Study and Prediction of Overload/Underload Effect on Fatigue Performance of Novel Fiber Metal Laminates under Two-Stage Loading

In order to have an in-depth understanding about the fatigue performance of novel fiber metal laminates in practical applications, this paper presents an approach for predicting the performance of fiber-reinforced 2060 Al-Li alloy (2/1 and 3/2) laminates under two-stage loading. Firstly, the fatigue S-N curves of these laminate materials are tested under different cyclic stresses, which have different cycle characteristics, such as constant amplitude loading with stress ratio, R = 0.06 and R = - 1, periodic single overload, periodic single underload, and high-low overload. Secondly, referring to constant amplitude loading R = 0.06, the fatigue performance of the laminate materials under different loading modes (periodic single overload, periodic single underload, and high-low overload) is analyzed based on the fracture mechanics and damage mechanics theories. Then, combining with the effect of overloading on the fatigue performance, the damage cumulative rule is modified based on the damage fracture coupling theory. On this basis, a piecewise linear constant life diagram is adopted for predicting the fatigue life of the laminate materials under two-stage loading with overloading. Finally, the accuracy of the model is verified by comparing the predicted results with experimental data.