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?