Question Bank for End – Sem Examination

Design of Machine Elements

1) What is stress concentration? What are the causes of stress concentration? With neat
sketches,explain the methods of reduction of stress concentration.
2) What is modifying factor to account for stress concentration? Explain Endurance
strength
Modifying factors?
3) Explain with neat sketch the Gerber curve, Soderberg and Godman lines?
4) Write a short note on Cumulative damage.
5) Explain modified Goodman diagram. Draw neat labeled sketches of modified Goodman
diagram for axial & Bending stresses.
6) Explain 1) Stress Concentration 2) Notch Sensitivity 3) Fatigue life 4) Endurance limit.
5)
Modified Goodman diagram
7) Explain modified Goodman diagram. Draw neat labeled sketches of modified Goodman
diagram for axial & Bending stresses. Explain Fatigue Design under Combined Stresses
8) A rotating bar made of steel 45C8(Sut = 630 MPa) is subjected to a completely reversed
bending stress. The corrected endurance limit of the bar is 315 N/mm2. Calculate the fatigue
strength of the bar for a life of 90,000 cycles.
9) A forged steel bar, 50 mm in diameter, is subjected to a reversed bending stress of 250
N/mm2. The bar is made of steel 40C8 (Sut= 600 N/mm2). Calculate the life of the bar for a
reliability of 90%. Take Ka = 0.44, Kb = 0.85, Kc = 0.897
10) A machine component is subjected to fluctuating stress that varies from 40 to
100N/mm2. Thecorrected endurance limit stress for the machine component is 270
N/mm2. The ultimate
tensile strength and yield strength of the material are 600 and 450 N/mm2 respectively. Find
the factor of safety using
(i) Gerber theory (ii) Soderberg line (iii) Goodman lineAlso, find the factor of safety
against static failure.
11) A cantilever beam of circular cross-section is made of alloy steel with Sut = 1500
N/mm2,is
fixed at one end and subjected to a completely force of 100 N at free end perpendicular to
axial and at distance 400 mm from fixed end. Take Ka = 0.79, Kb = 0.85, Kc = 0.868.
Temperature factor = 0.975 desired life of beam is 50000 cycles, Take factor of safety 1.5,
Theoretical stress concentration factor 1.33 and notch sensitivity factor 0.85. Find diameter
ofshaft.
12) A cantilever beam of circular cross section made of steel Fe 550 (Sut= 550 N/mm 2is
fixed at
one end andsubjected to a completely reversed load (P)of 15 kN is at the free end. He force P
is perpendicular to the axis of beam. The distance between force to fixed end is 200 mm.
Take Kt = 1.35,q = 0.85s,Ka = 0.8,Kc = 0.897,Kb are as follows The factor of safety is 2
Calculate the diameter d of the beam for infinite life.
d (mm) Kb
d≤ 7.5 1.0
7.5< d ≤ 50 0.85
d> 50 0.75
13) A cantilever beam made of cold drawn steel 4OC8 (Sut = 600 N/mm 2 and Syt =
380N/mm2)
is shown in Figure The force P acting at the free end varies from –50 N to +150 N. The
expected reliability is 90% and the factor of safetyis 2. The notch sensitivity factor at the
filletis 0.9. Determine the diameter ‘d’ of the beam at the fillet cross-section.
Take Ka = 0.77,Kb = 0.85, Kc = 0.897Kt = 1.44
14) A cantilever beam made of steel material with Sut=550 N/mm 2,Syt=320 N/mm2 as
shown in
figure is subjected to load which varies from –F to 3F Take Ka = 0.89,K� = 0.85, Kt = 1.42
q=0.9, fos=2. Determine maximum value of F which the cantilever beam can withstand for
infinite life.
15) Derive expression for torque required to raise the loads in case of square threads
16) Derive expression for torque required to lower the loads in case of square threads
17) Explain self-locking and over-hauling property of screw. Prove the condition for screw
to be
self-locking.
18) Derive and expression for maximum efficiency of square threads
19) What are the advantages of trapezoidal threads over square threads? State the meaning of
each term involved in designation Tr40×14(p7).
20) Explain with neat sketch, differential screw and Compound screw
21) Explain with neat sketch, re-circulating ball screw. State its application
22) The lead screw of a lathe has Acme threads of 50 mm outside diameter and 8 mm pitch.
The
screw must exert an axial pressure of 2500 N in order to drive the tool carriage. The thrust is
carried on a collar 110 mm outside diameter and 55 mm inside diameter and the lead screw
rotates at 30 r.p.m. Determine (a) the power required to drive the screw; and (b) the
efficiency of the lead screw. Assume a coefficient of friction of 0.15 for the screw and 0.12
for the collar.
23) A power screw having double start square threads of 25 mm nominal diameter and 5 mm
pitch is acted upon by an axial load of 10 kN. The outer and inner diameters of screw collar
are 50 mm and 20 mm respectively. The coefficient of thread friction and collar friction may
be assumed as 0.2 and 0.15 respectively. The screw rotates at 12 r.p.m. Assuming uniform
wear condition at the collar and allowable thread bearing pressure of 5.8 N/mm2, find: 1. the
torque required to rotate the screw; 2. the stress in the screw; and 3. the number of threads of
nut in engagement with screw. Also state the condition of screw
24) A C-clamp, as shown in Figure, has trapezoidal threads of 12 mm outside diameter and 2
mm pitch. The coefficient of friction for screw threads is 0.12 and for the collar is 0.25.
The mean radius of the collar is 6 mm. If the force exerted by the operator at the end of
the handle is 80 N, find: 1) The length of handle; 2) The maximum shear stress in the
body of the screw and where does this exist; and 3) The bearing pressure on the threads.
(08)
25) A vertical two start square threaded screw of 100 mm mean diameter supports a vertical
load of 18 kN. The nut of the screw is fitted in the hub of a gear wheel having 80 teeth
which meshes with a pinion of 20 teeth. The mechanical efficiency of the pinion and gear
wheel drive is 90 percent. The axial thru bearing 250 mm outside diameter and 100 mm
inside diameter. Assuming uniform pressure conditions, find, minimum diameter of
pinion shaft and height of nut, when coefficient of friction for the vertical screw and nut
is permissible shear stress in the shaft material is 56 MPa and allowable bearing pressure
is 1.4 N/mm2.
26) Write a note on: Bolts of uniform strength
27) Discuss the advantages and disadvantages
28) Explain the procedure for the design of bolts for eccentrically loaded bolted joints in
shear.
29) Discuss in brief strength of parallel fillet welds
30) Derive equations for strength of 1) Single transverse fillet weld 2) Double
31) Discuss the procedure for designing Axially Loaded Unsymmetrical Welded Sections
32) What are the assumptions made in the design of welded joint?
33) Prove that stress on the throat is equal to the ratio of force on weld to
34) The structural connection shown in Figure is subjected to an eccentric force an
eccentricity of 500 mm from the 2 is 200 mm, and the centre distance between bolts
identical. The bolts are made from plain carbon steel of safety is 2.5. Determine nominal
diameter of the bolts.
35) A bracket, subjected to a force of in Figure. The bracket is fastened by means of four
identical bolts to the structure. The boltsare made of plain carbon steel maximum shear
stress. Assume maximum s bolts and 20 mm pitch thrust on the screw is taken by a collar
0.15 and that for the collar bearing is 0.20. The of welded joints parallel fillet weld
0.707×s×l
36) CG of the bolts. The centre distance between bolts , 1 and 3 is 150 mm. All the bolts are
30C8 (Syt = 400 N/mm . 5 kN inclined at an angle of 600 with the vertical, is shown 30C8
 (Syt = 400 N/mm2) and the factor of safety is shear stress theory and determine the size of
the st P of 10 kN with1 and . mm2) and the factor) 5 based on hear
37) A bracket shown in figure is fixed to steel column by means of four bolts of sizeof W
acts on the bracket. Take is 45. Determine 1) Maximum load on bracket, 2) Cross section
of bolts.
38) A steel plate subjected to a force of bolts is shown in Figure. The bolts are made from
plain carbon steel and the factor of safety is 3. Specify the size of bolts.
39) An ISA 200 × 100 × 10 angle is welded to a steel plate by means of fillet welds as shown
in Figure. The angle is subjected to a static force of 150 kN the weld is 70 N/mm2.
Determine the lengths of weld at the top and bottom. (08)
40) Figure shows a welded joint subjected to a load of 20 kN. Find size of weld if
permissible
shear stress 80 MPa.(10) σ� = 84 MPa. If ratio B/t for cross section of the arm bracket
41) 5 kN and fixed to a channel by means of three identical 45C8 (S . and the permissible
shear stress for . M14. A load Syt = 380 N/mm2)
42) A rectangular steel plate is welded as a cantilever to a vertical column and supports a
single
concentrated load 40 kN, as shown in Figure. Determine the Maximum shear stress if size of
weld is 11.62 mm.
43) Explain the following terms for helical spring Active and inactive coils Spring index
Spring rate
44) Explain with the neat sketch, nipping of leaf spring
45) What is mean by spring surge and what is its effect
46) Explain shot peening
47) Derive the expression for the shear stress induced in a helical compression springs.
48) Explain A.M. Wahl’s factor and state its importance in the design of helical springs.
49) A helical spring is made from a wire of 6 mm diameter and has outside diameter of 75
mm. If the permissible shear stress is 350 MPa and modulus of rigidity 84 kN/mm load
which the spring can carry and the deflection per active turn.
50) Design a close coiled helical compression spring for a service load ranging from 2750 N.
The axial deflection of the spring for the load range isof 5. The permissible shear stress
intensity is kN/mm2. Neglect the effect of stress concentration. Draw a fully dimensioned
sketch of the spring, showing details of the finish of the end coils.
51) Design a helical compression spring for a pressure relief valve using following data;
52) Operating pressure = 14.5 Bar; Valve lift at 18% pressure rise = 7 mm; Diameter of valve
= 37 mm; Limiting mean coil diameter = 36 mm; Maximum shear stress = 465 MPa; G
GPa, Clash clearance = 15 % of Maximum deflection of spring, End style of spring is
square and ground std. Take spring wire diameter 6, 6.5, 7, 7.5, 8, 8.5 (mm)
53) Design a helical compression spring with following data; Maximum load = 4460 N;
Meancoil diameter = 85 mm; Maximum shear stress 265 N/mm2; Spring stiffnes = 67
kN/m; G= 81.5 kN/mm2; std wire diameter: - 14.5, 15, 15.5, 16, 16.5, 17 (mm)
54) A safety valve of 60 mm diameter is to blow off at a pressure of 1.2 N/mm2. It is held on
itsseat by a close coiled helical spring. The maximum lift of the valve is 10 mm. Design a
suitable compression spring of spring index 5 and providing an initial compression of 35
mm., . 6 mm. Assume a spring index . 420 MPa and modulus of rigidity84 gpa.
55) The maximum shear stress in the material of the wire is limited to 500 MPa. The modulus
of rigidity for the spring material is 80 kN/mm2. Calculate: 1) Diameter of the spring
wire, 2)Mean coil diameter, 3) Number of active turns, and 4) Pitch of the coil.
56) A mechanism used in printing machinery consists of a tension spring assembled with a
57) preload of 30 N. The wire diameter of spring is 2 mm with a spring index of 6. The
spring has 18 active coils. The spring wire is hard drawn and oil tempered having
following material properties: Design shear stress = 680 MPa; Modulus of rigidity = 80
kN/mm2 Determine: 1) the initial torsional shear stress in the wire; 2) Spring rate; and 3)
The force to cause the body of the spring to its yield strength.
58) A power screw on a machine has single start square thread with a non rotating bronze
nut. Axial force on the screw is 15 kN. Allowable stresses for screw material in
compression and shear are 85 MPa and 37 MPa respectively. Allowable bearing pressure
for the screw nut pair is 5 MPa. Find
(i) Core diameter of screw
(ii) Length of the nut
(iii) Efficiency of power screw in coefficient of friction between screw and nut is 0.12.
59) A helical spring is made from a wire of 8 mm diameter and has outside diameter 90 mm;
if the permissible shear stress is 350 N/mm2 and modulus of rigidity 84 kN/mm2, find
the axial load which the spring can carry and the deflection per active turn.
i) Neglecting the effect of curvature.
ii) Considering the effect of curvature
60) The lead screw of a lathe has square threads of 24 mm outside diameter and 5 mm pitch.
In order to drive the tool carriage, the screw exerts an axial thrust of 2.5 kN find the
efficiency of the screw and the power required to drive the screw if it is rotate at 30 rpm.
Neglect the bearing friction. Assume co-efficient of thread friction as 0.12.
61) Design a helical compression spring for a maximum load of 1200 N and deflection 30
mm using the value of spring index as 5. The maximum permissible shear stress for
spring wire is 420 MPa and modulus of rigidity is 84 KN.
62) A plate 75 mm wide and 12.5 mm thick is to be joined with another plate by single
transverse and parallel fillet weld, Maximum tensile and shear stresses are 70 N/mm2 and
56 N/mm2 respectively. Find the length of each parallel fillet weld if joint is subjected to
90 kN.
63) A closed coil helical spring is used for front suspension of an automobile. The spring has
stiffness 90 N/mm with square and ground ends. The load on the spring causes a total
deflection of 8.5 mm. By taking permissible shear stress of material as 450 MPa. Find
i) Spring wire diameter
ii) Length of spring Assume spring index = 6 and G = 80 × 103 N/mm2
64) Two steel plates 120 mm wide and 12.5 mm thick are to be connected together by double
transverse fillet weld. The maximum tensile stress for the plate and welding material is
not to exceed 70 N/mm2. Find the length of weld required for maximum static loading.
65) A wall bracket is attached to a wall by means of four bolts, two at a distance of 50 mm
from the lower edge and remaining two at a distance of 450 mm from the lower bolts. It
supports a load of 50 kN at a distance of 500 mm from the wall. Find the diameter of
bolts. Assume working stress in tension as 80 N/mm2.