On the Significance of the Stress Correction Factors for the Fatigue Stressing with Periodical Two Stress Amplitudes

Abstract

Previously, the authors studied the fatigue lives under the reversed stress with periodical two stress amplitudes. The equation predicting fatigue lives was modified by introducing the stress correction factors. Three kinds of carbon steel were tested under such load conditions and the values of stress correction factors were obtained. At that time, however, no physical or mathematical meaning was given for these factors.In this paper, the authors have investigated the significance of this stress correction factors by the analysis starting from the modified linear damage criterion. The conclusions obtained are as follows(1) The fatigue damage should be considered as the function of the practical strain amplitude (instead of the nominal strain amplitude). In this study, we introduced the damage function asD=CΣpj=1(ej1/mnj).(2) This strain ej should not be the strain of the virgin material but the practical strain after various stress histories.(3) The stress correction factors should be defined as the ratio of the 1/m-th power average of this practical strain to the nominal strain. Accordingly, these factors are not only experimental constants but the factors with sufficient physical significance.