This paper introduces a new phenomenological cumulative damage rule to predict damage and fatigue life under variable amplitude loading. The rule combines a residual S-N curve approach and a material memory concept to describe the damage accumulation behavior. The residual S-N curve slope is regarded as a variable with respect to the loading history. The change in slope is then used as a damage measure and quantified by a material memory degeneration parameter. This model improves the traditional linear damage rule by taking the load-level dependence and loading sequence effect into account, which still preserves its superiority. A series of non-uniform fatigue loading protocols are used to demonstrate the effectiveness of the proposed model. The prediction results using the proposed model are more accurate than those using three popular damage models. Moreover, several common characteristics and fundamental properties of the chosen fatigue models are extracted and discussed.

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 Wöhler curve.

In this paper, a concept of fatigue driving energy is formulated to describe the process of fatigue failure. The parameter is taken as a combination of the fatigue driving stress and strain energy density. By assessing the change of this parameter, a new non‐linear damage model is proposed for residual life estimation within high‐cycle fatigue regime under variable amplitude loading. In order to consider the effects of loading histories on damage accumulation under such condition, the load interaction effects are incorporated into the new model, and a modified version is thus developed. Life predictions by these two models and Miner rule are compared using experimental data from literature. The results show that the proposed model gives lower deviations than the Miner rule, while the modified model shows better prediction performances than the others. Moreover, the proposed model and its modifications are ease of implementation with the use of S–N curve.

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Fan blade is one of the key parts used in aircraft engine and its failure is mainly caused by fatigue fracture. This paper aims to predict fatigue life of fan blade during its service operation. First, the effective load and stress of fan blade are obtained by using finite element analysis and simulation. Second, the fatigue notch factor of fan blade is determined by using the nominal stress method. Then, the material properties of fan blade are used to correct and obtain the