A regression model of fatigue crack propagation under flight simulation loading

A multi-variable regression analysis is made of crack propagation data under flight simulation loading for the 2024-T3 and 7075-T6 alloys. The study is made using an effective stress range concept based on cracl closure considerations. A two-variable regression model of the equivalent stress range is suggested. The model is used to calculate fatigue crack propagation lives. Predictions using the proposed model are compared with empirical results. It is shown that the model accounts for the influence of maximum, minimum and mean stress levels of the load spectrum.