Mechanical Behavior Mostly Ceramics, Glasses and Polymers
Mechanical Behavior Mostly Ceramics, Glasses and Polymers
Mechanical Behavior Mostly Ceramics, Glasses and Polymers
fs
Mechanical Issues:
• Properties are significantly dependent on processing
– and as it relates to the level of Porosity:
• E = E0(1-1.9P+0.9P2) – where P is a fraction ‘porosity’
• sfs = s0e-nP -- s0 & n are empirical values and functions of porosity
brittle polymer
plastic
elastomer
elastic modulus
– less than metal
e
aligned, networked
cross- case crystalline
linked regions
case slide
semi-
crystalline amorphous
crystalline
case regions
regions align
elongate
Stress-strain curves adapted from Fig. 15.1, Callister 7e. Inset figures along plastic response curve adapted from Figs. 15.12 &
15.13, Callister 7e. (Figs. 15.12 & 15.13 are from J.M. Schultz, Polymer Materials Science, Prentice-Hall, Inc., 1974, pp. 500-
501.)
Predeformation by Drawing
• Drawing…(ex: monofilament fishline)
-- stretches the polymer prior to use
-- aligns chains in the stretching direction
• Results of drawing:
-- increases the elastic modulus (E) in the
stretching direction
-- increases the tensile strength (TS) in the
stretching direction Adapted from Fig. 15.13, Callister 7e.
-- decreases ductility (%EL) (Fig. 15.13 is from J.M. Schultz,
Polymer Materials Science, Prentice-
• Annealing after drawing... Hall, Inc., 1974, pp. 500-501.)
-- decreases alignment
-- reverses effects of drawing.
• Comparable to cold working in metals!
Tensile Response: Elastomer Case
s(MPa)
x brittle failure Stress-strain curves
adapted from Fig. 15.1,
Callister 7e. Inset figures
along elastomer curve
(green) adapted from Fig.
15.15, Callister 7e. (Fig.
plastic failure
x 15.15 is from Z.D.
Jastrzebski, The Nature
and Properties of
x Engineering Materials, 3rd
elastomer ed., John Wiley and Sons,
1987.)
final: chains
e are straight,
still
cross-linked
initial: amorphous chains are Deformation
kinked, cross-linked. is reversible!
• Decreasing T...
s(MPa)
-- increases E 80 4°C Data for the
-- increases TS semicrystalline
-- decreases %EL 60 polymer: PMMA
20°C (Plexiglas)
• Increasing 40 40°C
strain rate...
-- same effects 20
as decreasing T. to 1.3
60°C
0
0 0.1 0.2 e 0.3
Adapted from Fig. 15.3, Callister 7e. (Fig. 15.3 is from T.S. Carswell and J.K.
Nason, 'Effect of Environmental Conditions on the Mechanical Properties of
Organic Plastics", Symposium on Plastics, American Society for Testing and
Materials, Philadelphia, PA, 1944.)
Melting vs. Glass Transition Temp.
What factors affect Tm and
Tg?
• Both Tm and Tg increase with
increasing chain stiffness
(From
Modern
Plastics
Encyclope
dia, 1981–
82, Vol. 58,
No. 10A,
McGraw-
Hill Book
Company,
New York,
October
1981.)