Volume 24, Issue 4 (July 1996)
Fatigue Under Stress Cycling With Nonzero Means
Several models are available for mean stress correction on fatigue life when nonzero means are applied. Mean value adjustment may be necessary in some cases when maximum/minimum stress causes plastic deformation. Strain-cycled fatigue tests conducted for a mild steel suggest that there may be some strain ranges where the effect of mean strain/stress is contrary to the prediction of existing models. In this study, mild steel specimens have been stress-cycled under various combinations of stress amplitudes and nonzero mean stresses. The stress amplitudes are chosen to be equivalent to the ones applied in the strain-cycled tests in a sense that the strain response is in the elastic range during the first portion of life and subsequently develops into the plastic range. Experimental results confirm observations in the study where strain cycles were applied. The cyclic softening and cycle-dependent creep process have also been studied. Possible modifications to the existing models have been suggested for the stress ranges investigated.