A new approach to the investigation of load interaction effects and its application in residual fatigue life prediction

Fatigue damage under variable amplitude loading is related to load histories, such as load sequences and load interactions. Many nonlinear damage models have been developed to present load sequences, but load interactions are often ignored. This paper provides a new approach to present load interaction effects for nonlinear damage accumulation. It is assumed that the ratio of two consecutive stress levels is used to describe the phenomenon on damage evolution. By introducing the approach to a nonlinear fatigue model without load interactions, a modified model is developed to predict the residual fatigue life under variable amplitude loading. Experimental data from three metallic materials and welded joints in the literature are employed to verify the effectiveness of the proposed method under two-level loading. The result shows that the modified model predicts more satisfactory estimations than the primary model and Miner rule. Furthermore, the proposed method is calibrated and validated by the case of multilevel loading. It is found that the modified model shows a good estimation and its damage curve presents a typical nonlinear behavior of damage growth. It is also convenient to calculate the residual fatigue life by the Wohler curve.