanicalpropertyvalueabovewhichatleast99%ofthepopulationofvaluesisexpectedto
fall,withaconfidencelevelof95%
[ECSSEST32]
ADHEREND
Plateadhesivelybondedtoanotherplate
[ECSSQ7071]
ADHESION
The state in which two surfacesare held together at an interface by forces or the interlocking
actionofanadhesiveorboth
ADHESIVE
Asubstancecapableofholdingtwosurfacestogether
NOTE: Used to retain carbonfibre tube inserts in sandwich panels instead of the
conventionalpottingcompoundsusedforstandardtypesofinserts
ADHESIVE(FILM)
Asyntheticresinadhesive,usuallyofthethermosettingtypeintheformofathinfilmofresin
with or without a fibrous carrier or support; used for bonding the face sheets of sandwich
panelstothecore
NOTE: Filmadhesivesusuallyhavesometacktoenabletheirplacementduringassembly.
ADHESIVE(FOAMING)
A synthetic resin adhesive, usually of the thermosetting type which when cured produces a
foamlikematerial.[See:ADHESIVE(SYNTACTIC)]
ADHESIVE(SYNTACTIC)
A synthetic resin adhesive, usually of the thermosetting type that contains a hollow filler
material, often in the form of small glass microballoons, which when cured producesa foam
likematerial
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NOTE: Thesetypesofmaterialsarewidelyusedasapottingcompoundforretaininginserts
insandwichpanels.
AECMA
Association Europen des Constructeurs Matriel Arospatiale; European Association of
AerospaceIndustries
AFNOR
AssociationFranaisdeNormalisation;Frenchnationalstandardsorganisation
AIR
Frenchstandardsorganisation
AISI
AmericanIronandSteelInstitute,USA
ALLOWABLELOAD
maximumloadthatcanbepermittedinastructuralpartforagivenoperatingenvironmentto
prevent rupture, collapse, detrimental deformation or unacceptable crack growth [ECSSP
001]]]
ALLOWABLESTRESS
The maximum stress that can be permitted in a structural part for a given operating
environment to prevent rupture, collapse, detrimental deformation or unacceptable crack
growth[ECSSP001]
ALLOWABLES
Material values that are determined from test data at the laminate or lamina level on a
probabilitybasis(e.g.AorBvalues),followingASTMorotherteststandardsacceptedbythe
finalcustomer.[Seealso:ABASISDESIGNALLOWABLE;BBASISDESIGNALLOWABLE;A
VALUE,BVALUE]
ALLOY
Mixtureofabasemetallicelementwithoneormoreothermetallicornonmetallicelements
ALODINE
Aproprietorychemicaloxidisingprocess,i.e.anonelectrolyticprocess,forsurfacetreatment
which results in an electrically conductive, chromated (mixedmetal, chromiumoxide) film,
typicallylessthan1mthick
ALUMINIUM(Al)
Metallic element, melting point 660C, density 2700 kg m3. Uses: ubiquitous aerospace alloy
base, important component in oxidation resistant alloys and coatings and as part of basic
strengtheningmechanismfornickelbasedsuperalloys
AMBIENT
1Thesurroundingenvironmentalconditions,e.g.pressure,temperatureorrelativehumidity
2 usual work place temperature and humidity environmental conditions, e.g. room
temperature
ANISOTROPIC
Havingmechanicalorphysicalpropertieswhichvaryindirectionrelativetonaturalreference
axesinthematerial
ARALDITE
Arangeofepoxybasedstructuraladhesives;developedbyCibaGeigy,nowVantico
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ARAMID
A type of highly oriented aromatic polymer material. Used primarily as a highstrength
reinforcing fibre, of which Kevlar 49 and Twaron HM are most commonly used in
aerospaceapplications
AREALWEIGHT
Ameasurementoftheweightperunitareaofafabricorfabricprepreg;expressedasg/m
ARIANE
FamilyofEuropeanlaunchvehicles
ASTM
AmericanSocietyforTestingandMaterials;USAstandardsorganisation
B
BBASISDESIGNALLOWABLE(Bvalue)
mechanicalpropertyvalueabovewhichatleast90%ofthepopulationofvaluesisexpectedto
fall,withaconfidencelevelof95%
[ECSSEST32]
BALANCEDLAMINATE
Whereplieswithpositiveanglesarebalancedbyequalplieswithnegativeangles.Whileangle
plylaminateshaveonlyonepairofmatchedangles,balancedlaminatescanhavemanypairs,
plus0and90degrees.Abalancedlaminateisorthotropicininplanebehaviour,butanisotropic
inflexuralbehaviour
BATCH
Materialsproducedduringauniquesequence:
1.Fibre:Theamountwhichisproducedbytheconversionofanumberofprecursortowsunder
standard, controlled, processingplant conditions in one continuous operation, including any
surfacetreatmentandsizingofthefibre
2.Prepreg:Aquantity,irrespectiveofwidth,thatisproducedundernochangeconditionsin
onecontinuousoperationoftheimpregnatingplantfromonebatchofresinmixandonebatch
of fibre. A batch is expected to conform to a fixed manufacturing process and to have
homogeneous properties within prescribed tolerances over its whole width and length. A
maximumallowablelengthforaprepregbatchissometimesspecified
3.Resin:Aquantityofresinineitherfilmorliquidformproducedfromonemixofresins,resin
modifiersandcuringagents
BIDIRECTIONALLAMINATE
A reinforced plastic laminate with the fibres oriented in two directions in the plane of the
laminate;acrosslaminate.[Seealso:UNIDIRECTIONALLAMINATE]
BLIND
Fasteners:Installedfromonesideofacomponentonly
BONDLINE
The area between two materials that have been adhesively bonded; includes the layer of
adhesivebetweentheadherends
BOREHOLE
Aholemachinedinasandwichpanelofasuitablesizetoacceptaninsert
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BS
Britishstandard,controlledbytheBritishStandardsInstitute(BSI)
BSI
BritishStandardsInstitute,UK
BUCKLING
1Unstabledisplacementofastructuralpart,suchasapanel,causedbyexcessivecompression
or shear. Microbuckling of fibres in a composite material can also occur under axial
compression
2 Fibre: a failure mechanism which occurs under compressive loads where the reinforcing
fibresinacompositearedisplacedtransversly;fibrebucklingmodesareknownasextension
modeandshearmode.
C
CADMIUM(Cd)
Metallicelement,meltingpoint321C,density8650kgm3,Uses:alloyingadditions,protective
coatings:NOTFORSPACEUSE
CARBON/EPOXY
Acompositematerialcomprisingofacarbonfibrereinforcementinanepoxypolymermatrix
CARBONFIBRE
Fibre produced by the pyrolysis of organic precursor fibres, such as rayon, polyacrylonitrile
(PAN)andpitch,inaninertenvironment.Thetermisoftenusedinterchangeablywiththeterm
graphite;carbonfibresandgraphitefibresdo,however,differ.Thebasicdifferenceslieinthe
temperature at which the fibres are made and heattreated, and in the amount of elemental
carbonproduced.Carbonfibrestypicallyarecarbonisedintheregionof1315Candassayat93
to95%carbon,whilegraphitefibresaregraphitisedat1900Cto2480Candassayatmorethan
99%elementalcarbon
CARBONFIBRETUBEINSERT
AnonstandardtypeofinsertdevelopedbyDLRfortheRosettaLanderproject,[Seealso:A.03;
F.06]
CASA
ConstruccionesAeronauticasSA,(E);nowEADSCASA
CATALYST
Asubstancethatchangestherateofachemicalreactionwithoutitselfundergoingpermanent
changeinitscomposition;asubstancethatmarkedlyspeedsupthecureofacompoundwhen
addedinaquantitysmallcomparedwiththeamountsofprimaryreactants
CEN
ComitEuropendeNormalisation(EuropeanCommitteeforStandardization)
CFRP
Carbon fibrereinforced plastic. Letter G in this handbook stands for Glass, whereas in
Americanpublicationsitisusedforgraphite.[Seealso:GFRP]
CIS
standardsorganisation,Russia
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COCURE
Simultaneouscuringandbondingofacompositelaminatetoanothermaterialorparts,suchas
honeycombcoreorstiffeners,eitherbyusingtheadhesivepropertiesofthecompositeresinor
byincorporatinganadhesiveintothecompositelayup
COLLECTEDVOLATILECONDENSABLEMATERIAL(CVCM)
quantityofoutgassedmatterfromatestspecimenthatcondensesonacollectormaintainedata
specifictemperatureforaspecifictime
NOTE: CVCM is expressed as a percentage of the initial specimen mass and is calculated
fromthecondensatemassdeterminedfromthedifferenceinmassofthecollectorplatebefore
andafterthetest.
[ECSSQST7002]
COMPOSITESANDWICHCONSTRUCTION
panels composed of a lightweight core material, such as honeycomb, foamed plastic, and so
forth, to which two relatively thin, dense, highstrength or highstiffness faces or skins are
adhered
[ECSSEST3208]
CORE
1Alightweightmaterialinbetweenthefacesheetsofasandwichpanel,e.g.honeycombcore,
foam.Metallicorcompositesheetmaterialsarebondedtothecoretoformasandwichpanel
2Coresareoftenclassedaseithermetallicornonmetallicandarecommerciallyavailableina
widerangeofmaterialsandconfigurations,e.g.honeycombwitharangeofcellsizesandfoil
thicknesses,withorwithoutperforations
CORE(HEXAGONAL)
Acorematerialinwhichtheshapeoftheindividualcellsishexagonal
CORE(METALLIC)
Anycorethatismadeofmetal,e.g.oftenmadeofanaluminiumalloy
CORE(NONMETALLIC)
Anycorethatismadeofamaterialotherthanmetal;usuallymadeofglassreinforcedplastic
(GFRP)orNomexforspaceapplications
CORE(NONPERFORATED)
Acorematerialinwhicheachofthecellsisnotconnectedtoitsneighbours;airtrappedwith
thecellsofasandwichpanelcannotbeventedeasilywhenplacedinvacuum
CORE(PERFORATED)
Acorematerialinwhicheachofthecellsisconnectedtoitsneighboursbyoneormoresmall
holes in the cell walls; enables the removal of air trapped with the cells of a sandwich panel
whenplacedinvacuum
CORESPLICE
A joint or the process of joining one type of core to another; usually achieved by adhesive
bondingusinganadhesivewithgapfillingproperties
CROSSLINKING
1Appliedtopolymermolecules,thesettingupofchemicallinksbetweenthemolecularchains.
When extensive, as in most thermosetting resins, crosslinking makes one infusible super
moleculeofallthechains
2Thechemicalreactionthatoccursinthermosettingpolymersduetotheheatappliedduring
thecure
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CROSSPLY
Compositescontainingpliesofmaterial,normallyprepreg,atanglesof0and90
CROSSPLYLAMINATE
Special laminate that contains only 0 and 90 plies. This bidirectional laminate is orthotropic
and has nearly zero Poissons ratio. The other simple bidirectional laminate is the angleply,
whichpossessesonepairofbalancedoffaxisplies
CTE
See:COEFFICIENTOFTHERMALEXPANSION
CTEMISMATCH
1 difference in coefficient of thermal expansion between two or more materials within a
specifiedtemperaturechange,e.g.polymersandmetals.[ECSSQ7071]
2Thedifferenceincoefficientofthermalexpansionbetweenareinforcementandthematrixor
a coating and substrate within a specified temperature rise, e.g. carbon fibre (low/zero CTE)
andAlalloy(large+veCTE)
CURE
1changingthepropertiesofapolymerbasedmaterialbychemicalreactionaccomplishedby
heatorcatalyst(orboth)andwithorwithoutpressure,e.g.resin,adhesive,coating.[ECSSQ
7071]
2 chemical reaction during which a liquid resin is transformed to a solid material by the
processofcrosslinking
CURECYCLE
1periodwithadistinctivetime,temperatureandpressureprofiletoobtainspecific
propertiesofapolymerbasedmaterial,e.g.resin,adhesive,orcoating.[ECSSQ7071]
2 he cure cycle can include defined heatup and cooldown rates, isothermal holds for
specified periods and application and removal of negative or positive pressures at defined
timesortemperatures
3pottingcompounds:Dependsonthechemicalformulationoftheresinusedforpottingandif
theresinorassemblycanbecuredatelevatedtemperaturewithoutcausingdamage;atypical
cure cycle for potted inserts, using a twopart epoxybased resin system, is several hours at
roomtemperature
CURINGTEMPERATURE
Temperatureatwhichacast,mouldedorextrudedproduct,aresinimpregnatedreinforcement
oranadhesiveissubjectedtocuring
CURINGTIME
Thelengthoftimeapartissubjectedtoheatorpressure,orboth,tocuretheresin;intervalof
timebetweentheinstantrelativemovementbetweenthemovingpartsofamouldceasesand
theinstantpressureisreleased
NOTE: Furthercurecantakeplaceafterremovaloftheassemblyfromtheconditionsofheat
orpressure.[See:POSTCURE]
CVCM
CollectedVolatileCondensableMatter
CYCLICLOADING
fluctuating load (or pressure) characterized by relative degrees of loadingandunloading of a
structure
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NOTE For example, loads due to transient responses, vibroacoustic excitation, flutter,
pressurecyclingandoscillatingorreciprocatingmechanicalequipment.
[ECSSEST3201]
D
DAMAGE
A structural degradation or anomaly caused by service conditions or by abnormal operation,
e.g.impactdamagecausedbydroppedtoolsorotherforeignobjects
DAMAGETOLERANCE
The ability of a material, component or structure to retain an acceptable level of structural or
environmentalresistancepropertiesundertheeffectsofoperationalconditions,withoutriskof
failinginacatastrophicmanner,[See:DAMAGETOLERANT]
DAMAGETOLERANCECONTROL
The application of design methodology, material and processing control, manufacturing
technology,andqualityassuranceprocedurestopreventprematurestructuralfailureduetothe
initiationorpropagationofflawordamageduringfabrication,testingandservicelife
DAMAGETOLERANT
characteristic of a structure for which the amount of general degradation or the size and
distribution of local defects expected during operation, or both, do not lead to structural
degradationbelowspecifiedperformance
ECSSEST3201]
DAN
DeutscheAirbusNorm;GermanAirbusstandard
DEBOND
General:adefectiveareaofanadhesivebondwheretheadherendsarenolongerheldtogether.
Anareaofseparationwithinorbetweenpliesinalaminate,orwithinabondedjoint,causedby
contamination, improper adhesion during processing, or damaging interlaminar stresses [See
also:DELAMINATION]:
1Adhesivebond:adelaminationbetweentheadherends
2Sandwichpanel:adelaminationthatoccursbetweenthecoreandthefacesheet;causedby
contaminationordamagetoeitherthefilmadhesiveusedtojointhefacesheetlaminatetothe
core,facesheetlaminateitself,bondareaofthecoreormechanicaldamagetocorecellwalls,by
crushingormorelocaldamage
DEFECT
A manufacturing anomaly (crack, void, delamination) created by processing, fabrication or
assemblyprocedures.[Seealso:FLAW]
DEGRADATION
reduction of material properties (e.g. mechanical, thermal or optical) that can result from
deviationsinmanufacturingorfromrepeatedloadingorenvironmentalexposure.[ECSSQ70
71]
DELAMINATION
Physicalseparationorlossofbondofthelayersofmaterialinalaminate;locallyoroverawide
area
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DESIGNALLOWABLE
Material values that are determined from test data at the laminate or lamina level on a
probabilitybasis(e.g.AorBvalues),followingASTMorotherteststandardsacceptedbythe
finalcustomer.[Seealso:ABASISDESIGNALLOWABLE;BBASISDESIGNALLOWABLE;A
VALUE,BVALUE]
DESIGNVALUES/PROPERTIES
Material, structuralelement and structural detail properties that have been determined from
test data and chosen to assure a high degree of confidence in the integrity of the completed
structure
DIELECTRIC
Amaterialinwhichtheelectricalconductivityiszeroornearzero
DIMPLING
Sandwichpanels:thedisplacementunderloadofthefaceskinsbetweenthecellularstructureof
ahoneycombcore
DIN
DeutschesInstitutfrNormung;Germannationalstandardsorganisation
DLR
DeutschenZentrumfrLuftundRaumfahrt.Germanaerospaceorganisation
E
EGLASS
Electrical glass; a grade of glass fibre. A borosilicate glass containing less than 1% alkali
(combined sodium and potassium oxides); the type most used for glass fibres for reinforced
plastics;suitableforelectricallaminatesbecauseofitshighresistivity
ECSS
European Cooperation for Space Standardization. A cooperative effort of the European Space
Agency, National Space Agencies and European industry associations for the purpose of
developingandmaintainingcommonstandards,[See:ECSSwebsite:www.ecss.nl)
EDGECLOSEOUT
[See:EDGECLOSURE]
EDGECLOSURE
Sandwich panels: Protects the core from accidental damage, serves as a moisture seal and
providesedgereinforcementtoenabletransferanddistributionofedgeattachmentloads;also
knownasedgecloseoutandedgemember
EDGEMEMBER
[See:EDGECLOSURE]
EDGEDISTANCE
Thedistancebetweenaninsert,ormorepreciselythecentrelineofthepotting,andtheedgeof
asandwichpanel
ELASTICMODULUS
Stiffness
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ELASTICRELATION
Fully reversible, singlevalue, stressstrain relation. Loading and unloading follow the same
path; there is no hysteresis, or residual strain. Although nonlinear relation is admissible, the
relationforcompositematerialsisessentiallylinear
ELEMENT
1 A part of a more complex structural member, e.g. skin, stringers, shear panels, sandwich
panels,jointsorsplices,GlossaryRef.[Ref1]
2 A composite of subsystems, capable of performing an operational role only in conjunction
with other elements, e.g. SpaceVehicle, Ground Segment, Space Station Pressurised Module,
GlossaryRef.[Ref1]
ELONGATION
Deformation caused by stretching; the fractional increase in length of a material stressed in
tension. (When expressed as percentage of the original gauge length, it is called percentage
elongation)
EMATVCargoCarrier
Engineering model, Automated transfer vehicle integrated cargo carrier for ISS; International
SpaceStation
EN
EuroNorme(Europeanstandard),[See:CEN]
ENN
ERNONorm;standarddevelopedbyMBBERNO(Bremen),nowAstriumGmbH
ENVIRONMENT
External, nonaccidental conditions (excluding mechanical loading), separately or in
combination, that can be expected in service life and that can affect the structure, e.g.
temperature,moisture,UVradiationandfuel
ENVISAT
Polar Platform ESA Polar Platform satellite to carry the Envisat1 Earthobservation
instruments.DesignedtolaunchonAriane5anduseESAsDataRelaySatellitesystemforthe
transmissionofdatatoEarth.
EOS
Earthobservationsatellite
EPOXY
1 General: A family of thermosetting resins made by polymerisation of epoxides or oxiranes
withothermaterialssuchasamines,alcohols,phenols,carboxylicacids,acidanhydrides,and
unsaturatedcompounds;usedforthematrixphaseofcompositesandstructuraladhesives
2 Potting compounds: usually twopart epoxy resin systems combined with a suitable filler
that,whencured,producesafoamlikematerial,[Seealso:ADHESIVE(SYNTACTIC)]
ESACOMP
A software package for the analysis and design of composite laminates and laminated
structural elements; developed for ESA/ESTEC by Helsinki University and distributed by
ComponeeringInc
ESTEC
EuropeanSpaceResearchandTechnologyCentre,Noordwijk,NL
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EXOTHERMIC
A type of chemical reaction that produces heat, e.g. can occur during the crosslinking, or
curing,ofpolymerbasedresins,suchasepoxy
F
FABRIC
Anymaterialofwovenconstruction
FACE
1Outerplyofalaminate.
2Coveringsheetsofasandwichpanel
FACESHEET
Acompositelaminateormetalsheetthatformstheexternalsurfacesofasandwichpanel
FACING
A sheet material, usually thin and made of composite or metal, that is attached to a core
materialtoformasandwichpanel;alsoknownasfacesheet
FACTOROFSAFETY
Theratioofthedesignorultimateloadstothelimitorappliedloads.[See:LOADS]
FAILURE(STRUCTURAL)
Therupture,collapse,seizure,excessivewearoranyotherphenomenonresultinginaninability
tosustainlimitloads,pressuresandenvironments
[ECSSEST32]
FASTENER
itemthatjoinsotherstructuralitemsandtransfersloadsfromonetotheotheracrossajoint
[ECSSEST3201]
FATIGUE
1 cumulative irreversible damage incurred by cyclic application of loads to materials and
structures
NOTE1Fatiguecaninitiateandextendcracks,whichdegradethestrengthofmaterialsand
structures.
NOTE2Examples of factors influencing fatigue behaviour of the material are the
environment,surfaceconditionandpartdimensions.
[ECSSEST3201]
2Progressivecrackingmechanismcausedbyalternatingstress
FATIGUELIFE
Thenumberofcyclesofdeformationrequiredtobringaboutfailureofthetestspecimenunder
agivensetofoscillatingconditions
FATIGUESTRENGTH
1 The maximum cyclic stress a material can withstand for a given number of cycles before
failureoccurs
2Theresidualstrengthofamaterialthathasbeensubjectedtofatigue
FATIGUESTRESSRATIO
Theratiooftheminimumtothemaximumfatiguestress,usuallydenotedbyR
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FAULT
Manufacturing: an error or departure from the intended specified process which results in a
defectivematerialorstructure
FE
Finiteelement
FEA
Finiteelementanalysis
FEM
Finiteelementmodelormodelling
FEDERAL
AnAmericanspecification
FIBRECONTENT
Percentvolumeoffibreinacompositematerial.Mostcommoncompositesinusetodayhavea
fibre content between 45 volume % and 70 volume %. Percent weight of mass of fibre is also
used
FIBRECONTROLLED
A laminate layup where the properties are largely determined by those of the fibre, e.g.
0/45/0/45/0
FIBREREINFORCEDPLASTIC(FRP)
Afibrereinforcedthermosettingorthermoplasticpolymermatrixcompositematerial
FILLER
1 Fabric: Yarn oriented at right angles to the warp in a woven fabric; also known as fill, [See
also:WEFT]
2 A material incorporated into a synthetic resin to modify the inherent viscosity and flow
characteristics,e.g.usuallyintheformofglassmicroballoonsforpottingcompoundsusedto
embedinsertsinsandwichpanels
FILMADHESIVE
Asyntheticresinadhesive,usuallyofthethermosettingtypeintheformofathinfilmofresin
withorwithoutafibrouscarrierorsupport.
NOTE: Filmadhesivesusuallyhavesometacktoenabletheirplacementduringassembly
FINISHING
Finalmanufacturingprocesseswhichresultinacomponentreadyforassembly.Oftenusedto
describeminormachiningorcleaningoperations
FLAW
A local discontinuity in a composite structure such as; a scratch, notch, crack, void,
delamination,ordebonding.
NOTE: Somefracturemodelsalsodefineanotchasaflaw,e.g.WEK[Seealso:DEFECT]
FLOW
1Themovementofresinunderpressure,enablingallpartsofamouldorcavitytobefilled,
e.g.flowofpottingcompoundaroundaninsertwheninjectedintoaborehole.
2 Flow or creep is the gradual but continuous distortion of a material under continued load,
oftenatelevatedtemperatures.
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FLUSH(MOUNTED)INSERT
Thepositioningofaninsertsuchthattheuppersurfaceoftheinsertislevel,orflush,withthe
surfaceoftheupperfacesheet
FOAMINGADHESIVE
A synthetic resin adhesive, usually of the thermosetting type which when cured produces a
foamlikematerial.[See:ADHESIVE(SYNTACTIC)]
FOOTPRINT
Theareaofthenut,collarortailofaninstalledmechanicalfastenerthatisincontactwiththe
substratematerial;bearingsurface
FRP
Fibrereinforcedplastic
FULLPOTTING
Themaximumpossiblepottingheightisidenticaltothecoreheight,c;alsoknownasblindor
borne
FULLYPOTTEDINSERT
Aninsertinwhichthepottingmaterialisincontactwiththeinsideofthebottomfacesheet,
G
GAUGELENGTH
Part of a test specimen in which the characteristics of the material are determined; often
instrumentedwithstraingauges,extensometers
GELPOINT
The stage at which a liquid begins to exhibit pseudoelastic properties, also conveniently
observedfromtheinflectionpointonaviscosityversustimeplot
NOTE: AlsocalledGELTIME
GELTIME
Theexposureperiodrequiredataprescribedtemperaturetoconverttheresinfromafluidtoa
definedpartialcurestage
NOTE: Resinflowduringcurecanonlyoccursubstantiallybeforegelling
GENERALISEDHOOKESLAW
The most general linear elastic stressstrain relation for an anisotropic material from which
materialswithvarioustypesofsymmetriescanbederived
GFRP
Glassfibrereinforcedplastic
NOTE: InthishandbookG=glass,butinUSpublicationsG=graphite.[Seealso:CFRP]
GLASSFIBRE
Reinforcement fibres of which E, R and S grades are normally used in composites for
aerospaceapplications
NOTE: Eglass:electricalgrade;RandS:highstrengthgrades
GLASSTRANSITIONTEMPERATURE(Tg)
The temperature at which increased molecular mobility results in significant changes in the
propertiesofacuredresinsystem
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GRP
Glass reinforced plastic; an industrial composite not a highperformance structural composite
foraerospaceapplications,[See:GFRP].Sometimesusedfortabsontheendsofsomecomposite
testspecimens
H
HARDENER
1 A substance or mixture added to a plastic composition to promote or control the curing
actionbytakingpartinit
2Asubstanceaddedtocontrolthedegreeofhardnessofthecuredfilm[Seealso:CATALYST]
HEXAGONALCORE
A core material in which the shape of the individual cells is hexagonal, e.g. aluminium
honeycombcore
HIGHMODULUSCARBONFIBRES(HM)
Arangeofcarbonfibreswhichhaveatensilemoduligreaterthan310GPa,typically
HIGHSTRENGTHCARBONFIBRES(HS)
Arangeofcarbonfibreswhichhavetensilestrengthsupto3500MPaandtensilemoduliinthe
rangeof200GPato255GPa,typically
HIGHTENACITYCARBONFIBRES(HT)
A range of carbon fibres which includes HS high strength fibres and VHS very high strength
fibres
HM
Highmodulus;arangeofcarbonfibresthatalsoincludesUHMultrahighmodulusfibres
HONEYCOMB
Manufactured product of resinimpregnated sheet material (paper, glass or aramidbased
fabric)orsheetmetalformedintohexagonalshapedcells;usedasacorematerialinsandwich
construction;alsoknownasNIDAinEurope
HONEYCOMBSANDWICH
A sandwich construction in which the core material between the face sheets has a hexagonal
cellularformthatresembleshoneycomb
HRG
HauteRsolutionGomtrique,themainpayloadoftheSPOT5earthobservationsatellite
NOTE: ThestructureissimilartoHRVandHRVIRonSPOT3andSPOT4,respectively.
HS
Highstrength;arangeofcarbonfibres
HT
High tenacity (high strength/high strain); a range of carbon fibres which includes HS high
strengthfibresandVHSveryhighstrengthfibres;alsoknownashightension
HYGROSCOPIC
Tendingtoabsorbmoisturefromtheair
HYGROTHERMAL
Thecombinationofmoistureandtemperature
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I
IATP
Insertallowabletestprogramme,conductedintwostagesIATP1andIATP2;anESAfunded
study
IDH
Insertdesignhandbook
ILSS
Interlaminarshearstrength
IM
1Intermediatemodulus;arangeofcarbonfibresthathavetensilemoduliintherangeof255
GPato310GPa,typically
2IntegrationModel
INHOUSE
Aprocessorteststandardcreatedandusedwithinaparticularorganisation;oftenconsidered
asconfidentialandsonotdisclosedtootherparties
INSERT
1 An integral part of a plastic moulding, consisting of metal or other material which can be
mouldedintopositionorpressedintothemouldingafterthemouldingiscomplete
2Afixingdeviceortypeoffastenersystem,commonlyusedinsandwichpanels
INSERT(FLUSH)
Aninsertpositionedsuchthatitssurfaceislevelwiththatofthefacesheet
INSERT(FLUSHMOUNTED)
An insert positioned in a sandwich panel such that the upper surface of the insert is level, or
flush,withthesurfaceoftheupperfacesheet
INSERT(OVERFLUSH)
Aninsertpositionedabovethesurfaceofthefacesheet;alsoknownasprotrudinginsert
INSERT(PROTRUDING)
Aninsertpositionedsuchthattheendoftheinsertextendsbeyondthesurfaceofthesandwich
panel;alsoknownasproudoroverflush
INSERT(SUBFLUSH)
Aninsertpositionedsuchthattheendoftheinsertisbelowthesurfaceofthefacesheet;also
knownasrecessedinsert
INSERT(THROUGHTHETHICKNESS)
Aninsertwhichpassesthroughtheentiresandwichpanelthicknessalsoknownastransverse,
doublesidedorspool.
INSERT(TYPE)
The various types of inserts can be grouped by the means that they are embedded into a
sandwichpanel:
(A)forsimultaneousbondingduringsandwichproduction,alsoknownascocure;
(B) for an existing sandwich using either a thermosetting resin (usual potting process of
standard inserts) or for nonstandards inserts by an equivalent bonding process, e.g. carbon
fibretubeinserts;
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(C)formechanicalclampingorscrewingintoanexistingsandwich.
INSPECTION
Averificationmethodforphysicalcharacteristicsthatdeterminescompliancewithrequirement
without the use of special laboratory equipment, procedures, items or services. Inspection
makesuseofstandardmethodstoverifyrequirementsforconstructionfeatures,documentand
drawingcompliance,workmanship,physicalconditions,GlossaryRef.[Ref1]
INSPECTIONPROCEDURE
This document lists all the requirements to be verified by Inspection, grouping them in
categoriesdetailing the Verification Plan activity sheets, with planning of theexecutionanda
definitionoftheassociatedprocedures,GlossaryRef.[Ref1]
INSPECTIONREPORT
Thisdocumentdescribeseachverificationactivityperformedwheninspectinghardwareduring
manufacturing/integration and contains proper evidence that the relevant requirements are
satisfiedandtheindicationofanydeviation,GlossaryRef.[Ref1]
INTERLAMINARSHEARSTRENGTH(ILSS)
Theshearstrengthexistingbetweenlayersofalaminatedmaterial
INTERMEDIATEMODULUSCARBONFIBRES(IM)
Arangeofcarbonfibreswithtensilemoduliintherangeof255GPato310GPa,typically
IR
InfraRed
ISO
Internationalstandardsorganization
ISOTROPIC
Property that is not directionally dependent. [Having the same physical or mechanical
propertiesinallmaterialdirections].Metalsareoftenassumedtobeisotropic.Thisisnormally
not the case, but they do generally show considerably less anisotropy than fibrereinforced
composites
ISOTROP
[See:ISOTROPIC]
J
JIG
A fixture or tool that retains a material, sample or structure, e.g. for testing or during
processing;alsoknownasrigorfixture
JIS
JapaneseInstituteofStandards
K
K49
Kevlar49
KEVLAR
AgradeofaramidfibrefromE.I.DuPontdeNemours[Seealso:ARAMID]
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KFRP
Kevlarfibrereinforcedplastic
L
LAMINA
[See:PLY]
LAMINATE
Plateconsistingoflayersofuniormultidirectionalpliesofoneormorecompositematerials
LAYUP
1Handormachineoperatedprocessofplybyplylayingofamultidirectionallaminate
2Plystackingsequenceorplyorientationsofalaminate
LIGHTALLOY
Generaltermformetalalloysoflowdensity,e.g.aluminium,magnesium,whichusuallyhave
highspecificstrengths(ratioofstrengthtodensity)
LIMITEDSHELFLIFE
Aperiodoftime,usuallystatedbythemanufacturerorsupplier,thatwhenelapsedmeansthat
amaterialcannolongerbeprocessedtoproduceconsistentlystablefinalproperties,[Seealso:
SHELFLIFE]
LIMITLOAD
[See:LOADS]
LIMITLOAD(LL)
maximumload(s),whichastructureisexpectedtoexperiencewithagivenprobability,during
theperformanceofspecifiedmissionsinspecifiedenvironments.
[ECSSEST32]
[Seealso:LOADS]
LIMITSTRESS
[See:LIMITLOAD]
LINEARELASTICFRACTUREMECHANICS(LEFM)
Engineeringprincipletodescribethepropagationofasinglecrackthroughamaterial,usuallya
metalalloy,inwhichitisassumedthatallthematerialisbehavingelastically
LN
LuftNorm;aGermanstandard
LOADS
Strengthrequirementsarespecifiedintermsof:
1LimitLoads:Themaximumexternalloadstobeexpectedduringoperationaluse
2 Ultimate Loads: Limit loads multiplied by prescribed FACTORS OF SAFETY, e.g. the
ultimateloadsareoftenestablishedbyapplyingafactorofsafetyof1,5onlimitloads
LOADDEFLECTIONCURVE
Agraphicalrepresentationoftheextensionofamaterialunderanappliedload;oftenrecorded
duringthemechanicaltestingofasample
LOADSTRAINCURVE
Agraphicalrepresentationoftheextensionofamaterialunderanappliedload
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M
MACHINING
removal of material in a controlled manner by one or more mechanical, electrical or chemical
methods,e.g.turning,milling,drilling,electrochemicaldischarge,andultrasonic.[ECSSQ70
71]
MANMT
PartoftheGermanMANTechnologiecompany
MARGINOFSAFETY
Ratioofexcessstrengthtotherequired(calculated)strength
MASS(ofinsertsystem)
Calculatedby(pottingmass+massofinsertcomponents)(massoffacesheetremoved+mass
ofcoreremoved)
MASS(ofpotting)
Describes the volume of cured potting compound used to retain a potted insert within a
sandwichpanel;alsoknownaspottingmass
MATERIAL
raw, semifinished or finished purchased item (gaseous, liquid, solid) of given characteristics
fromwhichprocessingintoafunctionalelementoftheproductisundertaken
[ECSSP001]
MATERIALDESIGNALLOWABLE
materialpropertythathasbeendeterminedfromtestdataonaprobabilitybasisandhasbeen
chosentoassureahighdegreeofconfidenceintheintegrityofthecompletedstructure
[ECSSEST3208]
MATHEMATICALMODELLING
Analyticalverificationbasedonmathematicalmodellingofthesystem.Modellingisperformed
on the basis of known mathematical techniques, providing a representation of the system
featuresunderinvestigation,GlossaryRef.[Ref1]
MBBERNO
Part of the German MBB aerospace organisation located in Bremen. Original authors of the
insertdesignhandbook;nowpartofAstriumGmbH
MD
Multidirectional
MECHANICALLOAD
Mechanicallyappliedload,distinguishedfromcureorenvironmentinducedload
MECHANICALPART
pieceofhardwarewhichisnotelectrical,electronicorelectromechanical,andwhichperformsa
simple elementary function or part of a function in such away that it can be evaluated as a
whole against expected requirements of performance and cannot be disassembled without
destroyingthiscapability
[ECSSP001]
METALLICCORE
Anycorethatismadeofmetal,e.g.oftenmadeofanaluminiumalloy
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MICROBALLOONS
Afillermaterialmadeofverysmall,hollowglassspheresthatismixedintosyntheticresinsto
modifytheflowandviscositycharacteristicsoftheresultingpottingcompounds;alsoknownas
microspheres
MILA81596
Aluminumfoilforsandwichconstruction;USAspecification
MILA8625
Anodiccoatingsforaluminiumandaluminiumalloys;describesanodisingprocessesforinserts;
USAspecification
MILC5541
Chemical conversion processes on aluminium alloys; describes chromating processes for
inserts;USAspecification
MILC7438
Corematerialaluminum,forsandwichconstruction;USAspecification
MILC81986
Core Material plastic honeycomb: nylon paper base for aircraft structural applications; USA
specification
MILHDBK17
CompositeMaterialsHandbook;USAspecification
MILHDBK23
StructuralSandwichComposites;USAspecification.
NOTE: MILHDBK23isunderreviewforpartialincorporationasVolume6ofMILHDBK17
MILHDBK5
MetallicMaterialsandElementsforAerospaceVehicleStructures;USAspecification
MILstandardsandspecifications
InformationregardingcurrentMILdesignationspecifications(http://store.milstandards.com/)
MODULUS
Anelasticconstantdefinedastheratiobetweentheappliedstressandtherelateddeformation,
suchasYoungsmodulus,shearmodulus,orstiffnessmoduliingeneral
MOISTUREABSORPTION
Moistureabsorptioncausesthepropertiesofepoxytochange;itcanbedetrimentalincausing
theglassytemperatureoftheepoxytobesuppressed,andbeneficialbycounteractingswelling
duringstresses
MOISTURECONTENT
The amount of moisture in a material determined under prescribed conditions and usually
expressedasapercentageofthemassofthemoistspecimen,i.e.themassofthedrysubstance
plusthemoisturepresent
MOULDRELEASEAGENT
Lubricantappliedtomouldsurfacestofacilitatereleaseofthemouldedpart
M.S
Marginofsafety
MULTIDIRECTIONAL
1Havingmultipleplyorientationsinalaminate
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2 Composite laminates in which the properties are controlled by the orientation of the
reinforcementfibres,i.e.fibrecontrolled
N
NAS
NationalAerospacestandard
NDI
Nondestructiveinspection,[See:NONDESTRUCTIVE]
NDT
Nondestructivetesting,[See:NONDESTRUCTIVE]
NF
NormeFranaise;Frenchnationalstandard
NIDA
Europeantermforhoneycomb;atypeofcoreusedinsandwichpanels
NOMEX
An aramid fibre blend from E.I. Dupont de Nemours. Used as the reinforcement material in
nonmetallichoneycombcoresforsandwichconstructions
NONASSESSEDPROCESS
A process that has no history of previous use in the space environment, and for which no or
insufficientdataareavailablerelevanttotherequiredprojectapplication
NONMETALLIC(CORE)
Anycorematerialthatisnotmadeofmetal.Corematerialsofsandwichpanelsusedforspace
applicationsarenormallymadeofNomexorglassfibrereinforcedplastic
NONDESTRUCTIVE
Techniquesusedtoqualitativelyevaluateorquantitativelymeasurepropertiesordetectdefects
in materials, structural components or whole structures which do not cause a permanent
change to the item under test, e.g. ultrasound, holography, eddy current. The terms NDI
(inspection), NDT (testing), NDC (characterisation) and NDE (evaluation) tend to be
interchangeable.Nondestructiveinspectionsystemscanbemanuallyinterpretedorautomated
tosomeextent.Allrequirecalibration,andthedetectionlimitforeachtechniquevaries.
NOTE: Noonetechniqueiscapableofdetectingalltypesofdefects.
NSA
NormalisationSudAviation;Frenchstandard
O
OFFAXIS
Notcoincidentwiththeaxisofsymmetry
NOTE: Alsocalledoffangle
OFFGASSINGPRODUCT
organicorinorganiccompoundevolvedfromamaterialorassembledarticleorexperimentor
rack
[ECSSQST7029]
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OFFGASSING
1 General: Depending on the application, there are restrictions on the gaseous products
releasedfrommaterialsorfinishedarticlesinoperationalvacuumconditionsthatcan:
contaminateotherequipment,[Seealso:OUTGASSING];
contaminatetheairduringpreparatoryoroperationalconditionsformannedspacecraft.
2evolutionofgaseousproductsforanassembledarticlesubjectedtoslightradiantheatinthe
specifiedtestatmosphere
[ECSSQST7029]
NOTE: Itappliestomaterialsandassembledarticlestobeusedinamannedspacevehicle
crewcompartment.
ONAXIS
Coincidentwiththeaxisofsymmetry;alsoknownasonangle,[See:ORTHOTROPIC]
ORTHOTROPIC
Adescriptionofmaterialsymmetrywherethexaxisandyaxisofalaminatecoincidewiththe
longitudinalandtransversedirectionsofthematerial;alsoknowasonaxis
ORTHOTROPY
Havingthreemutuallyperpendicularplanesofsymmetry.Unidirectionalplies,fabric,crossply
andangleplylaminatesareallorthotropic
ORTHOGONALWEAVE
Afabricinwhichthewarpandweftdirectionsare90toeachother
OUTGASSING
1 General: Depending on the application, there are restrictions on the gaseous products
releasedfrommaterialsorfinishedarticlesinoperationalvacuumconditionsthatcan:
contaminateotherequipment(outgassing)
contaminate the air during preparatory or operational conditions for manned spacecraft,
[Seealso:OFFGASSING]
2Releaseofgaseousspeciesfromaspecimenunderhighvacuumconditions[ECSSQST70
02]
P
PA
ProductAssurance
PAN
Panaviastandard
PART
hardware item that cannot be disassembled without destroying the capability to perform its
requiredfunction
[ECSSP001]
PARTIALPOTTING
Thepottingheightisgenerallysmallerthanthecoreheight,c;alsoknownasblind,borneor
singlesided
PARTIALLYPOTTEDINSERT
Aninsertinasandwichpanelinwhichthereissomecoreremainingunderthepottedinsert,
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PASTE
Adhesive:asingleortwocomponentadhesivethatoftenincludesathickeningagent,suchas
microballoons,thatbehavesasaviscousliquid
PATRIAFINAVICOMP
Finnishaerospaceanddefencecompany
PEELPLY
Sacrificial sheets of material, usually a fabric, applied to the external surfaces of composites;
afterprocessingpeelpliesareremovedtoprovideaclean,contaminantfreesurface
PERMISSIBLELOAD
A load, proven by analysis and testing, with a known statistical confidence, that can be
supportedbyamaterialorassemblywithoutresultinginunacceptabledamageordegradation
throughouttheintendedperiod;alsoknowasallowableload
PLASTIC
A material that contains as an essential ingredient an organic substance of high molecular
weight, is solid in its finished state, and at some stage in its manufacture or processing into
finishedarticlescanbeshapedbyflow;madeofplastic
PLY
Asinglelayerofalaminatedstackofcompositematerial(orasinglepassforafilamentwound
configuration)
PLYDROP
Thepositioninsidealaminatewhereaplyisterminated,e.g.tocreateataperedthickness
PLYGROUP
Groupformedbycontiguousplieswiththesameangle
POISSONSRATIO
The ratio between the extension (Strain) of an elastic material in the axial direction and the
accompanyingcontractionsinthetransversedirectionswhenuniaxialstressisapplied.
NOTE: Thetransversestrainisaconstantfractionofthestraininthelongitudinaldirection,
e.g.forperfectlyisotropicelasticmaterials,Poissonsratio(xaxis)is0,25,whereasmostalloys
haveavalueofabout0,33,GlossaryRef.[Ref2]
POLYMER
high molecular weight organic compound, natural or synthetic, with a structure that can be
representedbyarepeatedsmallunit,themer
NOTE: E.g.polyethylene,rubberandcellulose
[ECSSEST3208].
NOTE: Synthetic polymers are formed by addition or condensation polymerisation of
monomers.Somepolymersareelastomers,someplastics
POLYMERISATION
A chemical reaction in which the molecules of a monomer are linked together to form large
moleculeswhosemolecularweightisamultipleofthatoftheoriginalsubstance
POSTCURE
Anadditionalelevatedtemperaturecure,usuallywithoutpressure,toimprovefinalproperties
or complete the cure. Complete cure and ultimate mechanical properties of certain resins are
attainedonlybyexposureofthecuredresintohighertemperaturesthanthoseofcuring
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POTLIFE
lengthoftimeacatalysedresinsystemretainsaviscositylowenoughtobeusedinprocessing
NOTE: AlsocalledWorkingLife.
[ECSSQ7071]
POTTEDINSERT
Aninsertthatisretainedinasandwichpanelbyavolumeofcuredpottingcompound
POTTEDINSERT(CLASSICAL)
The usual means of incorporating a standardtype of insert into a sandwich panel using a
pottingprocess;alsoknownasconventionalpottedinsert
POTTING
Theprocessofembeddinginsertsintoasandwichpanelusingapottingcompound
POTTING(FULL)
Themaximumpossiblepottingheightisidenticaltothecoreheight,c;alsoknownasblindor
borne
POTTING(MASSOF)
Thevolumeofcuredpottingcompoundusedtoretainapottedinsertwithinasandwichpanel
POTTING(PARTIAL)
Thepottingheightisgenerallysmallerthanthecoreheight,c;alsoknownasblind,borneor
singlesided
POTTINGCOMPOUND
A polymer resin system (base, hardener, catalyst) usually epoxybased, that often contains a
filler or thickening agent to modify the viscosity and flow characteristics; used for retaining
insertsinsandwichpanels
POTTINGMASS
A calculated quantity determined from the core properties (height and cell size) and insert
diameterandwhethertheinsertispartiallyorfullypotted
POTTINGPROCESS
The sequence of operations by which inserts are embedded into sandwich panels, e.g.
positioningoftheinsertinamachinedhole,mixingofresinandaddingthefiller,injectioninto
thesandwichpanel,curing(usuallyseveralhoursatroomtemperature)
POTTINGRESIN
A polymerbased resin system (base, hardener and catalyst) that is combined with a suitable
filler(tomodifytheviscosityandflowcharacteristics)toformapottingcompoundsuitablefor
pottingofinsertsintosandwichpanels;usuallyanepoxybasedresinsystem
PREPREG
wovenorunidirectionalplyimpregnatedwitharesin,usuallyadvancedtoBstage,readyfor
layuporwinding
NOTE: Shortforpreimpregnated.
[ECSSQ7071]
prEN
ProvisionalordraftENstandard
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PRIMER
Acoatingappliedtoasurfacebeforetheapplicationofanadhesive,lacquer,paint,enamelor
theliketoimprovetheperformanceofthebond
PROCESS
setofinterrelatedorinteractingactivitieswhichtransforminputsintooutputs
NOTE1Inputstoaprocessaregenerallyoutputsofotherprocesses.
NOTE2Processesinanorganizationaregenerallyplannedandcarriedoutundercontrolled
conditionstoaddvalue.
NOTE 3 A process where the conformity of the resulting product cannot be readily or
economicallyverifiedisfrequentlyreferredtoasaspecialprocess.
[ECSSP001]
PROOFTEST
test of flight hardware under the proof load or pressure, to give evidence of satisfactory
workmanshipandmaterialqualityortoestablishtheinitialcracksizesinthehardware
[ECSSEST32]
PROTRUDINGINSERT
Aninsertpositionedsuchthattheflange(s)oftheinsertprotrudesbeyondthesandwichpanel
surface;alsoknownasproudoroverflush
psi
Poundspersquareinch
PSSIDH
ReferstoESAPSS031202Issue1Revision1(September1990);apreviousversionoftheinsert
designhandbook
PVC
Polyvinylchloride
Q
QA
Qualityassurance
QC
Qualitycontrol
QUALIFICATION
Verification phase with the objective to demonstrate that the design meets the applicable
requirementsincludingpropermargins,GlossaryRef.[Ref1]
QUASIISOTROPICLAMINATE
Alaminateapproximatingisotropybyorientationofpliesinseveralormoredirections
R
Rratio
ratiooftheminimumstresstomaximumstress
[ECSSEST3201]
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RECESSEDINSERT
Aninsertpositionedbelowthesurfaceofthefacesheet;alsoknownassubflushinsert
RECOVEREDMASSLOSS(RML)
totalmasslossofthespecimenitselfwithouttheabsorbedwater
NOTE1 Thefollowingequationholds:
RML=TMLWVR.
NOTE2 TheRMLisintroducedbecausewaterisnotalwaysseenasacriticalcontaminantin
spacecraftmaterials.
[ECSSQST7002]
REFERENCESAMPLE
Usedtoassessthepottingprocess.Areferencesampleisproducedusingidenticalmaterialsto
theassembly(insert,facesheets,core,adhesive)atthesametimeasthemanufacturedassembly
andundergoesallthesameprocesses,e.g.machining,potting,curing;alsoknownaswitness
sample
REINFORCEDPLASTIC
Aplasticwithstrengthpropertiesgreatlysuperiortothoseofthebaseresin,resultingfromthe
presenceofreinforcementsembeddedinthecomposition
REINFORCEMENT
Astronginertmaterialbondedintoaplastic,metalorceramictoimproveitsstrength,stiffness
and impact resistance. Reinforcements are usually long fibres of glass, boron, graphite or
aramid, in woven or non woven form. To be effective, the reinforcing material must form a
strongadhesivebondwiththematrix
NOTE: Reinforcementisnotsynonymouswithfiller.
RELATIVEHUMIDITY(RH)
A measure of the moisture content of an atmosphere with respect to the fully saturated
atmosphereatthesametemperatureandpressure;expressedasapercentage
RELEASEAGENT
A material which is applied in a thin film to the surface of a mould to keep the resin from
bondingtoit
RELEASEFILM
A thin sheet of material applied to a composite surface to enable its removal from a mould;
usedinautoclaveprocessing
REPAIR
Operationsperformedonanonconformingitemtoplaceitinusableandacceptablecondition
accordingtoanauthorisedrepairprocedure/standard.Repairisdistinguishedfromrework
NOTE: Repair can consist of a component change with all its associated connections
includingthefixingdownofaliftedpadortrack.
RESIDUALFATIGUESTRENGTH
The retention ofstatic strength byalaminate that has been subjected to a certain fatigueload
history
RESIDUALSTRENGTH
The retention of static strength by a material or assembly that has been subjected to a load
history or environment, e.g. cyclic mechanical loading (fatigue test); thermal cycling; thermal
soak
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RESIDUALSTRESS
1Astressthatremainsinthematerialorstructure,owingtoprocessing,fabricationorprior
loading
2 Composites: Resulting from cooldown after cure and change in moisture content. On the
micromechanicallevel,stressistensileintheresinandcompressiveinthefibre.Onthemacro
mechanical level, it is tensile in the transverse direction to the unidirectional fibres, and
compressiveinthelongitudinaldirection,resultinginaloweredfirstplyfailureload.Moisture
absorptionoffsetsthisdetrimentalthermaleffectatbothmicroandmacrolevels
3Metals:Usuallyarisesfromheattreatmentormechanicalworking
RESIN
A solid, semisolid, or pseudosolid organic material which has an indefinite (often high)
molecularweight,exhibitsatendencytoflowwhensubjectedtostress,usuallyhasasoftening
or melting range, and usually fractures conchoidally. Most resins are polymers. In reinforced
plastics, the material used to bind together the reinforcement material, the matrix. [See also:
POLYMER]
RESINCONTENT
Theamountofresininalaminateexpressedasapercentoftotalweightortotalvolume
RF
Radiofrequency
R.F.
Reservefactor
RGLASS
Ahighstrengthgradeofglassfibre,[Seealso:GLASSFIBRE]
RH
Relativehumidity
RIG
Afixtureortoolthatretainsamaterial,sampleorstructure,e.g.fortestingandprocessing;also
knownasjigorfixture
RML
Recoveredmassloss
RMS
Rootmeansquare
ROSETTA
ESAcometrendevousmission.LaunchedinMarch2004,Rosettawillbethefirstmissioneverto
orbitandlandonacomet.FollowingthedecisionnottolaunchEuropescometchaser,Rosetta,
in January 2003, scientists and engineers in the programme examined several alternative
missionscenarios.Eachwasjudgedonthebasisoftheexpectedscientificreturn,thetechnical
risksrelatedtousingtheRosettadesigninthenewmission.InMay2003,Rosettawasprovided
withanewtarget(http://www.esa.int/science/rosetta)
RT
Roomtemperature
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RULEOFMIXTURES
Linear volume fraction relation between the composite and the corresponding constituent
properties; also known as Law of Mixtures e.g. For modulus of a composite Ec, the rule of
mixturesequationis:
Ec E f V f EmVm
where:
Ef=modulusofthefibre
Vf=volumefractionoffibreinthecomposite
Em=modulusofthematrix
Vm=volumefractionofthematrix
S
SANDWICH
1 Construction: An assembly composed of a lightweight core material, such as honeycomb,
foamedplastic,andsoforth,towhichtworelativelythin,dense,highstrengthorhighstiffness
facesorskinsareadhered,[Seealso:FACESHEET]
2Panel:Asandwichconstructionofaspecifieddimensions
NOTE: Thehoneycombandfaceskinscanbemadeofcompositematerialormetalalloy.
SATELLITE
Anunmannedspacecraftgenerallyorientedtoscientific,telecommunication,earthobservation
missions,GlossaryRef.[Ref1]
SCOTCHLITE
Aproprietarybrandofglassmicroballoons,manufacturedandsuppliedby3M
SD
Standarddeviation;astatisticallyderivedquantity
SECONDARYBONDING
Aprocesswherebymanufacturedcomponentpartsarejoinedbyanadhesive;canbeappliedto
compositepartsthathavealreadybeencuredormetalpartsorcombinationsthereof
NOTE: Thisisdifferentfromcocuring,[Seealso:COCURING].
SERVICECONDITIONS
The combination of mechanical loading and environmental effects experienced by a material,
componentorstructureinoperationoveritsintendedlife
SERVICELIFE
interval beginning with the last item inspection or flaw screening proof test after
manufacturing,andendingwithcompletionofitsspecifiedlife
[ECSSEST32]
SGLASS
A magnesiaaluminasilicate glass, especially designed to provide filaments with very high
tensilestrength
SHEARMODULUSRATIO
Ratio of the shear modulus of the core material to that of the face sheet in a sandwich
construction
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SHELFLIFE
1statedtimeperiodinwhichthemanufacturerguaranteesthepropertiesorcharacteristicsofa
productforthestatedstorageconditions,[ECSSQ7071]
2 Period of time during which a material can be processed to produce final properties with
consistentlystableparameters,[ECSSQST7022]
SHELFLIFE(LIMITED)
Aperiodoftime,usuallystatedbythemanufacturerorsupplier,thatwhenelapsedmeansthat
amaterialcannolongerbeprocessedtoproduceconsistentlystablefinalproperties,[Seealso:
SHELFLIFE]
SHOPLIFE
The shop life of a prepreg is that period following removal from the specified storage
conditions and attaining shopfloor temperature for which the prepreg remains workable in
termsoftack,andflowandcurecharacteristics
SHURLOK
Manufacturerandsupplierofstandardtypesofinsertsandacommonlyusedpottingresin
SI
Theinternationalsystemofunits,publishedbytheInternationalStandardsOrganisation(ISO)
SILEX
Semiconductor laser intersatellite link experiment. The ESAdeveloped SILEX terminal on
boardtheArtemissatellitehasenabledittoreceivepicturedatafromtheFrenchSpot4satellite
vialaser
SKIN
Asheetofmaterialappliedtooutsidesurfaceofacoreinordertomakeasandwichpanel;also
knownasfacesheetandfaceskin
SMH
Structuralmaterialshandbook;ECSSEHB3220
SNCURVE
Stresspernumberofcyclestofailure;agraphusedtodisplayfatiguetestingresults
SPACECRAFT
A space system which could be either manned or unmanned and could have any type of
mission objectives, i.e. telecommunications, transportation, earth observation, interplanetary
exploration,GlossaryRef.[Ref1]
SPACEPROVENMATERIALORMECHANICALPART
Onewhosepropertiesarewellunderstoodandthatisproducedbymeansofastableprocess,
usuallyconfirmedbyahistoryofcontinuousorfrequentproductionruns.Itmustbecompliant
witharecognisedsetofspecifications.Itwillhavebeenusedinspaceapplications,orwillhave
successfullycompletedanappropriateevaluationprocess
SPECIFICGRAVITY(SG)
A dimensionless quantity also known as Relative Density. Ratio between the density of a
materialandthatofwaterunderstandardconditions
SPECIFICSTIFFNESS
Themeasureofthestiffnessofamaterialwithrespecttoitsdensity
SPECIFICSTRENGTH
Themeasureofthestrengthofamaterialwithrespecttoitsdensity
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SPOOLINSERT
Throughthethicknessinsert
SPOT
AseriesofEarthobservationsatellitesprovidingdataformapping,disastermanagementand
controllingtheenvironment
SPOT5
TheCNESSPOT5satellitewassuccessfullyplacedintoSunsynchronousorbitinMay2002by
an Ariane 4 launcher. This, the fifth SPOT satellite to be launched, ensures the continuity of
SPOTEarthobservationdataandprovidesevenbetterhighresolutionimages
STACKINGORDERorSEQUENCE
Ply ordering in a laminate. Stacking sequence does not affect the inplane properties of a
symmetric laminate. Only the ply number and angles are important. But stacking sequence
becomes critical for the flexural properties, and the interlaminar stresses for any laminate,
symmetricornot;alsoknownaslayup
STANDARDORESTABLISHEDPROCESS
Onethatiswelldocumented,hasaprevioushistoryofuse,iswellunderstoodandforwhich
standard inspection procedures exist. Such a process would generally be covered by ECSS
specificationsorotherinternationalornationaldocuments
STATICFATIGUE
Failureofapartundercontinuedstaticload;analogoustocreeprupturefailureinmetaltesting,
butoftentheresultofageingacceleratedbystress
STIFFNESS
Ratiobetweentheappliedstressandtheresultingstrain.Youngsmodulusisthestiffnessofa
material subjected to uniaxial stress; shear modulus to shear stress. For composite materials,
stiffness and other properties are dependent on the orientation of the material. [See:
MODULUS]
STORAGELIFE
Thelengthoftimethatamaterialcanbekeptunderpredeterminedconditionsandnotdegrade,
e.g. Prepreg: usually 18 C for thermosetting resin systems, with subsequent factory floor
operationsatroomtemperature,[Seealso:SHELFLIFE]
STRAINGAUGE
Widely used device for point measurement of strain. Usually thin film metals which, when
strained,changeinelectricalresistance
NOTE: Requirecalibrationandtemperaturecompensation.
STRENGTHRATIOorSTRENGTH/STRESSRATIO
Measure related to MARGIN OF SAFETY. Failure occurs when the ratio is unity; safety is
assuredforexamplebyafactorof2iftheratiois2.Theratioisparticularlyeasytoobtainifthe
quadraticfailurecriterionisused
STRENGTH
Maximum stress that a material can sustain. Like the stiffness of a composite material, this is
highly dependent on the direction as well as the sign of the applied stress; e.g. axial tensile,
transversecompressive,andothers
STRESSAMPLITUDE(R)
Fatiguetest:therangeofstressesinducedinalaminatewhenacyclicloadisapplied,[Seealso:
R]
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STRESS
Intensityofforceswithinabody.Thenormalcomponentsinducelengthorvolumechange;the
shear component, shape change. The numerical value of each component changes as the
reference coordinate system rotates. For every stress state there exists a principal direction, a
uniquedirectionwhenthenormalcomponentsreachmaximumandminimum,andtheshear
componentvanishes
STRESSSTRAINCURVE
A graphical representation of a materials response to increasing load. Often used to depict
relationshipsbetweenstress(load)andstrain(elongation),e.g.stiffness,strength(s)andstrainto
failure
STRESSSTRAINRELATION
Alinearrelationisusuallyassumedforcalculatingstressfromstrain,orstrainfromstress.For
multidirectional laminates, it can be generalised to include inplane stressstrain, and flexural
stressstrainrelations.Allanisotropicrelationsaresimpleextensionsoftheisotropicrelation
STRUCTURALCOMPONENT
Amajorsectionofthestructure(e.g.wing,body,fin,horizontalstabiliser)thatcanbetestedas
acompleteunittoqualifythestructure
STRUCTURALFAILURE
[See:FAILURE(STRUCTURAL)]
STRUCTURALSUBCOMPONENT
A major threedimensional structure that can provide complete structural representation of a
sectionofthefullstructure(e.g.stubbox,sectionofspar,wingpanel,wingrib,bodypanelor
frames)
STRUCTURE
Allitemsandassembliesdesignedtosustainloadsorpressures,providestiffnessandstability,
orprovidesupportorcontainment
STYCAST
Aproprietarytypeofpottingresin,producedbyEmersonandCumin
SUBASSEMBLY
Asubdivisionofanassemblyconsistingoftwoormoreitems
NOTE: VerificationleveltypicalofUSstandard,GlossaryRef.[Ref1].
SUBSYSTEM
1Afunctionalsubdivisionofapayloadconsistingoftwoormoreitems
2 A set of functionally related equipment, connected to each other, that performs a single
categoryoffunctions,e.g.structure,power,attitudecontrol,thermalcontrol,GlossaryRef.[Ref
1]
SWARF
Wastematerial,usuallymetallic,producedduringmachiningprocesses
SYMMETRICLAMINATE
Possessing midplane symmetry. This is the most common construction, because the curing
stresses are also symmetric. The laminate does not twist when the temperature and moisture
content change. An unsymmetrical laminate on the other hand twists on cooling down and
untwistsafterabsorbingmoisture
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SYNTACTIC
1General:Highlyordered
2Apottingcompoundcontainingafillermadeofhollowglassmicrospheresthat,whencured,
hasafoamlikestructure,[Seealso:ADHESIVE(SYNTACTIC)]
SYSTEM
Thecompositeofelements,skillsandtechniquescapableofperformingtheoperationalroles.A
system includes all operational equipment, related facilities, materials, software, services and
personnelrequiredforitsoperation,e.g.launchsystem,onorbitsystem,GlossaryRef.[Ref1]
T
T
Toxichazardindex
TAB
Amaterial,usuallyfixedtoeachendofatestspecimen,whichenablesloadtobetransferredto
thetestspecimenwithoutcausingdamagetothetestspecimen;compositetestspecimensoften
havelightalloyorglassfibrebasedcompositetabsadhesivelybondedtothetestspecimen
TACK
Stickinessofaprepregorfilmadhesive;animportanthandlingcharacteristic
TAN
TransallNorm;aspecification
TEST
A verification method wherein requirements are verified by measurement of performance
relativetofunctional,electrical,mechanicalandthermalparameters.Thesemeasurementscan
require the use of special equipment, instrumentation and simulation techniques, Glossary
Ref.[Ref1]
TESTPROCEDURE
AdocumentwhichprovidesdetailedstepbystepinstructionstotheTestteamsforconducting
thetestactivitiesinagreementwiththeTestSpecificationrequirements,GlossaryRef.[Ref1]
TESTSPECIFICATION
AdocumentpreparedforeachmajortestactivitydescribedintheVerificationPlantasksheets
withtheobjectivetodetailthetestrequirements,Ref.[Ref1]
Tg
Glass transition temperature; the temperature at which a material changes from a glassy to
ductilestate,givingasteepincreaseinfreevolume
THERMALCONDUCTIVITY
Ability of material to conduct heat; the physical constant for quantity of heat that passes
throughaunitcubeofasubstanceinunittimewhenthedifferenceintemperatureoftwofaces
is1degree
THERMALCYCLING
The repeated change of temperature experienced by a material, component or structure; the
maximumandminimumtemperaturesarenormallythoseassociatedwithorbitingtheEarth
THERMALEXPANSION
[See:COEFFICIENTOFTHERMALEXPANSION]
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THERMALLOAD(STRESS)
The structural load (or stress) arising from temperature gradients and differential thermal
expansionbetweenstructuralelements,assemblies,subassembliesoritems
THERMALSHOCK
Suddenandrapidchangeintemperature,usuallyoveralargetemperaturerange
THERMALSOAK
Aperiodoftimethatamaterial,componentorstructureisexposedtoanelevatedtemperature,
e.g.structuresunderneaththermalprotectionsystems
THERMOCOUPLE
Deviceformeasuringtemperatureconsistingoftwodissimilarconductorsjoinedattheirends
which,whenheated,developacharacteristicEMF.Thetemperatureisindicativeofthatofthe
junctionofthepairinthethermocouple,i.e.apointmeasurementdevice.
NOTE: Calibrationandcompensationarerequired.
THERMOPLASTIC
Organicmaterial,thestiffnessofwhichcanbereversiblychangedbytemperaturechange.One
unique property of this material is its large strain capability, e.g. PEEK. On the other hand,
processingrequireshighertemperaturesandpressuresthanthoseforthermosettingplastics
THERMOSETTING
Organic material that can be converted to a solid body by crosslinking, accelerated by heat,
catalyst, ultraviolet light, and others. This is the most popular type of material for the matrix
phaseofcompositematerials,adhesivesandpottingresins,[Seealso:EPOXY]
THROUGHTHETHICKNESSINSERT
Aninsertwhichpassesthroughtheentiresandwichpanelthickness,alsoknownastransverse,
doublesided,spoolorthruspool
TITANIUM(Ti)
Metallicelement,meltingpoint1670C,density4540kgm3.Uses:alloyingadditions,classof
aluminide.Matrixalloyforcomposites,structuralmaterialsforaerospaceusesgenerallywhere
operational temperatures exceed those possible with aluminium. Manufacture of structural
shapes with superplastic forming/diffusion bonding technique, [See also: SPF/DB]. Extremely
difficulttocast.Sensitivetopresenceofhydrogenandoxygen
Tm
Meltingtemperatureatwhichthematerialchangesfromthesolidstatetothemoltenstate,in
C
TML
Totalmassloss.[Seealso:OFFGASSING,OUTGASSING]
TOTALMASSLOSS(TML)
totalmasslossofmaterialoutgassedfromaspecimenthatismaintainedataspecificconstant
temperatureandoperatingpressureforaspecifiedtime
NOTE: TMLiscalculatedfromthemassofthespecimenasmeasuredbeforeandafterthetest
andisexpressedasapercentageoftheinitialspecimenmass.
[ECSSQST7002]
TOUGHNESS
Theenergyrequiredtobreakamaterial,equaltotheareaunderthestressstraincurve
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TOXIC
Substances causing serious, acute or chronic effects, even death, when inhaled, swallowed or
absorbedthroughtheskin
[ECSSQ7071]
TOXICHAZARDINDEX(T)
ratiooftheprojectedconcentrationofeachoffgassedproducttoitsSMACvalueandsumming
theratiosforalloffgassedproductswithoutseparationintotoxicologicalcategories
NOTE FurtherdetailsonthecalculationofthisTvaluecanalsobeobtainedinNASASTD
6001.
[ECSSQST7029]
TOXICITY
[See:TOXIC]
TRACEABILITY
The ability to trace the history, application, use and location of an item through the use of
recordedidentificationnumbers
TRANSITIONTEMPERATURE
Thetemperatureatwhichthepropertiesofamaterialchange.[Seealso:GLASSTRANSITION
TEMPERATURE]
TRANSVERSEISOTROPY
Materialsymmetrythatpossessesanisotropicplane;e.g.aunidirectionalcomposite
TYPE(INSERT)
The various types of inserts can be grouped by the means that they are embedded into a
sandwichpanel:
(A)forsimultaneousbondingduringsandwichproduction,alsoknownascocure;
(B) for an existing sandwich using either a thermosetting resin (usual potting process of
standard inserts) or for nonstandards inserts by an equivalent bonding process, e.g. carbon
fibretubeinserts;
(C)formechanicalclampingorscrewingintoanexistingsandwich.
TYPEA(INSERT)
Usedforsimultaneousbondingduringsandwichstructureproduction
TYPEB(INSERT)
Used for an existing sandwich structure; embedded with a thermosetting potting compound
(pottingofstandardinserts),orbyanequivalentbondingprocedure(nonstandardsinserts)
TYPEC(INSERT)
Usedformechanicalclampingorscrewingintoanexistingsandwichstructure
U
UD
Unidirectional
UHM
Ultrahighmodulus;arangeofcarbonfibres
ULTIMATELOAD
[See:LOADS]
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ULTIMATESTRENGTH
the maximum load or stress that a structure or material can withstand without incurring
ruptureorcollapse
NOTE It is implied that the condition of stress represents uniaxial tension, uniaxial
compression,orpureshear.
[ECSSEST32]
ULTIMATETENSILESTRENGTH(UTS)
Highest stress sustained by a material before catastrophic failure. The ultimate or final stress
sustainedbyaspecimeninatensiontest;thestressatmomentofrupture
NOTE: UTSsometimesdenotesultimatetensilestress.
ULTRAHIGHMODULUSCARBONFIBRES(UHM)
Arangeofcarbonfibresinwhichthetensilemodulusexceeds395GPa,typically
ULTRAVIOLET(UV)
Zone of invisible radiation beyond the violet end of the spectrum of visible radiation. Since
ultravioletwavelengthsareshorterthanthevisible,theirphotonshavemoreenergy,enoughto
initiatesomechemicalreactionsandtodegrademostplastics
UNAVIA
Italianstandardsorganisation(newsystem)
UNDERCURING
Anincorrectprocessinwhichthereisinsufficienttimeortemperaturetoenablefullandproper
curingofanadhesiveorresin
UNI
Italianstandardsorganisation(oldsystem)
UNIDIRECTIONALCOMPOSITE
Acompositehavingonlyparallelfibres
UNSYMMETRICLAMINATE
Alaminatewithoutmidplanesymmetry
USA
UnitedStatesofAmerica;alsodenotedasUS
UTS
UltimateTensileStrengthorStress;[See:ULTIMATETENSILESTRENGTH]
UV
[See:ULTRAVIOLET]
V
VANTICO
Formerly CibaGeigy, UK. Manufacturer and supplier of Araldite range of epoxybased
adhesivesandpottingresins
VCM
VolatileCondensableMaterial
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VERIFICATION
The verification is a process oriented to demonstrate that the system design meets the
applicable requirements and is capable of sustaining its operational role along the project life
cycle,Ref.[Ref1]
VERYHIGHSTRENGTHCARBONFIBRES(VHS)
Arangeofcarbonfibresinwhichthetensilestrengthexceeds3500MPa,typically
Vf
Volumefractionofreinforcementfibreswithinacompositematerial,expressedasapercentage
VHS
Veryhighstrengthcarbonfibres
VISCOSITY
1measureofthefluidityofaliquid,incomparisonwiththatofastandardoil,basedonthe
timeofoutflowthroughacertainorificeunderspecifiedconditions,[ECSSQ7071]
2Thepropertyofresistancetoflowexhibitedwithinthebodyofamaterial,expressedinterms
ofrelationshipbetweenappliedshearingstressandresultingrateofstraininshear
VOID
Air or gas trapped in a material during cure, e.g. air or gas bubbles present in the mass of
pottingaftercure
NOTE: Indicatestheneedforproperventingduringthepottingprocess.
VOIDCONTENT
Volumepercentageofvoids,e.g.calculatedfromthemeasureddensityofacuredmaterialand
thetheoreticaldensityofthestartingmaterial
NOTE: Implies that voids are uniformly distributed throughout the body, which is not
alwaysthecase.
VOLATILECONTENT
Ameasureofthemasslossfromasamplesubjectedtoprescribedtestconditions.Thevolatile
loss is an indication of the solvent content of the material, which can result in highlevels of
voids remaining after cure. Occurs due to the vaporisation of the usually lowboilingpoint
solventwithintheresinconstituentduringcure.
VOLATILES
Materials in a sizing or a resin formulation capable of being driven off as a vapour at room
temperatureorslightlyabove
VOLUMEFRACTION
Fractionofaconstituentmaterialbasedonitsvolume;ameasureofthequantityofonephasein
acompositematerial,usuallythereinforcementfibrecontent,e.g.denotedasVfandexpressed
asapercentage
W
WAISTED
Atypeoftestspecimenorcouponwherethegaugelengthisnotparallelfortheentirelength
WARP
1 The yarn running lengthwise in a woven fabric; a group of yarns in long lengths and
approximately parallel, put on beams or warp reels for further textile processing, including
weaving
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2Achangeinshapeordimensionofacuredlaminatefromitsoriginalmouldedshape
WATERABSORPTION
Ratiooftheweightofwaterabsorbedbyamaterialuponimmersiontotheweightofthedry
material.[Seealso:MOISTUREABSORPTION]
WATERVAPOURREGAINED(WVR)
Massofthewatervapourregainedbythespecimenaftertheoptionalreconditioningstep.
NOTE: WVRiscalculatedfromthedifferencesinthespecimenmassdeterminedafterthetest
for TML and CVCM and again after exposure to atmospheric conditions and 65 % relative
humidityatroomtemperature(223)C.
[ECSSQST7002]
WEAVE
Theparticularmannerinwhichafabricisformedbyinterlacingyarnsandusuallyassigneda
stylenumber
WEFT
Thetransversethreadsorfibresinawovenfabric;fibresrunningperpendiculartothewarp.
NOTE: Alsocalledfill,filler,filleryarn,woof
WERKSTOFFLEISTUNGSBLATT
Germanstandardsorganisation
WETTING
Flowandadhesionofaliquidtoasolidsurface,characterisedbysmooth,evenedgesandlow
contactangle
WITNESSSAMPLE
A sample made of identical materials to that used in a composite laminate that undergoes
exactly the same processing as the laminate. The objective is to ensure that all the
manufacturing processes applied, e.g. layup and cure, are correct. Testing and inspection of
witnesssamplesprovideconfidencethatthepropertiesoftheassemblymeetthosestipulatedin
thedesign;alsoknownasREFERENCESAMPLEforinserts
WOVENFABRICS
Fabricsproducedbyinterlacingstrandsmoreorlessatrightangles
WRINKLE
1 A surface imperfection in laminated plastics that has the appearance of a crease in one or
moreoutersheetsofthepaper,fabric,orotherbasewhichhasbeenpressedin
2Sandwichpanels:deformationofthefaceskins;apotentialfailuremode
WROUGHTMETALPRODUCT
Metallic stock material, e.g. in the form of sheet and strip, plate, bar, which is produced by
methods involving large amounts of plastic deformation (such as forging, rolling, extrusion)
thatresultsinamaterialwithawroughtmicrostructure,oftenwithsomelevelofanisotropy
Wt%
Weightpercent
WVR
WaterVapourRegained
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X
XMM
Xraymultimirrortelescope
Y
YIELDSTRENGTH
maximumloadorstressthatastructureormaterialcanwithstandwithoutincurringaspecified
permanentdeformationoryield
NOTE Theyieldisusuallydeterminedbymeasuringthedepartureoftheactualstressstrain
diagramfromanextensionoftheinitialstraightproportion.Thespecifiedvalueisoftentaken
asaunitstrainof0,002.
[ECSSEST32]
YIELDSTRESS(YS)
Stressatwhichpermanentdeformationcommencesinamaterial.Thelimitofreversibleelastic
behaviour,[Seealso:PROOFSTRESS]
YOUNGSMODULUS
Theratioofamaterialssimpletensilestress,withinelasticlimits,totheresultingstrainparallel
tothedirectionofthetensilestress
Z
notermsorabbreviations
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4
Insert system
4.1.1 Inserts
An insert is part of a detachable fixation device, which enables the interconnection of honeycomb
sandwich structures; connection between such structures and other structural parts, e.g. frames,
profiles,brackets;mountingofequipment,e.g.boxes,feedlines,cableducts.
The system consists of a removable and a fixed structural element. The removable part is either a
screw or other threaded element adapted to a nutlike part, the insert. This is connected to the
honeycombstructure by using a potting compound; normally a twopart epoxy resin system, [See
also:7.1Pottingcompound].
Figure41showsthecomponentsofastandardtypeofinsertsystem,[Seealso:5.2].
NOTE Nonstandard types of inserts are described in A.3 and carbon fibre
reinforcedplastictubeinsertsinF.6.
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ATypicalstandardtypeinsert
Face sheet
Core
Face sheet
Potting
Honeycomb panel
[See also: 8.1] Structural sandwich concept
BTypicalstandardtypeinsertembeddedinhoneycombpanel
Figure41:Insertsystem:Components
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Table41:Insertsystem:Generaldefinition
Malethreadedelement
Insert Femalethreadedelement(eitherfixedor [See:Table51]
replaceable)
INSERTSYSTEM
Mechanicalclampingorscrewing Notadvised
Bondingwithresin:
Joining
method simultaneouslyduringsandwichproduction,or
[See:Table51]
integrationintoanexistingsandwich(bypottingor
anequivalentmethod).
Facesheet
Sandwich Bondingcomponent [Seealso:6.1]
Core
NOTE The terms used to describe the different types of inserts vary across
theindustry,e.g.:
Partiallypotted,alsoknownas:blind,borne,singlesided.
Fully potted, also known as: throughthethickness, doublesided,
transverse.
[Seealso:Figure87]
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P
Q
Tension
Shear
Pull-out
M T
Bending
Torque
Rotation
NOTE Insertwithflangesillustrated,butloadingmodesapplytoalltypesof
inserts,[See:5.1].
[SeeFigure88forthenotationforforcesactingonaninsert]
Figure42:Insertsystem:Summaryofloadingmodes
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5
Insert
5.1 General
Insertsareusuallydescribedbytheir:
Type,e.g.groupedbythemeansinwhichtheyareembeddedintoasandwichstructure,[See:
5.2].
Size,[See:5.3].
Material,[See:5.4].
Surfaceprotection,[See:5.5].
5.2 Types
5.2.1 General
There are three types of insert which are distinguished by the method of integration into the
honeycombsandwichstructure;asshowninTable51.Theseare:
GroupAforsimultaneousbondingduringsandwichproduction;
GroupBforanexistingsandwichusingathermosettingresin,e.g.:
usualpottingprocessofstandardinserts.
anequivalentbondingprocedurefornonstandardsinserts.
GroupCformechanicalclampingorscrewingintoanexistingsandwich.
5.2.2 Group A
Theseinsertsareusedonlyinratherthinsandwichstructures,i.e.lowcoreheight,andcanbeapplied
onlyincaseswherenoparticularlockingdemandsexist.Moreover,itisratherdifficulttopositionthe
insertexactlyatthepointatwhichitisneededforconnectionpurposes.Forthisreason,theinserthas
a large diameter to enable the drilling of a bore hole and thread cutting to provide a margin of
between3mmand6mmformisalignment.
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Table51:Typesofinserts
Floating Nut
Diameter Potting Torque Thread
Type Shape Material Exchange Standards Comments
(mm) Considerations Locking Locking
Capability
Type A: Bonding during sandwich manufacture
None or The bore hole is drilled after
Full bonded
1 17 to 30 Al square e.g. Locktite No - sandwich bonding.
with core filler
shape Only for small core height.
Partially or Planes or
7 19 to 70 Al e.g. Locktite No - For high loads
fully potted riffles
NAS 1835
Al: Extended and heavy type for
Partially or Planes or Deformation PAN 3829
8 19 to 25 Insert Yes applying floating nuts and
fully potted riffles of thread ENN 379
Ti: Nut exchanging capacity.
NSA 5072
Carbon fibre
9 7 to 20
CFRP /
Al
tube bonded N/A
e.g. Locktite,
helicoils.
No No
Carbon fibre tube inserts,
[See also: A.3 and F.6]
into core
Al
Adhesive
14 to 22 (St) - - No - -
bonding
(Ti)
Key: St:steel;Ti:titanium;CFRP:carbonfibrereinforcedplastic
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5.2.3 Group B
Inserts potted by means of curing epoxy resin are the most important group. The main part of this
handbookisconcernedexclusivelywithinsertsofthistype.
Nonstandard alternatives, in which the normal potting is replaced by an equivalent bonding
procedure,aredescribedinAnnexAandAnnexF,[See:A.3andF.6].
A normal potted insert, incorporated in honeycombsandwich structures by potting, has the basic
shapeshowninFigure51.
Figure51:Typicalinsert
Ahollowcylindricalbodywithflangedendsisthestandardconfiguration.Boththediscsandflanges
provide a formlocking connection with the resin and prevent applied loads from being transferred
onlybyadhesionshearforcesbetweenresinandinsert.
Theupperflangeispiercedbytwoholes,onefortheinjectionofthepottingresinandoneforventing
purposes.
The cylindrical section and the lower flange have a riffled surface, or the lower flange has flats on
opposite sides. Both provisions increase the shearload capability when the insert is subjected to
torsion.
Athincircularsheetinthelowerflangeprotectsthethreadfromresincontaminationduringpotting.
Arecessintheupperpartofthecylindricalbodypermitsthreaddeformationbycompression.Thisis
toensureselflockingofthematedscrew.
[Seealso:10.3forflangedinserts]
5.2.4 Group C
Themechanicallyfastenedinsertshavesignificantdisadvantages:
Nodirectconnectionwiththesandwichcorewhichcauseslowloadcarryingcapability;
Anindividualadaptedsizeforeachcoreheight;
Torquecanbetransferredbyadhesivebondingonly.
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Table52:Pottingmethods
Potting Potting Expected
Device Comments
method level(1) filling
Feasiblebutimpracticablemethod.A
resinreservoirisneededaboveeach
full verygood
inserttocompletefillingduetoresin
Resinfunnel shrinkage.
Casting
apparatus
Nolongerinuse.
partial bad Sandwichplatehastobeturnedover
beforecuring.
Compressedair full good(2) Veryeconomicalmethodwhenalarge
cartridges(Semco
partial good numberofinsertsarefitted.
cartridges)
Usualforasmallnumberofinserts,e.g.
Injection
Manualinjection repair.
full good(2)
(bysmallmedical Injectionmethodsenablehandlingof
partial good
squirter) sandwichplateimmediatelyafter
potting.
Usualwheninsertsarepottedduring
Foaming no full good
sandwichmanufactureprocess.
Notadvisableforstandardpotting,i.e.
Paste full fillingofhoneycombcells.
spatula bad
application partial PreferredmethodforCFRPtubeinserts,
[Seealso:A.3;F.6].
NOTE(1) Seealso:Figure87forschematicoffullandpartialpotting.
NOTE(2) 100%fillingisnotpossiblebecauseasmallamountofairalwaysremainstrappedatthetopof
corecells.
5.2.6 Injection
Theinjectionmethodisthemostfrequentlyusedbecauseofitsadvantageswhenalargenumberof
insertsarefitted.
NOTE Except for data in Annexes, the data given in this handbook for
standardinsertsarebasedupontestresultsfromspecimensprepared
bytheinjectionmethodinaccordancewiththestatedmanufacturing
procedure,[See:23.3].
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5.3 Sizes
5.3.1 General
There are a wide variety of sizes, shapes and dimensions available because inserts were developed
separatelyinvariouscountriesbydifferentcompanies.
Theproductscanbegroupedas:
Commerciallyavailable,whicharestandardspecifieditems,[Seealso:A.2];
Nonstandard, which are designed and manufactured inhouse for a particular project
application,[Seealso:A.3]:
basedonconventionalinsertdesigns,wheredimensionsormaterialsusedaredifferent,
[Seealso:F.1forcasestudies];
novel insert designs, e.g. carbon fibre tube inserts, [See also: A.3; F.6 for an example of
theirusewithintheRosettaLanderproject].
5.3.2 Standards
Many inserts have been qualified to meet company standards, projectrelated standards or, after
approvalbynationalairworthinessauthorities,nationalstandards.
AlistofsomestandardsisgiveninTable53.
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Table53:Listofinsertstandards
1832
1833
NationalAerospaceStandard NAS 1835
1836
1837
65187
65188
65189
DeutschesInstitutfrNormung DIN 65190
65191
65192
65193
16487
16488
TransallNorm TAN
16489
16490
3825
3826
PanaviaStandard PAN 3827
3828
3829
DeutscheAirbusNorm DAN 214
5345
NormalisationSudAviation NSA
5074
366
377
ERNONorm ENN 379
386
398
5.3.3 Strength
Themostimportantparametersrelatedtostrengthare:
Insertoveralldiameterdi;
Insertoverallheighthi
Consequently, within this handbook, the insert loadcarrying capabilities are based on these two
parameters.
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NOTE Testprogr.denotesdiametersinvestigatedin[Ref.[51]].
Key:(*)SeealsoTable51
Figure52:Standardisedinsertdiameter
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Key:(*)SeealsoTable51
Figure53:Standardisedinsertheight
Whenstandardisedinsertheightsareplottedasafunctionofstandardisedinsertdiameters,asshown
inFigure54,thedashedlinesdenoteexamplesoflineardependencies.
Anadvisedsetofinsertheightswasderivedonthebasisofthestraightlinethatconnectsthecrossing
ofpreferreddiameterswithheightsinwholemillimetres.
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Figure54Preferredsetofinsertheights
5.4 Materials
5.4.1 General
The majority of standard commerciallyavailable inserts are made from certain grades of metals or
combinationsthereof,thesebeing:
AluminiumAlloys
TitaniumAlloys
Steels,bothcarbonsteelandstainlessalloys.
[Seealso:ECSSQ7071]
Nonstandardinsertscanbemadefromthesameordifferentgradesofmetalsor,morerecently,from
carbonfibrereinforcedplastics,[Seealso:A.3].
AsummaryofinsertsusedinspaceapplicationsisgiveninAnnexAfor:
commercialproducts,[See:TableA1]
nonstandarditems,[See:TableA2].
[Seealso:AnnexFforcasestudies]
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Table54:Inserts:Aluminiumalloyequivalents
Country EquivalentGrade(1) StandardsOrganisation
Europe AW2024 CEN
3.1354T851 WerkstoffLeistungsblatt
Germany
AlCuMg2 DIN
3L65
U.K. BS../CommonFiles/GlossaryB.pdf
2024
AU4G1 AIR9050/C
France
2024 AFNOR
PAC4,5GM UNAVIA81102
Italy
9002/4(3583) UNI(oldsystem)
QQA225/6T8511 Federalspecification
U.S.A. 2024T8511 MILHDBK5
2024 ASTM
Japan 2024 JIS
Russia 1160 CIS
Key:(1)Chemicalcompositionsofequivalentalloysarenotalwaysidentical.
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5.4.4 Steels
5.5.1 General
All inserts need protection to prevent corrosion. Some typical insert materials and their surface
protectionaregiveninTable55.
AsummaryofinsertsusedinspaceapplicationsisgiveninAnnexAforbothcommercialproducts,
[See:TableA1],andnonstandarditems,[See:TableA2].
[Seealso:AnnexFforcasestudies]
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Table55:Typicalinsertmaterialsandsurfaceprotection
Someapplicable Appliedsurface
Materialdesignation
specifications protection
3.1354T8511Werkstoff
Leistungsblatt
2024(AlCuMg2) 2024T8511
Aluminiumalloys
AA606
AlMgSiCu
3.3214LN Chromated
softannealedtemper
81105UNAVIA
Titaniumalloy
3.7164.7WerkstoffLeistungsblatt
Ti6AI4V Normallynotnecessary.
TiAl6V4
MILHDBK5 Anodisedforspecial
solutiontreatedandaged
COMP.TA6V cases.
AIR9183
AISI303
ASTMA582
Stainlesssteel PassivatedLN9368
1.4305DIN
303BS
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5.5.2.1 Stainless steel
Insertsofstainlesssteelarepassivatedtoaspecifiedstandard,e.g.LN9368,CodeNo.1200.
5.6 References
5.6.1 General
[51] R.Hussey&J.WilsonRJTechnicalConsultants
LightAlloysDirectoryandDatabook,
Chapman&Hall,ISBN0412804107(1998)
[52] N.LavalSonacaSA,Belgium
Insertswithflanges
WorkingGroupcontribution(2004)
[53] J.BlockDLR,Germany
WorkingGroupcontribution(2004)
[54] MILHDBK5
MetallicMaterialsandElementsforAerospaceVehicleStructures
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6
Sandwich panels
Table61:Effectofsandwichcomponentsoninsertloadbearingcapability
Contributionofsandwichcomponenttoinsertloadbearing
Loadtype capability
Core Facesheet Core/facebond
Tension High Medium Verylow(1)
Compression High Medium Low
Shear Low High Verylow(1)
Bending High Medium Low
Torsion High Low Low
NOTE(1)Contributionincaseofnonmetallicfacesheetscanneedreconsideration.
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Figure61:Sandwichandcore:designation
6.2.1.1 Strength
The strength values of the face sheets do not usually influence the tensile or compressive load
carryingcapabilityofaninsert.
6.2.1.2 Stiffness
The capability of an insert under tensile and compressive loading is influenced by the bending
stiffness,B,ofthefacesheets.
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Figure62:Facesheetproperties:Isotropic,anisotropicandquasiisotropic
characteristics
Thustherelevantpropertiesofthefacesheetsare:
f facesheetthickness
Ef Youngsmodulusoffacesheets
f Poissonsratiooffacesheets
fy yieldstrengthoffacesheets
For an analytical determination of the insert loadcapability, these values should be applied in the
equationsdevelopedinAnnexC.
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6.2.1.4 Anisotropic face sheets
Thecouplingandflexuralstiffnessisusedinthecalculationoftheloadcontributionforanisotropic
facesheets.
Acloseapproximationcanbemaderegardingtheslightinfluenceofthefacesheet(about10%to20%)
attypicalfacesheettocorecombinations.
Efand f2inEqn.[6.21]arereplacedby(ExEy)and(xy)respectively,wherethesevaluesarethe
resultsoftheinplanelaminatetheory.
Theconversion,showninEqn.[6.21],enablestheinsertcapabilitydiagramstobeused.
Thesediagramsweregeneratedforsandwichstructureswithdifferentaluminiumfacesheets,butalso
appliedtosandwichstructureswithanisotropicfacesheets.
E x E y 1 Al
2
f Al
f an
4
E Al 1 x y
[6.22]
where:
fAl facesheetthicknessaluminium
fan facesheetthicknessanisotropicmaterial
Ex Emodulusxdirection
Ey Emodulusydirection
Al Poissonsratioaluminium
x Poissonsratioxdirectionanisotropic
y Poissonsratioydirectionanisotropic
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a)Tensilefailure b)Shearoutfailure
c)Dimplingfailure d)Bearingfailure
Figure63:Possiblefailuresmodes:Anisotropicfacesheetsundershearloading
Table 62 shows the shearload capabilities of tested CFRP face sheets, manufactured from two
materialsoftenusedinspacecraft.
Where the material or stacking sequences of the composite face sheets deviate, the shearload
capabilitiescanonlybeagrossindicationforthedesign.Inthiscase,adetailedinvestigationofthe
pinloadedshearcapabilityoftheselectedcompositehastobeperformed.
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Table62:FailuremodeandshearloadcapabilityoftestedCFRPfacesheets
Fibre E0basis 0max.
orientation test basistest Pmax. Failure Tension
0 dins/w(2)
() E0 theory(1) test(N) modes Compression
theory(1)
outer / inner (N/mm2) (N/mm2)
812 2653 dimpling T
0/90 75.047
790 2760 dimpling C
812 2253 dimpling T
90/0 75.047
790 2160 dimpling C
151 2660 bearing T
45/45 13.086
914CT300
0/90 95.542
410 2128 dimpling C
0.25
80 1931 T
45/45 12.518 tensile
118 2069 C
914CT300
bearing/
151 2234 T
tensile
45/45 13.086 0.16
bearing/
228 1849 C
tensile
NOTE(1)Propertiesshownwithgreybackgroundweredeterminedbylaminatetheory.
NOTE(2)Insertdiameter/Specimenwidth.
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Figure64:Corestrength:Deviation(%)ofactualstrengthfromguaranteedvalues
Thecorepropertiesaremoreimportantforinsertssubjectedtonormallyactingtensileorcompression
loads.Thesepropertiesarethe:
Shearmodulus,[See:6.4];
Shearstrength,[See:6.5];
Tensilestrength,perpendiculartothesandwichplane,[See:6.6];
Compressivestrength,perpendiculartothesandwichplane,[See:6.7].
Table63givesthemechanicalpropertiesofcommontypesofaluminiumcores.Mechanicalproperties
forsomecommontypesofnonmetalliccoresareshowninTable64.
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Table63:Mechanicalpropertiesofcommonaluminiumalloyhexagonaltypecores
NOTE(1)Designation:cellsizecorealloyfoilthickness
NOTE(2)Basisofinsertcapabilityplots,[See:AnnexB];P=90%values;Nottestedvaluesfromsuppliersdatasheets
NOTE(3)TTensile;CCompressive
NOTE(4)guar.guaranteed;typ.typical;min.minimum;av.average
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Table64:Mechanicalpropertiesofcommonnonmetallichexagonaltypecores
NOTE(1)Designation:materialcellsizedensity NOTE(4)guar.guaranteed;typ.typical;min.minimum;av.average
NOTE(2)Basisofinsertcapabilityplots,[See:AnnexB] NOTE(5)Notavailable
NOTE(3)TTensile;CCompressive NOTE(6)Nylonfibre/phenolresin
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GW
Gc 3
[6.41]
Where:
GW shearmodulusinWdirection.
[See: Table 63 for GC values for common types of aluminium cores; Table 64 for GC values for
commontypesofnonmetalliccores].
Thisappliesforguaranteedaswellasfortypicalshearstrengthvalues.
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Where:
0 critt tensilestrengthofcorematerial:
270N/mm2forAA5052H38(fromMILHDBK5),or
330N/mm2forAA5056H38.
c coredensity,e.g.32kg/m2for3/165052.0007core.
0 densityofcorematerial,e.g.2800kg/m2foraluminium.
ThetypicalvaluesccritttyplistedinTable63arebasedonthetypicalcoredensityctyp.
Theminimumvaluesccrittmintakeintoaccountthemaximumallowablescatterofcoredensityvalues
of10%.
c crit t min 0.9 0 crit t c
0 [6.62]
Theminimumvaluesccrittminwascalculatedby:
c crit t min 0.9 0 crit c typ [6.63]
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Thecompressivestrengthccritcofthecoreperpendiculartothesandwichplaneisgivenas:
ccritcmin minimumcompressionstrength:
o metalliccores:MILC7438F
o nonmetalliccores:suppliersdata.
ccritctyp typicalcompressionstrengthofcore,takenfromcoresuppliersdata.
[See:10.4]References
[61] MILHDBK5MetallicMaterialsandElementsforAerospaceVehicle
Structures
[62] MILC7438FCoreMaterial,Aluminum,ForSandwichConstruction
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7
Embedding of inserts
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Table71:Example:Insertpottingcompoundsforspaceapplications
Cure Tensile Compressive Shear Tensile Temp.
Supplier: Density
temp. strength strength strength modulus use
Source[]
R R crit R R crit ER
Productcode C C
kg/m3 N/mm2 N/mm2 N/mm2 N/mm2
Emerson & Cuming: 0.6 to MBB-ERNO [3]
14 36 10 2300 <100
Lekutherm X227 0.7 [See: 25.1; 25.3]
Altropol: CASA [1]; Patria [4]
Neukadur EP 270 + [7]; Astrium UK [7]
RT/24h
3M Scotchlite 0.64 14 36 10 2300 <100 with T3 hardener
+ 60/2h
H20/1000 micro-
ballons
Vantico: [2]; Sonaca [7];
Araldite 2011 (AW Case study: F.2; F.3
106/HV953U)
Vantico: Daimler-Benz Aero.
Araldite 2004 [1]; Sonaca [7]
RT
(Araldite AV138M/ [See: ECSS-Q-70-71]
HV 998)
3M Scotchweld [2]; Sonaca [7]; Case
EC2216 study: F.3; F.10
Emerson & Cuming: CASA [1]; Patria [4];
Stycast 1090/9 Kongsberg [6];
RT 73 (average)
Astrium UK [7]; See
also: IATP E.2
180 Alcatel Espace [1]
Emerson & Cuming: CASA [1]; Alenia-
Stycast 1090 SI: RT Spazio [1]; Astrium
UK [7]
Shur-lok: SLE 3010 CASA [1]; [2];
LVC Contraves [1, 2, 5];
RT
Case study:F.4; F.5;
F.7; F.9; F.10; F.11
Scheufler: DLR [7]; [8]; Case
RT/18h
L160 / H163 + glass study F.6; A.3
0.58 17 43 13 to 15 2000 <90
micro-ballons +
90/12h
Aerosil
Cytec/Cyanamid: FM Contraves [1]; Sonaca
150 (foam adhesive)
410-1 [7] for co-cured inserts
Others: [See: Suppliers websites for product information] [1]
Altropol: - - - - - - DASA-RI [1]
Neukadur EPX227/
RT
Durosehlt3 + 3M
microballons
Emerson & Cuming - - - - - - Alenia-Spazio [1]
(Possehl):
Lekutherm +
microballons
Silmid: AY103; - - - - - - Westlands [1]
RT/18h
AV121; HY951; BJO
60/1h
0930
3M RT - - - - - - BAe Airbus [1]
Loctite-Hysol RT - - - - - - BAe Airbus [1]
Vantico RT - - - - - - BAe Airbus [1]
Source [6] IATP2InsertAllowableTestProgramNo.2KongsbergGruppenAS,Test
[1] InsertTechnologyIndustrySurvey(1995) ReportNo.02TR68040906(Oct.1997)
[2] MatraMarconiSpaceContributiontoESAInsertDesignHandbook; [7] ECSSinsertdesignhandbookworkinggroupsurvey(2004)
MMSRef.NT/102/BG/355013.96(Dec.1996) [8] StudyonCarbonFibreTubeInsertsJ.Block,R.Schtze,T.Brander,K.
[3] FromESAInsertDesignHandbook(1987) Marjoniemi,L.Syvnen,M.Lambert:DLRBraunschweig/HelsinkiUniversity.
[4] Privatecommunication(Feb.2002) Technology/Patria;ESTECContractNo.16822/02/NL/PA,(2004)
[5] Privatecommunication(Feb.2002)
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Figure71:Pottinggeometry
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7.2.1.2 Type B insert
ThesedimensionsarevalidfortheTypeBinsert,[See:Table51].
Forcarbonfibretubeinserts,[See:Table51,TypeB9],thepottingdimensions,asdepictedinFigure
71,arereplacedbyequivalentparameters,[See:A.3andF.6fordetails].
7.2.2.1 General
Thecapabilityofaninsertcanbeimprovedbyincreasingthepottingradius,[Ref.[73]].Inpractice,
thiscanbeachievedbyopeningeachcellwithintheborehole.
7.2.2.2 Example
Table72showstheeffectofincreasingthepottingradiusforapartiallypottedinsert,[Ref.[73]].
Insert(single):
ShurlokSL601M615.9S;
diameter17.4mm,height15mm.
Sandwichpanel:
facesheets:aluminiumAZ5GUT6(7075T6),1mmthick.
core:nida440AG5,heightc=40mm.
Potting:SLE3010;RTcure.
Table72:Example:Effectofincreasedpottingradiusoninserttensilecapability
Borehole Averagevalue(N) Minimumvalue(N) No.ofsamples
Normal 7895 6240 4
Improved(1) 8850 7180 5
NOTE(1)AdditionalcellsopenedcomparedwithNormalborehole,[Ref.[73]].
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1
bp
n bn
[7.31]
Theeffectivepottingradius,bpdependson:
Insertradius,bi;
Sizeofcorecell,Sc;
Locationofinsertcentrewithinthehexagonalcell.
NOTE1 Theequationsprovidedhereassumeclassicalinsertpotting.
NOTE2 For carbonfibre tube inserts and other nonstandard insert designs,
the equations remain valid when an equivalent definition for bp is
used,[See:A.3andF.6fordetails].
Nonperforatedcore:
b p min 0.9bi 0.7 S c [7.33]
Nonperforatedcore:
b p typ bi 0.8 S c [7.35]
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Figure72:Effectivepottingradiusasafunctionofinsertdiameter
NOTE Improveddatausing(Eqn.[7.34])and(Eqn.[7.35])
[See also: Table 122 for perforated aluminium core, Table 123 for
nonperforated,nonmetalliccore].
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F N F
b R
R
PC
C
[7.41]
Where:
NPC numberofcorecellsfilledinwithpottingresin
FC crosssectionalareaofonecorecell:
Where:
0.95reductionforimperfecthexagonalshapeofcell;
SC nominalsizeofcorecell;
30forhexagonalhoneycomb;
FC 8.4mm2ifSC=3.2mm;
FC 19.0mm+ifSC=4.8mm.
Like the effective potting radius bp [See: 7.3], the real potting radius bR depends on bi, SC and the
positionoftheinsertcentrewithrespecttothehexagonalcell.bRisrelevanttothetensilefailureofthe
potting.
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Figure73:Realpottingradiusasafunctionofinsertdiameter
Thiscaseiscalledfullpotting.
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Thevalueof7mmresultsfromthe:
Boreholeshouldbe3mmto4mmdeeperthantheinsertheight;
Core,underneaththeinsert,hasatleasttobeconnectedbythepottingresinoveradepthof3
mm.
hp min, which is independent of core height, should be used for the derivation of permitted design
minima.
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Figure74:Pottingheightasafunctionofthehoneycombcoreheight
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Figure75:Meanweightofpottingmassesversuscoreheightandinsertdiameter
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Figure76:Correctioncoefficientforweightofinsertheights
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f bi
2
[7.61]
massofremovedcore(negligible).
7.7 References
7.7.1 General
[71] ERATechnologyLtd./RJTechnicalConsultants
InsertTechnologyforSpaceApplications
EuropeanIndustrialSurvey1995
[72] StandardisationofDesignAnalysisandTestingofInsertsinStructural
Elements.
Finalreport.ESTECContractNo.3442/77/NL/PPRider1
[73] MatraMarconiSpaceContributiontoESAInsertDesignHandbook;
MMSRef.NT/102/BG/355013.96(Dec.1996)
[74] J.Block,R.Schtze,T.Brander,K.Marjoniemi,L.Syvnen,M.Lambert:
DLRBraunschweig/HelsinkiUniv.Technology/Patria
StudyonCarbonFibreTubeInserts,
ESTECContractNo.16822/02/NL/PA,(2004)
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8
Mechanics of sandwich structures
Figure81:Schematicofstructuralsandwichpanelsubjectedtobothinplaneand
outofplaneexternalloading
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A sandwich assembly consists of two thin, stiff and strong face sheets separated by a thick, light,
compliant and weaker core material, [See: Figure 81]. The face sheets are adhesively bonded to the
coretoenableloadtransferbetweenthecomponents.
Inastructuralsandwich,thefacesheetsacttogethertoformanefficientstresscouplecounteracting
the external bending load, whereas the core resists shear and stabilises the face sheets against
buckling.
Theadvantagesgivenbysuchadesignconceptarenumerous,including:
Highstiffnesstoweightratio;
Highstrengthtoweightratio;
Integrationoffunctions,suchasthermalandacousticinsulation;
Highenergyabsorptioncapability;
Fewdesigndetails.
However,giventhelistofadvantages,currentlythemostimportantdrawbacksare:
Complicatedqualitycontrol;
Loadingandjoiningdifficulties,includingtheuseofinserts;
Lackofknowledgeconcerningtheeffectofdamage.
8.1.1.1 General
Thedesignofastructuralsandwichpanelisanintegratedprocessofsizingandmaterialsselection,
anditisthetaskofthedesignertoutiliseeachmaterialcomponenttoitslimit.
8.1.1.3 Core
Thecorematerialisjustasimportantasthefacesheetmaterial,eventhoughitdoesnotappearsoat
first.Usuallyitisthematerialcomponentthatthedesignengineerhastheleastknowledgeof.
Thepropertiesofprimaryinterestforthecorecanbesummarisedas:
Lowdensity;
Highstiffnessandstrengthperpendiculartofacesheets;
Highshearstiffnessandshearstrength;
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Thermalconductivity(loworhighdependentontheactualapplication);
Dielectricproperties,e.g.forantennaapplications.
Commonly used core materials for spacecraft applications are aluminium, Nomex and GFRP
honeycombs,andmorerarelypolymericcellularfoams,suchasPVCorpolyurethanefoams.
Figure82:Signconventionsforsandwichbeamelement
Consider a sandwich beam subjected to arbitrary external support and loading conditions, and
assumethatthefacesheetsareidentical,i.e.f1=f2=f.
For such a sandwich beam, it is recognised that two deflection parts contribute to the overall
deflectionpattern;asshowninFigure83:
Deflectionsduetobendingmoments:bendingwb
Deflectionsduetotransverseforces:shearingws
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Figure83:Deformedsandwichbeamelement:deflectioncontributionsfromboth
bendingandshearing
For a sandwich beam with thin face sheets (compared with the core thickness), the two deflection
partsmaybesuperimposedas(partialdeflectionsapproach):
w wb ws [8.11]
Thebendingdisplacementwbiscalculatedaccordingtoclassicalbeamtheory:
d 2w M
2
dx D [8.12]
M
wb dxdx C1 x C 2
D
Where:
C1andC2areintegrationconstantstobedeterminedfromtheboundaryconditions
oftheproblem;
Distheflexuralrigidityofthesandwichbeam.
ForsandwichbeamswithidenticalfacesheetstheflexuralrigidityDcanbeexpressedas:
f 3 f (c f ) 2 c3
D b E f E c [8.13]
6 2 12
Where:
b widthofthesandwichbeam
Ef elasticmoduliofthefacematerial.
Ec elasticmoduliofthecorematerial.
For sandwich beams with thin face sheets and low stiffness core material Eqn. [8.13] can
approximatedby:
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bf (c f ) 2
D Ef ForfcandEfEc
2
TheexpressiongivenforDinEqn.[8.14]correspondstoEc 0,whichin[Ref.[82]]isreferredtoas
anantiplanecore(theinplanestiffnessofthecorematerialisnegligible).
TheshearingdeflectionwscorrespondingtooverallshearingofthesandwichbeamisshowninFigure
84,whereitisassumedthattheshearingdeformationonlyoccursinthecore,i.e.Gf=,andthatthis
deformationislinear(assumingconstantcoreshearingstrainandstressoverthecorethickness).
Figure84Shearingdeformationofsandwichbeamelement
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dws Q c
0
dx S (c f )
[8.18]
M 0 cx
ws C3
S (c f )
Where:
C3 anintegrationconstant.
S thesandwichbeamshearingstiffness,whichisdefined by:
(c f ) 2
S Gc [8.19]
c
Eqn.[8.19]togetherwithEqn.[8.12],constitutesthecompletedisplacementsolutiontothesandwich
beamproblem.
Consequentlytherearefourconstants(C1,C2,C3, 0),whicharedeterminedfromthestatementofthe
boundaryconditions.
Thestressesinthesandwichbeam,i.e.thenormalstressesinthefacesheets(thefacesheetshearing
stresses are usually ignored) and the normal and shearing stresses in core material can be
approximatedintheform(validforEc<<Efandf<<c):
c c
Mz 2 f z2
xf E f where
D c c
z ( f )
2 2
[8.110]
Mz c c
xc Ec where z
D 2 2
Q
c
b(c f )
Usuallytheinplanecorenormalstressxcisofinsignificantmagnitudeandisthereforeignored,i.e.:
Ec=0xc0forantiplanecore.
8.1.2.1 Application
Theprinciplesappliedinthederivationspresentedprovideaverysimpletheory,whichnevertheless
includesthemainfeaturesofthemechanicsofsandwichbeams.Thusthetheoryaccountsfor:
The face sheets carry the bending moment loading and the core carries the transverse shear
loading.
Bothbendingandshearingcontributessignificantlytothedeformations.
The derived theory is valid for sandwich beams, but the same principles also apply for a sandwich
plateandshelltheories.
In the derivations it was assumed that the thickness of the face sheets was thin compared with the
corethickness,butthetheorycanbeextendedtosandwichpanelswiththickfacesheets.
Thiscomplicatesthetheoryasthebendingstiffnessofthefacesheetsthemselvescannotbeignoredin
thecaseofthickfacesheets.
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However,sandwich panelsfor spacecraftapplications are usually characterised by having very thin
face sheets compared with the core thickness, and the simple sandwich theory presented herein
providesaccurateresultswithrespecttopredictionofgloballoadresponsecharacteristics.
(A)Faceyielding/fracture.
(B)Coreshear.
(C)Shearcrimping.
(D)Generalbuckling.
(E1)and(E2)Facewrinkling(localbuckling).
(F)Facedimpling(intercellbuckling)
(G)Localindentation(localbendingoffacesheet).
Figure85:Failuremodes:HoneycombcoresandwichpanelsThefailuremodescanbe
groupedas,[See:Figure85]:
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Global:(A)to(D)areassociatedwiththegloballoadresponsecharacteristicsofthesandwich
panel.
Local:(E)to(G)areassociatedwithlocalloadresponsecharacteristics,orjustlocaleffects.
NOTE Theconceptoflocaleffectsinthiscontextreferstoscenarioswhere
thefacesheetstendtobendabouttheirownmidsurfacesratherthan
aboutthemidsurfaceofthesandwichpanel.
8.3.1 General
Asimplesandwichtheorywhichincludesthemostimportantaspectsofthemechanicsofsandwich
panels(atleastwithrespecttopredictionofgloballoadresponsecharacteristics)isoutlinedin8.1.
Thepossibleorlikelyfailuremodesarediscussedin8.2.
Thecausesoflocalbendingeffectsaredescribedfurtherhere.
Thesimpleclassicalantiplanetypeoftheory,[See:8.1],isbasedontheassumptionthatthedistancec
+ f between the middle surfaces of the face sheets remains unchanged during deformation, [See:
Figure 82 Thus, it is implicitly assumed, that the transverse stiffness of the core material (Ec in the
thicknessdirection)isinfinitelylarge.Obviously,thisisnottrue,andinregionsofloadintroduction
as well as in regions where material and geometric discontinuities are present, the assumption of
constantsandwichpanelthicknessdoesnothold.
Insuchregionsthefacesheetstendtoactasbeamsorplatesbendingabouttheirownmiddlesurface,
andsignificanttransversenormalandshearstressconcentrationsarepresentintheinterfacesbetween
thefacesheetsandthecorematerial.
The simplest possible case of local bending in a sandwich beam is given in Figure 86, [Ref. [84]],
whichshowsasandwichbeamunder3pointbending.
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Figure86:Schematicoflocalbendingeffectsinsandwichbeamsubjectedto3
pointbending
Itshowsthatthesandwichbeamrespondstotheloadintwoways:
Global load response, which can be accounted for using the simple classical antiplane
sandwichbeamtheory,anda
Local bending response, which cannot be accounted for using simple classical antiplane
sandwichbeamtheory.
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Joints between adjoining structural sandwich panels or sandwich panels and monolithic
structuralcomponents,e.g.Tjoints,cornerjoints;
Sandwichpanelswithinsertsandmechanicalfasteners.
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modelled as a special type of transversely isotropic solid where only the outofplane stiffness is
accountedfor.Theprinciplesbehindthishigherordersandwichbeamtheoryhasbeenadaptedand
extended, [Ref. [89], [810]], with the purpose of analysing sandwich plates with inserts (potted
insertsofthethroughthethicknessandfullypottedtypes).
Unfortunately,thehigherordertheoriesaremuchmorecomplexthanthesimpleclassicalantiplane
theoriesinamathematicalsense.Itisnotpossibletoderivesimpledesignformulaefromthehigher
order theories because they cannot be solved in closed form. Their solutions can only be achieved
usinganumericalapproach.
The higherorder theories can, however, account for the local bending effects leading to structural
failureofsandwichpanelsinquantitativeterms.
[See:8.5foradiscussionofthesedesigntheories]
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Figure87:Schematicofpottedinserttypesforsandwichpanelsusedfor
spacecraftapplications
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Figure88:Modeldefinitionofsandwichplatewiththroughthethicknessinsert
Inthemodellingofasandwichplatewithaninsert,itisassumedthattheinteractionbetweenadjacent
inserts, as well as the interaction between the considered insert and the plate boundaries or other
sourcesoflocaldisturbances,canbeignored.
Figure88definestheconstituentparts,thegeometryaswellasthepossibleexternalloadcases.The
sharp separation between the potting and the honeycomb core, [See: Figure 88] is a strong
idealisation,asthepottingtohoneycombintersectionisnotdefinedpreciselyinageometricalsense,
[Seealso:FigureD1].
Theboundaryconditionsimposedintheanalysisare:
r = bi: the throughthe thickness insert is considered as an infinitely rigid body to which the
facesheetsandthepottingmaterialarerigidlyconnected(clampingconditions);
r=bp:continuityofsolutionacrosspottingtohoneycombintersection;
r = a: it is assumed that the face sheets as well as the honeycomb midsurface are simply
supported,enablingshearstresstransferinbothfacesheetsandcore.
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8.4.4 Example
Topfacesheet:quasiisotropicFRPlaminate,Ef1=40GPa,f1=0.3.
Bottomfacesheet,sameastopfacesheet,i.e.Ef2=Ef1;f2 = f1.
Pottingcompound:bulkepoxy,Ep=2.5GPa;Gp=0.93GPa.
Honeycomb core: honeycomb 3/1650560.0007; Properties: Eh =310MPa; Gh (GW + GL)/2 =
138MPa.
Insert:throughthethickness;hi=f1+c+f2=12mm.
Externalload:compressiveoutofplaneload;P=1kN
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0
-0.05
-0.1
-0.15
-0.2
w1, wc, w2, mm
-0.25
-0.3
w1, wc, w2
-0.35
-0.4
-0.45
-0.5
0 25 50 75 100 125 150
r, mm
NOTE Outofplanedisplacements(coremidsurface):w1,w2,wc.
Load:Compressive(outofplane)P=1kN
Theory:Numericalhigherorder
Figure89:Example:Lateraldisplacementsofasymmetricsandwichplatewith
insertsubjectedtocompressiveoutofplaneload
Figure 89 shows the outofplane (lateral) deflections of the face sheets (w1, w2), and the core
midsurface,wc.InFigure89,Figure810andFigure811,rbp=30mmcorrespondstothepotting
region,whereasr>30mmcorrespondstothehoneycombregion.
Fromtheresults,[See:Figure89],theoutofplane(lateral)deflectionsofthetwofacesheetsandthe
corematerialmidsurfacesarealmostidentical.
As expected due to the symmetry of the sandwich plate considered, the outofplane (lateral)
displacementsofthetwofacesheetsw1,w2areidentical.
Themidsurface,outofplane(lateral)displacementofthecorematerialwc(pottingandhoneycomb),
however, is slightly different from w1, w2 close to the inserttopotting and pottingtohoneycomb
interfaces(difficulttoseeonthefigure),wherethecorechangesabruptly.Thedifferencebetweenthe
outofplane (lateral) face sheet and core displacements, encountered at these locations, causes the
inducementoftransversenormalstresses(c)inthepottingandthehoneycombcore.
Figure 810 shows the stress distribution in the core material. The values of the transverse normal
stress c aregivenattheinterfacebetweenthetopfacesheetandthecore (c top) andattheinterface
betweenthebottomfaceandthecore (c bottom).
Accordingtothehigherordersandwichplatetheory,c varieslinearlyoverthecorethickness.
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Figure 810 also shows the distribution of the transverse core shear stress component c, which is
assumedtobeconstantovertheheightofthecorematerial.
Consideringthe cdistribution,thepresenceoftransversenormalstressesisalocalphenomenon,as
significantc ccontributionsareonlypresentcloseto r = bi = 10 mm(i.e.closetotheinsert)andclose
to r = bp = 30 mm(i.e.closetothepottingtohoneycombintersection).Also, c top and c bottom areof
oppositesigns,i.e.whenoneiscompressivetheotheristensileandviceversa.
1.2
1
rz
0.8
0.6
c bottom
0.4
Core stress, MPa
0.2
-0.2
-0.4
-0.6
c top
-0.8
0 25 50 75 100 125 150
r, mm
NOTE Corestresscomponents:rz = c , ctop, cbottom
Load:Compressive(outofplane)P=1kN
Theory:Numericalhigherorder
Figure810:Example:Corestresscomponentsofsymmetricsandwichplatewith
insertsubjectedtooutofplanecompressiveforce
Consideringtheshearstressdistributioninthecorematerial,theoveralltendencyisthat c decreases
with increasing r-values. The overall tendency of decreasing c-values with increasing r is a
consequence of the fact that the total transverse shear stress resultant Pr total = Pr1 + Pr2 + cc is
inverselyproportionalto r (verticalequilibrium,P=2 r Pr total), andthatthemainpartofPiscarried
bythecorematerial, i.e. by c.
Figure 810 also shows that the abrupt change of core stiffness at the pottingto honeycomb
intersectiononlycausesminorfluctuationsofthec -distribution.
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Pertainingtothecombinedinfluenceofthetransversenormalandtheshearstresscomponentsonthe
pottingandhoneycombmaterials,themechanicalpropertiesofthetwomaterialsareverydifferent.
Thus, the stiffness and strength properties of the honeycomb material are usually an order of
magnitudelowerthanthoseofthepotting.
From Figure 810, the magnitude of the peak stresses in the potting and honeycomb regions are of
about the same magnitude, so a weak spot is located at the position of the pottingtohoneycomb
intersection(atr=bp)aswellasashortdistanceintothehoneycombmaterial.
Itisconcludedthatthestressconcentrationsinthepottingregion(closesttotheinsert)arenotlikely
tocauseafailure,exceptforthepossibilityoffailureduetoweakbondsbetweentheinsertandthe
potting as well as between the face sheets and the potting. However, the stress concentrations
encountered at the pottingtohoneycomb intersection and immediately after that, can provoke a
prematurefailure.
Theactivefailuremechanismsarelikelytobeoneoutofthree:
Honeycomb topsurface: Tensile ctop-stresses can cause a failure in the (weak) bond between
thetopfacesheetandthehoneycomb.
Pottingtohoneycomb intersection: Shear c-stresses can cause a shear rupture of the core
surroundingthepottingmaterial.
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0.5
-0.5
Mr1, Mr2, Nmm/mm
-1 M ,M
r1 r2
-1.5
-2
-2.5
-3
-3.5
0 25 50 75 100 125 150
r, mm
NOTE Radialbendingmomentresultants:Mr1,Mr2
Load:Compressive(outofplane)P=1kN
Theory:Numericalhigherorder
Figure811:Example:Radialbendingmomentresultantsinfacesheetsof
symmetricsandwichplatewithinsertsubjectedtooutofplanecompressiveforce
These results demonstrate that complicated loadtransfer mechanisms are active in sandwich plates
withinserts.Thisisespeciallypronouncedintheregionsclosetotheinsertandclosetothepottingto
honeycomb interface, i.e. in regions where significant changes of geometry and stiffness properties
takeplace.
Away from the locations of discontinuous change of geometry or material properties, the core
materialcarriestheloadinpureshearandnolocalstressconcentrationsarepresent.Intheseregions
classicalantiplanesandwichplatetheoryiscapableofdescribingthestressstateaccurately,[Seealso:
8.5forabriefsummaryofusinghigherordertheoryversusclassicalantiplanetheory].
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8.4.5.1 General
The actual purpose or function of the potting compound in the inserttosandwich plate system has
tworoles.
8.4.6.1 Structural
Make the radial extension of the potting compound denoted by bpbi, [See: Figure 88] as large as
possible.bpbiisofcourseverydifficulttocontrolinpractice,asthepottingradiusbpisdeterminedby
the flow of potting material into those of the honeycomb cells that have been left open during
machining,i.e. bpbi is determined by the manufacturing process.However, from a purely structural
pointofview,bpbiofatleast0.5bi,ensuresamaximumreliefofthefacesheetbendingandshearstress
concentrations, while, at the same time, the full shear stress transfer capability of the potting
compoundisutilised.
8.4.6.2 Stiffness
Ifpossible,theratioofthepottingstiffnesstothehoneycombstiffness,Ep/Eh,ischosensothatEp/Eh3
to 4. This ensures a good compromise between the peak stress level in the face sheets and in the
pottingandhoneycombmaterials.WhereEp/Eh3to4,thepeakbendingandshearstressesintheface
sheets are raised, while the transverse normal and shear stresses in the potting and honeycomb
materialsaredecreased.TheoppositeisseenforEp/Eh3to4.
The choice of potting stiffness properties invariably ends up being a tradeoff between having the
mostseverestressconcentrationsinthefacesheetsorinthepottingandhoneycombmaterials.
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8.4.6.3 Bending and shear
Thecapabilityofthefacesheetstoresistthepeakbendingandshearstressesadjacenttotheinsert,can
beimprovedconsiderablybyreinforcingthefacesheetsinthezoneswhereinsertsaremounted.Such
reinforcements,whichareusuallyusedforlaminatedFRPfacesheets,canbemadebyaddingextra
plies(suchasUDormultidirectionalprepregs)ontheoutersurfacesofthefacesheets.Thishasthe
effect of increasing the bending stiffness of the face sheets locally, thus causing a raise of the total
shearloadtransferthroughthefacesheets.Thiscausesadecreaseofthepeakstressesinthepotting
andhoneycombmaterials.
8.4.6.5 Elongation
Potting and adhesive materials with long elongation to failure properties are needed to counter
unavoidablesignificantstressconcentrationsinthepottingmaterialandinthebondlinesbetweenthe
honeycombcoreandfacesheets.
8.5 Remarks
8.5.1 General
The introduction to the mechanics of sandwich structures, [Ref. [814]] has provided an overall
impression of the structural behaviour of sandwich structures, [See: 8.1], [See also: 8.4 for potted
inserts].
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the intersection between the potting and the honeycomb. The peak shear stress in the honeycomb
material is located exactly at the pottingtohoneycomb intersection, and this stress component is
predictedaccuratelybyclassicalantiplanesandwichtheory.
In other words, for the outofplane load case classical antiplane and higherorder theories yield
almost exactly the same results with respect to the predicted shear stress distribution in the potting
andhoneycombmaterials,[See:Figure810forshearstressdistribution].Thus,itispossibletopredict
the loadbearing capability of sandwich plates with inserts subjected to outofplane loading using
simpledesignformulasderivedfromclassicalantiplanesandwichtheory.
[See also: Annex D for design formulae; Annex B for design graphs (derived on the basis of these
simpleexpressions)]
8.5.4 ESAComp
ESAComp is a software package for the design and analysis of composite laminates and structural
elementsfordesignengineersandstressanalysts,availablefromComponeeringInc.,Finland,[Ref.[8
13],[824]].
Addition of modules for the analysis of sandwich plates with throughthethickness, fully potted
andpartiallypottedinsertsundergeneralloadconditions,basedonthehigherordersandwichplate
theoryarefeasible.
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8.6 References
8.6.1 General
[81] Plantema,F.J.
SandwichConstruction
JohnWiley&Sons,NewYork,USA,1966.
[82] Allen,H.G.
AnalysisandDesignofStructuralSandwichPanels,PergamonPress,
Oxford,UK,1969.
[83] Stamm,K.andWitte,H.
Sandwichkonstruktionen(inGerman),SpringerVerlag,Wien,Austria,
1974.
[84] Zenkert,D.
AnIntroductiontoSandwichConstruction:Clause12:LocalisedLoads.
EMASPublishing,WestMidlands,UK,1995.
[85] StructuralMaterialsHandbook,Vol.1,ESAPSS03203,(1994):Clause
26Sandwichstructures;[Seealso:ECSSstandards]
[86] Frostig,Y.andBaruch,M.
BendingofSandwichBeamswithTransverselyFlexibleCore,AIAA
Journal28,pp.523531,1990.
[87] Frostig,Y.
OnStressConcentrationintheBendingofSandwichBeamswith
Transversely FlexibleCore,CompositeStructures24,pp.161169,
1993.
[88] Frostig,Y.andShenhar,Y.
HighOrderBendingofSandwichBeamswithaTransverselyFlexible
Core&UnsymmetricalLaminatedCompositeSkins,Composites
Engineering5,pp.405414,1995.
[89] Thomsen,O.T.
AnalysisofSandwichPlateswithThroughtheThicknessInsertsUsinga
HigherOrderSandwichPlateTheory,ESA/ESTECReportEWP1807,
1994.
[810] Thomsen,O.T.
AnalysisofSandwichPlateswithFullyPottedInsertsUsingaHigher
OrderSandwichPlateTheory,ESA/ESTECReportEWP1827,1995.
[811] W.Hertel,W.PaulandD.WagnerERNORaumfahrttechnikGmbH,
StructuresDept.,Bremen,D.
StandardisationProgrammeforDesignandTestingofInserts,ESACR
(P)1498,ESAContractNo.3442/77/NL/PP,1981.
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[812] W.Pauland D.WagnerERNORaumfahrttechnikGmbH,
StructuresDept.,Bremen,D.
StandardisationProgrammeforDesignandTestingofInserts,RiderII,
ESACR(P)1665,ESAContractNo.3442/77/NL/PP,1981.
[813] Saarela,O;Palanter,M;Hberle,J;Klein,M.
ESACOMP:APowerfulToolfortheAnalysisandDesignofComposite
Materials,ProceedingsoftheInternationalSymposiumonAdvanced
MaterialsforLightweightStructures,ESTEC,Noordwijk,March1994,
ESAWPP070,pp.161169.
[814] O.T.ThomsenCompConsult
WorkOrderNo.6ESTECContractNo.10.983/94/NL/PP(1996)
[815] O.T.ThomsenAalborgUniversity,DK
Privatecommunication(July2004)
[816] O.T.Thomsen
SandwichPlateswithThroughtheThicknessandFullyPottedInserts:
EvaluationofDifferencesinStructuralBehaviour
CompositeStructures,Vol.40,No.2,pp.159174.(1998)
[817] O.T.Thomsen&W.Rits
AnalysisandDesignofSandwichPlateswithInserts:AHighOrder
SandwichPlateTheoryApproach
CompositesPartB,Vol.29B,pp.795807(1998)
[818] O.T.Thomsen&W.Rits
AnalysisofSandwichPanelswithInsertsUsingaHigherOrder
SandwichPlateTheory.
Proceedingsofthe10thInternationalConferenceonCompositeMaterials
(ICCM10,Eds.K.StreetandA.Poursartip),Vancouver,Canada,Vol.5,
pp.3542.(1995)
[819] O.T.Thomsen
SandwichPlateswithInsertsModelling,AnalysisandDesign
ProceedingsoftheESAConferenceonSpacecraftStructures,Materials
andMechanicalTesting
ESTEC,Noordwijk,TheNetherlands,pp.619626(1996)
[820] O.T.Thomsen
LoadIntroductionAspectsinSandwichPanelswithHardPoints.
ProceedingsoftheFirstInternationalConferenceonCompositeScience
andTechnologyICCST/1(Eds.A.AdaliandV.E.Verijenko),Durban,
SouthAfrica,pp.539544(1996)
[821] O.T.Thomsen
HigherOrderEffectsinSandwichPlateswithInserts.
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ProceedingsoftheXIXthInternationalCongressonTheoreticaland
AppliedMechanics,Kyoto,Japan(1996)
[822] O.T.Thomsen
SandwichPlateswithThroughtheThicknessorFullyPottedInserts:
DifferencesinStructuralBehaviourandProperties.
EuropeanMechanicsColloquium(EuroMech360):Mechanicsof
SandwichStructures,Sainttienne,France,pp.407414.(1997)
[823] J.Stoer,R.Bulirsh
AnIntroductiontoNumericalAnalysis,
SpringerVerlag,NewYork,1980.
[824] M.Palanter:ComponeeringInc,Finland:
Privatecommunication(June2004)
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9
Design aspects
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Table91:Summaryofthebasicinsertdesignparameters
SPECIAL
GEOMETRY MATERIAL LOADS FAILUREMODE
CONDITIONS
Face sheet
Face sheet Mechanical loads Strength and stability Reliability
thickness
aluminium Short term and long design
GFRP term manufacture
CFRP control
testing
Life and residual
Core Core Static loads
strength
height foam tensile
cell size honeycomb: shear:
foil thickness Al 5052 + symmetric
perforated
Al 5056 + antisymmetric
GFRP torsion
bending moment
Nomex
magnitude of load
direction of load
Insert Insert Dynamic loads Failure of core
diameter aluminium shock shear
height steel vibration normal
titanium quasistatic buckling
cyclic
Potting Potting Conditions Failure of face sheets
diameter Classical: glass amplitude tensile
height bubble + epoxy exceedances shear out
configuration Other, [See: sequence dimpling
A.3; F.6 direction bearing
Insert-to-edge
Preload Failure of insert
distance
thermal fracture on insert flange
environment fracture on thread or
mounting stress screw
Insert-to-insert
Thermal Failure of potting
distance
same normal quasistatic resin fracture on basic
load dynamic plane
opposite shear fracture on
normal load cylinder
Physical load
radiation
vacuum
humidity
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There is no standardised method to handle joints realised by inserts. In general, some of the
parameters are already available, e.g. global stiffness, thermal or moisture stability or functionality
aspects.
An insert joint is designed for the existing structure. However, a designer has a possibility to make
localchangestotheglobalstructuretoobtainabetterjointusinganinsert.
Figure91illustratesthevariousdesignalternativesandparameters.
Figure91:Basicaspectsofinsertdesign,analysisandtesting
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AfurtherconsequenceofsandwichpanelwithCFRPfacesheetsrelatestothedesignprocedure.Itis
not possible to select inserts independently of the panel design. The panel global capability is
significantlyinfluencedbytheholecuttoincorporatetheinsert.Inparallelaretheinsertloadcarrying
capabilitiesunderinplaneloadingwhicharereducedbytheglobalmembranestressappliedtothe
panelfacesheet.
Consequentlythedesignerisconfrontedwiththeinteractionofglobalandlocalrequirements.
Figure92:Insertloadcases
Figure93:Insertoutofplaneload
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C om p r es sion T en sion
Tor sion
Figure94:Insertinplaneload
9.3 References
9.3.1 General
[91] L.Sylvnenetal:PatriaFinaviacompOy,Finland
AnalysismodelsforinsertdesignrulesinsandwichpanelswithCFRP
facings
Patriareport:GS1PFCRP0002(January2003)
ESTECContractNo.14076/99
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10
Design considerations
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B Singleinsertnearedges [See:18.1;18.2]
C Insertaxisparalleltofacings
Figure101:TypicalinsertarrangementsLoad capability
Variousinsertarrangementsaredescribedinmoredetail:
CaseA:Singleinsertwithoutedgeinfluences,[See:12.1].
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CaseB:Singleinsertnearedge,[See:17.1;17.2]
CaseC:Insertaxisparalleltofacesheets.
NOTE Tobeavoidedduetotheverylowloadcarryingcapability.
CaseD:Adjacentinsertsaxialloading(samedirection),[See:19.1].
CaseE:Adjacentinsertsaxialloading(oppositedirection),[See:19.2].
CaseF:Adjacentinsertsinline(profilejunction),[See:19.1].
CaseG:Adjacentinsertsingroup(bracketjunction),[See:19.1].
10.2.1 General
Aninserttransfersfivebasictypesofload,whichcanactsinglyorcombined.Theseare:
Tensile, where the load is normal to the plane of the sandwich away from the surface, [See:
12.1];
NOTE Alsoknownaspullout.
Compressive,wheretheloadisnormaltotheplaneofthesandwichtowardsthesurface,[See:
13.1];
Shear,wheretheloadisintheplaneofthefacesheet,[See:14.1];
Bending,[See:15.1];
NOTE Alsoknownasrotation.
Torsion,[See:16.1].
NOTE Alsoknownastorqueout.
TheloadconditionsaresummarisedinFigure102.
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Loadcapability
Loadintheplaneofthefacing
c [See:14.1]
Shearload
Bendingload
d [See:15.1]
alsoknownasrotation
Torsionalload
e alsoknownas [See:16.1]
torqueout
Figure102:Insertloadconditions
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10.2.1.1 Tensile, compression and shear
Adesigngivespreferencetoloadingsintheinsertaxisortransversetoit,i.e.tensile,compressiveor
shearloading;[See:Figure102a,bandc].
Whenaloadactsinadirectionthatformsanacuteanglewiththeinsertaxis,thisloadcanberesolved
into two rectangularlyacting components, thus producing tension and shear or compression and
shear.
10.2.1.2 Bending
Bending loads should be avoided because of the low bending strength and stiffness of an insert
system.
10.2.1.3 Torsion
Torsionalloadsonsingleinsertsarerestrictedtoscrewingandlockingtorquesonly.
[Seealso:10.6forgeneralguidanceoninsertselection]
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Figure103:Sandwichpanelwithmetallicfacesheets:Generaldesignrules
Thegeneraldesignrulesensurethat,[101]:
Compressiveloadsaretransmittedviathefacesheetintheareaofthepotting.Thebracketor
footneedstohaveatleastthemaximumextensionofthepotting;[See:Figure103a].
The insert flange remains parallel to the face sheet such that under inplane loads it cannot
movebelowthefacesheet;showninFigure104b.
Loadsinplaneofthefacesheetareusuallytransmittedbybearingpressurebetweentheouter
insertflangeandthefacesheet;showninFigure104a.
Theborderofthefacesheetaroundtheinsertiswellsupportedtoaccommodateahighbearing
stress,createdinsidebythepottingandoutsidebythebracketorfoot.
Underasufficientpreloadoftheinsertboltminororsecondarybendingmomentsarecorrectly
reacted;asshowninFigure105a.
Major moments in plane of face sheets are introduced by a couple of inserts. Moment
introductiontoaninsert,asshowninFigure104b,shouldbeavoided.
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Figure104:Insertdesignunderinplaneload
Support of insert by an
a adequate diameter of
the counterpart
Introduction of bending
b to the insert (to be
avoided)
Figure105:Insertdesignloadedbymoments
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Formetallicfacesheets,theinsertsareinstalledsuchthattheirflangesareflush,i.e.inplanewiththe
outer plane of the face sheet in order to maintain the advantages summarised by the design; [See:
10.2.2Designguideformetallicfacesheets].Thetoleranceofinstallationissuchthattheflangecanbe
below the outer plane of face sheet by 0.03 mm but never exceeding the face sheet, i.e. protruding
insertsshouldbeavoided,[101].
An insert potted in accordance with this tolerance does not loose a significant part of its preload
whenitisexposedtoelevatedtemperature.
If an insert flange is protruding slightly out of the face sheet due to inadequate manufacturing
tolerances,itcanbemachinedsothatitbecomesflush.Thispracticeissometimesappliedsuccessfully
withaluminiumfacesheet.
Figure106:CFRPfacesheets:Effectofsmallchamferoninsertflangeonload
transfertofacesheet
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10.3.1 General
Positioning of inserts with respect to the surface of the sandwich panel depends upon mounting
needs,[Seealso:10.6forselectionofinserts;10.2forloadconditions].
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A Flushmountedinsert
Recessedinsert
B
0mm<x<0.03mm
Protrudinginsert
C
withbondedflange
Figure107:Insertmountingmodes
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10.4.1 General
To achieve a satisfactory junction of components, the brackets should exhibit a sufficiently large
contactareaattheconnectingpoint.
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Incorrect design
Incorrect design
Figure108:Connections
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10.5.3 Examples
Someexamplesoftheuseofinsertsinspaceapplicationsareprovidedfrom:
IATPinsertallowabletestprogramme,[See:E.1];
CasestudiesofsomeEuropeanprojects,[See:F.1];
Jigsandfixturesappropriatefortestinginserts,[See:H.1].
10.6.1 General
The terms used to describe the standard forms of inserts varies across the industry, [See also: Table
51;Figure87].e.g.:
Partiallypotted,alsoknownasblind,borneorsinglesided.
Fullypotted,alsoknownasblindorborne.
Throughthethickness,alsoknownastransverseordoublesided.
Nonstandardformsofinsertscanbevariationsorcombinationsofthestandardtypes,[See:A.3].
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Figu
re109:Selectionofinserts:Partiallypotted
10.6.1.3 Through-the-thickness
Theseareusedwhenlocalbendingmomentsareappliedtosingleinserts.Thisenablesthebendingto
be transferred directly to the sandwich panel face sheets, as shown in Figure 1010.These forces are
thencounteredbytheinplaneforcesineachfacesheet.
Throughthethickness inserts are also used where a bolted connection to each side of the sandwich
panelisnecessary,e.g.ASAP5,[101]
Figure1010:Selectionofinserts:Throughthethickness
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10.6.3.1 Example
ThemechanicalpartsoftheEMATVCargoCarrierconsideredadditionalsafetyfactors(SFadd),which
wereappliedto,[102]:
Bonding,structuralinserts(axial):Ultimate:
Tested:1.0
Nottested:1.2
Equipmentinsertsinhoneycomb:Ultimate:
Tested:1.1
Nottested:3.0
Where:
Fy Flim SFadd J E [10.62]
10.7.1 Minimum
TheminimuminsertcapabilitiesPSS min,[Seealso:12.5]arerelatedtotheminimumvaluesof:
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manufacturingspecification,[See:23.1;24.1;25.1];
qualityassurancespecification,[See:26.1;27.1;28.1].
If the minimum material data and potting dimension apply, the probability of exceeding the given
minimumloadcapabilityis99%withaconfidencelevelof95%.
10.7.2 Average
TheaverageinsertcapabilitiesPSS av[See:12.7;AnnexB],arerelatedtotheaverageortypicalvalues,
respectively,of:
ccrittyp,ccritttyp,ccritctyp
10.8 Pre-design
The design methods detailed within this handbook have been successfully applied to numerous
applications. Some different or simplified hypotheses that have been suggested for predesign are
summarisedhere.Allinformationpresentedistakenfrom[101].
NOTE1 Whatever the analysis method used to determine insert capability,
validation tests are necessary for critical cases, i.e. where safety
marginsobtainedbyanalysisaretoolow.
NOTE2 Guaranteedloadcapabilityvaluesare:
highlydependantonmanufacturingprocessesandtheircontrol;
reliantuponadequatequalityassuranceprocedures.
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10.8.1.1 General
Ithasbeenconsidered,andconfirmedbyexaminationoftherupturemode,thatthistypeofloadis
transferredbybearinginthefacesheet.Theallowableforceisthengivenby:
Fall bearingall t [10.81]
Where:
bearing all allowablebearingstressoffacesheetmaterial;
t thicknessofcontactareabetweeninsertandfacesheet;
diameterofcontactareabetweeninsertandfacesheet.
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Figure1011:Predesign:Throughthethicknessinsertunderbending
Thisanalysisapproachcorrelateswellwithtestresults,butitassumesthattheinsertandboreholeare
ofthecorrectdimensions,i.e.theboreholeismachinedpreciselyfortheinsertused.Iftheboreholeis
toolarge,thentheallowableforceisseverelyreduced.
[Seealso:23.10fordefects]
where:
all allowableshearstressofbonding,e.g.10MPa,typically;
Sbonding areaofbonding.
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Figure1012:Predesign:Facesheetshearoutfailuremode
Theloadcapacitycanbedeterminedby:
Fall 2 d t all [10.83]
where:
d distancefromthepaneledge;
t facesheetthickness;
all allowableshearstressoffacesheetmaterial.
where: D diameterofpotting,[See:Figure1013].
h coreheight;
all allowableshearstrengthofhoneycomb.
NOTE1 Forpartiallypottedinsertswithalowheightcomparedwiththecore
height,thecalculationisnotvalid.
NOTE2 A pessimistic assessment can be obtained by substituting the
heightoftheinsertforthecoreheight(h)inEqn.[10.84].
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Figure1013:Predesign:Throughthethicknessinsertundertransverseforce
10.9.1 General
Failurecanoccurinthesandwichstructurewithinsertsinmanydifferentwaysanddependson,e.g.:
Designparameters;
Loadcases;
Conditions;
Manufacturing.
Generally, the failure occurs in the core by shear stresses under outofplane loads and in the face
sheetunderinplaneloads,[101].
Failure modes are listed in Table 101.Failure occurring in the insert, fasteners and other attachable
devicesisnotconsidered.
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Table101:Failuremodesofinsertjoint
Failure
Failuretype Loadcase(1)
component
Shearfailure Outofplane(T,C)
Core
Tensionfailureunderneathpotting Outofplane(T)
Compressionfailureunderneathpotting Outofplane(C)
Tensilefailureunderneathinsert Outofplane(T)
Potting
Inserttearout Outofplane(T)
Adhesionfailurebetweeninsertandpotting Outofplane(T)
Adhesion
Adhesionfailurebetweencoreandfacesheet Outofplane(T)
Tensionfailure Inplane
Bearingfailure Inplane
Facesheet Dimplingfailure Inplane
Wrinklingfailure Inplane
Shearoutfailure Inplane
Insert Lowerflange,thread,fastener,screw Notconsidered
Key:T=Tension;C=Compression
10.9.2.1 General
An outofplane load can be either tension or compression. It is good design practise to carry the
bendingmomentsbytheoutofplaneforceonpairsofinserts,asshowninFigure1014,[101].
TheloadistransferredthroughtheinsertsandwichsystemasshowninFigure1015.
Figure1014:Failuremodes:Momentload
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Figure1015:Failuremodes:Loadtransferinoutofplanecase
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10.9.2.2 Study of several cases
10.9.2.2.1 Overview
TheseveralcasesareshowninFigure1016andexplainedintheclauses10.9.2.2.2to10.9.2.2.5.
Figure1016:Failuremodes:Insertasafunctionofcoreheight
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10.9.2.2.4 Case C - partially potted
Thecrosssectionareaofthesinglecellfoilsundershearstressdependsonthecoreheight.Whenthe
crosssection area is large enough, the load carrying capability of the core in shear exceeds the load
carryingcapabilityofthecoreintensionandtheruptureoccursinthecoreunderneaththepotting.
Filled cell
Insert
NPC = 16
NPC = 16 Number of failing single cell wall = 26
Number of failing single cell wall = 24
Figure1017:Failuremodes:Noncorrelationbetweennumberofthefilledcells
andnumberofthefailingcellwalls
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Crossedcellwall
NPC = 17
Number of failing single cell wall = 24
Figure1018:Failuremodes:Unsymmetricalpottingandcrossedcell
It can be concluded that it is impossible to consider in advance how much bigger the real potting
shape is and semiempirical formulae for potting radius are used in the analysis of the insert load
carryingcapability,[101].
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10.9.3.1 General
Aninplaneloadcanbeeithertensionorcompression.Agooddesignpractiseisthattorsionloadsare
carriedbyinplaneloadsonseveralinserts.TheloadsareshowninFigure1019,[101].
Tension
Compression
Torsion
Figure1019:Failuremodes:Inplaneandtorsionloads
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ForCFRPfacesheetsunderinplaneloads,thefailuremodestobeconsideredareillustratedinFigure
1020:
Tensilefailure(tension);
Shearoutfailure(tension);
Dimplingfailure(compression);
Bearingfailure(tensionorcompression);
Wrinkling.
Figure1020:Failuremodes:CFRPfacesheets
A tensile failure occurs in a large panel with a sufficientlylargeedge distance. A localfailure starts
fromtheedgeofthehole;asshowninFigure1020(a).
Ashearoutfailureoccurswhentheedgedistancefromtheholeissmall.Thefailurelinecanbeatany
angledependingonthelayupofthefacesheetlaminate.
Undercompressionloading,afacesheetcanbuckleordimpleintothespacesbetweenthehoneycomb
corewalls.Thustheedgeandfrontareclamped.Dimplingofthefacesheetsdoesnotleadtofailure
unlesstheamplitudeofthedimplesbecomeslargeandcausesthedimplesorbucklestogrowacross
thecellwalls,whichresultsinaglobalfailureknownaswrinkling,[Seealso:8.2].
A bearing failure occurs in cases in which both the edge distance and the panel width are large in
comparisonwith the insert diameter.Such damage islocalised.The failure is usually notassociated
withacatastrophicfailureofacompositestructure.Theinitiationofsuchafailurecanbecausedby
compressivebearingatthebaseoftheinserthole.Assumingasinusoidalstressdistribution,themost
susceptibleareaislocatedinfrontofthecentralpointofthehole,[101].
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10.10 References
10.10.1 General
[101] L.Sylvnenetal:PatriaFinaviacompOy,Finland
AnalysismodelsforinsertdesignrulesinsandwichpanelswithCFRP
facings
Patriareport:GS1PFCRP0002(January2003)
ESTECContractNo.14076/99
[102] N.Laval:SonacaS.A.,Belgium
Insertswithflanges
WorkingGroupcontribution(September2003)
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11
Design flow chart
11.1 Introduction
In order to achieve anappropriate design using the guidelines providedin this handbook, it isalso
helpfultohavethestepsintheformofaflowchart.Owingtodifferentdesignconstraints,itisquite
oftenthecasethatnostraightforwardprocedureorguidecanbegivenforeverydayuse.Themain
constraintscanbedefinedas:
The sandwich design and the geometry of the joint are frozen, then the appropriate insert
geometryisdefined.
Thesandwichparametersaregivenandthecorrespondingnumberofinsertsandtheirsizeare
selected.
For an optimum design, the sandwich can be designed at the same time as an adequate number of
insertsandtheinsertgeometryaredefined.
In the case where the sandwich is predefined and the loads are given, [See: 11.2]. Where two main
parameters,e.g.geometryandnumberofinserts,canvary,[See:11.3].
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1 Input given:
Sandwich parameter
Number of connections to sandwich and distances
Set of load conditions on each connection point, e.g.
include preloads caused by tolerances, deflection,
temperature.
yes
is the
is increase
minimum load no
of insert diameter
sufficiently
possible?
high?
no
yes
Determine insert influences of:
Distance between them, [See also: 10.1, 19]
6 Edge distance, [See also: 18]
Temperature, [See also: 22]
Combined shear and normal load, [See also: 17]
are the
superimposed influencing
factors reasonably covered
by the load factor no
of 1.5?
yes
change to selection
loop 2 or 3
End of initial design
Figure111:Flowchart:Predefinedsandwichandloads
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1 Input given:
Sandwich parameter
Support geometry
Set of max. loads on strut, e.g. include preloads
caused by tolerances, deflection, temperature.
is an
appropriate design
of support no
possible?
yes
are the
superimposed influencing
factors reasonably covered
by the initial load no
factor of 2?
yes
change to selection
End of initial design
loop 3
NOTE Itcanbenecessarytorepeattheloop.Anadditionalconsiderationof
thedamagetoleranceaspectsisessential.
Figure112:Flowchart:Variablemainparameters
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11.4 References
11.4.1 General
[111] JesusGmezGarcia:EADSAstrium(Bremen),D
DesignGuideline
WorkingGroupcontribution(2004)
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12
Tensile strength
12.1.1 General
Thestaticstrengthcapabilitiesofastandard,singlepottedinsertwithoutedgeinfluences,orwithout
interferencefromsurroundinginserts,underoutofplanetensileloadaredescribed.
The design guidelines presented here cover partially and fullypotted inserts. For throughthe
thickness inserts the same procedures can be used if the nonapplicable failure modes are ignored.
Throughthethickness(spool)insertscannotfailbycoreorpottingtensionbeneaththeinsert.
Forthestrengthcapabilityofnonstandardinsertdesigns,[See:A.3;F.6].
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Figure121:Failuremodesinrelationtothecoreheight
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Thecriterionthatthisloadcanbetransmittedbybothfacesheetshasnotbeentakenintoaccountin
thedesigngraphsprovidedinAnnexB,[See:B.2].
NOTE Thistypeofcheckisnotnecessaryforinsertsinmetalliccoresbecausethe
modelhasbeenverifiedbymanyteststhatimplicitlycoveredthispoint.
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Table121:Propertiesfordeterminingpottedinsertcapability:Tensileload
Propertiesof MinimumvaluesPSStmin AverageorTypicalvaluesPSStav
components accordingto: accordingto:
Thickness f f
Sheet
Youngs
Ef Ef
modulus
Poissonsratio f f
Figure64 Figure64
Effectiveradius bpmin Table122 bptyp Table122
Table123 Table123
Potting
Figure71 Figure71
Realradius bRmin Table122 bRtyp Table122
Table123 Table123
Height hpmin Figure72 hptyp Figure72
Tensilestrength Rcritmin =9N/mm2 Rcrittyp =12N/mm2
Height c c
Table63 Table63
Shearmodulus Gc Gc
Table64 Table64
Core
Table63 Table63
Shearstrength ccritmin ccrittyp
Table64 Table64
Table63 Table63
Tensilestrength ccritmin ccrittyp
Table64 Table64
Perforatedcore RC =(1.720.0063c0.2641f) RC =(1.2070.00544c0.2088f)
RC(1)
Unperforated
RC =0.91 RC =1
core
NOTE(1)Modelcorrelationcoefficient,[See:12.3].
c=coreheight,formerlyshownashcinPSSIDH.
NOTE(2)[Seealso:AnnexGforlistingofequations]
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Table122:Perforatedcores:Effectiveandrealpottingradiusversusinsert
diameter
Corecellsize,Sc=4.8mm 3/16
Insertdiameter,di 9 11 14 17.5 22 mm
min 7.70 8.63 10.03 11.66 13.75 mm
Pottingradius,bp
typ 8.28 9.28 10.78 12.54 14.79 mm
min 6.18 7.18 8.64 10.43 12.68 mm
Realpottingradius,bR
typ 6.9 7.9 9.4 11.15 13.4 mm
Corecellsize,Sc=3.2mm 1/8
Insertdiameter,di 9 11 14 17.5 22 mm
min 6.33 7.26 8.66 10.29 12.39 mm
Pottingradius,bp
typ 6.81 7.81 9.31 11.07 13.32 mm
min 5.62 6.62 8.12 9.87 11.12 mm
Realpottingradius,bR
typ 6.1 7.1 8.6 10.35 12.6 mm
NOTEPerforatedcores,e.g.aluminium.
bpmin=0.93192bi+0.874Sc0.66151 bRmin=bi+0.35Sc
bptyp=1.002064bi+0.94035Sc0.7113 bRtyp=bi+0.5Sc
bi=0.5di
Table123:Nonperforatedcores:Effectiveandrealpottingradiusversusinsert
diameter
Corecellsize,Sc=4.8mm 3/16
Insertdiameter,di 9 11 14 17.5 22 mm
min 7.41 8.31 9.66 11.24 13.26 mm
Pottingradius,bp
typ 8.34 9.34 10.84 12.59 14.84 mm
min 6.18 7.18 8.64 10.43 12.68 mm
Realpottingradius,bR
typ 6.9 7.9 9.4 11.15 13.4 mm
Corecellsize,Sc=3.2mm 1/8
Insertdiameter,di 9 11 14 17.5 22 mm
min 6.29 7.19 8.54 10.12 12.14 mm
Pottingradius,bp
typ 7.06 8.06 9.56 11.31 13.56 mm
min 5.62 6.62 8.12 9.87 12.12 mm
Realpottingradius,bR
typ 6.1 7.1 8.6 10.35 12.6 mm
NOTENonperforatedcores,e.g.Nomex,GFRP.
bpmin=0.9bi+0.7Sc bRmin=bi+0.35Sc
bptyp=bi+0.8Sc bRtyp=bi+0.5Sc
bi=0.5di
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where:
P appliedoutofplaneload
coreshearstress
f facesheetthickness;assumingfacesheetsaresimilar
f1,f2 individualfacesheetthicknesses
h totalsandwichthickness=c+f1+f2
outerradiusofpanel
bp effectivepottingradius
bR realpottingradius
Ip momentofinertiaofthepanel
f1 f 2 (h c) 2
= [12.22]
4(h c)
Is moment of inertia of the face sheets
3 3
f1 f 2
= [12.23]
12
I = I p + Is
ratio of stiffness between core and face sheets
Gc (h c) I
= [12.24]
E c f1 f 2 I s
Gc shear modulus of the core
Es
E = [12.25]
1 s
2
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Table124:Outofplanecapability:Effectofcomponentsoncoreshear
Originalvalues +5%values Increase Influence
(N) (N) (N) (%)
bp 11.42 mm 3784 11.99 mm 3974 190 5.02
c 30.00 mm 3784 31.50 mm 3959 175 4.62
ccrit 1.46 MPa 3784 1.53 MPa 3973 189 4.99
f 0.30 mm 3784 0.32 mm 3825 41 1.08
NOTE Example case: Partially potted; D17, 3/160.001P; c = 30 mm, f = 0.3
mm.Failuremode:Coreshear.
Table125:Outofplanecapability:Effectofcomponentsoncoretension
Originalvalues +5%values Increase Influence
(N) (N) (N) (%)
bp 8.64 mm 6258 9.07 mm 6660 402 6.42
c 40.00 mm 6258 42.00 mm 6270 12 0.19
ccritt 8.45 MPa 6258 8.87 MPa 6389 131 2.09
ccrit 1.46 MPa 6258 1.53 MPa 6439 181 2.89
f 0.30 mm 6258 0.32 mm 6329 71 1.13
NOTE Examplecase:Partiallypotted;D14,1/80.001P;c=30mm,f=0.3mm.
Failuremode:Coretension.
Thecontributionsofthedifferentcomponentsfor,[121]:
CoreshearinFigure122
CoretensioninFigure123
Sensitivity of Out-of-plane
Core shear
f
7%
bp
32% Example case:
Partially potted
c crit D17,3/16-0.001P,
32% c = 30mm, f = 0.3mm
Pult = 3784N
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Sensitivity of Out-of-plane
Core tension
f
9%
Example case:
c crit
Partially potted
23% D14,1/8-0.001P,
c = 40mm, f = 0.3mm
Pult = 6258N
bp
50%
c crit t Total improvement 775N
16% c
2%
Figure123:Outofplanecapability:Contributionsofthemaincomponentson
improvedcoretension
BasedontheresultsinFigure122andFigure123,itcanbeconcludedthatthefacesheetthickness,f,
has very limited influence on outofplane capacity when the failure mode is core shear or core
tension,[121].
12.3.1 Overview
Twolevelsofinsertcapabilitieshavebeendeterminedandplottedasafunctionofcoreheight:
MinimuminsertcapabilitiesPSS min
AverageinsertcapabilitiesPSS av
[Seealso:13.2;AnnexB]
12.3.2.1 General
Theminimuminsertdesignvaluesarebasedupon:
Minimumstrengthproperties;
Minimumpottingdimensions;
Modelcorrelationcoefficient,RC
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Othertypesofcore:
RC=0.91
NOTE c=coreheight,formerlyshownashcinPSSIDH.
12.3.3.1 General
Theaverageinsertvaluesarebasedupon:
Averagestrengthproperties;
Averagepottingdimensions;
Modelcorrelationcoefficient,RC.
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Othertypesofcore:
RC=1
NOTE1 c=coreheight,formerlyshownashcinPSSIDH.
NOTE2 Verification of reliability coefficients applies to the sandwich panel
dimensionsinthishandbook.Paneldimensionsexceeding80mmby
0.8mmneedadifferentmethod.
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12.5.1 General
Standard type partially and fullypotted inserts are covered by the design rules provided here. For
throughthethicknessinsertsthesameprocedurescanbeusedifthenonapplicablefailuremodesare
ignored. Throughthethickness (spool) inserts cannot fail by core or potting tension beneath the
insert.
[Seealso:A.3;F.6fornonstandardinserts]
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12.5.3.2 Average values
ThePSS t av valuesareachievedinqualitycontroltesting,[See:28.1].
Inaddition,70%oftheaveragecapabilityvaluesareapplicabletodesignwithoutfurtherinvestigation
providedthatthe:
Core properties meet at least the typical or average values listed in Table 63 (metallic) and
Table64(nonmetallic).
Manufacturingconformswithmanufacturingandqualityassuranceprocedures,[See:23.1;24.1
and25.1formanufacturing;26.1;27.1and28.1forQA].
Loadtransferismaintainedbyasetofinsertsclosetogetherwithdifferentloads.Bypotential
loadredistribution,areducedfactorofsafetycanbeconsidered.
Where:
hi basicinsertheight=9mm
hi* newinsertheight
cI cvalueatcurvebreakforbasicinsertheighthi
cI* newcvalueatcurvebreakfornewinsertheighthi*
TheshiftisshownschematicallyinFigure124.
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Figure124:Influenceofinsertheightoninsertcapability
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Theincreaseinhi increasestheinsertcapabilityonlyforthosecaseswherethefailureoccursinthe:
Coreunderneaththepotting,or
Pottingunderneaththeinsert.
Anincreaseinhiisadvisedespeciallyifruptureofthepottingunderneaththeinsertisanticipated.
E Ex Ey [12.71]
Poissonsratio:
xy yx [12.72]
12.8 References
12.8.1 General
[121] LassiSyvnen,KariMarjoniemi,AriRipatti,MarkkuPyklinen:Patria
FinaviacompOy,Finland
AnalysismodelsforinsertdesignrulesinsandwichpanelswithCFRP
facings
Patriareport:GS1PFCRP0002(January2003)
ESTECContractNo.14076/99
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13
Compressive strength
13.1.1 General
Thegeneralstatementsmadein12.1fornormaltensileloadactingonpottedinsertsarealsovalidfor
compressiveoutofplaneloadwithsomeexceptions,describedhere.
Partially and fullypotted inserts are covered by the design rules presented here. For throughthe
thickness inserts the same procedures can be used if the failure modes which cannot occur are
ignored.Throughthethickness(spool)insertscannotfailbycorecompressionbeneaththeinsert.
Forthestrengthcapabilityofnonstandardinsertdesigns,[See:A.3;F.6].
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13.1.5.1 Minimum
Theminimuminsertcapabilityisgivenby:
PSScmin=RCPcritmin [13.11]
where: RC=0.89
13.1.5.2 Average
Theaverageinsertcapabilityisgivenby:
PSScav=RCPcritav [13.12]
where: RC=1
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Support of the CFRP laminate can be compromised by slight variations in tolerance of the
components,i.e.:
finishing operations performed on protruding inserts after potting can damage thin CFRP
laminates,
slippagebetweenthebracketsandfacing,e.g.undervibrationloads,cancausedamageonthe
surfacesoftheCFRPfacings,
Misalignment or poor fabrication can result in gapping in the contact area, such that the
intendedsupportaroundtheinsertholeisnotachieved.
Oneoptionistouseaprotrudinginsert,asshowninFigure131.Inthiscasetheborderoftheinsert
holeisbondedwithresinduringpotting[Seealso:10.2,10.3].
Figure131:Compressivestrength:Protrudinginsert
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14
Shear strength
where:
bp pottingradius.
Thisisnecessarytoprovidesufficientclampingoftheinsertandpreventtheinsertfrombeingpushed
undertheupperfacesheet;asshowninFigure141.
Figure141:Shearloadedinserts:Clampingconditions
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where:
Wcrit shearstrengthofcoreinWdirection.
NOTE Thecriticalshearloadisquasiindependentofthecoreheight,c.
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Thepermissibleshearload,QSS,whichcanbetheappliedtotheinsertisgivenbythesemiempirical
formula:
QSS 8bp2 W crit 2 f b p fy for bp 11 mm [14.21]
Where:
bp pottingradius,[See:7.3;Table122;Table123
Wcri t shearstrengthofcoreinWdirection,[See:Table63;Table64].
fy yieldstrengthoffacesheets,accordingtostandards,[See:6.6].
f thicknessofupperfacesheet.
[Seealso:14.3forcompositefacesheets]
This expression is limited to values of bp less than 11 mm due to the difficulty of clamping greater
pottingradii,[See:Figure141].
NOTE bp=11mmisusedinEqn.[14.21]forbp>11mm.
14.3.1 Strength
Thesecommentsapplytoinsertsremotefromedgesorotherdisturbances.Theanalysismethodforin
planeloadisbasedontestdata.However,theresultsoftheseanalysesdonotcorrelateverywellwith
thetests,[141].
Thebestcorrelationiswithmetallicfacesheetsandfacesheetswith0/90fibreorientations.
The worst correlation is with face sheets with 45 fibres orientations and HT high tenacity or HM
highmodulusfibres.
ThecorrelationisshowninFigure142andFigure143,[142].
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Figure142:Correlationbetweencalculatedandtestedinplanecapabilitieswith
fibreorientation
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Figure143:Correlationbetweencalculatedandtestedinplanecapabilitieswith
fibrestrength
TheinplaneloadQ,appliedtotheinsertisconsideredtoactinthemidplaneoftheupperfacesheet.
Thediameterofthefootoftheattachedpartshouldbeatleastaslargeasthetypicalpottingdiameter.
Ageneraldesignapproachconsistsoffourprimaryelements,wherethecapabilityofthesandwich
insertsystemisinvestigatedwithrespecttothe:
Globalstressactingasaremotestressintheareaoftheinsert;
Stressconcentrationimposedbytheinsertholeinthepanel;
Inplaneloadsloadingtheholebybearingpressure,then
Radialandcircumferentialstressesimposedbytheloadnormaltothefacesheet.
Inaddition,theeffectofseveralinsertsclosetoeachother,theirrelativedirectionofloadsaswellas
theeffectoftheirdistancefromfreeboundariestakenintoaccountinanapproximatemanner.
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where:
ts facesheetthickness,
bp pottingradius,
sy yieldstrengthofthefacesheet.
Foranunsymmetricalloadcase:
QSttt _ unsymm. 2t s b p sy [14.32]
In the partially potted case the core contribution should be taken into consideration by the semi
empiricalexpression:
Qc 8 b p2 Wcrit [14.33]
where:
Qc corecontributionofinplaneloadcarryingcapability.
Wcrit shearstrengthofcoreinWdirection.
Thepermissibleshearloadcarryingcapabilityforapartiallypottedinsertisgivenby:
QS 8 bp2 W crit 2 ts bp sy [14.34]
14.3.3.1 Overview
AtleastfourdifferentfailuremodesofCFRPfacesheetsarepossibleunderinplaneloads,[Seealso:
Figure63]:
Tension;
Shearout;
Dimpling;
Bearing.
NOTE Theanalysisgivenappliestofacesheetswith0/90 fibre directions
only.
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14.3.3.2 Tension (net section)
Thebasicequationtoestablishthemaximuminplaneload,Qtagainstfailureintensionis:
1
Qt ( w bi )t s t ,ult [14.35]
K e'
where,[See:Figure144fornomenclature]:
Ke stressconcentrationfactordependinguponbi/wande/w,[See:Figure145];
w panelwidth;
bi insertdiameter;
ts facesheetthickness;
t,ult ultimatetensilestrengthoffacesheet;
E edge distance.
P
P
w
bi
Figure144:Nomenclature:Ultimateinplaneloadagainstfailureintension
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Figure145:Shearstrength:Stressconcentrationfactor
14.3.3.3 Shear-out
ThebasicequationforthemaximuminplaneloadQtagainstshearoutfailureis:
bi 1
Qs 2t s (e ) s [14.36]
2 cos
Where,[See:Figure146fornomenclature].
angleoffailuredirection;
s inplaneshearstrengthoffacesheet.
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Figure146:Shearstrength:Failureangle
14.3.3.4 Dimpling
The maximum inplane load at which dimpling of the sandwich face sheet occurs, shown in Figure
147,isgivenintheempiricalexpression:
2
2 Es ts
Qd bp t s K D [14.37]
1 s2 Sc
where:
bp typicalpottingradius;
ts facesheetthickness;
Es Youngsmodulusoffacesheet;
s Poissonsratiooffacesheet;
Sc corecellsize.
KD dimpling coefficient; which depends on the plate geometry, boundary
conditionsandtypeofloading.
TheanalysisoftestdatagaveavalueofKDof2.0.WhereasfromFigure147,itcanbeconcludedthata
constantvalueofKD=2.0isnotsupportedbytestresultsinthewholerangeofts/Sc.
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Figure147:Shearstrength:Criticalstressesforintracellularbuckling(dimpling)
underuniaxialcompression
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14.3.3.5 Bearing
ThebasicequationforthemaximuminplaneloadQtagainstbearingfailureis:
2
Qb K b bi t s comp [14.38]
where:
Kb coefficient which depends on: panel geometry and stress
introduction;
BasedonpreviousteststheKbvalueof2.2waschosen.
Bi insertdiameter;
ts facesheetthickness;
comp ultimatecompressionstrengthofthefacesheet.
where:
Q*crit insertcapabilityundershearload,reducedbyedgeinfluence;
Qcrit initialshearcapabilityofinsert;
EQ edgecoefficientforshearloadedinsert.
Formetallicfacesheets:
e e
EN 0.66 0.06 for e 3bp [14.310]
bp bp
and: EN 1 for e 3bp
where:
e distancebetweeninsertcentreandpaneledge;
bp pottingradiusofinsert.
TheedgecoefficientEQisplottedagainsttherelativeedgedistance,e/bpinFigure148.
Owing to the complicated nature of fibrereinforced composites, it can be concluded that tests are
necessarytoobtainreliabledataforedgecoefficients.
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Figure148:Shearstrength:Influenceofedgedistance
Thesensitivityiscalculatedfora5%deviationofeachcomponent.Thecontributionsofthedifferent
componentsareshowninFigure149.
Table141:Inplanecapability:Effectofcomponentsoncoreshear
Original values +5% values Increase Influence
(N) (N) (N) (%)
bp 11.42 mm 3097 11.99 mm 3311 214 6.91
sy 289.00 mm 3097 303.45 mm 3196 99 3.20
w 1,07 MPa 3097 1.12 MPa 3153 56 1.81
ts 0.3 mm 3097 0.32 mm 3196 99 3.20
NOTE Example case: D17, 3/160.001P, c = 30 mm, ts = 0.3 mm. Partially
potted.Failuremode:Coreshear.
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Sensitivity of In-plane
ts
21%
Example case
Partially potted
bp
46%
D17,3/16-0.001P,
w c=30mm, ts=0.3mm
12%
Qult=3097N
Figure149:Inplanecapability:Contributionsofthemaincomponentson
improvedcoreshear
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14.4 References
14.4.1 General
[141] LassiSyvnen,KariMarjoniemi,AriRipatti,MarkkuPyklinen:Patria
FinaviacompOy,Finland
AnalysismodelsforinsertdesignrulesinsandwichpanelswithCFRP
facings
Patriareport:GS1PFCRP0002(January2003)
ESTECContractNo.14076/99
[142] W.Hertel,W.Paul&D.Wagner
Standardisationprogramondesign,analysisandtestingofinserts
FinalreportESACR(P)1498,February1981
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15
Bending strength
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Figure151:Insertsloadedinbending:Clampingconditions
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Face sheet 2
D1
Neutral Axis
Face sheet 1
Figure152:Bendingload:Schematicofloadtransfer
Itisbaseduponthepremisethatthesumoftheloadinfacesheet1plusfacesheet2iszeroforapure
moment.Theallowableisthereforedependentupontheweakestfacesheet,[See:14.2].
Inthecaseofamomentplusashearload,themomentaddstotheshearononesideandsubtractfrom
the shear on the other face. Depending upon the relative strengths of the two face sheets and the
loadingconditions,theaddedshearloadcanincreaseordecreasethepermittedmoment.
Under the conditions given in 15.1, the permissible bending load, MSS to which the insert can be
subjectedisgivenby:
M ss PSSc bi [15.21]
were:
PSSc permissiblecompressiveloads,[See:13.2].
bi radiusofinsert.
Where:
Pcrit criticaloutofplaneload;
bi insert(hole)diameter.
This expression does not take into account coupling of the potting on the lower face sheet and
becomesmoreconservativeforafullypottedinsert.
Itisalsopossibletoobtainahighercriticalbendingmoment,Mcrit,byusingalargerfootprintinsert,as
showninFigure153.
Owing to the complexity of CFRP face sheets, bending moments should be carried by a couple of
inserts.
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Figure153:Bendingload:Insertfootprintonmomentloading
AlthoughCFRPfacesheetsarecomplex,thesituationisgenerallysomewhatsimilartometallicface
sheets,wherebytorsionandbendingmomentsarecarriedbyacoupleofinserts.
[Seealso:10.2]
15.4 References
15.4.1 General
[151] LassiSyvnen,KariMarjoniemi,AriRipatti,MarkkuPyklinen:Patria
FinaviacompOy,Finland
AnalysismodelsforinsertdesignrulesinsandwichpanelswithCFRP
facings
Patriareport:GS1PFCRP0002(January2003)
ESTECContractNo.14076/99
207
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16
Torsional strength
16.2.1 General
Themostunfavourablecaseisashearruptureofthecellwallsenclosingthepotting,withoutanyload
participationbyotherpartsofthesandwichinsertcombination,[Seealso:16.3].
were:
bR realpottingradius,[See:Table122].t0 corefoilthickness,[See:Table63].
NOTE Althoughminimum,averageandtypicalvaluesarestated,minimum
valuesareapplied.
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where:
bR realpottingradius,
t0 foilthicknessofcore,
0crit shearstrengthofcorematerial.
[Seealso:Figure161fornomenclature]
Owing to the complexity of CFRP face sheets, torsional moments are carried collectively by several
inserts.
Figure161:Torsionalload:Nomenclature
AlthoughCFRPfacesheetsarecomplex,thesituationisgenerallysomewhatsimilartometallicface
sheets,wherebytorsionandbendingmomentsarecarriedbyacoupleofinserts.
[Seealso:10.2]
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16.4 References
16.4.1 General
[161] LassiSyvnen,KariMarjoniemi,AriRipatti,MarkkuPyklinen:Patria
FinaviacompOy,Finland
AnalysismodelsforinsertdesignrulesinsandwichpanelswithCFRP
facings
Patriareport:GS1PFCRP0002(January2003)
ESTECContractNo.14076/99
210
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17
Combined loads
Figure171:Insertsubmittedtoaninclinedload
where:
P=Fsin componentinnormal(outofplane)direction;
Q=Fcos componentinshear(inplane)direction;
F appliedinclinedorangleload;
anglebetweenappliedloadFandsandwichplane.
WithknowncomponentsQandP,itisshownthat:
P 2
PSS
Q 2
QSS 1 [17.11]
Withgivenangleofresultant,theallowableFSSbecomes:
PSS QSS
FSS 2 [17.12]
PSS cos 2 QSS
2
sin 2
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where:
PSS permissibletensileorcompressiveload,[See:12.5tensile;13.2compression
QSS permissibleshearload,[See:14.2;Eqn.[14.21].
1
P 2
PSS
Q 2
Q SS
M 2
M SS
T 2
TSS
where:
PSS permissibletensileorcompressiveload,[See:12.5tensile;13.2compression
QSS permissible (inplane) shear load, [See: 14.2; Eqn. [14.21]. For throughthe
thickness inserts, the value of QSS is the lowest value
determinedforeachfacesheet.
MSS bendingpermissibleload,[See:15.2;Eqn.[15.21].
TSS torsionpermissibleload,[See:16.2;Eqn.[16.21].Bendingandtorsionloads
need to be covered by adequate design, e.g. by large footprints, groups of
inserts,[Seealso:15.1;16.1]
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Anadequatemarginofsafetyshouldbefullyconsideredandappliedtovariables.
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18
Edge influence
P
*
P SS
SS EN
[18.11]
Where:
P*SS insertcapabilityundernormalload,reducedbyedgeinfluence.
PSS initialcapabilityofinsert,[See:19.1;19.2].
EN edgecoefficient,fornormallyloadedinserts.
Theedgecoefficient,EN isdeterminedby:
EN 0.55 e
bp 0.05 e
bp for e 5bp
[18.12]
EN 1 for e > 5bp
NOTE Forsandwichpanelswithcloseouts, EN 1 .
Provided that the closeout material, has some minimal degree of
stiffness.
where:
e distancebetweeninsertcentreandpaneledge.
bp pottingradiusofinsert.
NOTE Anedgedistancecannotbesmallerthanbp (e < bp ).
The edge coefficient for normally loaded inserts, EN , is plotted as a function of the relative edge
distancee/bpinFigure181.
[Seealso:18.2foredgecoefficients,EQforshearloadedinserts;18.3forcompositefacesheets
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Figure181:Edgedistance:Effectoninsertstaticstrengthcapability
18.2.1 General
Theedgeofasandwichpanelcanbeeitherfree,i.e.withoutanyformofclosure,orclosed,i.e.with
some form of closeout or edge member. The effect on the loadbearing capacity of the insert,
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presentedhere,appliestofreeedgesonly.Forsandwichpanelswithacloseoutontheedge,theedge
coefficientis1,[Seealso:18.1fornormallyloadedinserts,ENvalues].
Investigation of stress concentrations of shear (inplane) loaded metallic structures has shown that
severeinteractionsbetweentwoormoreholesexist.Thisisespeciallytruewhentheholesconsidered
are:
Pinloadedholeslocatedclosetoasandwichpanelsedge.or
Severaladjacentholesareloadedindifferentloaddirections.
Thisresultsinacombinedstressdistribution,i.e.combinedpanelstress,holestressandpinloading.
Thereducedloadcarryingcapacityofinsertsundershearloadinglocatedclosetoafreepaneledge,
canbeexpressedby:
*
Q SS
Q
SS EQ
[18.21]
where:
Q*SS shearloadcapabilityoftheinsert,reducedduetotheproximityofthepanel
edge.
QSS initialshearloadcapabilityofinsert,[See:14.1]
EQ edgecoefficientforshearloadedinserts.
[See:Figure181foredgecoefficients(EQ)ofshearloadedinserts]
where:
e distancebetweeninsertcentreandpaneledge.
bp pottingradiusofinsert.
NOTE Anedgedistancecannotbesmallerthanbp (e < bp ).
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18.4 References
18.4.1 General
[181] LassiSyvnen,KariMarjoniemi,AriRipatti,MarkkuPyklinen:Patria
FinaviacompOy,Finland
AnalysismodelsforinsertdesignrulesinsandwichpanelswithCFRP
facings
Patriareport:GS1PFCRP0002(January2003)
ESTECContractNo.14076/99
217
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19
Insert groups
19.1.1 General
Iftwoadjacentinsertsaresimultaneouslyloadedinthesamedirection,thestaticstrengthcapabilityof
eachinsertisreducedbythestressfieldoftheotherinsert,accordingto:
*
P SS 1 IS 1 P SS 1
[19.11]
Where:
P*SS1 reducedcapabilityofinsert1,duetoinsert2.
PSS1 initialcapabilityofinsert1,withoutinfluenceofinsert2.
Dependingontheirdistanceapart,theinterferenceeffectofoneinsertontheothercanbeconsidered
aseither:
Close,or
Distant.
[Seealso:19.2;19.3]
IS1 interferencecoefficientofinsert1,whensimultaneouslyloadedinthe
samedirectionasinsert2:
b p1
b p2 a 1
IS1 1 [19.13]
1 b p1 5b p1 1 b p1
b p 2 b p 2
where:
bp1 pottingforinsert1.
bp2 pottingradiusforinsert2.
a centretocentredistancebetweeninserts.
[Seealso:Figure191]
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Where:
IS2 interferencecoefficientofinsert2,whensimultaneouslyloadedinthe
samedirectionasinsert1:
1
b p1
b
p1
b p2
1 a bp2
[19.15]
1
5b p1 1
b
1 p1
1 b p1
b p2 b p2
Insert2sreductionofthecapabilityofinsert1,givenbyIS1,isonlyfullyeffectiveifinsert2is
itselfloadeduptoitsowncapability:
*
P SS 2 IS 2 P SS 2
[19.16]
where:
P*SS2 reducedcapabilityofinsert2,duetoinsert1.
I
1 1 P 2
* [19.17]
IS 1 IS 1
P SS 2
Thiscasecanberelevantifbothinsertsarenotsimultaneouslyloadeduptotheirrespective,reduced
capabilitiesP*SS1andP*SS2.
In Figure 191, IS1 and IS2 are plotted as a function of the relative insert distance a/bpi ; where the
parameteristheratioofpottingradiibp1 /bp2.
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Figure191:Insertgroups:Reducedinsertcapabilitytwoadjacentinsertsloaded
inthesamedirection
19.2.1 General
Iftwoadjacentinsertsaresimultaneouslyloadedinoppositedirections,i.e.P1 = -P2,thestaticstrength
capabilityofeachinsertisonlyslightlyreducedbythestressfieldoftheotherinsert.
Dependingontheirdistanceapart,theinterferenceeffectofoneinsertontheothercanbeconsidered
aseither:
close,or
distant.
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Fordesignpurposes,thereducedcapabilityoftwoinsertsloadedinoppositedirectionsisgivenby:
P SS
*
P SS IC
[19.21]
where:
P*SS capabilityofinsert1reducedbytheinsert2.
PSS initialcapabilityofasingleinsert
IC interferencecoefficientforoppositeloading.
[Seealso:19.1;19.3]
[Seealso:Figure191forgeometricconfiguration]
19.3.1 Overview
Theeffectoncapabilityforaseriesofinsertsisconsideredfor:
Firstandlastinserts,and
Intermediateinserts.
Thisisillustratedbyanexample.
P*SS1 = PSS1IS1
where:
P*SS1 capabilityoffirstorlastinsertreducedbysecondorlastbutoneinsert
PSS1 initialcapabilityoffirstorlastinsert
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IS1 interferencecoefficientoffirstorlastinsertrelatedtothesecondorlastbut
one insert, [See: 19.1; Eqn. [19.12]].
Figure192:Insertgroups:Seriesofinsertsloadedinsamedirection
P
*
SSi
P SSi
ISl
ISr
1 [19.31]
where:
P*SSi capabilityofintermediateinsertinfluencedbybothadjacentinserts.
PSSi initialcapabilityofintermediateinsert.
ISl interferencecoefficientofintermediateinsertrelatedtoleftinsert;[See:Eqn.
19.1;[19.12]],with:
bp1=pottingradiusofintermediateinsert,
bp2=pottingradiusofleftinsert,and
a=al=distancebetweenthecentresofintermediateandleftinsert.
ISr interferencecoefficientofintermediateinsertrelatedtotherightinsert;[See:
19.1;[19.12]],with:
bp1=pottingradiusofintermediateinsert,
bp2=pottingradiusofrightinsert,and
a=ar=distancebetweenthecentresofintermediateandrightinsert.
19.3.4 Example
Determinationoftheinsertcapabilityforaconfigurationwhere:
Seriesof5equalinserts;
Equalpottingradiusbpforallinserts;
Equalinsertdistancea=6bp.
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19.3.4.1 Interference coefficient
FromFigure191,theinterferencecoefficientcorrespondingtobp1/bp2=1anda/bp1=6isidenticalfor
allinserts,i.e.:
IS1=ISl=ISr=0.8
19.3.4.3 Validation
These formulae are considered valid if the distance a between the insert and its neighbour is large
enough,i.e.
Otherwise,thenextbutoneinsertalsoinfluencestheinsertconsidered.
Inthiscase,thetotalcapabilityoftheseriesP*SS (asdeterminedbytheformulaecited)remainsvalid,
whereasthedistributionoftheloadovertheinsertsisincorrect.
19.4.1 Overview
Figure193showstheloadingconfiguration.
Figure193Insertgroups:seriesofinsertsloadedinoppositedirections
Thereducedloadcapabilityofeachinsertcanbeestimatedforthe:
Firstandlastinsert,and
Intermediateinserts.
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P SS1
*
P SS 1 IS 1 IC
[19.41]
P
*
SSi
P SSi ISl
ISr
1 IC
[19.42]
where:
=0.9 fora5(bpi1+bpi2)
IC [19.43]
=1.0 fora>5(bpi1+bpi2)
a distancebetweeninsertseries.
bpi1 pottingradiusforinsertNo.ioffirstseries.
bpi2 pottingradiusforinsertNo.iofsecondseries.
[Seealso:Figure193]
19.5.1 General
Higherloadscanbeappliedtoanumberofinsertsusingbrackets,e.g.agroupof3,4,5or6inserts,as
showninFigure194.
G P SS
*
P SS [19.51]
where:
P*SS reducedcapabilityofinsert.
PSS initialcapabilityofsingleinsert.
G interferencecoefficientforagroupofequidistantinserts,dependingonthe
numberofinserts:
n 1 1
G
2
n
IS
0.5
n
[19.52]
where:
n numberofinsertsinthegroup;
IS interferencecoefficientfor2insertsloadedinthesamedirection,[See:19.1;
Eqn.[19.11]]withbpi=bp1=bp:i.e.bp1/bp2 =1,gives:
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G= 1 fora/bp=10orIS=1
(nofurthermutualinterference)
G= 1/n fora/bp=0orIS=0.5
(ninsertsconcentratedin1insert)
19.5.2.2 Validity
Eqn.[19.52]andEqn.[19.53]areonlyvalidfora 10bp.
Foragreaterinsertdistance:
Figure194showsaplotofEqn.[19.52]andEqn.[19.53].
Figure194:Insertgroups:Interferencecoefficientforagroupofequaland
equidistantinserts
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19.7 References
19.7.1 General
[191] LassiSyvnen,KariMarjoniemi,AriRipatti,MarkkuPyklinen:Patria
FinaviacompOy,Finland
AnalysismodelsforinsertdesignrulesinsandwichpanelswithCFRP
facings
Patriareport:GS1PFCRP0002(January2003)
ESTECContractNo.14076/99
[192] W.Hertel,W.PaulandD.WagnerERNORaumfahrttechnikGmbH,
StructuresDept.,Bremen,D.
StandardisationProgrammeforDesignandTestingofInserts,ESACR
(P)1498,ESAContractNo.3442/77/NL/PP,1981.
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[193] W.Pauland D.WagnerERNORaumfahrttechnikGmbH,
StructuresDept.,Bremen,D.
StandardisationProgrammeforDesignandTestingofInserts,RiderII,
ESACR(P)1665,ESAContractNo.3442/77/NL/PP,1981.
[194] ReevaluationofPottingProcedureFinalReport,July1990.MBBERNO
(Bremen).ESTECContractNo.7830/88/NL/PH(SC)
[195] Standardisationofdesignanalysisandtestingofinsertsinstructural
sandwichelementsFinalReport.MBBERNO(3442/77/NL/PP)
[196] Standardisationofdesignanalysisandtestingofinsertsinstructural
sandwichelementsFinalReport.MBBERNO(3442/77/NL/PPRider1)
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20
Stiffness
20.1 Introduction
20.1.1 Overview
The insert stiffness can be an important factor for the evaluation of loads at fixing points. Two
particularcasesarehighlighted,[201]:
Rotationalstiffness
Inplanestiffness
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20.2.1 General
The different values of insert stiffness determined by analysis and testing are described, using an
examplefromtheSILEXproject,[201].
Generalcommentsregardingthe determinationinsertstiffnessforsandwichpanelshavingcomposite
facesheetsarealsogiven.
20.2.2 Analysis
HandcalculationsorFE,indicatestiffnessvaluesof,[201]:
Rotationalstiffness:K=1104mN/rad;
Inplanestiffness:Kin-plane=1108N/m.
20.2.3 Testing
20.2.3.1 Configuration
IntheSILEXproject,testsoninsertconfigurationsdeterminedthestiffnessvalues.Table201liststhe
sandwichconstructionandinserts,[201].
Table201:Insertstiffness:SILEXtestconfiguration
Facesheets CFRPM55J/914;Quasiisotropiclayup.Thickness=0.8mm
Core 5056320;height=16.5mm
Standard:14mmdia.;h=15mm
Inserts
Specialthrough:14mmdia.;h=18.1mm
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Table202:Insertstiffness:Comparisonofanalysisandtest
Insertstiffness Analysis Test
Rotational(mN/rad) 1104 2103<K<4103
Inplane(N/m) 1108 1107<Kinplane<5107
Outofplane(N/m) 5106<Koutofplane<1.2107
20.3 References
20.3.1 General
[201] MMSContributiontoESAInsertDesignHandbook
MatraMarconiSpaceReportNo.NT/102/BG/355013.96(December1996).
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21
Fatigue
21.1.1 General
Theloadcarryingcapabilityofallthecomponentpartsofapottedinsertsystem,i.e.core,potting,face
sheet,insertandbolt,canbedegradedbyrepeatedloadingastheservicelifeincreases.
The failure of the insert element itself is not experienced provided that there is an adequate fillet
radiusofthelowerflangeconnection,whichisdefinedinmoststandards.
Failuresofthefacesheetshaveneverbeenexperiencedinspacecraftinsertpaneldesign.
NOTE Thedimensionsofthebracketfootcanberelevant,[See:21.4].
Boltsininsertsarenotcoveredhere,andarespecifiedinaccordancewithappropriatestandards,[See:
ECSSQST7046].
Theremainingcomponentsrelevanttodegradationunderoperationalloadsarethe:
Potting,
Honeycombcore.
21.1.2 Potting
A correctly potted body is not subject to fatigue degradation if the surface treatment of the inner
flangeprovidesagoodadhesivebondwiththeresin,[211].[Seealso:5.5].Thestrengthofthepotting
bodyunderoperationalconditionisinfluencedbyelevatedtemperatures,[Seealso:22.1].
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21.2.1 General
ThecoreshearstressaroundapottedinsertisdeterminedusingthemathematicalmodelinAnnexC.
TheultimatetensilecapabilitiesPSSarebasedonthecorec crit minvalues.
NOTE For guidance, Annex B contains examples of plots for individual
insert configurations. These implicitly contain the loadcore stress c
data.
C2Kr
c
bc
max
F [21.21]
p
with:
c crit min
C Kr
*
max
[21.22]
P SS min 2b c p
ThereforethecircularstresscunderaloadPis:
c crit min
F [21.23]
c
P SS min
[Seealso:Table63andTable64forcoreproperties]
PSSvaluesareshowninFigure211,[Seealso:AnnexB].
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[See:Table63andTable64]
Figure211:Staticstrengthvalueswithcoreheight
21.2.3 Example
Giventhesandwichinsertconfiguration:
Aluminiumcore:3/165052.0007P;
Coreheight,c=30mm;
Aluminiumfacesheets:0.4mmthick;
Insertdiameter=14mm.
Thiscorestress,cisseenasthemaximum(axiallysymmetrical)grossvalueoccurringinthevicinity
ofthefullypottedbodyinaninfinitesandwichplate.Consequentlyitdoesnotcontain:
Shearstressvariationversusheightinducedbypartialpotting;
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Influencesfromtheedgesclosetotheinsert;
Influencesfromotherinsertsadjacenttotheconsideredinsert;
c local = c Kt [21.25]
s
with:
K t
K t j [21.26]
j 1
where:
s=numberofeffectsapplicable(tobesuperimposed).
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Table211:Fatigue:Stressconcentrationfactorsforlocalstress
Effect Stressconcentrationfactor(Kt) Comment/Link
n
c
Partialpotting K tpp n=0.8foraluminium
h p
core
1
K tFB FB
FB
Influenceoffreeborder (1) 2 [See:18.1]
1
K tAJ AJ
AJ
Insertsclosetoeachother(1) 2 [See:19.1]
1
Elevatedtemperature (1) K TN [See:22.1]
TH
1
Longterminfluences (1) K tLT [See:22.1]
LT
Combinationof: ProvidedthattheloadQ
Normalloads,Fand
tQ
1 K
actsinplaneofface
Shearloads,Q. sheet,[See:17.1].
NOTE(1)Thesevaluesareforpreliminarydesignandneedtobesupportedbytesting.
s
local K t i i1
NOTE(2)Localstress:
Inthisexamplecase,assumingthattheinsertloadisrelatedlinearlytoacceleration,eachseti, i+1of
cyclicloadwithconstantamplitudeisrepresentedby:
Meanload: P mean i ,i 1
Loadamplitude: P Ai ,i 1
Numberofcycles: N i ,i 1
N i 1 N i
Figure212showsaschematicofadesignloadspectrum,[Seealso:21.4].
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Figure212:Schematic:Designloadspectrum
21.3.1 General
Theloadorlocalstresssequencecanbesinusoidalwithanamplitudeof localstressa,andamean
valueofmean:
mean 1a sin (t ) [21.31]
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R
mean
A
[21.32]
mean
A
F 2P a
[21.33]
1 R
2 a
[21.34]
1 R
21.4.1 General
Withinadesign,differentsetsofloadamplitude(Rratios)andnumberofoccurrencescanbeneeded.
Thesespectraarealsopresentedasadistribution.
21.4.2 Example
Figure 212 shows the number of times a certain acceleration level is exceeded with constant mean
acceleration, which can also be approximated by certain steps, i. N is the accumulated number of
timesacertainloadlevelisexceeded.
Astheamplitude(FA i. i+1)isdifferentforeach step,themeanstressratio Risalso differentforeach
individualstep.
Specialattentionisnecessaryifthetotalsequenceofloadhistoryisformedbydifferentspectrawith
significantlydifferentmeanloads.Sometimesthesevariationsformthemajorpartoftheloadhistory
withrespecttofatiguedamage,e.g.thegroundtoairtogroundcycle.Suchvariationsofmeanloads
shouldbeconsideredasadditionalcycles.
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ThecoefficientCdependsonthemeanstressmean,whichcanbeconsideredasequaltothealternating
stressA.
AsthemeanstressratioR,[See:21.3;Eqn.[21.32]isusuallynotconstant,thenEqn.[21.52]ismore
suitablefortheanalysis:
m
2
ccrit
1
C N for [21.52]
K
a A
1 R t
Often,stressesareavailableforthemaximumpeakloadFresultinginamaximumlocalpeakstress
.
With:
2
a [21.53]
1 R
Eqn.[21.52]becomes:
m 1
2
C N
1
[21.54]
1 R
A
Togetherwith:
2b c
F
p
* c [21.55]
CK r max
And:
K
c [21.56]
t
[See:21.2]
m 1
2b p c 2
C N
1
F [21.57]
K 1 R
*
CK
A
r max t
orwith:
P
c
SS
crit
[21.58]
[See:21.2]
m 1
1 2
F P SS
1
C N [21.59]
ccrit min K t 1 R
A
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CoefficientsforEqn.18.05.9fordifferenthoneycombtypesaregiveninTable212
Inaccordancewithstaticstrengthcapabilities:
minimumvaluesarebasedon:
Minimumstaticcorestrength,
Minimumbutproperpottingsize,and
Lowerboundaryvariationofthemathematicalmodel.
typicalvaluesarebasedon:
Averagetypicalstrengthofcore,
Typicalpottinggeometry,and
Typicalvaluesofthemathematicalmodel.
NOTE It is advisable to use minimum data only to ensure safety and
reliabilitywherethefailureofonesingleinsertshouldbeavoided.
Based on these findings, the linear reduction of CA by the ratio Wmin/Wactual and Wtyp/Wactual
usedpreviouslywasfoundrathercrudeandtooconservativeforN<200000.
AreevaluationofthevaluesCA and1/,[211]isshowninbracketsinTable212.
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Table212:Fatigue:Coefficientstodeterminepeakload
Coretype(metallic) CA(1)(3) 1/(1)(3)
Correctivecoefficientsaretabulatedfor:
Facesheetthickness;
Coreheight(Fcf):
Partialpotting(Fpp);
Productofcorrectionfactors(Fcf Fpp).
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21.5.4.2 Links to fatigue life data
Table213:Linkstofatiguelifedata
Insertdiameter.(mm) Correctionfactors Fatiguegraph
9 Table214 Figure213
11 Table215 Figure214
14 Table216 Figure215
17.5 Table217 Figure216
22 Table218 Figure217
NOTE Allgraphsbasedon:
Coretype:3/165052.0007p;Coreheight20mm;
Facesheet:2024aluminium,0.1mmthick;
Insertheight9mm.
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Table214:Insertdiameter9mm:Fatiguecorrectionfactors
Multiplythegivencorrectionfactors(Fcf)and(Fpp)withtheloadvaluesfromFigure213.
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[SeeTable214]
Figure213:Insertfatiquelife:Insertdiameter9mm
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Table215:Insertdiameter11mm:Fatiguecorrectionfactors
Multiplythegivencorrectionfactors(Fcf)and(Fpp)withtheloadvaluesfromFigure214.
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[SeeTable215]
Figure214:Insertfatiquelife:Insertdiameter11mm
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Table216:Insertdiameter14mm:Fatiguecorrectionfactors
Multiplythegivencorrectionfactors(Fcf)and(Fpp)withtheloadvaluesfromFigure215.
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[SeeTable216]
Figure215:Insertfatiquelife:Insertdiameter14mm
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Table217:Insertdiameter17.5mm:Fatiguecorrectionfactors
Multiplythegivencorrectionfactors(Fcf)and(Fpp)withtheloadvaluesfromFigure216.
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[SeeTable217]
Figure216:Insertfatiquelife:Insertdiameter17.5mm
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Table218:Insertdiameter22.5mm:Fatiguecorrectionfactors
Multiplythegivencorrectionfactors(Fcf)and(Fpp)withtheloadvaluesfromFigure217.
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[SeeTable218]
Figure217:Insertfatiquelife:Insertdiameter22.5mm
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n
D i
k [21.61]
i
N i
Where:
ni numberofcyclesapplied;
Ni numberofcyclesapplicableuptofailure,underloadamplitude.
Under constantamplitude load, an accumulated sum of damage is acceptable provided that the
degreeofconfidenceinthefatiguedataandtheprobabilityofhavingnofailuremeetthespecification.
Avalueofk=0.25iscommonlyusedforinitialassessments.
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Figure218:Fatiguelife:NonmetallicGFRPcore
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Figure219:Fatiguelife:NonmetallicNomex core
21.9 References
21.9.1 General
[211] StandardizationofDesignAnalysisandTestingofInsertsinNon
metallicStructuralSandwichElements.
PhaseIReport,ESTECContractNo.440/80/NL/AK(SC).
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22
Environmental effects
22.1.1 General
Thermalconditionscanreduceinsertcapabilities,[221].
Figure221showsthereductionresultingfromthreedifferenttypesofthermalconditions,i.e.
Mechanicalloadinginathermalenvironment;
Mechanicalloadingafterexposuretoathermalenvironment;
Mechanicalloadingafterthermalcycling.
[Seealso:22.2foreffectsonpermissibleloads]
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Figure221:Thermaleffects:Reductionofinsertcapability
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Figure222:
Thermaleffects:Reductionofpottingresinstrength
where:
PTi permissibleloadreducedbythermalenvironment;
P permissibleloadwithoutthermalinfluence,
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[See:12.5;13.2;15.212.2]
Ti coefficientofthermaldegradation,
Where:i=c,a,borR
[See:Figure221;Figure222]:
Figure223summarisesthethermaldegradationcoefficientbythethermalconditions,[Seealso:22.1]:
Mechanicalloadinginathermalenvironment,where:
Ta,thepermissibleloadsarelimitedbythecoreproperties;
TR,thepermissibleloadsarelimitedbythepropertiesofthepottingcompound.
Mechanicalloadingaftersubmissiontoathermalenvironment,i.e.Tb
Mechanicalloadingafterthermalcycling,whereTc isvalidfor100cyclesintherange160Cto
+150C.
[Seealso:Figure221;Figure222]
Figure223:Thermaleffects:Coefficientofthermaldegradation
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Humidity,underatmosphericenvironmentalconditions;
Vacuum,underspaceenvironmentalconditions;
Radiation.
[Seealso:ECSSQST70;ECSSQ7071]
Eachoftheseconditionscandegradethepottingmassandconsequentlydecreasetheinsertcapability
toacertainextent.
The potting mass is usually wellprotected by the surrounding structure, often made of aluminium,
whichmeansthatadeteriorationofthepottingmassonlyoccursunderextremeconditions.
Particularattentionisneededintheselectionofapottingmassthatishighlyresistantwhenextreme
conditionsareexpected.
22.5 References
22.5.1 General
[221] LassiSyvnen,KariMarjoniemi,AriRipatti,MarkkuPyklinen:Patria
FinaviacompOy,Finland
AnalysismodelsforinsertdesignrulesinsandwichpanelswithCFRP
facings
Patriareport:GS1PFCRP0002(January2003)
ESTECContractNo.14076/99
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ECSSQ7071 Datafortheselectionofspacematerialsand
processes
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23
Manufacturing procedures
23.1 Sequence
23.1.1 General
Figure 231 summarises a basic manufacturing sequence for potting standardtypes of inserts into
existingsandwichpanels.Italsoincludeslinkstoappropriateinformation.
NOTE The manufacturing procedure for nonstandard inserts, in particular
carbonfibre tube inserts, is described in Annex A, [See: A.3] and by
exampleinAnnexF,[SeeF.6].
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Incominginspection[See:26.1]
Drillboreholes
[See: 24.2]
Perforatedcore
Fitinserts
Referencesample[See:23.6
[See: 23.2]
Tearouttest[See:23.6
Nonperforatedcore
Introduce
pottingcompound
[See: 23.3]
Curecycle
[See:23.4]
Finalmachining
[See: 23.5]
Figure231:BasicmanufacturingsequenceFit inserts
23.2.1 General
Inserts are only fitted after the bore holes have been machined, [See: 24.2], inspected and any
correctiveactionstakentopreventbentordislocatedcellwallsimpedingthe:
Displacementoftrappedair;
Flowofpottingcompound.
23.2.2 Positioning
Standard, commerciallyavailable inserts are normally supplied with a positioning tool which aids
theirplacement,i.e.flushorrecessedsubflush,[2316].
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Special,nonstandardinsertsandthosepositionedoverflushorprotrudingoftenneedaspecialtool
toensureacceptableflatnessofaninsertoragroupofinserts,[2316].
[Seealso:F.6forcarbonfibretubeinserts]
Figure232:Insertswithconnectedpottingmass
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Innerdiameterexceeds0.3mm
Outerdiameter,oftheorderof1.5mm
Theendsarecutdiagonallyatanangleofabout45.
Theventtubecanremaininthepottingorberemovedbeforecuring.
NOTE If the vent tube remains in the potting, it should be made from an
acceptablematerialforspaceuse.
Figure233:Ventingofnonperforatedcore
23.3.1 General
Injectionoftheinsertpottingcompoundiscarriedoutwhenallthepreparationstagesarecomplete
andshowntomeetwithqualitycontrolprocedures,[Seealso:28.1].
Forstandardtypesofpottedinserts,theapplicablestepsare:
Boreholes:
drilling,[See:24.1];
inspection,[See:28.2].
Insertpretreatment,[See:25.1].
Fittinginserts,[See:23.2].
Perforatedcores;
Nonperforatedcores,withadditionalventing.
Mixingpottingcompound,[See:25.2].
[Seealso:F.6fornonstandardcarbonfibretubeinserts]
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23.3.2 Process
23.3.3.1 General
Factorsaffectingtheflowofpottingcompoundaroundinsertsinsandwichpanelsinclude:
Materialcharacteristics,e.g.viscosity,[See:7.1;25.3
Boreholegeometry,[See:23.2;28.2].
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23.3.3.4 Perforated core
Duringthefillingprocess,theperforationsenableventingofairtrappedwithintheboreholeduring
potting,[2314].
23.4.1 General
Whenalltheinsertshavebeencorrectlypottedinthesandwichpanel,thepottingcompoundisthen
cured.
The cure cycle used largely depends on the chemical formulation of the resin used for potting and
whether the resin or assembly can be cured at elevated temperature without causing damage, e.g.
thermallyinduced damage to composite face sheets; adhesive bond between core and face sheets;
cores.Incaseswheretheinsertsarecocured,thepottingresinissubjectedtothesamecurecycleas
therestoftheassembly.
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23.5.1 General
Onceaninsertis pottedintoasandwichpanel,therearelimitedopportunitiestocorrectanyerrors.
Thisiswhypropermanufacturingprocesses,andtheircontrol,areessential.
23.5.2.1 General
The processes described are used when a potted insert is found to deviate from the stated
requirements during the manufacture. Final machining processes can be stipulated as part of the
overallprocessing,ratherthansolelyascorrectiveactions.Forexample,machiningofflangedinserts
toimproveflatness,changefrictioncoefficientandpreventstressconcentrationsbetweenattachment
pointsandpanels,[Seealso:Table51;10.3].
23.6.1 General
Reference (or witness) samples assess the potting process. The reference sample is produced at the
same time as the manufactured assembly and undergoes all the same processes, e.g. machining,
potting, cure. The potting process is evaluated by a vertical insert pullout strength test. This is a
destructivemechanicaltestthattearstheinsertoutofthereferencesample,[Seealso:27.3].
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23.6.2 Materials
Thereferencesampleismadefromexactlythesamematerialsusedinthemanufacturedassembly,i.e.
thesame:
Sandwich;
Insert;
Pottingmaterial.
23.6.3 Manufacture
Referencesamplesare:
Pottedatthesametimeastheproductionsandwichpanel;
Curedtogetherwiththeproductionsandwichpanel.
NOTE Allreferencesamplesareclearlyidentified,e.g.bydrawingnumber;
markingwithadhesivetape.
N
n 1 ges
[23.61]
standard
100
N
n 2 ges
[23.62]
safetycrit
10
where:
n roundeduptowholenumberofsamples;
Ngesnumberofpottedinsertsproducedperday,i.e.dailycharge,fromthesame
mix,[2317].
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Figure234:Referencesample:PulloutstrengthtestspecimenProof load
Proofloadingofinsertsinflightdestineditemscanbestipulatedforhighreliabilityapplications.
Thelevelofproofloading,i.e.howmuchhigherthanlimitload,hasbeeninvestigated,[2313].
NOTE Proof loading and loadlevels conform to those defined within the
structuraldesigndocumentation.
23.8 Inspection
Thebasicsetofinspectioncriteriaforstandard,pottedinsertsare:
Machinedboreholeforinsert:
actualdiameter;
actualdepth;
Checkfordetachmentoffacesheetsfromthehoneycombcore;
Cleanlinessoftheboreholepriortothepotting;
Insertposition,withrespecttosandwichfacesheet:
flush:maximumtolerance0.03mm;
Perpendicular:maximumtolerance:0.5.
Fillingoftheinsertinjectionandventingholeswithpottingcompound.
Otherinspectioncriteriacanbestipulatedfornonstandardinserts.
NOTE All inspection criteria are checked, documented and compared with
the requirements to establish if potted inserts are acceptable or
unacceptable.
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23.9 Repair
23.9.1 General
Therepairofinsertsisoccasionallynecessaryto:
Replaceadamagedinsert;
Reinforceadamagedcoresurroundinganinsert;
Replaceaninsertwithanother,e.g.increasestrength;
Repositionaninsert,e.g.
originalslightlymisplaced;
fixingpointchanged.
The repair process used depends on whether the core and face sheets are damaged or not. The
processes described apply to standardtype inserts. Nonstandard types can need different repair
methods.
23.9.2.1 Process
Drilloutoldinsert;
NOTE Avoidoverheatingandhighdrillingforces;drilldiameter:d i 2mm.
Extendboreholebymilledundercut,asshowninFigure235;
Extendboreholebypuncturingcuredpottingcompoundandunfilledcorecells,Figure235
Removeresidualupperflangeofoldinsertwithtweezers;
Reamborehole:tolerance0to+0.03mm;
Apply appropriate amount of potting compound, i.e. to fill the hole and support the lower
flangeofthenewinsert;
Fitnewinsert,[See:23.2];
Potnewinsert,[See:23.3].
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Repairdimensions:
1.0
a ri 23 S c
b hi 3.0 1.0
c 1.5 1.0
Figure235:Insertrepair:Geometry
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23.10 Defects
Themajorityofdefectscanbeavoidedbythecreation,strictadherenceto,andcontrolofallprocess
procedures,covering:
Incominginspection:
Honeycomb,[See:26.2];
Resin,[See:26.3].
Manufacture:
Processes,[Seealso:Figure231];
Mechanicaltests,[See:27.1;29.1;AnnexH];
NonDestructivetest,[See:27.1].
Qualityassurance:
Borehole,[See:28.2];
Potting,[See:28.3];
Core,[See:28.4].
Theeffectsofsomedefectsoninsertcapabilityaredescribed,alongwithanycorrectiveactionstaken,
[2316].
[Seealso:23.5]
Table231:Insertcapability:Effectofpoorstorageofpottingcompound
Tensile load (1)
No. of
Storage
Average Minimum samples
(N) (N)
Good 6830 6080 5
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Table232:Insertcapability:Effectofpoordistributionofpottingcompound
Pull-out
Insert tensile load No. of
Potting samples
Average (N)
Table233:Insertcapability:Effectofpoorpositioningofinsert
Shearload
InsertPosition No.ofsamples
(N)
Good 3670 calculated
2760
Poor 2
3788
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Table234:Insertcapability:Effectofoversizedborehole
Holediameter Shearload
No.ofsamples
(mm) (N)
2760
11.48 2
3788
600
12.4 2
800
23.11 References
23.11.1 General
[231] Insertsforsandwichstructures,closed,selflockingwithfloatingand
removablenut,screwsecuring
ENN366(MBBERNO)
[232] Titlenotstated
ENN379(MBB/ERNO)
[233] Insertsforsandwichstructuresclosed,selflocking
ENN386(MBB/ERNO)
[234] Insertsforsandwichconstructions,closed,withscrewlockinghelicalcoil
insert
ENN398(MBB/ERNO)
[235] Bondingtabs
ENN34602(MBB/ERNO)
[236] Designationofthesurfacetreatment
LN9368(BeuthVerlag,Germany)
[237] Standardclimateconditions
DIN50014(BeuthVerlag,Germany)
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[238] Instructionsfortheissuanceoffailuremessagesandfailureelimination
RL0008021
[239] SLE301072970:Productdata
[2310] LekuthermX227+T3:Processinginstructions
BayerGmbH
[2311] Applicationoftoxic,volatile,nonflammablesolventsforcleaning
purposes
UVV11.2(VBG87)
[2312] Applicationofadhesivewitheasilyvolatile,flammablesolvents
VBG81
[2313] StandardizationofDesignAnalysisandTestingofInsertsinNon
MetallicStructuralSandwichElements,PhaseIReportNo.
440/80/NL/AK(SC)
[2314] ReevaluationofPottingProcedureFinalReport,July1990.MBBERNO
(Bremen).
[2315] ESTECContractNo.7830/88/NL/PH(SC)
[2316] MMSContributiontoESAInsertDesignHandbook
MatraMarconiSpaceReportNo.NT/102/BG/355013.96(December1996).
[2317] ESTEC/MMSUKPrivatecommunication(April1999).
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24
Sandwich panel machining
24.1.1.1 Diameter
Theboreholediameterisdefinedbytheparticularinsertdiametertobeused.
NOTE Nolargetolerancesareacceptable.
24.1.1.2 Depth
The bore hole depth should be optimised because it defines the freevolume under an insert, which
affectstheflowofpottingcompound,[242].
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24.2 Processing
Drilling of bore holes for inserts can be achieved by two different methods using single or
combinedtools,i.e.:
Drillfacesheetthencuthoneycombcore.
Drillfacesheetandhoneycombcore.
NOTE Lubricants or coolants cannot be used during any drilling or cutting
processes.
Alldrillingprocessesshouldavoiddamageto thesurroundingcore.Coredamagecanoccurduring
the drilling process when the core is stressed in a direction other than its highstiffness (normal)
direction.
The increasing demands for placing (and easy replacement) of brackets and boxes on sandwich
panels, using inserts, means that the precision provided by coordinate drilling is replacing the
previoussequencedrillingprocesses,[242].
Figure241:Sandwichpanelmachining:Combineddrillandpunchtool
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Figure242Sandwichpanelmachining:Seriesofsingletoolsandtheiruses
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Aspecialdrillisusedthatonlycutstheouterdiameterofthebore.Thisproducesadiscintheface
sheet;asshowninFigure242(No.2).
NOTE Whenacoordinatedrillingmachineisavailable,thespecialdrillcan
beusedwithoutsettingacentrebore.
Thefacesheetdiscisthenpulledoffthecorewithapairoftweezers.
NOTE Thetolerancesoftheboreholeinthefacesheetarewithin0to+0.03
mmofthenominalinsertdiameter.
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24.4.1.2 Cores
Perforatedaluminiumcoresareeasytodrill.
UnperforatedcorewiththinfoilsandthetighttypeofNomexandGFRPcorecancreateproblems
duetothepossiblelowgaspressurewithintheclosedcells;causedbythesandwichbondingprocess.
Thiscanresultin:
Deformationofthefacesheetonthebackfaceacrosstheborediameter;
Corefailureduetoinstabilityofcellwalls.
Althoughitisdifficulttoavoidsuchdistortions,e.g.byventingwiththeaidofaneedle,itisusefulto
knowthattheyarelikelytooccur.
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24.5 References
24.5.1 General
[241] MILHDBK17CompositeMaterialsHandbook
[242] MILHDBK23StructuralSandwichComposites
NOTE MILHDBK23isunderreviewforpartialincorporationasVolume6
MILHDBK17.
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25 Potting
25.1 General
The comments apply to the manufacturing process of potting inserts into sandwich panels or
structuresforspacevehicles,[See:25.2;25.3;23.1].
[Seealso:ECSSE30series;ECSSQST70materialsandprocessrelatedstandards]
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25.3.1.1 General
Theflowcharacteristicsofthepottingcompoundhaveastronginfluenceonthesuccessorfailureof
insertpotting.Flowisaffectedby,[2513]:
Resinsystemviscosity;
Type,shape,contentanddistributionoffillermaterial,e.g.glassmicroballoons;
Appliedpressure;
Temperature:
Mixedresinexothermicreaction;
Ambient.
The precise control of individual materialrelated variables (resin, hardener, filler) has proven to be
extremely difficult, e.g. batch variations; dryness, settling and size distribution of filler. Therefore
control of the mixed potting compound viscosity just before its use is necessary to aid potting
reproducibility.
Atypicalviscosityrangeisbetween45Pa.sand58Pa.s,[2513].
NOTE Low viscosity potting compounds (below 3Pa.s) produce severe
pottingdefects,[2513].
Viscosityisalsotheparameterwhichdeterminesusablepotlife,whichisstipulatedaspartofprocess
controlactivities.
25.3.1.2 Processing
Althoughmadeofaninertsubstance,glassmicroballonsareusuallydriedbeforeincorporationinto
theresin.Thisavoidsanymoisturepresentaffectingthecureorresultingproperties.
Pottingcompoundsareprocessedwiththeaidofacompressedaircartridge,e.g.Semco.
Theinjectionpressureappearstohavenoeffectonthedistributionofthepottingcompound,although
the size and shape of the injection tool needs to be optimised. An injection pressure of 1 bar has
provensuccessful,[2513].
Themixedresinundergoesanexothermicreactionduringcure.Thisisacceleratedbythepresenceof
low thermal conductivity fillers, e.g. glass microballoons. As the ambient temperature also affects
viscosity,ittooneedscontrol,[2513].
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25.4 References
25.4.1 General
[251] Insertsforsandwichstructures,closed,selflockingwithfloatingand
removablenut,screwsecuring
ENN366(MBBERNO)
[252] Titlenotstated
ENN379(MBB/ERNO)
[253] Insertsforsandwichstructuresclosed,selflocking
ENN386(MBB/ERNO)
[254] Insertsforsandwichconstructions,closed,withscrewlockinghelicalcoil
insert
ENN398(MBB/ERNO)
[255] Bondingtabs
ENN34602(MBB/ERNO)
[256] Designationofthesurfacetreatment
LN9368(BeuthVerlag,Germany)
[257] Standardclimateconditions
DIN50014(BeuthVerlag,Germany)
[258] Instructionsfortheissuanceoffailuremessagesandfailureelimination.
RL0008021
[259] SLE3010:Productdata(72970)
[2510] LekuthermX227+T3:Processinginstructions
BayerGmbH
[2511] Applicationoftoxic,volatile,nonflammablesolventsforcleaning
purposes.UVV11.2(VBG87)
[2512] Applicationofadhesivewitheasilyvolatile,flammablesolvents.VBG81
[2513] ReevaluationofpottingprocedureFinalReport,
July1990.MBBERNO(Bremen).ESTECContractNo.
7830/88/NL/PH(SC)
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26
Incoming inspection
26.1 Tests
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26.3.1 Strength
26.3.1.1 General
Testingisnecessarywhenaguaranteedvalueofpottingresinstrengthisneededfor,e.g.:
Coredensitiesexceeding50kg/m3
Largecoreheightwithpartialpotting.
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Table261:Incominginspection:Pottingresinstrengthtests
Sampledimensions Acceptancestrength(1)
Testmethod Teststandard
(mm) (N/mm2)
Bending DIN53452 31580 110
Tensile DIN53455 320150 60
(1)Proposedacceptancevaluesapplytopureresinswithoutfilleradditives,e.g.microballoons.
26.3.2 Hardness
A hardness test on each batch of mixed resin and hardener provides a cure check on the potting
compound.Thiscanformpartofthemanufacturingprocesscontrol,[261].
[Seealso:27.1]
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4pointflexuraltest,toprovidevaluesof:
Strength;
Stiffness.
Thesetestsareconductedinaccordancetorecognisedstandards,e.g.ASTMorequivalents.
NOTE Testsamplesreplicateexactlythesandwichfacesheet,e.g.materials,
layup,numberofplies,curecycle.
26.4.3 Consumables
Itisincreasinglycommonforconsumablesusedincompositeprocessing,e.g.releaseplies,peelplies
andcleaningagents,to besubjectedtoincominginspectionprocedures.Thisisespeciallytruewhere
structuraladhesivebondingisusedasanassemblyprocess,e.g.bondingCFRPfacesheetsontocores
toproducesandwichpanels,[Seealso:ECSSEHB3221].
26.5 References
26.5.1 General
[261] InsertAllowableTestProgrammeIATP2
KongsbergGruppenReportNo.02TR68040906(October1997).
[262] MILC7438
Corematerialaluminum,forsandwichconstruction
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27
Manufacture control
27.1 Testing
27.1.1 General
Thetestsconductedaspartofmanufacturecontrolaregroupedas:
Mechanical,[See:27.3];
Nondestructive,[See:27.4].
[Seealso:Clause29fortestmethodsfordeterminingpermissibleloadsanddesignallowables]
27.1.2 Mechanical
Destructivemechanicaltestsareconductedonreferencesamples,[See:23.6].
[See:27.3]
27.1.3 Non-destructive
Nondestructivetesting(orinspection)iscarriedouton:
Samples,and
Manufacturedflightarticle.
[See:27.4]
27.1.4.1 General
Teststodetermineinsertstrengthvalues(notcoveredbythishandbook)canbenecessary,e.g.:
Specialtypesofcore;
Nonstandardinserts,[Seealso:AnnexFforcasestudies];
Novelinsertarrangements.
Basictestprogrammeinformationisgivenin[271],[272].
[Seealso:Clause29]
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27.1.4.2 Potting process
Thefactorstestedandinspectedinthedevelopmentofapottingprocess,[273],include:
Borehole,e.g.drilling,dimensions,adjacentcellwalls;
Core,e.g.perforation;
Pottingcompound,e.g.viscosity,temperature.
Otherfactorswhichcanhaveaninfluenceare:
Features at the bottom of the bore hole, e.g. corner at coretobottom face sheet, which can
affectflowofpottingcompound;
Injectionpressureprofileonflowofpottingcompound;
Injectionnozzleshapeandsize.
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27.3.1.1 Sample
Reference samples are manufactured at the same time as the flight structure from exactly the same
materials,[See:23.6;Figure234].
NOTE The sandwich sample height, H in Figure 234 is the same as that of
theflightstructure.Test fixture
Figure271showsasimpletestfixtureforoutofplanetensileloadingtestsonsandwichspecimensof
80mm80mmsizewithacentrallylocatedinsert.Aversionforcompressionorfatigueoutofplane
testingisshowninFigure272fortwodifferentsandwichthicknesses,[275].
Whenloadisactingontheinsert,thesandwichplateispressedagainstone(forpuretension)ortwo
(fortensionandcompression)aluminiumplateswhichbothhaveacentralhole,70mmindiameter,to
ensureasufficientfreeareaaroundtheinsert.
Thetestfixtureissuitableforsandwichthicknesses,(c +2f)ofupto60mmandforinsertdiameters,di
upto22mm.Itcanbeusedineitherstaticordynamic(servohydraulic)testmachines.
[Seealso:H.1fortheengineeringdrawingsofthetestfixture.AphotoisshowninFigureF12]
Notethatforinsert/sandwichconfigurationswithhigherloadbearingcapability,asizeof80mm80
mmforthesamplesandthecorrespondingcoverplatesofthetestfixturecanbetoosmall.Underhigh
outofplaneforcestheremainingsmallsupportareaofthecoverplateoutsidethecentralholeof 70
mmdiametercanthenleadtosuchstressconcentrationsthatstrongcrushingofthehoneycombcore
isobserved[275].Inthiscase,anenlargementofthedimensionsto100mm100mmorevenmoreis
necessary.
Figure271:Manufacturecontrol:Outofplanetestfixturefortension(pullout)
tests
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Figure272:Manufacturecontrol:Outofplanetestfixtureforcompressionor
fatiguetests
27.3.1.3 Test
Thetestisperformedinanelectronicallycontrolledtensiletestingmachinethatcanrecordtheload
deflection.Asuitableloadingrateis1mm/min.Loadingisstoppedafterthemaximumloadhasbeen
reached,i.e.atabout2mmconstantdeflectionofthefacesheet.Thismakesiteasiertojudgefracture
conditionsaftersampleshavebeentaken,[275].
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Indynamic(fatigue)teststheforceisappliedinbothdirections.Thereforethereisasecondcrossbar
on the top side of the base plate. In order to avoid slipping of the sandwich specimen, the exact
positionofthissecond(upper)crossbarcanbeadjustedbymeansofeccentricscrewsaccordingtothe
actualspecimensize.
The test fixture is suitable for sandwich specimens of 80 mm 80 mm; as shown. The maximum
sandwich thickness, (c+2f) depends only on the screw length between the two plates. The insert
diameter,dicanbe20mmforflushmountedinserts,butslightmodificationsoftheloadingbarcan
benecessaryforlargerorprotrudinginserts.
[Seealso:H.3fortheengineeringdrawingsofthetestfixture.AphotoisshowninFigureF12]
Figure273:Manufacturecontrol:InplanetestfixtureforshearBendingtest
Figure274showsatestfixtureforstaticbendingtestsoninserts.Thesandwichspecimenof80mm
80 mm size with a thickness of up to 60 mm is fastened in a cage of aluminium plates, which is
mounted on a back side structure attached to the test machine. There is a free area of 70 mm in
diameteraroundtheinsert,[275].
Thebendingmomentisappliedbymeansofarigidcantileverbeam,linkingtothecrossheadofthe
test machine. The distance at which the crosshead links to the cantilever beam is adjustable. The
threadconnectionandthecontactareabetweenthebeamandtheinsertarepreciselyaligned.
[Seealso:H.4fortheengineeringdrawingsofthetestfixture.AphotoisshowninFigureF12]
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Figure274:Manufacturecontrol:Bendingtestfixture
Figure275:Manufacturecontrol:Torsiontestfixture
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27.4.1 Radiography
TheactualconditionofpottingmassaftermanufacturingcanonlybejudgedbyanXrayviewparallel
totheaxisofaninsert.However,thisonlyprovidesa2dimensionalviewofthepotting.
Thefeaturestobeexaminedare:
Numberoffilledcells;
Numberofconnectedcellwalls;
Estimation of potting height: by comparing the Xray with potted inserts of known potting
height;
Largeairinclusionsinthepottingmass.
NOTE Knowingthenumberofconnectedcellwallsisparticularlyimportant
to:
reducevariabilityofstrengthvalues,or
calculatetheactualloadcarryingcapabilityofaninsert.
[See:7.3]
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27.6 References
27.6.1 General
[271] StandardizationofDesignAnalysisandTestingofinStructural
SandwichElements,Finalreport.ESTECContractNo.3442/77/NL/PP.
[272] StandardisationofDesignAnalysisandTestingofInsertsinStructural
Elements,Finalreport.ESTECContractNo.3442/77/NL/PPRider1.
[273] ReevaluationofPottingProcedureFinalReport,
July1990.MBBERNO(Bremen).ESTECContractNo.
7830/88/NL/PH(SC)
[274] MMSContributiontoESAInsertDesignHandbookMatraMarconi
SpaceReportNo.NT/102/BG/355013.96(December1996).
[275] J.Block,R.Schtze,T.Brander,K.Marjoniemi,L.Syvnen,M.Lambert:
DLRBraunschweig/HelsinkiUniv.Technology/Patria/ESTEC
StudyonCarbonFibreTubeInserts,
ESTECContractNo.16822/02/NL/PA(2004)
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28
Quality control
28.1 General
Qualitycontrolactivitiesconductedatvariousstagesofdesign,manufacturingandtestingformpart
of the overall quality assurance plan associated with the project. The precise details are given in
appropriatestandardsandspecifications,[See:ECSSwebsite:www.ecss.nl].
28.1.1.1 Overview
All standard activities related to quality control of materials and processes are applied to sandwich
panelsandtheircomponentparts,includingbutnotlimitedto,[See:ECSSQST70;ECSSQ7071]:
Materials,
core;
facesheet;
adhesive;
coatings.
Components:
inserts;
fasteners.
Processes:
machining,[See:28.2];
potting,[See:28.3].
28.1.1.2 Potting
Control of the potting process is particularly important because it is a chemical process that is
sensitivetoinaccuraciesthatcanresultinfailures,[Seealso:23.10fordefects].
NOTE Permissiblevaluescitedwithinthishandbookarebasedonacorrectly
performedpottingprocesswithoutsignificantfailures.
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28.1.3 Personnel
All aspects relating to personnel using materials, processes and their control are applied and
documentedinaccordancewiththegoverningstandards.
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Freefromanybentcellwalls,[281];
Dislocatedlayersofcorefoil.
Undercutting or detachment of the core from the face sheet caused by mechanical damage or
overheatingcannotexceedtheradiusbymorethan2mm.
Radius of core bore hole is never less than the nominal dimensions of the insert flanges. This
leads to a strength reduction below the minimum permissible values, [See: 28.3; Figure 281,
part4].
NOTE1 This can occur if a blunt or damaged punching tube is used or the
boreholedrillingandreamingprocessisinsufficient.
NOTE2 Toavoidcontamination,lubricantsorcoolingfluidcannotbeused.
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Air inclusion
Toolowviscosityofpotting
2 underneath
mass
insertboreholes
Figure281:QA:PoorpottingcausingstrengthdegradationTable281:QA:Potting
failureanddetectability
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Effect Detectableby
100%Loadcontrol
Dynamicloadloss
Referencesample
Processcontrol
Strengthloss
Totalloss(1)
Outgassing
Item Reason
1 mixingratio
Resin, 2 poormixing
hardener,filler
(5),(6) 3 wrongcomponent
4 storage(2)
5 poorcleaning
Adhesion
6 contamination(4)
7 boreholefailure
8 poorfilling(5),(6) (3)
Process
9 airbubbles(small)
10 humidity
(1) Tearoutatlowload.
(2) Incorrectstorageorshelflifeexpired.
(3) Inspectionofboreholesafterfilling.
(4) Postcleaning.
(5) Viscositycontrolofmixedpottingcompoundnecessary,[281].
(6) Temperaturecontrolofmixedpottingcompoundandworkingenvironmentnecessary,[281].
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1 Standard
Material Procurement (1)
2 Incoming Inspection
3 Compliance
REJECT
to Standard (1)
No
Yes
(1)StandardMILC7438
Figure282:QA:Honeycombcoreincominginspection
28.5.1 Procedure
Todeterminethedensityundernominaldegreeofexpansion,theprocedureusedis:
Cuttestpiecesfromcorematerial(MILC7438);
Weighsamples;
Calculateactualdensity;
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Determinationofactualcellsizebycounting10cellsandmeasuringtheiroveralllengthinW
direction;
Calculateofactualdegreeofexpansion,in%,by:
actual cell size
nominal cell size
100 [%] [28.51]
Determinethecorrectionfactor,Kex;anexamplecurveisshowninFigure283;
Correctactualdensity,toobtainnormaliseddensity,N:
N K ex act [28.52]
Figure283:QA:Coredensitycorrectionfactorfordegreeofexpansion
28.6 References
28.6.1 General
[281] ReevaluationofPottingProcedureFinalReport,
July1990.MBBERNO(Bremen).
ESTECContractNo.7830/88/NL/PH(SC)
[282] MILC7438
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29
Testing
29.1 General
The Test procedures and techniques for determining permissible loads and design features are
described.Thesecover:
Insertstaticstrength,[See:29.2]:
Outofplane;
Inplane;
Bending;
Torsion.
Geometriceffectsoninsertstaticstrength,[See:29.3]:
Edgedistance;
Insertproximity.
Insertdynamictests,[See:29.4]:
Sinusoidalloading;
Staticresidualstrength.
[Seealso:27.1;27.3;AnnexHforothermechanicaltestsandassociatedtestjigsusedinmanufacture
control]
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T e n s i o n Co m p r e s s i o n
Figure291:Testing:Insertstaticoutofplanestrengthfixture
Thetestsamplesizeisatleast80mm80mm,[291]stipulates100mm100mm.Largerdimensions
are necessary for insert/sandwich configurations with high loadbearing capability to ensure a
sufficient support area around the central hole of 70 mm. Otherwise, at higher outofplane forces,
honeycombcorecrushingcanoccur.
Thetestisperformedinatensiletestingmachine,whichenablestherecordingofloaddisplacement
values.
Aloadingrateof2mm/minwaschosenbecauseadeflectionof2mmincludestheultimateloadforall
sandwich conditions. One minute is a typical loading time and failures usually occur after about a
minute.
Loadingisstoppedafterthemaximumloadhasbeenreached,whenthedeflectionofthefacesheetis
about 2 mm. This makes it easier to judge fracture conditions when samples are subsequently
examined.
NOTE The test conditions stated are also valid for specimens that are pre
treatedbydynamicorthermalloading.
A typical forcedisplacement curve has a linear region at first, then a nonlinear region before the
maximumload.Theendofthelinearregionismeasuredfromthecurvesandthevalueisknownas
thefirstpeakvalue.
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Figure292:Testing:Insertstaticinplanestrengthfixture
Thetestisperformedinatensiletestingmachine,whichenablestherecordingofaloaddisplacement
curve.
Theloadingrateis2mm/min.
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Strap plates
Test sample
Figure293:Testing:ASTMinsertstaticinplanestrengthfixture
Thedimensionsofthespecimensare180mm60mm.Thestrapplatesare130mm40mm5mm
fora throughthethickness specimen in the symmetric load case. For other cases, the dimensions of
thestrapplatesare200mm40mm5mm.
Thetestisperformedinaseriesofsequentialsteps:
1. The temperature and humidity measurement system of the test room is activated. The
measured temperature and humidity values are stored in a computer. The test is
performedatroomtemperature.
2. Strapplates areclampedfirsttothelowergripandthentotheuppergripofthetesting
machine.Throughthethicknesstestsneedspecialfixtures.Oneofthetwothroughthe
thickness testing fixtures, connected to the specimens with the shear pin, is clamped to
theuppergripofthetestingmachine.Theothertestingfixtureisclampedtothelower
grip of the testing machine. The lower grip is then raised to enable the connection
betweenthestrapplateandthelowertestingfixturebymeansofanothershearpin.
3. Avisualinspectionisperformedtoverifythealignmentofthespecimenwiththetesting
machine.
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4. Theloadisappliedatarateof2mm/min;strokecontrolisused.
5. At the beginning of the test, slippage occurs between the insert flange and the strap
plates.Slippageisconsideredtooccurwhenaconstantordecreasingvalueoftheloadis
registeredwhilethestrokeisstillincreasing.Theloadatwhichslippageoccursisnoted.
6. A failure of the specimen is considered to occur when a load drop equal to 20% of the
maximumloadisregistered.Thefailureloadisrecorded,i.e.thepeakvalue.
7. Thefailuremodeisdeterminedandthespecimenphotographedfrombothsides.
Figure294:Testing:Bendingfixture
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Figure295:Testing:Edgedistancefixture
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Figure296:Testing:Insertproximitytensilefixture
The tensioncompression proximity testing fixture for inserts, i.e. loaded in opposite directions, is
showninFigure297.
Figure297:Testing:Insertproximitytensilecompressionfixture
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Table291:Testing:Dynamictestloadlevelsandnumberofcycles
%ofStatic Frequency
Loadlevel Cycles
ultimateload (Hz)
High,S1 80 ~500 ~50
Medium,S2 60 ~5000 ~50
Low,S3 45 ~50000 ~50
The load levels givenareestimations that can be adjusted depending upon the real number of load
cyclessupportedbythefirstsampletobetested.
The load and deflection amplitudes are recorded during the dynamic test. For high and medium
numbersofloadcycles,recordsaretakenatchosenintervals.Theyshowincreaseddeflectioncaused
bythedamagegrowthduringloading.Theloadamplitudeiskeptconstant.
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Figure298:Testing:Determinationofpointsforresidualstrengthtest
29.5 References
29.5.1 General
[291] L.Syvnenetal:PatriaFinaviacompOy,Finland
AnalysismodelsforinsertdesignrulesinsandwichpanelswithCFRP
facings
Patriareport:GS1PFCRP0002(January2003)
ESTECContractNo.14076/99
[292] ASTMF606
Standardtestmethodsfordeterminingthemechanicalpropertiesof
externallyandinternallythreadedfasteners,washers,andrivets
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Annex A
Inserts
A.1 Introduction
InsertsusedinEuropeanspaceapplicationsaresummarised,[293],[294],[295].Thesearegrouped
as:
Commerciallyavailable,i.e.standardspecifieditems,thatarenormallysuppliedbyShurlok,
[Seealso:A.2];
Non standard, i.e. designed and manufactured inhouse for particular project applications,
[See:A.3]andcoversthose:
based on conventional insert designs, where dimensions or the materials used are
different;
novel insert designs, e.g. Carbonfibre tube inserts, [See: A.3], which were originally
developedfortheROSETTALanderproject,[Seealso:F.6forcasestudy].
[Seealso:AnnexFCasestudies]
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TableA1:Commerciallyavailableinsertsusedinspace
ProductCode Comment/Project Company/[References]
AA2024(3.1354.T851);anodisedto
ENN366 DASARI[293]
MILA8625
AA2024(3.1354.T851);anodisedto
ENN379 DASARI[293]
MILA8625
AA2024(3.1354.T851);anodisedto DASARI[293]
ENN398
MILA8625 AleniaSpazio[293]
LN9038 AleniaSpazio[293]
LN9499 AleniaSpazio[293]
NAS1834 BAeAirbus[293]
NAS1836 BAeAirbus[293]
CASESPOT5:Equipment
SL100530 SONACA[294]
[See:F.7Casestudy]
SILEX:Structure;Equipment
SL10068 MANTech.[294]
[See:F.9Casestudy]
NILESAT(battery):Structure;panel
SL10068 assembly;satelliteinterface. BTS[294]
[See:F.11Casestudy]
Supplier:Shurlok
SL1019608 BAeAirbus[293]
SL10218H394/Z Contraves[293]
SL10218M494/Z Contraves[293]
SL10253 BAeAirbus[293]
SL10414 Steel;cadmiumplated Westlands[293]
SL10417 Steel;cadmiumplated Westlands[293]
SL10571 Steel;cadmiumplated Westlands[293]
SL10807 AleniaSpazio[293]]
SL10807 CASA[293]
SL10968 CASA[293]
SL600 BAeAirbus[293]
SL601 AleniaSpazio[293]
UMSSST:Structure
SL601M49.5A Aerospatiale[294]
[See:F.8Casestudy]
ASAP4(AR4):Structure;equipment;
SL601M615.9S I/Fmicrosatellite UTAIndustrie[294]
[See:0Casestudy]
SL604 BAeAirbus[293]
SL606 AleniaSpazio[293]
SL607 Steel;cadmiumplated Westlands[293]
ARIANE4:Equipment
SL607 CASA[294]
[See:F.3Casestudy]
ARIANE5:Equipment
SL607 MMSUK[294]
[See:F.5Casestudy]
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A.3 Non-standard
Table A2 summarises an industry survey of insert technology, [293], and compilation of insert
applicationsinEuropeanspaceprojects,[294].
Nonstandardinsertscanbegroupedas:
Inhouse,or
Noveldesign
NOTE [294] covers axisymmetrical inserts fitted in sandwich panels only.
Cocuringpanelswithinsertsandedgeinsertsareexcluded.
[Seealso:AnnexFforcasestudies]
A.3.1 In-house
Insertsaredesignedandmanufacturedinhousewherecommerciallyavailablestandardinsertsare
inadequate,e.g.throughthethicknessinsertsinthicksandwichpanels.
Inhouseinsertstendtofollowtheconventionalinsertdesign,e.g.metalliccomponentspottedinto
sandwichpanels;withtheuseofnuts,boltsandhelicoilsasthemechanicalconnectionmethod.
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TableA2:Nonstandardinsertsusedinspaceapplications
Company/
Description Project/Comment
[References]
HRGCL:Electronicequipment
AA2024T351 MATRADef.[294]
[See:F.10Casestudy]
ARIANE4:Structurehandling
AA2024T4 CASA[294]
[See:F.4Casestudy]
Aluminium Urenco[293]
Aluminium(AA7075;AA6061);Titanium
AlcatelEspace[293]
(TA6V;T40);cocuredwithpanel
Aluminiumalloy,anodised.Through
AleniaSpazio[293]
thickness;highloads
Throughthickness Contraves[293]
ASAP4(AR4):Structure
Throughthickness;AA2024T6 UTAIndustrie[294]
[See:F.4Casestudy]
Supplier:Inhouse
SILEXGEO:Structure
Throughthickness;AA7075T73 MANTech.[294]
[See:F.9Casestudy]
NILESAT(battery):Structure
Throughthickness;AA7075T7351or
handling;radiatorplate. BTS[294]
AA7175T7351
[See:F.11Casestudy]
SPOT5:I/Fplatformstructure
Throughthickness;AA7175T7351 SONACA[294]
[See:F.7Casestudy]
ASAP5:Structure;separation
systemminiandmicro
Throughthickness;AA7175T7351 MMSUK[294]
satellites
[See:F.5Casestudy]
Throughthickness;AluminiumAU4G1 UMSSST:Structure
Aerospatiale[294]
T351 [See:F.8Casestudy]
Throughthickness;spools CASA[293]
Aluminium Raufoss[293]
Carbonfibretubeinserts ROSETTALander, DLR[295]
(withaspreadableCFRPtubebondedin ESAstudyoncarbonfibretube
thecoreandwithmetallicendcaps) inserts
[See:F.6Casestudy]
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C la s s i c p o tt e d i n s e rt Ca rb o n fi bre tu b e in se rt
FigureA1:Carbonfibretubeinserts:Comparisonofdesignprinciples
The load introduction from the metallic insert part into the sandwich is not performed by
conventional epoxy resin potting, but by means of an extremely stiff, thinwalled carbon fibre tube
whichfitsexactlybetweenthefacesheetsandisbondedtothehoneycombcorebyaepoxyadhesive
layer. This adhesive layer can be relatively thin. Only a small amount of resin is needed to ensure
goodcontactwiththesurroundingcellwallsofthehoneycombcore.
However,thefulllengthofthe(extremelystiff)carbonfibretubeactivelycontributestotheshearload
transfer into the (much softer) honeycomb core, because the tube always goes through the whole
sandwich thickness. The formlocking contact under both face sheets makes the sandwich in the
vicinityoftheinsertpracticallyincompressible.
The carbon fibre tube contains unidirectional highmodulus carbon fibres and is slit lengthways
duringmanufacture.Thisallowsfoldingoroverlappingtoreducethediameterforfeedingitthrough
theboreholeinthefacesheet;showninFigureA2.
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FigureA2:Carbonfibretubeinserts:FittingofspreadableCFRPtube
After placement, the carbon fibre tube is spread and aligned by means of a simple tool, so that the
endsofthetubefitjustunderneaththefacesheets.Theinnerradiusofthetubeisidenticalwiththe
boreholeradiusofthefacesheets.
After curing of the adhesive, the carbon fibre tube is ready for fitting of one or two metallic insert
caps.Twobasictypeshavebeendeveloped.Theseareknownas,[295]:
Type1,whichreplacestheconventionalthroughthethicknessinsert;asshowninFigureA3.
Type2,whichreplacestheconventionalpottedinsert;asshowninFigureA4.
A.3.3.2 Type 1
Athreadelementisinsertedintothebottomsandwichface,i.e.oppositetothesidefromwhichthe
screwisfitted.Thesmallermetalliccaponthetopsideservesonlyasaguidingelementforthescrew.
Itcaneitherbeflushorprotrudebeyondthesurfacebyanydistanceneeded,[See:FigureA3].
Type 1 tube inserts are particularly suited for high forces, where both face sheets contribute to the
loadcarryingcapability.
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FigureA3:Carbonfibretubeinsert:Type1cap
A.3.3.3 Type 2
FigureA4showsType2,whichneedsonlyasinglemetalliccap;thisreplacestheconventionalpotted
insert,e.g.usedforunilateralfixationofpayloadunits.
FigureA4:Carbonfibretubeinsert:Type2cap
The cylindrical metallic part has collars at the top and bottom; shown in Figure A5. The standard
diameterofthesecollarsis11mm,correspondingtotheinnerdiameterofthecarbonfibretubeinsert.
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FigureA5:Carbonfibretubeinsert:Type2insertcapandcarbon
fibresleeve
Betweenthetwocollars,theradiusisreducedby0.7mmtoenableaslitcarbonfibresleeveof0.6mm
wall thickness to snap around it. When the assembled cap is bonded into the carbon fibre tube
insert,the0.1mmclearanceisfortheadhesivelayer.Thecarbonfibresleeveiscutpreciselytolength
sothat,oncesnappedaroundthemetallicpart,accurateformlockingcontactbetweenthetwocollars
isachievedandanyslippingisavoided.
ThelengthoftheType2capdeterminesthesizeofthebondedareabetweenthecarbonfibresleeve
on the cap and the carbon fibre tube in the sandwich. The loadbearing capability can be chosen
accordingly.GoodadhesivebondingcanbereadilyachievedbetweenthetwoCFRPcomponents.
[Seealso:F.6forexperimentalandanalyticalresults,[295]]
A.3.3.4 Advantages
Threesignificantadvantagesofcarbonfibretubeinsertsare:
Close mounting: The radius of a carbon fibre tube insert, consisting of the radius of the tube
itself plus a thin adhesive layer, is smaller than the radius of a conventional potted insert of
equivalent loadbearing capability. Consequently the insert density per area of the sandwich
canbehigher.
Masssaving:Duetothelowweightofthecarbonfibretubesandthesmallamountofadhesive
needed,themasscontributionisonly~0.05grammespermillimetreofsandwichthicknessplus
themassofthemetallicinsertcap(from1.9gforM3upto3.2gforM6).Thisissignificantly
lighter than comparable potted inserts for sandwich thicknesses up to 50 mm. For very thick
sandwiches, carbon fibre tube inserts may become slightly heavier (due to the long tube) but
theiroutofplaneloadbearingcapabilityisfarsuperior.
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Easy implementation: The implementation of carbon fibre tube inserts into bore holes in the
sandwich is relatively easy. Special expertise and training regarding the proper injection of
pottingcompoundisnotnecessary.Thiscanplayapartinreducingcosts.
A.4 References
A.4.1 General
[293] InsertTechnologyIndustrySurvey(1995)
[294] MatraMarconiSpaceContributiontoESAInsertDesignHandbook;
MMSRef.NT/102/BG/355013.96(Dec.1996)
[295] J.Block,R.Schtze,T.Brander,K.Marjoniemi,L.Syvnen,M.Lambert:
DLRBraunschweig/HelsinkiUniv.Technology/Patria/ESA/ESTEC
StudyonCarbonFibreTubeInserts
ESTECContractNo.16822/02/NL/PA,(2004)
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Annex B
Permissible loads
B.1 Introduction
Thesetofdesigngraphs,presentedinB.2,arebasedontheanalyticalexpressionsfor:
Predictingstaticloadcarryingcapabilityofinsertssubjectedtooutofplaneloading,[See:D.1].
ReliabilitycoefficientsRC,[See:D.7;TableD2]
ThisAnnexpresentsgraphsof:
Tensilepermissibleloads.
Compressivepermissibleloads.
NOTE See:B.2forindextodesigngraphs
Seealso:D.8foradescriptionofthegraphs.
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When the core height approaches 40 mm, the permissible tensile load is determined for all three
potting behaviours, i.e. fully potted, partially potted and potting rupture; and the lowest value
obtainedisapplied;asshowninTableB2.
NOTE This applies to tensile permissible loads only. Compression
permissibleloadsdonotshowsuchatransitioneffect.
TableB1:Coreheight:Permissibletensileloadstransitionpoints
Insert Facesheet Transitionpoint(1)
Core (mm) (mm) Coreheight(mm)
dia. height thickness Min. Ave.
3/1650560.0007 14 9 0.2 42 45
3/1650560.0007 14 9 0.4 43 46
3/1650560.0007 14 9 0.6 42 45
3/1650560.0007 14 9 0.8 38 44
NOTE (1) Transition from 'fully potted' to 'partially potted' behaviour.
TableB2:Coreheight:Examplepermissibletensileloads
Minimumtensilepermissibleload(N)
Method
Fullypotted Partiallypotted Pottingfailure
Calculated,[296] 2200 1748 1896
FromIDH,[297] 2200
NOTE Core: Type 3/16-5050-0.0007; height: 55 mm; Insert: diameter = 14 mm;
height = 9 mm; Face sheet thickness = 0.4 mm
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TableB3:Designgraphs:Indextopermissiblestaticloads
CoreType CoreDesignation(1)
3/1650520.0007
3/1650520.001
1/850520.0007
1/850520.001
Aluminiumalloy
3/1650560.0007
3/1650560.001
1/850560.0007
1/850560.001
HRH103/162.0
HRH103/163.0
Nomex HRH103/164.0
(aramidtypefibre/phenolresin) HRH101/81.8
HRH101/83.0
HRH101/84.0
GFRP HRP3/164.0
(glassfibrereinforcedplastic) HRP3/165.5
NOTE(1)
Aluminiumalloy:cellsizecorealloyfoilthickness.
Nonmetallic:materialcellsizedensity.
B.3 References
B.3.1 General
[296] M.AGygax:ContravesSpace(CH):
ESAPSS031202Issue1Rev.1FaxcommunicationtoESTEC;October
1997
[297] ESAPSS031202(Issue1,Revision1)September1990:Insertdesign
handbook
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Annex C
Analytical determination
C.1 Introduction
TheanalysispresentedinAnnexCappliestothedeterminationofthestaticcapabilityofaninsertina
largesandwichpanel,withtheloadnormaltothepanel.
NOTE The principles discussed here relate to the MBBERNOderived
antiplane theory. An extended antiplane theory is presented in
AnnexD.
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PRcrit<Pcrit,and
PRcrit<Ppcrit
Tensile rupture of the potting resin should be avoided. This is described in C.3 and C.4; using
supplementaryequations:(Eqn.[C.311]);(Eqn.[C.43]);(Eqn.[C.411]);(Eqn.[C.412]).
[C.21]
Where:
(r) shearstressinthecoreatradiusr;asshowninFigureC1.
P appliedoutofplaneload
coreshearstress
ts facesheetthickness;assumedthatbothfacesheetsaresimilar
h totalsandwichthickness=c+ts1+ts2
outerradiusofpanel
bp effectivepottingradius
b R realpottingradius
Ip momentofinertiaofthepanel
ts1ts 2 (h c) 2
=
4(h c)
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Is momentofinertiaofthefacesheets
3 3
ts1 ts 2
=
12
I = Ip+Is
ratioofstiffnessbetweencoreandfacesheets
Gc (h c) I
=
E c t s1 t s 2 I s
Gc shearmodulusofthecore
Es
E =
1 s
2
:Fullypotted
insert
Forr,aandb >5,themodifiedBesselfunctionsbecometheexponentialfunctions:
e 2x
x 12
I1(x) =
[C.22]
= e 2 x
1
x 2
K1(x)
Substitutionof(Eqn.[C.22])into(Eqn.[C.21])gives:
r PI m
K [C.23]
bh c I
With:
b b e r b
e
a r b
a e a r
e
a r
K 1 r
e
a b a a b
[C.24]
r ab e
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Or:
b b sinh r b a sinh a r
K 1 r [C.25]
r ab sinh a b
Forr < a, agoodapproximationforKis:
b r b r
be
K 1 [C.26]
r
Forf'=f,byrearrangementoftheequations:
Im=
f c f 2
2
3
If=
f 6
f c 2 cf 2 f 3
2 2
I=
1 G c
12 1 2 1 32
2
[C.27]
f E f
f
P 1
(r ) K
2 bc
2
2 4 3 [C.28]
With:
=c/f [C.29]
For10,i.e.c10mmandf1mm,(Eqn.[C.27])and(Eqn.[C.28])canbeapproximatedby:
1 G c
12 1 1 2 2
[C.210]
f E f
f
P
(r ) K [C.211]
2 bc 1
Withanerroroflessthan0.5%.
Thecoreshearstressdistributioncanbeexpressedby:
*
(r ) nom C K [C.212]
With:
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nom p / 2 bc [C.213]
C* / ( 1) [C.214]
b r b r
be
K 1 [C.26]
r
r max b
1 e c 2 ( b ) n
[C.215]
With:
c2 =0.931714
n =0.262866
Thevalueofr maxisusedin(Eqn.[C.26])toobtainKmaxthatisusedin(Eqn.[C.21])togive:
Ifmaxreachesthecoreshearstrength C crit,theinsertcapabilityisgivenby:
NOTE Eqn.[C.217]isvalidforbothtensileandcompressiveloads.
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FigureC2:Partiallypottedinsert
Theseloadcomponentsaregivenby:
PF
P max 2r max c max [C.31]
2
PN r2max c [C.33]
With:
hp min hi 7 mm [C.35]
NOTE 7mmisusedwhateverthecoreheight,c.
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Thetypicalvalueofh pdependsonthecoreheight:
hp min A tanh(c hmin )
hp typ [C.36]
hp min
Where:
A=5 forcellsizeSC=4.8mm(1/8core);
A=2.5 forcellsizeSC=3.2mm(3/16core).
tanhisahyperbolictangent
NOTE Eqn.[C.36]isonlyvalidforpartialpotting,i.e.c > h i+7mm.
PS :islimitedbythecoreshearstrength c crit.
PN :islimitedbythecore:
tensilestrengthc crit t;
compressivestrengthc crit c;
Theoretically,foralinearbehaviour,thetwofailuremodesdonotoccurtogether,i.e.:
shearrupture;
tensile(orcompressive)ruptureofcore.
But in reality, owing to nonlinearity effects, the shear strength and the tensile (or compressive)
strengthofthecorearereachedtogether.
Thereforethecomponentsofthecriticalloadofpartiallypottedinsertsare:
Where:
crit=ccrittfortensileload;
crit=ccritcforcompressiveload.
Thus,thecapabilityofapartiallypottedinsertisgivenby:
Where:
Psspp=Permissibleloadofapartiallypottedinsert(hp<c).
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From(Eqn.[C.217]):
2bp c c crit
Pss pf [C.312]
C * K max
Where:
Psspf=Permissibleloadofapartiallypottedinsert(hp=c).
0.62
1 hp
[C.313]
K t pp c
Where:
1/Ktpp=Stressconcentrationfactor.
For c > 2.5 h p , the permissible load of a partially potted insert in a nonmetallic core is considered
quasilinear.
PSR : load component carried as shear stress in the core around the potting, over the insert
height,givenby:
PNR :loadcomponentcarriedbynormalstressinthepottingresinundertheinsert:
Where:
hi=insertheight;
bR=realpottingradius,[See:Note];
R=tensilestrengthofthepotting;
PR=PF+PSR+PNR [C.43]
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NOTE bR isnotidenticaltotheequivalentpottingradius,binC.2,[Seealso:
7.4].
PNRcanalsobeexpressedby:
PF ( PR 2 PF )(c hi )
PNR
c [C.44]
PF (1 2 ) PR
Where:
c h c
i
[C.45]
PF PNR 1 2 PR 1 2 [C.46]
hi
PSR PRC * K max r max b c
[C.410]
When(Eqn.[C.46])and(Eqn.[C.410])aresubstitutedinto(Eqn.[C.43]),thecriticalinsertloadunder
whichthepottingresinfailsisgivenby:
[C.411]
1
1 2 C *K max r max hi
bc
Where:
Rcrit=tensilestrengthofpottingresin.
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where:
PSSfp=Permissibleloadofapartiallypottedinsert(hp<c).
2bp c c crit
Pss fp [C.312]
C * K max
0.62
1 h
p [C.313]
K t pp c
PSSppisquasiconstantforc>2.5hp.
Pottingfailureofaninsertinanonmetalliccoreisconsideredtooccurwhen:
where:
bR=realpottingradius;
Rcrit=tensilestrengthofpottingresin.
PRC * K max
Hence max
2bc
From(Eqn.[C.31]):
2bc 2c
PF max max r max
2C * K max 2
bc
Hence PF max c r max
C * K max
From(Eqn[C.41]):
PSR 2hi max r max
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PRC * K max
Hence PSR 2r max hi
2bc
From(Eqn.[C.43]):
PR PF PSP PNR
1 C * K max c
Hence PNR PR r max hi
2 bc 2
From(Eqn.[C.42]):
PNR bR2 R
Rearrangingtheabove,gives:
bR2 R
PR
0.5 C
* K max
bc
r c
max 2 hi
Thusatc = 2 hi
bR2 R
PR
0.5
Where:
Pcritcomesfrom(Eqn[C.217])
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C.5.1.2 Partially potted inserts
Pp crit c 2r max h p max r2max c crit c [C.52]
Where:
0.62
1 hp
[C.313]
K t pp c
C.6 Reliability
TableC1:Correlationcoefficients
Correlation Standard
Potting Appliedload coefficient deviation
(CC)(1) (G)
Fullypottedinsert,orbehavingas Tensile
0.993 0.059
fullypotted(2) Compressive
Partiallypotted Tensile 1.043 0.52
Partiallypotted Compressive 0.998 0.072
NOTE (1) CC=Pcrittest/Pcrittheory
NOTE (2) Seealso:C.1todeterminefullorpartialpotting.
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TableC2:Reliabilitycoefficients
Tensile Tensile Compressive
Metallicun
perforated Metallic
Core Metallicperforated
GFRP (alltypes)
Nomex
Minimumvalue:
RC =1.1720.0063.c0.2641.f 0.91 0.89
Averagevalue:
RC =1.2070.00544.c0.2088.f 1 1
NOTEc=coreheight,formerlyshownashc,inPSSIDH[2913].
C.7 References
C.7.1 General
[298] S.BrownESTECYME/SIIKOSS(Fax1997)
[299] Erickson,W.S.Thebendingofacircularsandwichplateundernormal
load,ForestProductsLaboratoryReportNo.1828(1953)
[2910] Young,W.S.andKuenzi,E.W.Stressesincludedinasandwichpanelby
loadappliedataninsert,ForestProductsLaboratoryReportNo.1845
(1955)
[2911] Standardisationofdesignanalysisandtestingofinsertsinstructural
sandwichelementsFinalReport.MBBERNO(3442/77/NL/PP)
[2912] Standardisationofdesignanalysisandtestingofinsertsinstructural
sandwichelementsFinalReport.MBBERNO(3442/77/NL/PPRider1)
[2913] ESAPSS031201(Issue1,Revision1)September1990:Insertdesign
handbook
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Annex D
Estimation of static load-carrying
capability
D.1 Introduction
The approximation, presented in Annex D, applies to the determination of the static loadcarrying
capabilityofaninsertinalargesandwichpanel,[2914].
NOTE As far as loads normal to the sandwich panel are concerned, the
principlesdiscussedhererelatetoextendedantiplanetheory.
[See also: Annex C for analysis by MBBERNOderived antiplane
theory]
D.1.1 Background
Thegeneralproblemofanalysingasandwichpanelloadedthroughaninsertisdifficult,[See:section
8]. The constituent parts of the sandwich panel interact in complex ways in the regions close to the
insert; hence in the active loadtransfer mechanisms appear to be very complicated. Much of this
results from local changes in the sandwich panel. The individual face sheets of the sandwich panel
tend to bend about their own neutral planes rather than about the neutral plane of the sandwich
panel.
Fromthepointofviewofpracticaldesign,theevidentconclusionisthatclassicalantiplanesandwich
theory, which is very simple, generally cannot be used for predicting the loadbearing capability of
sandwichplateswithinsertssubjectedtoarbitraryexternalloads.
Thereis,however,oneveryimportantexceptiontothis.Inthecaseofsandwichpanels withinserts
loadednormaltotheplaneofthesandwichpanel(tensileorcompressiveloading),theactivefailure
mechanismisnearlyalwaysshearruptureofthehoneycombcoreattheinterfacebetweenthepotting
andthehoneycomb;especiallybyshearruptureoftheundoubledcorefoils.
The peak shear stress in the honeycomb material is located exactly at the pottingtohoneycomb
interface, and this stress component is predicted with sufficient accuracy by classical antiplane
sandwich theory, [[2915] to [2918], [2925]; provided that the correct location is assumed for peak
shearstress,r = bp.
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Tension,[See:D.3;Eqn.[D.32]];
Compressionloadingandthickfacesheets,[See:D.6;Eqn.0].
If the insert height hi and, especially, the potting height hp are smaller than the core height c, two
quantitieshavetobedetermined:
The static loadcarrying capability, Pcrit of an identical insert system, which is assumed to be
fullypotted(throughthethickness)usingexpressions:
tension:(Eqn.[D.32]),or
compression:(Eqn.0).
Thestaticloadcarryingcapability,Pp crit ofthepartiallypottedinsertusingexpressionsfor:
tension,[See:D.4]:aluminiumcore:(Eqn.[D.410]);nonmetalliccore:(Eqn.[D.411]).
compression and thick face sheets, [See: D.6]: aluminium core: (Eqn. [D.61]); non
metalliccore:(Eqn.[D.62]).
NOTE Thelowerofthetwoinsertstrengthpredictionsisused.
IfPcrit < Pp crit,apartiallypottedinsertbehaveslikeafullypotted(throughthethickness)insert.
IfPcrit > Pp crit,thenthepartiallypottedinsertbehaveslikeatruepartiallypottedinsert.
In addition to the above design calculations, it is necessary to ensure that tensile rupture does not
occurinthepottingresinunderneaththeinsertorunderneaththepotting.
Thiscanbedeterminedusingtheexpressions:
aluminiumcore,[See:D.5;Eqn.[D.59]];
nonmetalliccore,[See:D.5;Eqn.[D.511]].
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FigureD1Outofplaneloading:Circularsandwichplatewith
throughthethicknessinsert
Assumingthatthe elastic modulusofthecore,i.e.pottingand honeycomb,ismuchsmallerthanthe
elasticmoduliofthefacesheets,i.e.Ec<<Ef1, Ef2(effectivelyassumingtheinplanestiffnessofthecore
tobeEc 0,i.e.antiplanecore),thecoreshearstressisnearlyconstantovertheheightofthecore,and
thefacesheetshearstressesvaryparabolicallyoverthefacesheetthicknesses.
The shear stresses in the core and in the face sheets can be calculated using the approximate
expressions,where rbi,[See:FigureD1].
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Qr (r ) E f 1 f1 E f 2 f 2 d
c (r )
D E f 1 f1 E f 2 f 2
P E f 1 f1 E f 2 f 2 d
2rD E f 1 f1 E f 2 f 2
Qr (r) E f 1
2
f
f 1(r, z) (d e) 1 z
2
D 2 2
[D.22]
P E f 1
2
f1
(d e) z2
2rD 2 2
f1 f
(d e) z (d e) 1
2 2
Qr (r) E f 2 f2
2
f 2 (r, z) e z
2
D 2 2
P E f 2 f2
2
e z
2
2rD 2 2
f2 f
e z e 2
2 2
where:
c(r) =core(pottingcompoundandhoneycombcore)shearstress.
f1(r,z) =shearstressintopfacesheet.
f2(r,z) =shearstressinbottomfacesheet.
z =thicknesscoordinatemeasuredfromtheneutralsurfaceofthecore.
c =corethickness.
d =d=f1/2+c+f2/2;distancebetweenthefacesheetmiddlesurfaces.
e eEf1f1d/(Ef1f1+Ef2f2);distancefromneutralsurfaceofthecoretothemiddle
surfaceofthebottomfacesheet.
f1 =thicknessesoftopfacesheet.
f2 =thicknessesofbottomfacesheet.
Ef1 =elasticmodulioftopfacesheet.
Ef2 =elasticmoduliofbottomfacesheet.
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ForEc<<Ef1,Ef2,thesandwichplatestiffnessD(Eqn.[D.22])canbeapproximatedby:
E f 1 f f31 E f 2 f f32 E f 1 f1 E f 2 f 2 d 2
D [D.23]
12(1 f 1 ) 12(1 f 2 ) E f 1 f1 E f 2 f 2
2 2
where:
P 1 f
f 1 (r , z ) ( d e) 1 z
2rD f1 2
f1 f
( d e) z ( d e) 1
2 2
P 1 f
f 2 (r , z ) e 2 z
2rD f 2 2
f2 f
e z e 2 [D.24]
2 2
From(Eqn.[D.24]),itisseenthat:
cisconstantovertheheightofthecore,and
f1,f2approximatelyvarieslinearlyoverthethicknessofthefacesheets.
externalload,Piscarriedprimarilybythecorematerial,and
cisproportionalto1/r,i.e:
cdisplaysahyperbolicdependencyoftheradialcoordinater,[See:FigureD1].
The approximations imposed in the derivation of (Eqn. [D.24]), i.e. that Ec<<Ef and c>>f1, f2, are
nearlyalwaysfulfilledforsandwichpanelsforspaceapplications.
Theresultsobtainedusing(Eqn.[D.24])arethereforesufficientlyaccuratefordesignpurposes.
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Atthislocation,thecoreshearstresscanbecalculatedusingthefirstpartof(Eqn.[D.24]).Theresult
obtainedis:
P P
cmax c (r bp ) [D.31]
2bp d 2bp d
Failureoccurswhen c max reachesthecoreshearstrength c crit,andthestaticloadcarryingcapability
Pcrit canbeestimatedby:
NOTE (Eqn. [D.32]) is valid for both tensile and compressive outofplane
loading,P.
NOTE LoadP,wheresubscript'p'referstoapartiallypottedinsert.
FigureD2:Partiallypottedinsert:outofplaneloading
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Pp = Pf + Ps + Pn [D.41]
where:
Pf Loadpartcarriedbytheupperfacesheet.
NOTE It is assumed that the upper and lower face sheets, despite the
possibledifferencesinmaterialpropertiesandthicknesses,carryloads
ofequalmagnitude.
Ps Loadpartcarriedbyshearstressesinthecorearoundthepotting.
Pn Loadpartcarriedbynormalstresses inthehoneycombcoreunderneaththe
pottingmaterial.
NOTE Pfisusuallyquitesmall,comparedwithPs ,forf1, f2<<c,aspredicted
by(Eqn.[D.24]);[See:D.2]
ThecontributingloadpartsPf,Ps andPncanbeestimatedbytheexpressions:
Pf
P c max 2b p c c max [D.42]
2
Pn bp c
2
[D.44]
where:
P cmax 2bp d cmax
Loadcarriedbyfullypottedinsert,correspondingtocmax.
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PcmaxbecomesPcritforcmax=ccritaccordingto(Eqn.[D.32]).
hp Pottingheight.
For an insert with height hi [See: Figure D2], the minimum potting height hp min needed can be
specifiedbytheempiricalresult[2919];[2920]:
Empirically,ithasbeenfoundthatthetypicalvalueofhp dependsonthecoreheightc,accordingto,
[2919];[2920]:
c hp min
hp typ hp min A tanh [D.46]
hp min
where:
A=5forhoneycombcellsizeSc=4.8mm(3/16core)
A=2.5forhoneycombcellsizeSc=3.2mm(1/8core)
NOTE (Eqn. [D.46]) is valid for partial potting only, i.e. for c > hi + 7 mm,
[2919];[2920].
Furthermore:
NOTE Psislimitedbythecoreshearstrengthc crit.
Pnislimitedbyeither:
coretensilestrengthc crit t,or
corecompressivestrengthc crit c.
Theoretically,thetwofailuremodesdonotoccursimultaneously,i.e.
Shearrupture,and
Tensileorcompressivecorerupture.
Inreality,theshearstrengthandthetensileorcompressivestrengthofthecorearereached(almost)
simultaneouslyduetononlineareffects,[2919];[2920].
Thus,theloadcomponentsofthecriticalload,Pp crit,forapartiallypottedinsertinasandwichplate
canbeexpressedas:
Pf crit
P
crit 2bp c ccrit
[D.47]
2
Pncrit bp ccrit
2
[D.49]
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where:
Using(Eqns.[D.47]to[D.49]),thestaticloadcarryingcapabilityPpcritforapartiallypottedinsertina
largesandwichplatecanbewrittenas:
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For a given insert height hi and a given potting height hp [See: Figure D2], these tensile potting
stressesincreasewithincreasingcorethickness,c.
For a certain core thickness, the tensile potting stresses, which are assumed to be uniformly
distributedunderneaththeinsert,canexceedthetensilestrengthR critofthepottingresinbeforethe
tensilestrengthofthehoneycombc crit t underneaththepottingisreached.Thisisthecaseforhigh
densityhoneycombcores,andmayalsooccurforfullypottedinserts,[2919];[2920].
A furtherincreaseofcorethicknesscresultsinaslightdecreaseoftheinsertloadbearingcapability
Pcrit,becausePcritforthisspecificfailuremodeisdeterminedbyR crit.
Owing to the relatively high rigidity of the potting compared with the honeycomb (the potting
materialisusually5to10timesstifferthanthehoneycomb),noadvantagecanbetakenfromthecore
shear strength, because the core shear stresses around the potting decrease with increasing core
thicknessc,[2919];[2920].
where:
Pf Loadpartcarriedbytheupperfacesheet.
PsR Load part carried by shear stresses in the core around the potting over the
heightoftheinsert.
PnR Load part carried by normal stresses in the potting resin underneath the
insert.
NOTE Pf isusuallyquitesmallcomparedwithPs,[See:D.4].
ThethreecontributingloadpartsPf,PsRandPnRcanbeestimatedby:
Pf
P c max 2bp c cmax [D.42]
2
PnR bR 2 R [D.53]
where:
R Tensilestressinthepottingresin,whichisassumedtobeuniformoverthe
areaofthepottingcompound(bR2).
bR Realpottingradius,[See:7.4].
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hi Insertheight.
NOTE bR is the radius of a circle with area equal to the real crosssectional
areaofthepotting.
bpistheeffectivepottingradius(analyticalquantitythatdescribesthe
radialinfluencezoneofthepottingresin).
[Seealso:7.2forpottingdimensions]
PnRcanberewrittenintheform:
c hi
PnR Pf ( PR 2 Pf )
c [D.54]
Pf (1 2 ) PR
PnR
Pf PR [D.55]
1 2 1 2
where:
c hi
[D.56]
c
PsRcanbeexpressedintermsofPR using(Eqn.[D.31]):
PR
PR 2bp d c max 2 c max [D.57]
bp d
Inserting(Eqn.[D.57])into(Eqn.[D.52])givesanexpressionforPsRintermsofPR:
hi
PsR 2bp hi c max PsR PR [D.58]
d
Introducing (Eqn. [D.55]) and (Eqn. [D.58]) into (Eqn. [D.51]) gives the critical tensile load PR crit
underwhichthepottingresinunderneaththeinsertfails(expressedintermsofPnR crit):
1
PRcrit 2PnRcrit 1 2 [D.59]
1 h
i
1 2 d
where:
and:
Rcrit =Tensilestrengthofpottingresin.
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D.5.1.2 High-density non-metallic core
InD.4,apartiallypottedinsertinanonmetallichoneycombcoreisdescribed,e.g.NomexorGFRP.
Aconservativeestimateofthestaticloadcarryingcapability Pp non-metallicofsuchaninsertisgiven
in(Eqn.[D.412])and(Eqn.[D.413]),[2919];[2920].
Pottingfailureunderneaththeinsertinanonmetalliccoreisconsideredtooccurwhen:
Where:
bR =Realpottingradius,[See:7.4].
Rcrit =Tensilestrengthofpottingresin.
D.6.1 Introduction
The upper face sheet does not contribute to the loadcarrying capability under compressive outof
planeload,ifthethicknessofthe(aluminium)facesheetexceeds0.6mm,[2919];[2920].
The reason for this is that tensile rupture of the bond between the core and the upper face sheet
adjacenttotheinsertisinduced.
Thus, in estimating the static loadcarrying capability it is necessary to neglect the loadcarrying
contributionoftheupperfacesheet,[2919];[2920].
NOTE This applies to inserts in sandwich plates with thick face sheets
subjectedtocompressiveoutofplaneloading.
Pcrit
Pcritc bp c ccrit [D.61]
2
where:
Pf crit and Ps crit (with full core height) are introduced according to (Eqn.
[D.4-7]) and (Eqn. [D.4-8]).
Pcrit is given by (Eqn. [D.3-2]).
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D.6.2.2 Partially potted insert
Inasimilarmanner,thestaticloadcarryingcapabilityforapartiallypottedinsertisreducedto:
Ppcritc Pscrit Pncrit
[D.62]
Ppcritc 2bp hp ccrit bp ccrit
2
where:
PscritandPncrit arefrom(Eqn.[D.48])and(Eqn.[D.49]).
P 1
Pcrit c crit bp c ccrit [D.63]
2 K tpp
Where:
KtppStressconcentrationfactorforpartialpotting;asgivenby(Eqn.[D.413]).
Table D1 gives CC values for the various insert configurations.The correlation between test results
andtheoryisverygoodfor:
Fullypottedinsertsundertensileandcompressiveloading;
Partiallypottedinsertsundercompressiveloading.
However, the correlation with respect partially potted inserts under tensile loading is considerably
lessfavourable,asseenbythestandarddeviationonthecomparativeresults,[See:TableD1].
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TableD1:Correlationcoefficients
Correlation Standard
Insert Load
coefficient(CC) deviation(G)
Tensile
Fullypotted(1) 0.993 0.059
Compressive
Tensile 1.043 0.52
Partiallypotted
Compressive 0.998 0.072
NOTE(1)Includingthroughthethicknessandinsertsbehavinglikefullypottedinserts,
[Seealso:D.1fordeterminingpotting].
TableD2:Reliabilitycoefficients
Reliabilitycoefficient(RC)
Core
Minimumvalue (2) Averagevalue(3)
RC 1.172 0.0063 c 0.2641 f RC 1.207 0.00544 c 0.2088 f
Aluminium,
Tensile(1)
Outofplaneloading
Aluminium,
Compressive
NOTE(1) Assumingfacesheetsofidenticalthickness,i.e.f1=f2=f.
NOTE(2) Exceededbyaprobabilityof90%
NOTE(3) Exceededbyaprobabilityof50%
NOTE(4) e.g.unperforatedaluminium,NomexandGFRP.
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ReliabilitycoefficientsRC,[See:D.7;TableD2]
Pcritforthroughthethicknessandfullypottedinserts
[D.81]
Pss=RC
Ppcritforpartiallypottedinserts
Where:
PcritandPpcritaredeterminedaccordingtoD.1.
C C hi hi [D.82]
where:
hi Basicinsertheight,i.e.hi=9mm.
hi* Newinsertheight.
C Coreheightatcurvebreakforbasicinsertheighthi.
C Newcvalueatcurvebreakcorrespondingtothenewinsertheighthi*.
*
NOTE The curve break in the design graph signifies a change of failure
modefromeither:
coresheartocorefailureunderneaththepotting,or
coresheartopottingfailureunderneaththeinsert.
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[Seealso:D.4;D.5and12.6formoreinformationonthisfailuremode
change]
Anincreaseinhi(fromhi =9mminthedesigngraphs)increasesthestaticloadcarryingcapabilityPss
forthosecaseswherefailureoccursinthe:
Coreunderneaththepotting,or
Pottingunderneaththeinsert.
NOTE Anincreaseinhi isespeciallyadvisedifapottingfailureunderneath
theinsertisexpected.
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D.10 References
D.10.1 General
[2914] O.T.ThomsenCompConsult;Estimationoftheloadcarrying
capabilityofaninsertinalargesandwichpanel;ESTECContractNo.
10.983/94/NL/PPWorkOrderNo.6(March1996)
[2915] Plantema,F.J.SandwichConstructionJohnWiley&Sons,NewYork,
USA,1966
[2916] Allen,H.G. AnalysisandDesignofStructuralSandwichPanels
PergamonPress,Oxford,UK,1969
[2917] Stamm,K.andWitte,H. Sandwichkonstruktionen(inGerman);
SpringerVerlag,Wien,Austria,1974
[2918] Zenkert,D. AnIntroductiontoSandwichConstructionEMAS
Publishing,WestMidlands,UK,1995
[2919] W.Hertel,W.PaulandD.WagnerERNORaumfahrttechnikGmbH,
StructuresDepartment,Bremen,Germany. StandardisationProgramme
forDesignandTestingofInserts;ESACR(P)1498.ESAContractNo.
3442/77/NL/PP(1981)
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[2920] W.PaulandD.WagnerERNORaumfahrttechnikGmbH,Structures
Department,Bremen,Germany.StandardisationProgrammeforDesign
andTestingofInserts,RiderII;ESACR(P)1665.ESAContractNo.
3442/77/NL/PP)(1981)
[2921] Thomsen,O.T.AnalysisofSandwichPlateswithThroughthe
ThicknessInsertsUsingaHigherOrderSandwichPlateTheory
ESA/ESTECReportEWP1807(1994)
[2922] Thomsen,O.T.AnalysisofSandwichPlateswithFullyPottedInserts
UsingaHigherOrderSandwichPlateTheory;ESA/ESTECReportEWP
1827(1995)
[2923] Saarela,O.,PalanterM,.Hberle,J.andKlein,M.ESACOMP:A
PowerfulToolfortheAnalysisandDesignofCompositeMaterials;
ProceedingsoftheInternationalSymposiumonAdvancedMaterialsfor
LightweightStructures(ESAWPP070),ESTEC,Noordwijk,(March
1994),p.161169
[2924] Section8Referencesformorerecentworkonsandwichplatemechanics
byO.T.Thomsen,AalborgUniversity,DK.
[2925] M.Palanter:ComponeeringInc,Finland
ESACompprivatecommunication(2004)
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Annex E
IATP
E.1 Introduction
A summary is presented of test data generated under the ESTECfunded IATP insert allowable test
programme,conductedbetween1995and1997.
TheaimoftheprogrammewastoprovideinputforanESTECevaluationofthereliabilitycoefficient,
RCforselectedCFRPsandwichpanelconstructionsandinsertconfigurations,[2926];[2927].
Thesummarydescribes:
Materials,[See:E.2];
Testing,[See:E.3];
Data,[See:E.4].
NOTE Noanalysisofthereliabilitycoefficient,RCisgiven.
E.2 Materials
TableE1liststhevariousmaterialsusedinIATP2,[2927].
NOTE IATP2usedfullyqualifiedmaterialsfortheENVISATPolarPlatform
Program.
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TableE1:IATP:Materials
Fibre:60%2%
Resin:69%3%
Voids:<2%
Arealweight(g/m2):
prepreg:29515%
dryfabric:1958%
VICOTEX Volatile:2%(weight)
FIBREDUX914/34%/G829 ILSS: 40N/mm2(min)
Fabric NOTE:ContainsM40andT300carbon 45N/mm2(average)
fibres. 4POINTFLEXURAL
Strength:
480MPa(min)
600MPa(average)
Stiffness:
155GPa(min)
160GPa(average)
Compressivestrength:
HEXCELCRIII50563/16.0015 Stabilised:
Honeycomb Perf.Thickness45mm 3.38MN/m2(min)[490psi]
Perf.Thickness80mm Density:
70.48kg/m3[4.4lb/ft3]
Filmadhesive REDUX319L
Primer REDUX109
Potting Compressivestrength(average):
STYCAST1090/Catalyst9
compound 73MPa
StandardEquipmentUnitInsert: Singlesideinsert.
TypeEM6 Dia.:17.5mm;Length:15mm
Inserts(1) Throughspool
TypeFF6 Dia.:21.3mm;
Length=panelthickness
NOTE(1)AsdefinedinPPFMMS.
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E.3 Testing
IATPusedinhousetestmethods.FigureE1showsthetestjigfor:
sheartesting,[2926];
pullouttesting:testspeed1.5mm/min,[2926];[2927].
FigureE1:Manufacturecontrol:Inserttensilepullouttestfixture
[Seealso:27.3fortextfixturesandsamplesizes]
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TableE2:IATP:Sheartestpanelconfigurations
Core Skin Insert
IATP/Case Height Thickness Dia.
Layup Type
(mm)(1) (mm) (mm)
1/7 20 1.08 (0,+60,60)s TypeF2thruspool 21.3
1/8 20 1.08 (0,+60,60)s TypeEM6 17.5
1/9 20 1.08 (0,+60,60)s TypeF3thruspool 21.3
1/13 20(2) 2.47 notstated TypeF4thruspool 25/17.5
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TableE3:IATP:Pullouttestpanelconfigurations
Core Skin Insert
IATP/Case Height Thickness Dia.
Layup Type
(mm) (1)
(mm) (mm)
1/6 20 1.08 (0,+60,60)s TypeF2thruspool 21.3
1/12 20(2) 2.47 notstated TypeF4thruspool 25/17.5
1/10 20(2) 4.32 notstated TypeF3thruspool 21.3
1/14 20(2) 4.94 notstated TypeF4thruspool 25/17.5
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TableE4:IATP:Sheartestdata
Core Skin Insert ShearLoadTestData(N)(4)
IATP/
Height Thickness Dia.
Case Layup Type Rm MeanRm SD
(mm)(1) (mm) (mm)
12250
15875
TypeF2
1/7 20 1.08 (0,+60,60)s 21.3 16000 15455 2000
thruspool
15400
17750
8625
6575
1/8 20 1.08 (0,+60,60)s TypeEM6 17.5 6600 7645 980
8250
8175
Def.load:
25200
22400
35200
28000 Def.load: Def.load:
TypeF3 24000 26960 5040
1/9(5) 20 1.08 (0,+60,60)s 21.3
thruspool Peakload: Peakload: Peakload:
46600 47575 2021
n/a
45200
49400
49100
36100
33900
TypeF4 25/
1/13 20(2) 2.47 notstated 32600 34180 1256
thruspool 17.5
34000
34300
Def.load:
27000
26000
25000
25400 Def.load: Def.load:
TypeF3 24000 25480 1119
1/11
(5) 20
(2) 4.32 notstated 21.3
thruspool Peakload: Peakload: Peakload:
48200 48880 482
49400
48600
49200
49000
Def.load:
29250
27400
30000
28000 Def.load: Def.load:
1/15 TypeF5 25/ 31000 29130 1461
(5)
20(2) 4.94 notstated
thruspool 17.5 Peakload: Peakload: Peakload:
46500 47400 3460
42700
48700
46900
52200
1/3 45 1.08 (0,+60,60)s TypeEM6 17.5 8250 8588 640
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TableE5:IATP:Pullouttestdata
Core Skin Insert Pull-out Test Data (N) (4)
IATP/
Height Thickness Dia.
Case Lay-up Type Mean Rm SD
(mm) (1) (mm) (mm)
Rm
6400
6375
Type F2
1/6 20 1.08 (0, +60, -60)s 21.3 6575 6625 270
thru'spool
7025
6750
16600
16925
Type F4 25 /
1/12 20 (2) 2.47 not stated 17075 16860 176
thru'spool 17.5
16900
16800
1st peak:
16000
n/a
18600
14300 1st peak: 1st peak:
1/10 Type F3 17500 16600 1867
20 (2) 4.32 not stated 21.3
(5) thru'spool Peak: Peak: Peak:
17300 19130 1980
20800
21250
16900
19400
22250(4)
30200
Type F4 25 /
1/14 20 (2) 4.94 not stated 28600 29400 655
thru'spool 17.5
29400
29400
6580
5560
Type E M6
1/2 45 1.08 (0, +60, -60)s 17.5 5970 6090 359
Single sided
5950
6390
1/Envi Type F1
45 1.08 (0, +60, -60)s 21.3 not stated
(3) thru'spool
1/Envi Type E M6
45 2.16 (0, +60, -60)s 2 17.5 not stated
(3) Single sided
1/Envi Type F2
45 2.16 (0, +60, -60)s 2 21.3 not stated
(3) thru'spool
5650
Fabric only: 6275
Type E M6
2/5 45 4.86 (0, +60, -60)s 17.5 6450 6055 330
Single sided
4, (0,+60,-60) 5800
6100
16425
Fabric only: 16350
Type F6
2/6 45 4.86 (0, +60, -60)s 21.3 16225 16295 330
thru'spool
4, (0,+60,-60) 16125
16350
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TableE6:IATP:Sheartestresultsversusdesignallowables
Core Skin Insert ShearLoadTestData(N)(3)
IATP/
Height Thickness Dia. Design
Case Layup Type MeanRm SD
(mm)(1) (mm) (mm) Allowable
TypeF2
1/7 20 1.08 (0,+60,60)s 21.3 15455 2000 10560
thruspool
1/8 20 1.08 (0,+60,60)s TypeEM6 17.5 7645 980 3816
Def.load: Def.load:
1/9 TypeF3 26960 5040
(4)
20 1.08 (0,+60,60)s 21.3 42224
thruspool Peakload: Peakload:
47575 2021
TypeF4
1/13 20(2) 2.47 notstated 25/17.5 34180 1256 25000
thruspool
Def.load: Def.load:
1/11 TypeF3 25480 1119
(4)
20(2) 4.32 notstated 21.3 42224
thruspool Peakload: Peakload:
48880 482
Def.load: Def.load:
1/15 TypeF5 29130 1461
(4)
20(2) 4.94 notstated 25/17.5 50000
thruspool Peakload: Peakload:
47400 3460
1/3 45 1.08 (0,+60,60)s TypeEM6 17.5 8588 640 3818
Type30mm
1/1 45 2.16 (0,+60,60)s2 counterbore 17.5 13300 657 6311
M4std.
Fabriconly:
1/16 45 3.24 TypeEM6 17.5 14500 1148 8810
(0,+60,60)s3
Fabriconly: TypeF3
1/17 45 3.24 21.3 48120 2244 31668
(0,+60,60)sx3 thruspool
Fabriconly:
1/4 45 4.86 (0,+60,60)s4, TypeEM6 17.5 14750 1040 12553
(0,+60,60)
Def.load: Def.load:
Fabriconly:
1/5 TypeF1 41138 2260
(4)
45 4.86 (0,+60,60)s4, 21.3 48283
thruspool Peakload: Peakload:
(0,+60,60)
74850 7593
NOTE(1) Aluminium5056PType3/160.0015
NOTE(2) Aluminium5056PType1/80.002
NOTE(3) Deflectionload:pointwhereloaddeflectioncurveisnolongerlinear(Rp).
Peakload:Max.load+clippingofbolts.
NOTE(4) Greyedconfigurationsdidnotmeetcalculatedallowable,[2926]
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E.4.3.2 Pull-out test
TableE7comparesIATP1pullouttestdatawithdesignallowables,[2926],[2928].
TableE7:IATP:Pullouttestresultsversusdesignallowables
Core Skin Insert ShearLoadTestData(N)(3)
IATP/
Height Thickness Dia. Design
Case Layup Type MeanRm SD
(mm)(1) (mm) (mm) Allowable
TypeF2
1/6 20 1.08 (0,+60,60)s 21.3 6625 270 3408
thruspool
TypeF4
1/12 20(2) 2.47 notstated 25/17.5 16860 176 6270
thruspool
1stpeak: 1stpeak:
1/10 TypeF3 16600 1867
(5)
20(2) 4.32 notstated 21.3 20000
thruspool Peak: Peak:
19130 1980
TypeF4
1/14 20(2) 4.94 notstated 25/17.5 29400(4) 655 15100
thruspool
TypeEM6
1/2 45 1.08 (0,+60,60)s 17.5 6090 359 4770
Singlesided
Fabriconly:
TypeEM6
2/5 45 4.86 (0,+60,60)s4, 17.5 6055 330 notstated
Singlesided
(0,+60,60)
Fabriconly:
TypeF6
2/6 45 4.86 (0,+60,60)s4, 21.3 16295 330 notstated
thruspool
(0,+60,60)
TypeEM6
2/3 80 1.08 (0,+60,60)s 17.5 6310 1176 notstated
Singlesided
TypeF6
2/4 80 1.08 (0,+60,60)s 21.3 13670 2107 notstated
thruspool
Fabriconly:
2/1 80 4.86 (0,+60,60)s4, TypeEM6 17.5 6940 911 notstated
(0,+60,60)
Fabriconly:
TypeF6
2/2 80 4.86 (0,+60,60)s4, 21.3 16345 477 notstated
thruspool
(0,+60,60)
Def.load: Def.load:
Fabriconly:
TypeF1 41138 2260
1/5 45 4.86 (0,+60,60)s4, 21.3 48283
thruspool Peakload: Peakload:
(0,+60,60)
74850 7593
NOTE(1) Aluminium5056PType3/160.0015
NOTE(2) Aluminium5056PType1/80.002
NOTE(3) NodatafromKongsbergsENVISATvalidationstated,[2927].
NOTE(4) Aluminiumtestrigdeformedduringfirsttest;earlyfractureoftestsample.Newsteeltestrigusedfor
remainingsamples.
NOTE(5) Greyedconfigurationsdidnotmeetcalculatedallowable,[2926]
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E.5 References
E.5.1 General
[2926] InsertAllowableTestProgrammeIATP1
KongsbergGruppenReportNo.01TR68040906
(May1995)
[2927] InsertAllowableTestProgrammeIATP2
KongsbergGruppenReportNo.02TR68040906
(October1997)
[2928] CommunicationfromMMStoKongsberg
PPFMMBTFX509(13thOctober,1994)
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Annex F
Case studies
F.1 Introduction
ThisclauseprovidesasummaryofinsertapplicationsthathavebeenappliedinsomeEuropeanspace
projects,ispresented,[2929],[2933].Thecasestudiesgiveinformationabout:
Materialsandconfiguration:
insert(s);
sandwichpanel(facesheets,core);
potting.
Testing:
methodandsample;
data.
NOTE Only axisymmetrical inserts subsequently installed in honeycomb
sandwichpanelsarecovered,i.e.cocuringofpanelsisexcluded.
Edge inserts and metallic fittings integrated within sandwich panels
arenotincluded.
ThecasestudyconcerningROSETTALanderalsoincludesmoregeneralaspectsofthenoveldesign
carbonfibretubeinsertsfrommorerecentevaluationstudies,[2933].
[Seealso:A.3]
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ROSETTA Lander (DLR Braunschweig): Sandwich panels, with CFRP composite face sheets
andaluminiumhoneycombcorewithadhesivelybonded,novelcarbonfibretubeinserts,[See:
F.6;A.3].
SPOT5equipmentbay(SONACA):Sandwichpanels,withCFRPcompositefacesheetsanda
thick aluminium honeycomb core with standard Shurlok aluminium alloy or special
aluminiumalloypottedinserts,[See:F.7];
UMS (Arospatiale): Sandwich panels, with CFRP composite face sheets and an aluminium
honeycomb core, with standardShurlok aluminium alloy orspecialaluminium alloy potted
inserts,[See:F.8];
SILEX structure (MAN Technologie): Both standard, Shurlok and special aluminium alloy
potted inserts were used in composite CFRP sandwich panels with aluminium alloy
honeycombcores,[See:F.9];
HRG (MATRA Defense): Special aluminium alloy inserts were potted into sandwich panels
havingCFRPcompositefaceskinsandanaluminiumalloyhoneycombcore,[See:F.10];
NILESAT battery (BTS): Standard Shurlok and special aluminium alloy inserts potted into
sandwichpanelswithaluminiumalloyfacesheetsandhoneycombcore,[See:F.11].
Aworkedexampleoftheinsertverificationprocessisgivenforaboxmountedonasandwichpanel
usingpottedinsertsatthefourcorners,[See:F.12].
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TableF1:Casestudy:ARIANE1equipmentbay/ASAP4Allowabletensileload
F.2.2 Testing
F.2.2.1 Methods
Aschematicofthetensiletest(insertpullout)isshowninFigureF1.
FigureF1:Casestudy:ARIANE1equipmentbay/ASAP4tensile
(pullout)testmethod
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F.3.2 Testing
Testsamplescorrespondtothestructure.
F.3.2.1 Methods
Testingincluded:
Tensiletest(insertpullout),asshowninFigureF4.
Sheartest,asshowninFigureF5.
TableF2:Casestudy:ARIANE4materialsandconfiguration
Project ARIANE4Case1 ARIANE4Case2
Standard Special
Type
Partiallypotted Partiallypottedwithcollar
Ref. ShurlokSL607
Sandwichpanel:
Aluminium2014T6 Aluminium2014T6
Facesheets
Thickness:0.5mm Thickness:0.5mm
5056440perforated 5056440perforated
Core
Height:23mm Height:notstated
NOTE(1)Withrespecttosurface.
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FigureF2:Casestudy:ARIANE4Case1
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FigureF3:Casestudy:ARIANE4Case2
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FigureF4:Casestudy:ARIANE4tensile(pullout)testmethod
FigureF5:Casestudy:ARIANE4sheartestmethod
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TableF3:Casestudy:ARIANE4equipmentbayAllowabletensileload
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F.3.2.3 Allowable shear load
Table F-4 summarises shear test data.
TableF4:Casestudy:ARIANE4equipmentbayAllowableshearload
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F.4 ASAP 4
The design consists of sandwich panels, with aluminium alloy face sheets and an aluminium
honeycombcore,andusingstandardShurloksteelorspecialaluminiumalloypottedinserts.
F.4.2 Testing
F.4.2.1 Methods
Tensiletests(insertpullout)wereconductedon:
Singleinsert;asshowninFigureF1;
Group;asshowninFigureF8andFigureF9.
TableF5:Casestudy:ASAP4materialsandconfiguration
Project ASAP4(Ariane4)1 ASAP4(Ariane4)2
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:Casestudy:ASAP4
(AR4)1
FigureF7:Casestudy:ASAP4(AR4)2
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FigureF8:Casestudy:ASAP4(AR4)tensile(pullout)methodA
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FigureF9:Casestudy:ASAP4(AR4)tensile(pullout)methodB
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TableF6:Casestudy:ASAP4interferenceandedgeeffects
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F.5 ASAP 5
Design consisting of sandwich panels, with aluminium alloy face sheets and an aluminium
honeycombcore,usingspecialaluminiumalloypottedinserts.
Special throughthethickness (fully potted) inserts were used in thick sandwich structures, i.e. core
height=60mm.
F.5.2 Testing
Special throughthethickness (fully potted) inserts were used in thick sandwich structures, i.e. core
height=60mm.
Theeffectofpottingfromoneorbothsidesofthesandwichwasexamined.
Testresults,whencomparedwithanalysismethodsinthishandbook,showthattheminimum
valueexceedsthecalculatedtypicalvalue.
Insertproximityeffectswereinvestigated.
F.5.2.1 Method
Nodetailsgiven,[2929].
TableF7:Casestudy:ASAP5materialsandconfiguration
Project ASAP5
Structure:
Application
Separationsystemminiandmicrosatellites
Insert: [See:TableF10]
Specialthroughthethickness
Type
(Fullypotted)
Ref.
Position(1)
Material 7175T7351
Chromicanodised,notsealed.Alodine1200(contact
Surfacetreatment
surface).
Thread Nonlocking,phosphorbronzeCdfree.
Lubrication Molicote106
Potting: SLE3010LVC+primer
Sandwichpanel:
Facesheets Aluminium2024T81Thickness:0.8mm
Core 5056440perforatedHeight:60mm
NOTE(1)Withrespecttosurface.
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FigureF10:Casestudy:ASAP5
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TableF8:Casestudy:ASAP5Allowabletensileload
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TableF9:Casestudy:ASAP5interferenceandedgeeffects
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FigureF11:ROSETTALander:Twostructuralcomponents
Thetightconstraintsofthemassbudget,thegiventhicknessofthesandwichplates,andthenumber
ofinsertsperunitareamadeitinevitablethatconventionalpottedinsertdesignhadtobereplacedby
anoveldesign,[2930];knownasacarbonfibretubeinsert,[Seealso:A.3fordetails].
The concept is based onan extremelystiff, thinwalled carbonfibre tube which fits exactlybetween
the face sheets and is bonded to the honeycomb core only by a thin layer of epoxy adhesive. The
pottingradiusisthereforenotmuchlargerthantheinsertradiusitself.
Thefulllengthoftheextremelystiffcarbonfibretubeactivelycontributestotheshearloadtransfer
into the much softer honeycomb core, because the tube always passes through the whole sandwich
thickness.Theformlockingcontactunderbothfacesheetsmakesthesandwichinthevicinityofthe
insertpracticallyincompressible.
In the course of the verification process of theROSETTA Lander,the qualification of the new insert
design was performed with regard to the specific mission requirements and the specific structural
configuration.
A preliminary test campaign was performed, [[2931], [2932]], and the final flight readiness was
proven by successful mechanical tests at Lander level (spacecraft level). However, a qualification of
theinsertdesignundermoregeneralconditionsremainedtobedone.
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F.6.3 Qualification
BasedontheexperiencefromtheROSETTALanderproject,thepotentialofcarbonfibretubeinserts
was investigated more thoroughly by DLR and two Finnish partners, PATRIA Finavicomp Oy and
HelsinkiUniversityofTechnology,duringanESAfundedstudy,[2933].
The influence of the sandwich parameters on the static and dynamic strength of the inserts under
different load cases was systematically investigated. The influence of thermal conditioning before
testing,edgeeffectsandtheeffectoftheinsertsizewerealsoconsidered.Alltestsweremadeonboth
typesofmetallicinsertcaps;asdescribedinA.3.
The experimental investigations were performed with the test fixtures; shown in Figure F12, [See
also:AnnexH].
Parallel, analytical investigations and numerical calculations based on a detailed FE model were
carriedout.
Bendingandtensioncompressiontests(toprow)
Torsionandsheartests(bottomrow)
FigureF12:ROSETTALander:Tensioncompression,shear,bending
andtorsiontests
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TableF10:Carbonfibretubeinserts:Outofplanetension
facesheetthickness
criticalinsertload
criticalinsertload
meanvalue(of8)
honeycombcore
honeycombcore
honeycombcore
onA,B,Clevel
insert12mm (95%confidence)
thickness
cellsize
density
TensionTest
outofplane
A B C
1mm/min
c f s
[mm] [mm] [kg/m3] [mm] [kN] [kN] [kN] [kN]
TableF11:Carbonfibretubeinserts:Outofplanecompression
critical insert load
honeycomb core
honeycomb core
Compression Test
(95% confidence)
insert 12 mm
face sheet
thickness
thickness
cell size
out-of-plane
density
1 mm / min
A B C
99% 95% 90%
c f s
[mm] [mm] [kg/m3 ] [mm] [kN] [kN] [kN] [kN]
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TableF12:Carbonfibretubeinserts:Inplaneshearload
critical insert load
honeycomb core
honeycomb core
honeycomb core
(95% confidence)
insert 12 mm
face sheet
thickness
thickness
cell size
density
1 mm / min
Shear Test
A B C
in-plane
c f s
[mm] [mm] [kg/m3 ] [mm] [kN] [kN] [kN] [kN]
FigureF13:Carbonfibretubeinsert(type2):Withcapforunilateral
fixing
The critical insert failure load Fc was determined from each individual load curve; where Fc is a
generaltermforthecriticalstaticstrengthinthedifferentloadcases,e.g.PSSfortensioncompression;
QSSforinplaneshear;TSSfortorsion;MSSforbending.
Inallcases,Fcwasdefinedastheloaduponwhichthefirstfailureorplasticdeformationoccurs.Itis
observable as the first maximum of the curve or as the obvious end of the linear elastic range; as
showninFigureF14.InmanycasestheloadincreasedevenbeyondFcuptoamaximumvalueFmax.
However, Fc was regarded as the only relevant parameter; in line with a conservative design
philosophy.
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FigureF14:Carbonfibretubeinserts:Definitionofthecriticalinsert
failureload,Fc
Normally there were 8 experimentally determined critical load values per test scenario, i.e. per
combinationofsandwichtype,insertcaptype,andloadcase.
NOTE MeanvaluesarelistedintherighthandcolumnofTableF10toTable
F12,inclusive.
The data were processed by the Weibull ++5.0 computer program from Relia Soft. For each test
scenarioaWeibulldistributionwasgenerated,whichindicatessurvivablecriticalloadlevelswithout
anyinsertfailuresorplasticdeformation.ThesecriteriaaresummarisedinTableF13.
TableF13:Carbonfibreinserts:Weibullanalysiscriteria
99%probabilityof
1%probabilityoffailure socalledAlevel
survival
95%probabilityof
5%probabilityoffailure socalledBlevel
survival
90%probabilityof
10%probabilityoffailure socalledClevel
survival
All three levels were determined on a statistical confidence level of 95%. They are, of course, lower
thanthemeanvalue;thedifferencedependsonthescatterwithinthedistribution.
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F.7 SPOT 5
Design consisting of sandwich panels, with CFRP composite face sheets and a thick aluminium
honeycomb core (height of 80 mm), and using standard Shurlok aluminium alloy or special
aluminiumalloypottedinserts.
F.7.2 Testing
Nodetailsgivenin[2929].
TableF14:Casestudy:SPOT5materialsandconfiguration
Project SPOT5CASE SPOT5
Chromicanodise,notsealed. Chromicanodise,notsealed.
Surfacetreatment
Alodine1200contactface. Alodine1200remachinedface.
M12,nonlocking.Phospher
Thread M4
bronze,Cdfree.
Lubrication Molicote106 Molicote106
Potting: SLE3010LVC+primer SLE3010LVC+primer
Sandwichpanel:
CFRP CFRP
Facesheets
Thickness:1mm Thickness:1mm
5056316perforated 5056316perforated
Core
Height:80mm Height:80mm
NOTE(1)Withrespecttosurface.
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:Casestudy:
SPOT5Case
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FigureF16:Casestudy:SPOT5StructureI/Fplatform
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F.8 UMS
Design consisting of sandwich panels, with CFRP composite face sheets and an aluminium
honeycomb core, and using standard Shurlok aluminium alloy or special aluminium alloy potted
inserts.
F.8.2 Testing
TableF15:Nodetailsgiven,[2929].Casestudy:UMSMaterialsandconfiguration
Project UMSSST UMSSST
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FigureF17:Casestudy:UMSSST1
FigureF18:Casestudy:UMSSST2
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F.9 SILEX
Both standard, Shurlok and special aluminium alloy potted inserts were used in composite CFRP
sandwichpanelswithaluminiumalloyhoneycombcores.
F.9.2 Testing
NOTE Nodetailsoftestmethodsgivenin[2929].
TableF16:Casestudy:SILEXMaterialsandconfiguration
Project SILEX SILEXGEOMPCS
Structure
Application Structure
Equipment
Insert: [See:FigureF19] [See:FigureF20]
Standard Special
Type
Partiallypotted Fullypotted
Ref. ShurlokSL10068
Position(1) 00.05
Material Aluminium2024T4 Aluminium7075T73
Surfacetreatment AnodisedMILA8625 Chromicanodised,notsealed
Thread Nonlocking Stainless,nonlocking
Lubrication Nuflon(onbolt) Nuflon
Potting: ShurlokSLE3010LVC ShurlokSLE3010LVC
Sandwichpanel:
CFRP: CFRP:
Facesheets
Thickness:0.8mm1.6mm Thickness:0.8mm1.6mm
5056: 5056:
420 420
Core 320 320
328 328
345 345
NOTE(1)Withrespecttosurface.
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FigureF19:Casestudy:SILEXinsert
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FigureF20:Casestudy:SILEXGEOMPCSinsert
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F.9.2.2 Allowable tensile load
TestresultsarefortransversetensileloadingaresummarisedinTableF17.
TableF17:Casestudy:SILEXAllowabletensileload
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F.9.2.3 Allowable shear load
The results of in-plane shear testing are summarised in Table F-18.
TableF18:Casestudy:SILEXAllowableshearload
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TableF19:Casestudy:SILEXAllowablebendingmoment
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TableF20:Casestudy:SILEXAllowabletorsionmoment
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F.10 HRG
HRG HauteRsolution Gomtrique is the main payload ofSPOT5. The structure is similar to HRV
andHRVIRonSPOT3andSPOT4,respectively.
SpecialaluminiumalloyinsertswerepottedintosandwichpanelshavingCFRPcompositefaceskins
andanaluminiumalloyhoneycombcore.
F.10.2 Testing
TableF21:Casestudy:HRGMaterialsandconfiguration
Project HRGCL
Application Electronicequipment
Insert: [See:FigureF21]
Special
Type
Partiallypotted,withcollar
Ref.
Position(1) +0.10
Material Aluminium2024T351
Surfacetreatment Alodine1200
Thread Stainless,nonlocking
Lubrication Nuflon(titaniumfixings)
Potting: SLE3010LVC
Bonding:(2) EC2216
Sandwichpanel:
CFRP
Facesheets
Thickness:2mmor3mm
5056440perforated.
Core
Height:43mm
NOTE(1)Withrespecttosurface.
NOTE(2)Collaradhesivelybondedtosandwichpanelfacesheet.
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FigureF21:Casestudy:HRGInsert
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TableF22:Casestudy:HRGTensileload
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FigureF22:Casestudy:HRGTestmethod
F.11 NILESAT
StandardShurlokandspecialaluminiumalloyinsertspottedintosandwichpanelswithaluminium
alloyfacesheetsandhoneycombcore.
F.11.2 Testing
Nodetailsgiven,[2929].
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TableF23:Casestudy:NILESATmaterialsandconfiguration
Project NILSATBattery1 NILSATBattery2
Structure;panelassembly;
Application Structure;handling.
satelliteI/F.
Insert: [See:FigureF23] [See:FigureF24]
Standard Special(2)
Type
Partiallypotted Fullypotted
Ref. ShurlokSL10068
Position(1) +0.1/0
Aluminium7075T7351
Material Aluminium2024T4
Aluminium7175T7351
Surfacetreatment AnodisedMILA8625 Alodine1200
Thread Stainless,locking Nonlocking
Lubrication Molicote(titaniumfixings) None(titaniumfixings)
Potting: SLE3010LVC SLE3010LVC
Sandwichpanel:
Aluminium6061Thickness:0.3 Aluminium6061Thickness:0.3
Facesheets
mm mm
5056428perforatedHeight:not 5056428perforatedHeight:25
Core
stated mm
NOTE(1)Withrespecttosurface.
NOTE(2)FromTELECOM2
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FigureF23:Casestudy:NILESATbattery1
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FigureF24:Casestudy:NILESATbattery2
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F.12.1 Mounting
Aboxismountedonasandwichpanelusinginsertsatthefourcorners,asshowninFigureF25.
FigureF25:Example:Insertverificationdimensions
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F.12.3 Loads
Pult 22001.5
4
=825N
F.12.4.1 Tension
PSS(bi=11)=1090N [See:12.5;B.1]
PSS(bi=14)=1220N [See:12.5;B.1]
F.12.4.2 Compression
PSS(di=11)=900N [See:13.2;B.1]
PSS(di=14)=1050N [See:13.2;B.1]
NOTE Where the compressive strength is insufficient, increasing the foot
diameter to exceed the potting element 2bp can avoid using a larger
insert.
bpmin (di=14)=10.03mm
And:
w=0.32N/mm2 [See:Table63]
f = 0.3 mm
fy =270N/mm2 [See:6.6]
For(di=11): QSS =88.63 0.32+20.38.63270
2
=1589N
For(di=14): QSS =810.0320.32+20.310.03270
=1882N
NOTE Theallowablesexceedbyfartherequirements.
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is is a
b p1
1 ; b p1 b p 2 1 =10.4
For(di=14):
is is a
bp1
0.9 ; b p1 b p 2 1 =0.95
where:
a=90mm(inaccordancewithFigure191)
NOTE Thedistanceinthelongitudinaldirectionexceeds10bp1,sothereisno
interferenceeffecthere.
and:
For(di=11): EN=0.95
For(di=14): EN=0.90
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Themeanratio,with FA F :
F 2 FA F 2 F
R F
F
1
Thecorrectionsfortheactualgeometryare:
hc=30mm,
f=0.3.
FEF 1.2766
} Fc f Fpp =1.411
Fpp 1.1052
Consideringthesweeprate,thenumberofcyclesoccurringduringsweepthroughtheeigenfrequency
isdeterminedby:
N0=fet
Where:
t=timetopassthroughthebandwidth,BW.
Withascatterfactorof4,ithastobeshownthat:
N4N0
NOTE Baseduponthetestconditions,theoptionsaretoeither:
acceptaninsertdiameterof2bi=11mm;
repeatthefatiguecheckusinganinsertdiameterof14mm.
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F.13 References
F.13.1 General
[2929] MatraMarconiSpaceContributiontoESAInsertDesignHandbook;
MMSRef.NT/102/BG/355013.96(Dec.1996)
[2930] ROSETTALanderSubsystemSpecificationStructure
ROLSTSP3601,Issue4/0,para.2.2.4(2001)
[2931] TestProcedureInsertQualificationTestsfortheROSETTALander.
DASAdocumentQTINRSTTPR0001(1998)
[2932] TestReportInsertQualificationTestsfortheROSETTALander.DASA
documentQTINRSTTR0001(1998)
[2933] J.Block,R.Schtze,T.Brander,K.Marjoniemi,L.Syvnen,M.Lambert:
DLRBraunschweig/HelsinkiUniv.Technology/Patria/ESTEC
StudyonCarbonFibreTubeInserts
ESTECContractNo.16822/02/NL/PA,2004
[2934] ESAPSS031202(Issue1,Revision1)September1990:Insertdesign
handbook
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Annex G
Formulae
G.1 Introduction
ExcludingthoseinAnnexes,alistofallthemathematicalformulaeandexpressionsstatedthroughout
thehandbookaregivenhere.Theseareprovidedwithoutexplanationandareintendedforhandbook
userscreatingtheirowncalculationsoftware.[Seealso:G.2fornomenclature].
Each equation is referenced by the equation number used in the handbook and hyperlinked to the
relevantsection,e.g.:
a=bc (Eqn.22.11)
Clause
Topic
Sequentialnumber
G.2 Nomenclature
a centretocentredistancebetweeninserts
A onesixthofhexagonalcellcircumference
AA AmericanAluminiumAssociation
av averagevalue
B bendingstiffness
bi insertradius
bp pottingradius
bpmin minimumpottingradius
bptyp averageortypicalpottingradius
bR realpottingradius
bRtyp averageortypicalrealpottingradius
c coreheight
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C correctionfactorforstrengthcapabilitieswithheightsofcore,c>9mm
D footdiameterofanattachedstructuralpart
di insertdiameter(also=2bi)
dp pottingdiameter
e distanceofinsertfromthesandwichpaneledge
E Youngsmodulus
Ef Youngsmodulusofisotropicfacesheetmaterial
ER tensilemodulusofpottingcompound
Exy Youngsmodulusofanisotropicfacesheetmaterial
F appliedinclinedload
f facesheetthicknesswhenf1=f2
f1 thicknessofupperfacingsheet
f2 thicknessoflowerfacingsheet
FSS staticstrengthcapabilityunderloadsinclinedtoplaneoffacing
GC effectivecoreshearmodulus
GL shearmodulusofcoreinLdirection
guar guaranteedvalue
GW shearmodulusofcoreinWdirection
hi insertheight
hp pottingheight
hpmin minimumallowablepottingheight
hptyp typicalpottingheight
Kt magnificationfactorduetofatigue
Ktpp stress concentration factor due to partially potted inserts in nonmetallic
cores
L longitudinaldirectionofahoneycombcore
LN LuftfahrtNorm(aeronauticalstandard)
MSS allowablebendingmomentrelatedtostaticinsertstrength
M bendingmoment
min minimumvalue
N newton
n numberofinsertsinaninsertgroup
NPC numberofcorecellsfilledwithpottingresin
p loadnormaltoplaneoffacing
P*SS reducedstaticstrengthcapabilityofaninsertduetoedgeeffects
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pcritmin insert load capability due to minimum properties of the components (core,
facing,resin)
pcrittyp insertloadcapabilityduetothetypicalpropertiesofthecomponents
PSS staticstrengthcapabilityofaninsertunderloadsnormaltoplane
Psscmin minimuminsertloadcarryingcapabilityincompression
Psstav averageinsertloadcarryingcapabilityintension
Psstmin minimuminsertloadcarryingcapabilityintension
Q resultingshearload
Q*SS reducedshearloadforinsertsnearpaneledges
QC portionofQtakenbythecore
QSS allowableshearload
R rearstressrate
RC reliabilitycoefficient
RT roomtemperature
Sc corecellsize
to corefoilthickness
Tss allowabletorsionalload
typ typicalvalue
W transversedirectionofahoneycombcore
x distancebetweenfacingsheetuppersurfaceandinsertupperflangesurface
anglebetweeninsertloaddirectionandfacingplane
c densityoftheexpandedcore
o densityofthematerial
R densityofthepottingresin
EN edgecoefficientofinsertsloadedintensionorcompression
EQ edgecoefficientofshearloadedinserts
hG interferencecoefficientofagroupofequidistantinserts
IC interferencecoefficientofinsertsloadedinoppositedirections
IS interferencecoefficientoftwoneighbouringinsertsloadcapabilityreduction
coefficientoftwoneighbouringinserts
T coefficientofthermaldegradation
TA loadcapabilityreductioncoefficientofinsertexposedtoelevatedtemperature
TC loadcapabilityreductioncoefficientofinsertsexposedtothermalcycling
Tb loadcapabilityreductioncoefficientofinsertatRTafter20hoursexposureto
elevatedtemperature
TR reductioncoefficientofpottingresinstrengthatelevatedtemperatures
f Poissonsratioofisotropicfacingsheetmaterial
424
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x,y Poissonsratioofanisotropicfacingsheetmaterial
ccritc corestrengthincompression
ccritt corestrengthintension
ccritcmin minimumcompressionstrengthofcore
ccritctyp typicalcompressionstrengthofcore
fy yieldstrengthoffacingsheetmaterial
Rcrit tensilestrengthofpottingresin
c coreshearstrength
ccrit coreshearstrengtheffectivetoinsertstrength(circular)
ccritmin minimumallowablecoreshearstrength
ccrittyp typicaloraveragecoreshearstrength
Lcrit criticalshearstrengthofcoreinLdirection
Rcrit shearstrengthofpottingresin
Wcrit criticalshearstrengthofcoreinWdirection
E x E y 1 Al
2
f Al
f an
4
E Al 1 x y
[6.22]
G G C
W
3
[6.41]
c crit t 0 crit t c
0 [6.61]
425
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1
bp
n bn
[7.31]
F N F
b R
R
PC
C
[7.41]
bR bi 0.35 S C [7.43]
hp c for c hi c 7 mm [7.51]
hp min hi 7 mm [7.52]
h p typ h p min A tgh c h p min h p min [7.53]
426
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Massoffacesheethole= f bi
2
p [7.61]
w wb ws [8.11]
d 2w M
2
dx D [8.12]
M
wb dxdx C1 x C 2
D
f 3 f (c f ) 2 c3
D b E f E c [8.13]
6 2 12
bf (c f ) 2
D Ef Forf<<candEf>>Ec [8.14]
2
uupper ulower
0 [8.15]
c
dws c
( 0 )
c f
[8.16]
dx
c Q
[8.17]
Gc Gc (c f )
dws Q c
0
dx S (c f )
[8.18]
M 0 cx
ws C3
S (c f )
427
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(c f ) 2
S Gc [8.19]
c
c c
Mz f z
xf E f where 2 2
D c c
z ( f )
2 2
[8.110]
Mz c c
xc Ec where z
D 2 2
Q
c
b(c f )
Pf Pss 2b p c [12.11]
428
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P Ip 1 I1 r b p K ( b p ) a K 1 ( a )
(r ) (
(h c) I r a b p I1 ( a ) K 1 ( b p ) I1 ( b p ) K 1 ( a )
[12.21]
K 1 ( r ) a I1 ( a ) b p I1 ( b p )
)
a b p I1 ( a ) K 1 ( b p ) I1 ( b p ) K 1 ( a )
t s1t s 2 (h c) 2
Ip [12.22]
4(h c)
3 3
t s1 t s 2
Is [12.23]
12
Gc (h c) I
[12.24]
E c t s1 t s 2 I s
Es
E [12.25]
1 s
2
RC=1.1720.0063c0.2641f [12.31]
RC=1.2070.00544c0.2088f [12.32]
*
C I* C I hi hi [12.61]
E Ex Ey [12.71]
xy yx [12.72]
PSScmin=RCPcritmin [13.11]
429
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PSScav=RCPcritav [13.12]
Qc 8b p2 W crit [14.12]
Qc 8 b p2 Wcrit [14.33]
QS 8 b p2 W crit 2 t s b p sy [14.34]
1
Qt ( w bi )t s t ,ult [14.35]
K e'
bi 1
Qs 2t s (e ) s [14.36]
2 cos
2
2 Es ts
Qd bp ts K D [14.37]
1 s2 Sc
2
Qb K b bi t s comp [14.38]
430
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*
Qcrit Qcrit EQ [14.39]
e e
EN 0.66 0.06 fore3bp [14.310]
bp bp
and: EN 1 for e 3bp
QS 8 b p2 W crit 2 t s b p sy [14.311]
M ss PSSc bi [15.21]
P 2
PSS
Q 2
QSS 1 [17.11]
FSS 2
PSS QSS
[17.12]
PSS cos 2 QSS
2
sin 2
431
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P 2
PSS
Q 2
QSS
M 2
M SS
T 2
TSS 1 [17.21]
P SS
*
P SS EN
[18.11]
EN 0.55 e
bp
0.05 e
bp fore 5bp
[18.12]
EN 1 fore >5bp
*
Q SS
Q
SS EQ
[18.21]
EQ 0.66 e
bp
0.06 e
bp fore3bp
[18.22]
EQ 1 fore>3bp
*
P SS 1 IS 1 P SS 1
[19.11]
a 5(bp1 bp 2 ) [19.12]
b p1
IS1 b p2 a 1
1 [19.13]
1 b p1 5b p1 1 b p1
b p 2 b p 2
432
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1
b p1
b p1
b p2
1 a bp2
IS 2 1 [19.15]
5b p1 1
b
1 p1
1 b p1
b p2 b p2
*
P SS 2 IS 2 P SS 2
[19.16]
I
1 1 P 2
* [19.17]
IS 1 IS 1
P SS 2
P SS
*
P SS IC
[19.21]
P
*
SSi
P SSi ISl ISr
1 [19.31]
a5(bpi+bpi2) [19.32]
P SS 1
*
P SS 1 IS 1 IC
[19.41]
P
*
SSi
P SSi ISl
ISr
1 IC
[19.42]
=0.9 fora5(bpi1+bpi2)
IC [19.43]
=1.0 fora>5(bpi1+bpi2)
G P SS
*
P SS
[19.51]
n 1 1
G
2
n
IS
0.5
n
[19.52]
IS=1/2(1+a/10bp) [19.53]
433
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C2Kr
c
bc
max
F [21.21]
p
ccrit min
C Kr
*
max
[21.22]
P SS min 2b c p
ccrit min
F [21.23]
c
P SS min
0.57
cmin p
1290
[21.24]
1 4
4.4 10 2
p
mm
c local = c Kt [21.25]
K t
Ktj [21.26]
j 1
R
mean
A
[21.32]
mean
A
434
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F 2P a
[21.33]
1 R
2 a
[21.34]
1 R
1
a C N for mean A ccrit [21.51]
m
2
C N ccrit
1
for [21.52]
1 R K
a A
t
2
a [21.53]
1 R
m 1
2
C N
1
[21.54]
A
1 R
2b c
p
F * c
[21.55]
CK r max
[21.56]
c
K t
m 1
2b p c 2
C N
1
F [21.57]
K 1 R
* A
CK r max t
P
c
SS
crit
[21.58]
435
ECSSEHB3222A
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m 1
1 2
F P SS
1
C N [21.59]
ccrit min K t 1 R
A
F PSS
c c
h p 0.8 2 m 1
1 R CA N
1
[21.510]
n
D i
k [21.61]
i
N i
PTi P Ti [22.21]
N ges
n standard
1
100
[23.61]
N ges
n safetycrit
2
10
[23.62]
N K ex act [28.52]
436
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Annex H
Insert test fixtures
H.1 Introduction
Thisannexcontainsthetechnicaldrawingsofthefourinserttestfixturesforthestandardisedtesting
of80mm80mmsandwichpanelspecimenswithacentralinsert;asdescribedin27.3.
Thefourdifferenttestfixturesenabletheapplicationof:
Outofplaneloads(intensionorcompression),[See:H.2];
Inplaneshearloads,[See:H.3];
Bendingmoments,[See:H.4];
Torsionalmoments,[See:H.5].
Thefixturesaresuitableforstatictestmachinesaswellasforservohydraulictestmachines,e.g.for
fatigueloading.
ThetestfixtureswereoriginallydevelopedbyDLRforthequalificationofcarbonfibretubeinserts,
[2935],butarealsosuitableforanyothertypeofinsert.
NOTE These DLR technical drawings are also provided in standard .DXF
(drawing exchange file) format on the Insert design handbook
CDROM,andcanbeimportedintomostcommerciallyavailableCAD
software.
[See:CDROMdirectoryTestFixtureDXFs]
Forinsert/sandwichconfigurationswithhigherloadbearingcapabilitiesasizeof80mm80mmfor
thesamplesandcorrespondingcoverplatescanbetoosmall.
Underhighoutofplaneforces,theremainingsmallsupportareaofthecoverplateoutsidethecentral
70mmdiameterholecanproducestressconcentrationshighenoughtocrushthehoneycombcore.In
thiscase,itisnecessarytoincreasethesampleandcoverplatesizesto100mm100mmormore.All
otherdesignfeaturescanremainunchanged.
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Part3,inFigureH4
Part4,inFigureH5
Part5,inFigureH6
Part6,inFigureH7
Part7,inFigureH8
NOTE AllengineeringdrawingsreproducedcourtesyofDLR.
Master drawing
FigureH1:Testfixture:Tensioncompressionloadmasterdrawing
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H.2.1.2 Part 1
FigureH2:Testfixture:Tensioncompressionloadpart1
439
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H.2.1.3 Part 2
FigureH3:Testfixture:Tensioncompressionloadpart2
440
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H.2.1.4 Part 3
FigureH4:Testfixture:Tensioncompressionloadpart3
441
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H.2.1.5 Part 4
FigureH5:Testfixture:Tensioncompressionloadpart4
442
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H.2.1.6 Part 5
FigureH6:Testfixture:Tensioncompressionloadpart5
443
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H.2.1.7 Part 6
FigureH7:Testfixture:Tensioncompressionloadpart6
444
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H.2.1.8 Part 7
FigureH8:Testfixture:Tensioncompressionloadpart7
445
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FigureH9:Testfixture:Inplaneshearloadmasterdrawing
446
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H.3.1.2 Part 1
FigureH10:Testfixture:Inplaneshearloadpart1
447
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H.3.1.3 Part 2
FigureH11:Testfixture:Inplaneshearloadpart2
448
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H.3.1.4 Part 3
FigureH12:Testfixture:Inplaneshearloadpart3
449
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H.3.1.5 Part 4
FigureH13:Testfixture:Inplaneshearloadpart4
450
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H.3.1.6 Part 5
FigureH14:Testfixture:Inplaneshearloadpart5
451
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H.3.1.7 Part 6
FigureH15:Testfixture:Inplaneshearloadpart6
452
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H.3.1.8 Part 7
FigureH16:Testfixture:Inplaneshearloadpart7
453
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H.3.1.9 Part 8
FigureH17:Testfixture:Inplaneshearloadpart8
454
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455
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FigureH18:Testfixture:Bendingmasterdrawing
456
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H.4.1.2 Part 1
FigureH19:Testfixture:Bendingpart1
457
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H.4.1.3 Part 2
FigureH20:Testfixture:Bendingpart2
458
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H.4.1.4 Part 3
FigureH21:Testfixture:Bendingpart3
459
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H.4.1.5 Part 4
FigureH22:Testfixture:Bendingpart4
460
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H.4.1.6 Part 5
FigureH23:Testfixture:Bendingpart5
461
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H.4.1.7 Part 6
FigureH24:Testfixture:Bendingpart6
462
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H.4.1.8 Part 7
FigureH25:Testfixture:Bendingpart7
463
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H.4.1.9 Part 8
FigureH26:Testfixture:Bendingpart8
464
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H.4.1.10 Part 9
FigureH27:Testfixture:Bendingpart9
465
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H.4.1.11 Part 10
FigureH28:Testfixture:Bendingpart10
466
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H.4.1.12 Part 11. 12 and 13
FigureH29:Testfixture:Bendingparts11,12and13
467
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H.4.1.13 Part 14
FigureH30:Testfixture:Bendingpart14
468
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469
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FigureH31:Testfixture:Torsionmasterdrawing
470
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H.5.1.2 Part 1
FigureH32:Testfixture:Torsionpart1
471
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H.5.1.3 Part 2
FigureH33:Testfixture:Torsionpart2
472
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H.5.1.4 Part 3
FigureH34:Testfixture:Torsionpart3
473
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H.5.1.5 Part 4
FigureH35:Testfixture:Torsionpart4
474
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H.5.1.6 Part 5
FigureH36:Testfixture:Torsionpart5
475
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H.5.1.7 Part 6
FigureH37:Testfixture:Torsionpart6
476
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H.5.1.8 Part 7
FigureH38:Testfixture:Torsionpart7
477
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H.5.1.9 Part 8
FigureH39:Testfixture:Torsionpart8
478
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H.5.1.10 Part 9
FigureH40:Testfixture:Torsionpart9
479
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H.5.1.11 Part 10
FigureH41:Testfixture:Torsionpart10
480
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H.5.1.12 Part 11
FigureH42:Testfixture:Torsionpart11
481
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H.5.1.13 Part 12
FigureH43:Testfixture:Torsionpart12
482
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H.5.1.14 Part 13
FigureH44:Testfixture:Torsionpart13
483
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H.5.1.15 Part 14
FigureH45:Testfixture:Torsionpart14
484
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H.5.1.16 Part 15
FigureH46:Testfixture:Torsionpart15
485
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H.5.1.17 Part 16
FigureH47:Testfixture:Torsionpart16
486
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H.5.1.18 Part 17
FigureH48:Testfixture:Torsionpart17
487
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H.6 References
H.6.1 General
[2935] J.Block,R.Schtze,T.Brander,K.Marjoniemi,L.Syvnen,M.Lambert:
DLRBraunschweig/HelsinkiUniv.Technology/Patria/ESTEC
StudyonCarbonFibreTubeInserts,
ESTECContractNo.16822/02/NL/PA(2004)
488