A comparative study between a small time scale model and the two driving force model for fatigue analysis

A comparative study is performed to demonstrate the difference and similarity between the two driving force approach and a small time scale model under both constant and variable amplitude loading. The small time scale model is different from most existing fatigue analysis methodologies and is based on the instantaneous crack growth kinetics within one cycle. The two driving force approach is cycle-based and uses two driving force parameters to describe crack growth rate per cycle under constant amplitude loadings. A simple modified two driving force approach is proposed based on the concept of forward and reverse plastic zone interaction and is used to calculate the fatigue crack growth under general variable amplitude loadings. Extensive experimental data for various metallic materials are used to validate the two driving force model and the small time scale model.