13th International Conference on Fracture June 16–21, 2013, Beijing, China -6- corresponding to strain about 0.005 in Fig. 8 of the grey curve, higher than the failure stress of the composites, which indicates the limitation of the elastic model. So the damage models are introduced to the constituents of the C/SiC, and the corresponding stress-strain curve compared with no damage model is shown in Fig .8. The detailed damage process of the three constituents are shown in subsequent sections. Figure 8. The stress-strain curve 4.3. The matrix damage evolution The brittle cracking was introduced to matrix for its brittleness in fracture process. Fig. 9 shows the damage initiation and propagation process of the matrix in terms of STATUS, which represents the state of the element (1.0 means the element is active, shown in white; and 0.0 means the element is inactive, shown in black). It is found that the damage first occurs at the thinnest region close to the yarns in loading directions as predicted in the elastic model. In the upper(Y+) matrix, the damage initiates at the edge center of the RVE, while in the lower(Y-) matrix, it initiates at the center of the RVE. Then, the damage propagates in Z direction, vertical to loading. And the damage first runs through the Z direction in the lower matrix at the strain of 2200, while it happens to the upper matrix at the strain of 2600. The damage has already run through the cross section of the RVE at the strain of 2600. 800 900 1100 2200 2600 3500 10000 Figure 9. The damage process of the matrix 4.4. The fiber damage evolution The simulation of fiber damage was introduced by VUMAT in Abaqus, which aims at investigating the possible damage process of fiber bundle damage. Fig. 10 shows the damage initiation and propagation process of the matrix in terms of STATUS. It is found that the damage first occurs at the weaving center of the yarns in loading directions as predicted in the elastic model. Then, the damage propagates in Z direction, vertical to loading. And the damage first runs through the Z direction in longitudinal yarns at the strain of 5800, while it happens to the center yarns in
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