Small time scale fatigue crack growth analysis

A new fatigue crack growth formulation at the small time scale is proposed in this paper. This method is fundamentally different from the classical reversal-based fatigue analysis and is based on the incremental crack growth at any time instant within a cycle. It can be used for fatigue analysis at various time and length scales and is very convenient for the fatigue analysis under random variable-amplitude loadings without cycle-counting. Stress ratio effect is intrinsically considered in the proposed fatigue model since the stress state is directly used instead of using the cyclic stress range. In the proposed methodology, the reverse 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 both constant amplitude and variable-amplitude loadings. Statistical error analysis is used to compare the proposed model with existing fatigue crack growth codes. Generally, very good correlations are observed between model predictions and experimental observations.