Computation of Stress Intensity Factors for 3D Cracks in a Turbine Rear Fan Blade: Comparison of FEM and XFEM Solutions

This contribution presents the results of a comparative study of two methods for the computation of stress intensity factors (SIFs) in a state-of-the-art industrial damage tolerant analysis of engine compo-nents. Two methods are investigated: • the first method involves the classical Finite Element Method (FEM). In this approach, a pa-rameterised mesh of the crack is inserted in an un-structured original mesh. The two meshes are intersected and adapted. The parameterised mesh of the crack includes a mesh of the crack plane with triangles and a regular mesh centered on the crack front of which the first layer consists of quarter-point elements (also called Barsoum elements) and the next layers consist of hexaedra. The method, called FILI (for FIssure LIbre), was developed by Snecma- site de Villaroche [1]. It very much relies on the capabilities of the meshing utilities GHS3D and YAMS for the tedious mesh adaptation operations. The FE problem is solved using Samcef (though the method is also operational with Abaqus). The SIFs are obtained after computation of the J-integral in domain form, as implemented in Samcef. • the second method involves the eXtended Finite Element Method (XFEM). In this approach, the crack is handled by way of tangent and normal level sets. The discontinuity of displacement and the stress singularity are included by way of additional degrees of freedom and dedicated shape functions. The unstructured mesh does not need to conform to the crack. Appropriate enrichment, mesh refinement (with the Simmetrix meshing library) and SIF smoothing strategies were imple-mented in order to optimize the quality of the solution. The method was made available to Samce