Fatigue and creep fracture properties of plane-woven SiC/SiC composites at room temperature and 1473K

摘要

Fatigue tests of plane-woven SiC/SiC composites, which had carbon layer as the interphase on the surface of the fiber, were carried out at room temperature in air and at 1 473K in vacuum and also creep tests at 1 473K in vacuum. At room temperature, the S-N relation was almost flat and the level was slightly lower than the static strength, showing the fracture mechanism was similar to that of static fracture. On the other hand, at 1473K, fracture behavior was mainly caused by time-dependent creep mechanism. The fracture surface showed that debonding occurred between matrix and carbon interphase in the case of static tests at room temperature. On the other hand, in the cases of static, creep and creep fatigue tests at 1473K, debonding occurred between fiber and carbon interphase because of creep deformation of fiber. Delamination was also dominant for all cases. The length of delamination and debonding was longer in creep fatigue test at 1473K than in fatigue test at room temperature and creep test at 1473K because of reduction in sliding resistance of interface caused by cyclic loading. Thus, stress concentration caused by breakage of fiber and matrix was weaker in creep fatigue test than in creep test. The relation between the test time and the creep strain in creep tests could be evaluated quantitatively using the stress power law.