Abstract: Aiming at the problem of the residual strength of parts under multi-level loading not considering the loading sequence, the Schaff model is revised by introducing the loading sequence influence factor based on the Schaff model, and an equal damage ratio residual strength prediction model considering the effect of the loading sequence is established. With the aid of the shape parameter and size parameter of the Gamma function, the strength degradation process of the part is described. The fatigue test data of 45^# steel and 30CrMnSiA are used to verify the accuracy of the model. The results show that the prediction accuracy of the modified equal damage ratio residual strength model is better than that of the Schaff model, and the Gamma process is consistent with the strength degradation process of the parts.

Key words: multi-level loading, equal damage ratio, residual strength, strength degradation, Gamma process