w. Xiaojun et al./ Composites Science and Technology 66(2006)993-1000 H的B0hR0.5h 200um 2h国10h 25h顺AB50h 200um 200um ig. 4. Microcracks evolution at the notch front of 2D-C/Sic tensile creep along time at 1500C and 95 MPa in vacuum. Because of the stress concentration around the notch, gitudinal fiber bundles can cause serious damage and redis racks tend to appear more in this area, especially at notch tribution of stress. root, rupture has also been observed on the longitudinal fi- By using the same counting method, the amount of mi- rs near the notch root, as shown in Fig 9(a). Similarly, cro-cracks near the notch area has been counted during there is stress concentration around the weave porosity, creep course at 95 MPa and 1300C. The statistical re- and micro-cracks were easily observed near the porosity, sults of micro-cracks vs time on the top and on the lat- as seen in Fig. 9(b). Micro-cracks generally propagate eral side of the specimen are plotted in Fig. 10, the within bundles, as shown in Fig 9(c), though some of them results of 1500C at same stress level (95 MPa)have also may expand through the fiber interface and cause fracture been presented in the same graph. Note that all the statis- of longitudinal fiber bundles, as shown in Fig 9(d). As tical curves are very similar and can all be roughly divided the longitudinal fiber bundles of 2D-C/SiC normally bear into two stages: the fast developing stage of micro-cracks the main load applied on the sample [6, the fracture of lon- and the following slow increasing stage. The difference isBecause of the stress concentration around the notch, cracks tend to appear more in this area, especially at notch root, rupture has also been observed on the longitudinal fi- bers near the notch root, as shown in Fig. 9(a). Similarly, there is stress concentration around the weave porosity, and micro-cracks were easily observed near the porosity, as seen in Fig. 9(b). Micro-cracks generally propagate within bundles, as shown in Fig. 9(c), though some of them may expand through the fiber interface and cause fracture of longitudinal fiber bundles, as shown in Fig. 9(d). As the longitudinal fiber bundles of 2D-C/SiC normally bear the main load applied on the sample [6], the fracture of lon￾gitudinal fiber bundles can cause serious damage and redis￾tribution of stress. By using the same counting method, the amount of mi￾cro-cracks near the notch area has been counted during creep course at 95 MPa and 1300 C. The statistical re￾sults of micro-cracks vs. time on the top and on the lat￾eral side of the specimen are plotted in Fig. 10, the results of 1500 C at same stress level (95 MPa) have also been presented in the same graph. Note that all the statis￾tical curves are very similar and can all be roughly divided into two stages: the fast developing stage of micro-cracks and the following slow increasing stage. The difference is Fig. 4. Microcracks evolution at the notch front of 2D-C/SiC tensile creep along time at 1500 C and 95 MPa in vacuum. W. Xiaojun et al. / Composites Science and Technology 66 (2006) 993–1000 995