Fundamentals of Materials Science and Engineering: An Integrated Approach, 3e

GTBL042-07 GTBL042-Callister-v2 August 6, 2007 12:43

240 • Chapter 7 / Mechanical Properties

the modulus of elasticity and tensile strength

at room temperature [20◦C (68◦F)], and com-

pare these values with those given in Tables

7.1 and 7.2.

7.30For the high-density polyethylene polymer,

whose stress strain behavior may be observed

in the “Tensile Tests” module ofVirtual Mate-

rials Science and Engineering(VMSE), deter-

mine the following:

(a)the yield strength,

(b)the tensile strength, and

(c)the approximate ductility, in percent elon-

gation.

How do these values compare with those for

the high-density polyethylene material pre-

sented in Table 7.2?

Viscoelastic Deformation

7.31In Figure 7.34, the logarithm ofEr(t) versus

the logarithm of time is plotted for PMMA at

a variety of temperatures. Make a plot of log

Er(10) versus temperature and then estimate

itsTg.

7.32On the basis of the curves in Figure 7.26, sketch

schematic strain–time plots for the following

Time (h)

Relaxation modulus (MPa)

0.001 0.01 0.1 1 10 100 1000

0

10

100

1000

40 °C

60 °C

80 °C

92 °C

100 °C

110 °C

112 °C

120 °C

115 °C

125 °C

135 °C

Figure 7.34 Logarithm of

relaxation modulus versus

logarithm of time for

poly(methyl methacrylate)

between 40 and 135◦C. (From

J. R. McLoughlin and A. V.

Tobolsky,J. Colloid Sci.,7,555,

1952. Reprinted with
      permission.)

polystyrene materials at the specified temper-

atures:

(a)Crystalline at 70◦C

(b)Amorphous at 180◦C

(c)Crosslinked at 180◦C

(d)Amorphous at 100◦C

7.33Make two schematic plots of the logarithm

of relaxation modulus versus temperature

for an amorphous polymer (curveCin Fig-

ure 7.29).

(a)On one of these plots demonstrate how the

behavior changes with increasing molecu-

lar weight.

(b)On the other plot, indicate the change in

behavior with increasing crosslinking.

Hardness

7.34 (a)A 10-mm-diameter Brinell hardness in-

denter produced an indentation 2.50 mm

in diameter in a steel alloy when a load of

1000 kg was used. Compute the HB of this

material.

(b)What will be the diameter of an indenta-

tion to yield a hardness of 300 HB when a

500-kg load is used?