13th International Conference on Fracture June 16–21, 2013, Beijing, China -6- bottom one. Both matrix and fibers are assumed homogeneous and isotropic. Figure 7 (a) illustrates the axisymmetric model of cylinder RVE, and the mark numbers of selected nodes are shown in meshed model in Figure 7(b). (a) (b) Figure 7 (a) Axisymmetrical model (b) Selected node numbers The ablation morphology of C/C composites is determined by the temperature when the oxidation is adequate. As shown in Figure 8, it was indicated that the carbon fiber presented a cone head, and the carbon fibers took the shape of needles after ablation processes. The total ablation time was about 50 seconds. In the ablation process, the temperature of the material came to balance in 40s. The results indicate that the ablation morphology of C/C takes the shape of typically “needle clusters” due to the mismatch of the thermal property of the carbon fibers and matrixes. The analysis result is consistent with experimental results in Ref.9. Figure 9 illustrates that the temperature gradient of material surface exposed to the external environment changes greatly, which will increase the incidence of material surface damage. t=1s t=2s t=3s t=5s t=10s t=15s
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