13th International Conference on Fracture June 16–21, 2013, Beijing, China In order to push the lines of remeshing based techniques, a new algorithm as been developed. Our approach is mostly based on a fast and efficient crack insertion algorithm. The robustness and quickness of this method is obtained by the way the cracked mesh is represented (linked to element mesh size near the surface of discontinuity). In fact, each volumetric element of the initial mesh that crosses the crack surface is cut. An important assumption is that the generated surface can be approximated by the polygonals built on the input element edges intersection points. Some special treatments are also performed on element faces to carry out the crack front intersection and some topological difficulties that could arise for highly curved cracks. This resulting mesh is finally rebuilt using an adaptive remeshing strategy in order to eliminate bad quality elements and provide a suitable discretization for accurate finite element solution and stress intensity factors computation. The next section is related to the description of the crack insertion algorithm that builds a refined mesh closely to the crack front. The third section presents two numerical assessments (a validation problem and a complex crack growth simulation) computed using the software Z-Cracks (within all the herein presented algorithms have been implemented). Finally some conclusion and prospects to this work will be presented. 2. Crack insertion algorithm Usually, industrial component model for structural integrity analysis are described using constitutive solid geometry (CSG) and efficient automatic meshers are able to deliver correct input for standard finite element solvers. Thus, when cracked structure is concerned, it is necessary to be able to introduce an initial crack geometry in the corresponding model. The current approach is based on the modification of an initial uncracked finite element mesh, that will be modified due to the presence of the crack and refined in the front vicinity. For a 3D discrete problem, such an algorithm can be separated in five main stages: generating an accurate initial crack geometry. applying an adaptive refinement operation of the initial structure volumetric mesh. performing the “cutting” operation that builds a boundary mesh which contains the crack. performing an adaptive refinement operation on the cracked mesh for accurate finite element solution computation. boundary regeneration to separate the crack lips. The first stage is related to the design of a suitable geometry that represents the surface of the crack itself. Such geometry must be discretized and represented by a surface mesh made of linear triangular elements. Such elements must be small enough to represent with a good accuracy the initial crack surface geometry. The most common case is a penny shape initial crack. In this case a radial mesh is performed using a prescribe number of sectors (usually about 64, possibly more for higher values of maximal/minimal radius ratio for elliptic shapes). Then an adaptive remeshing process is always run: using the Yams surface remeshing software from Distene/Inria, the element size is reduced to a minimal prescribed value on the boundary of the surface (that corresponds to the crack front) and the edges element size is adapted where important local curvature has been observed, while the mesh quality is optimized. -2-
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