The fatigue data for a ductile cast iron are given as follows: stress amplitude [mpa (ksi)] cycles to failure 248 (36.0) 1 × 105 236 (34.2) 3 × 105 224 (32.5) 1 × 106 213 (30.9) 3 × 106 201 (29.1) 1 × 107 193 (28.0) 3 × 107 193 (28.0) 1 × 108 193 (28.0) 3 × 108

(a) make an s–n plot (stress amplitude versus logarithm cycles to failure) using these data.

(b) what is the fatigue limit for this alloy?

(c) determine fatigue lifetimes at stress amplitudes of 230 mpa (33,500 psi) and 175 mpa (25,000 psi).

(d) estimate fatigue strengths at 2 × 105 and 6 × 106 cycles.