Callister - An introduction - 8th edition

Questions and Problems • 621
McCrum, N. G., C. P. Buckley, and C. B. Bucknall,
Principles of Polymer Engineering, 2nd edition,
Oxford University Press, Oxford, 1997. Chapters
7–8.
Muccio, E. A., Plastic Part Technology, ASM International,
Materials Park, OH, 1991.
Muccio, E.A., Plastics Processing Technology, ASM
International, Materials Park, OH, 1994.
Rosen, S. L., Fundamental Principles of Polymeric
Materials, 2nd edition, Wiley, New York, 1993.
Strong, A. B., Plastics: Materials and Processing, 3rd
edition, Pearson Education, Upper Saddle River,
NJ, 2006.
Ward, I. M., and J. Sweeney, An Introduction to the
Mechanical Properties of Solid Polymers, 2nd
edition, Wiley, Hoboken, NJ, 2004.
QUESTIONS AND PROBLEMS
Stress–Strain Behavior
15.1 From the stress–strain data for poly(methyl
methacrylate) shown in Figure 15.3, determine
the modulus of elasticity and tensile
strength at room temperature [20C (68F)],
and compare these values with those given in
Table 15.1.
15.2 Compute the elastic moduli for the following
VMSE polymers, whose stress–strain behaviors may
be observed in the “Tensile Tests” module of
Virtual Materials Science and Engineering
(VMSE):(a) high-density polyethylene,(b) nylon,
and (c) phenol-formaldehyde (Bakelite).
Polymers
How do these values compare with those presented
in Table 15.1 for the same polymers?
15.3 For the nylon polymer, whose stress-strain behavior
may be observed in the “Tensile Tests”
VMSE
module of Virtual Materials Science and Engineering
(VMSE), determine the following:
(a) the yield strength, and
Polymers
(b) the approximate ductility, in percent
elongation.
How do these values compare with those for
the nylon material presented in Table 15.1?
15.4 For the phenol-formaldehyde (Bakelite)
VMSE polymer, whose stress–strain behavior may
be observed in the “Tensile Tests” module of
Virtual Material Science and Engineering
(VMSE), determine the following:
Polymers
(a) the tensile strength, and
(b) the approximate ductility, in percent
elongation.
How do these values compare with those for
the phenol-formaldehyde material presented
in Table 15.1?
Viscoelastic Deformation
15.5 In your own words, briefly describe the phenomenon
of viscoelasticity.
15.6 For some viscoelastic polymers that are subjected
to stress relaxation tests, the stress decays
with time according to
s1t2 s102 exp
t
a
t b
(15.10)
where (t) and (0) represent the timedependent
and initial (i.e., time 0) stresses,
respectively, and t and denote elapsed time
and the relaxation time; is a timeindependent
constant characteristic of the
material. A specimen of a viscoelastic polymer
whose stress relaxation obeys Equation
15.10 was suddenly pulled in tension to a
measured strain of 0.6; the stress necessary
to maintain this constant strain was measured
as a function of time. Determine E r (10) for
this material if the initial stress level was
2.76 MPa (400 psi), which dropped to
1.72 MPa (250 psi) after 60 s.
15.7 In Figure 15.28, the logarithm of E r (t) versus
the logarithm of time is plotted for polyisobutylene
at a variety of temperatures.
Make a plot of E r (10) versus temperature and
then estimate its T g .
15.8 On the basis of the curves in Figure 15.5,
sketch schematic strain–time plots for the following
polystyrene materials at the specified
temperatures:
(a) Amorphous at 120C
(b) Crosslinked at 150C