An approach in plastic strain-controlled cumulative fatigue damage

The rule for cumulative damage and the model for predicting the fatigue life under two amplitudes of plastic strain are studied and summarized in the present paper. Based on the length of the principal crack, obtained by a series of microscopic observations in SEM, an evolution law of this principal crack was established. It was found that, under (L-H) level loading sequence, Miner's linear damage rule and the propagation law of the main crack are completely fitted to predict the residual lifetime. While a big discrepancy was found between experimental results and Miner's rule prediction in the (H-L) loading sequence. Thus, an approach based on both Grover's formulation and the transition inter/transgranular propagation was proposed. The last was found to give relatively interesting results in terms of residual lifetime.