Analysis and prediction on total fatigue life problems of fiber reinforced metal laminates under two-stage loading

The new generation of aeronautical structural materials, fiber reinforced metal laminates have drawn increasing interests to the researchers. In order to have an in-depth understanding of such material for practical application, this paper presents a study on the total fatigue life problem of Al-Li alloy sheet and fiber reinforced Al-Li alloy laminates (2/1 and 3/2 laminates) under two-stage loading. Firstly, the fatigue life performance of these materials is tested under different cyclic stress, which has different cycle characteristics (periodic single overload, periodic single underload and periodic high-low overload). Secondly, based on the processing and statistical analysis of the test data, the distribution regulation of fatigue data is summarized and the relationship between fatigue lives is studied for three kinds of materials under the same loading mode. Then, the stress relationship between alloy and laminates materials is established based on composite laminate theory. By combining the stress relationship with the S-N curve equation, the model for predicting the fatigue life of laminates is established based on the life relationship between alloy and laminates. Finally, the accuracy of the model is verified by comparing the predicted results with the experimental data.