Small time scale fatigue crack growth analysis under variable amplitude loading

In this paper, a previously developed fatigue crack growth model at the small time scale is modified and validated under f variable amplitude loading. This method is based on the incremental crack growth at any time instant during a cycle and can be used for fatigue analysis at various time and length scales. It does not require cycle counting and is very convenient for the fatigue analysis under random variable amplitude loading without cycle-counting. In the proposed methodology, the reversed plastic zone concept is adopted to determine the lower integration limit during the time integral for crack length calculation. Model validation is performed using extensive experimental observations for various metallic materials under different types of variable amplitude loading. Statistical error analysis is used to compare the proposed model with existing fatigue crack growth codes. Very good agreements are observed between model predictions and experimental observations. Predictions of the proposed model are compared with those of the FASTRAN and AFGROW codes and the error analysis for the predictions indicates the small scale model has an overall better accuracy in the current investigation.