Suppose that the fatigue data for the steel alloy in Problem 8.24 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 revolutions 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)
(d) 275 MPa (40,000 psi)
Problem 8.24
The fatigue data for a steel alloy are given as follows:
Stress Amplitude [MPa (ksi)] | Cycles to Failure |
470 (68.0) | 104 |
440 (63.4) | 3 × 104 |
390 (56.2) | 105 |
350 (51.0) | 3 × 105 |
310 (45.3) | 106 |
290 (42.2) | 3 × 106 |
290 (42.2) | 107 |
290 (42.2) | 108 |
(a) Make an S–N plot (stress amplitude versus logarithm of cycles to failure) using these data.
(b) What is the fatigue limit for this alloy?
(c) Determine fatigue lifetimes at stress amplitudes of 415 MPa (60,000 psi) and 275 MPa (40,000 psi).
(d) Estimate fatigue strengths at 2 × 104 and 6 × 105 cycles.
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