A general model of fatigue crack growth under variable amplitude loading

Abstract

A general model of fatigue crack growth (FCG) in ductile alloys under variable amplitude loading is proposed based on the passivation-lancet theory and the crack closure concept. The model can capture the interactions of single cycle overloading and underloading, sequential loading and spectrum loading effectively. Moreover, the retardation effect due to overloads and the acceleration effect due to underloading can be described quantitatively by a transition function of crack opening stress. The fatigue test data in 2024-T351, 2024-T3 and 7075-T6 aluminum alloys under different types of variable amplitude loading and spectrum loading are used to validate the general model and the predictions by the general model are in good agreement with the test data. Furthermore, the predictions are also compared with the existing models, including FASTRAN, AFGROW and the state-space model, and the comparison results show that the general model predicts the FCG process more accurately.