13th International Conference on Fracture June 16–21, 2013, Beijing, China -5- isotropic bulk has a Young’s modulus E = 315 GPa and Poisson’s coefficient = 0.24, its isotropic coefficient of thermal expansion is taken as = (21 + 2) 3. In all cases, the polycrystal consists in a 8 × 8 grains with a grain diameter G = 0.8 m. Two types of loading can be considered, a thermal and mechanical one. Firstly, we do not account to the initial thermal stresses originating during the cooling after sintering. We apply an instantaneous load in terms of KI which is kept constant in time. The load is relaxed by intergranular failure. We consider a threshold stress n 0 = 400 MPa corresponding to 4% of the athermal stress c. In Fig. 5a, we have reported the distribution of the stress component yy for various stages of the crack advance. The crack tip can be identified as the region with the highest stress concentration. We report the crack velocity for different load levels in Fig. 5b, that are compared with the experimental data of SCG in polycrystals for sintered Yttrium Stabilized Zirconia conducted by Chevalier et al. [7], for comparable grain sizes. We also report the curve V-KI corresponding to the calibration of the cohesive zone for the zirconia single crystal. We observe that the predicted V-KI curve is shifted toward larger load values for the polycrystal compared to the case of a single crystal. The slope of the V-KI curve is comparable to the experimental data, but the predicted kinetics of SCG by simulation are faster than the experimental one. This difference may originate from 2D configuration in our simulation that promotes the crack advance in comparison with 3D configuration. Also, the initial thermal stress state is not considered here. Therefore, we now investigate their effect on SCG. Figure 4. Small scale damage configuration used for the analysis of SCG in a 2D polycrystal
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