Prediction of fatigue crack growth under real stress histories

A damage tolerance analysis methodology for cracks subjected to real loading is presented. A new retardation model, based on material hardening within the overload plastic zone, is developed for irregular stress histories. For the transformation of the irregular stress history into a stress history containing only distinguished cycles, a technique based on the rainflow counting method is used. The methodology is applied to real aircraft loading histories for the conventional 2024-T3 aluminum alloy and the advanced 8090-T8 aluminum–lithium alloy. Predictions agree well with the experimental results. Limitations of the prediction method are also discussed.