IMPROVED CRACK TIP ENRICHMENT FUNCTIONS AND INTEGRATION FOR CRACK MODELING USING THE EXTENDED FINITE ELEMENT METHOD

Abstract

This paper focuses on two improvements of the extended finite element method (X-FEM) in the context of linear fracture mechanics. Both improve the accuracy and the robustness of the X-FEM. In a first contribution, a new enrichment strategy is proposed to take into account the singular stress field at the crack tip that is meant to replace the traditional four-crack-tip enrichment functions. The efficiency of the new approach is demonstrated on mesh convergence experiments for two-dimensional straight and curved crack problems, using first- and second-order shape functions, both in terms of convergence rates and in terms of condition number of the system to solve. The second contribution revisits the problem of the numerical integration of the stiffness operator when singular functions like the tip enrichment functions are used. An original algorithm to build accurate and fast integration rules for elements in the enrichment zone, touching the crack tip singularity, or not, is presented. The effects on convergence rate of the choice of the integration rule are illustrated on numerical examples.