GTBL042-09 GTBL042-Callister-v3 October 4, 2007 11:53
2nd Revised PagesQuestions and Problems • 337(d)Estimate fatigue strengths at 2× 104 and
6 × 105 cycles.
9.13Suppose that the fatigue data for the steel al-
loy in Problem 9.12 were taken for bending-
rotating tests, and that a rod of this alloy is to
be used for an automobile axle that rotates at
an average rotational velocity of 600 revolu-
tions per minute. Give the maximum lifetimes
of continuous driving that are allowable for
the following stress levels:(a)450 MPa (65,000
psi),(b)380 MPa (55,000 psi),(c)310 MPa
(45,000 psi), and(d)275 MPa (40,000 psi).
9.14Three identical fatigue specimens (denoted A,
B, and C) are fabricated from a nonferrous
alloy. Each is subjected to one of the
maximum-minimum stress cycles listed be-
low; the frequency is the same for all three
tests.Specimen σmax(MPa) σmin(MPa)A + 450 − 150
B + 300 − 300
C + 500 − 200(a)Rank the fatigue lifetimes of these three
specimens from the longest to the short-
est.
(b)Now justify this ranking using a schematic
S–Nplot.
9.15 (a)Compare the fatigue limits for PMMA
(Figure 9.27) and the steel alloy for which
fatigue data are given in Problem 9.12.
(b)Compare the fatigue strengths at 10^6 cy-
cles for nylon 6 (Figure 9.27) and 2014-T6
aluminum (Figure 9.41).Factors That Affect Fatigue Life
9.16List four measures that may be taken to in-
crease the resistance to fatigue of a metal
alloy.Generalized Creep Behavior
9.17The following creep data were taken on an alu-
minum alloy at 480◦C (900◦F) and a constant
stress of 2.75 MPa (400 psi). Plot the data as
strain versus time, then determine the steady-state or minimum creep rate.Note:The initial
and instantaneous strain is not included.Time(min) Strain Time(min) Strain
0 0.00 18 0.82
2 0.22 20 0.88
4 0.34 22 0.95
6 0.41 24 1.03
8 0.48 26 1.12
10 0.55 28 1.22
12 0.62 30 1.36
14 0.68 32 1.53
16 0.75 34 1.77Stress and Temperature Effects
9.18For a cylindrical low carbon–nickel alloy spec-
imen (Figure 9.38) originally 19 mm (0.75 in.)
in diameter and 635 mm (25 in.) long, what ten-
sile load is necessary to produce a total elon-
gation of 6.44 mm (0.25 in.) after 5000 h at
538 ◦C (1000◦F)? Assume that the sum of in-
stantaneous and primary creep elongations is
1.8 mm (0.07 in.).
9.19A cylindrical component constructed from a
low carbon–nickel alloy (Figure 9.37) has a di-
ameter of 19.1 mm (0.75 in.). Determine the
maximum load that may be applied for it to
survive 10,000 h at 538◦C (1000◦F).
9.20 (a)Estimate the activation energy for creep
(i.e.,Qcin Equation 9.21) for the low carbon–
nickel alloy having the steady-state creep be-
havior shown in Figure 9.38. Use data taken at
a stress level of 55 MPa (8000 psi) and temper-
atures of 427◦C and 538◦C. Assume that the
stress exponentnis independent of tempera-
ture.(b)Estimate ̇sat 649◦C (922 K).
9.21Steady-state creep data taken for an iron at a
stress level of 140 MPa (20,000 psi) are given
here: ̇s(h−^1 ) T(K)
6.6× 10 −^41090
8.8× 10 −^21200If it is known that the value of the stress expo-
nentnfor this alloy is 8.5, compute the steady-
state creep rate at 1300 K and a stress level of
83 MPa (12,000 psi).