FATIGUE UNDER STRESS CYCLING WITH NONZERO MEANS

Several models are available for mean stress correction on fatigue lif e when nonzero means are applied. Mean value adjustment may be necessa ry in some cases when maximum/minimum stress causes plastic deformatio n. Strain-cycled fatigue tests conducted for a mild steel suggest that there may be some strain ranges where the effect of mean strain/stres s is contrary to the prediction of existing models. In this study, mil d steel specimens have been stress-cycled under various combinations o f stress amplitudes and nonzero mean stresses. The stress amplitudes a re chosen to be equivalent to the ones applied in the strain-cycled te sts 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 st rain cycles were applied. The cyclic softening and cycle-dependent cre ep process have also been studied. Possible modifications to the exist ing models have been suggested for the stress ranges investigated.