Abstract
A simple method to predict fatigue life is the linear cumulative damage rule. It is impossible to predict precisely the crack growth life under random loading in this method, because there is an effect of crack opening behavior on the fatigue life. In this study, it is proposed to use the effective stress range instead of stress amplitude in S-N curve in order to precisely predict the crack growth life. In addition, the crack growth life for the effective stress range is easily calculated by integrating the crack growth rate curve. To evaluate the validity of the proposed method, a series of fatigue test was carried out under several two step loading waves varied a ratio of high load amplitude to low load amplitude. Obtained fatigue life was compared with lives predicted by using the S-N curves obtained from the fatigue test under constant load amplitude and calculated from crack growth rate curve. As a result, it is confirmed that the proposed method has higher prediction accuracy than the linear cumulative damage rule used the S-N curve under constant load amplitude.
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