13th International Conference on Fracture June 16–21, 2013, Beijing, China Figure 4. Crack extension during a propagation simulation. During a crack propagation simulation, such kind of strategy will be adapted as a fewer number of operation is required. Starting from the current cracked mesh, an explicit surface will be generated as the extension of the crack front during a given time step (see figure 4). Thus, the current volumetric mesh, that is already sufficiently refined if the crack advance is small enough, will be directly cut by the crack extension surface. Then only the cleaning operations and a single adaptive remeshing step will be done, before the crack lips regeneration. 3. Numerical assessments Such a technique for cracked structure meshing has been implemented in our finite element suite ZSet [4]. A dedicated new module, Z-Cracks, that includes the meshing algorithms, an efficient stress intensity factor extraction post-processing [5,6] has been developed. This tool has been successfully applied to many complex simulations, and two examples will be herein presented: a validation of a crack growth experiment, and the numerical simulation of a very complex crack path will be presented. 3.1. Crack propagation on a biaxial notched specimen This example is based on the numerical simulation of a mixed mode crack propagation experiment done on a biaxial notched specimen. This specimen has been designed to be able to apply a controlled uniform stress field in its center. The notch is oriented with a 45° angle with the loading directions (see figure 5). Two loading phases are imposed: to initiate the crack in the direction of the notch, the same fatigue effort level is imposed on the both directions. when the crack has sufficiently advanced, the loading is changed in order to impose an approximate constant vertical stress field in the center part. The mechanical behavior is assumed to be isotropic linear elastic (E=210 000MPa as Young modulus and =0.3 as Poisson coefficient) under small deformations. -6Current crack surface Crack extension
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