Abstract: A general approach of curve fitting of fatigue test data and calculation of fatigue crack growth rates is developed in the preceding paper. The approach uses five points incremental cubic function to fit the fatigue test data and adopts the average weighted method to deal with the fitting results, which improves the fitting accuracy of fatigue crack length and fatigue crack growth rates significantly. Furthermore, the delta function is introduced in the average process of fitting results to account for the retardation effect due to overloads, which makes the general approach be suitable for fitting the fatigue test data under constant amplitude loading and constant amplitude loading with interval overloads and guarantees the continuity of the fitting process. Several sets of fatigue test data and predictions of the existing approach and the extended finite element method are used to demonstrate the correctness and validity of the general approach, which shows great consistency.

Key words: Curve fitting, Fatigue crack growth, Least-square principle, Overload, Piecewise curve