Y. Miyashita et al. /International Journal of Fatigue 24(2002)241-248 8m图 Number of cycles×10 Fig.8. Observation of fracture surface for the specimen of standard 5 90 SiC/SiC with frequency of 1 Hz at room temperature. 8 100000 200000 Number of cycles Fig 10. Relationship between MOR reduction, total crack length and number of cycles: (a) Type 1;(b) Type 2. 00 ig. 12 shows the MOR reduction at the point of specimen failure, the final MOR and the fracture stress The MOR reduction is calculated as the (final MOR/maximum MOR X100. As shown in Fig. 10, the MOR has a complicated dependence on the number of loading cycles. However, at failure the value of the MOR is reduced to about 85% of the maximum mOR. The MOR reduction merits further consideration as a para- meter for estimating fatigue damage of SiC/SiC com- 5. Conclusions (a)An SEM in-situ observation of fatigue damage Observation of fracture surface for the sp process in SiC/SiC composites was carried out at room with frequency of 10 Hz at 800oC. temperature and at 800C. Single edge V-notched speci- mens were used, and fatigue cracks initiated not only atY. Miyashita et al. / International Journal of Fatigue 24 (2002) 241–248 247 Fig. 8. Observation of fracture surface for the specimen of standard SiC/SiC with frequency of 1 Hz at room temperature. Fig. 9. Observation of fracture surface for the specimen of standard SiC/SiC with frequency of 10 Hz at 800°C. Fig. 10. Relationship between MOR reduction, total crack length and number of cycles: (a) Type 1; (b) Type 2. Fig. 12 shows the MOR reduction at the point of specimen failure, the final MOR and the fracture stress. The MOR reduction is calculated as the (final MOR/maximum MOR)×100. As shown in Fig. 10, the MOR has a complicated dependence on the number of loading cycles. However, at failure the value of the MOR is reduced to about 85% of the maximum MOR. The MOR reduction merits further consideration as a para￾meter for estimating fatigue damage of SiC/SiC com￾posite materials. 5. Conclusions (a) An SEM in-situ observation of fatigue damage process in SiC/SiC composites was carried out at room temperature and at 800°C. Single edge V-notched speci￾mens were used, and fatigue cracks initiated not only at