Life prediction of aerospace structures by combined XFEM and advanced fatigue models

An advanced fatigue life prediction for aerospace structures is developed by integration of an extended finite element method (XFEM) for mesh independent crack modeling with a small-scale fatigue model for stress ratio dependent and variable amplitude loading. Different from a traditional cycle-based fatigue analysis approach, the small scale model is implemented based on the incremental crack growth at any time instant during a cycle. The stress ratio effects are included using the forward and reverse plastic zone interaction. The concept of the reversed plastic zone is applied to determine the lower integration limit in a single load cycle. Given an arbitrary fatigue crack growth increment determined from the small scale model, a fast matching and narrow band technique is implemented to provide an efficient way to track a curvilinear crack growth without remeshing. Different from the existing post-fatigue analysis approach, the fatigue life is computed concurrently with the crack growth driving force along its front. A comparative study between the small time scale model and the two-parameter was performed for crack growth and life prediction at various stress ratios. Both the validity and computational efficiency of the developed advanced fatigue life prediction tool were demonstrated via its application to compact specimens.