w. Xiaojun et al. Composites Science and Technology 66(2006)993-1000 雨Hahw05h 200pm 200m R的10h 200um 200um 时啊25h50h Fig. 5. Microcracks evolution far from the notch of 2D-C/SiC tensile creep along time at 1500C and 95 MPa in vacuum. that, in both situations-on top surface of the specimen locates at the root of the notches. The stress value at the and on the lateral side of the specimen, there are obvi- area far from notch is only 71.1 MPa. According to the sta ously more micro-cracks at 1500C than at 1300C tistical results of micro-cracks by SEM, the growth rate of micro-cracks during creep process is 3.3. The stress redistribution during creep process ANSYS Software was used to simulate initial longitudi- where u is the micro-cracks growth rate, s stands for quan nal stress distribution of notched specimen. Fig. ll shows tity of micro-cracks, t for creeping time. At 1500C and stress distribution immediately after loading, before creep 95 MPa, micro-crack growth rates at the area far from strain accumulated. Because of the existence of notches, notches and near the notches(observed areas are equal the initial stress level near the notches is higher than that have been calculated by Eq(1), and the results have been far from the notches and the maximum stress(132. 8 MPa) gathered in Table 1, where Di is micro-crack growth rate forthat, in both situations-on top surface of the specimen and on the lateral side of the specimen, there are obvi￾ously more micro-cracks at 1500 C than at 1300 C. 3.3. The stress redistribution during creep process ANSYS software was used to simulate initial longitudi￾nal stress distribution of notched specimen. Fig. 11 shows stress distribution immediately after loading, before creep strain accumulated. Because of the existence of notches, the initial stress level near the notches is higher than that far from the notches and the maximum stress (132.8 MPa) locates at the root of the notches. The stress value at the area far from notch is only 71.1 MPa. According to the sta￾tistical results of micro-cracks by SEM, the growth rate of micro-cracks during creep process is v ¼ Ds=Dt; ð1Þ where v is the micro-cracks growth rate, s stands for quan￾tity of micro-cracks, t for creeping time. At 1500 C and 95 MPa, micro-crack growth rates at the area far from notches and near the notches (observed areas are equal) have been calculated by Eq. (1), and the results have been gathered in Table 1, where v1 is micro-crack growth rate for Fig. 5. Microcracks evolution far from the notch of 2D-C/SiC tensile creep along time at 1500 C and 95 MPa in vacuum. 996 W. Xiaojun et al. / Composites Science and Technology 66 (2006) 993–1000