1996 Volume 45 Issue 6Appendix Pages 123-130
The purpose of this study is to evaluate the lifetime distribution of ceramic fibers by a time-dependent Weibull function, from the viewpoint of materials reliability engineering. Static loading tests and constant loading rate tests of a boron fiber, one of representative ceramic fibers, were carried out in air at 300°C, and the relevant Weibull parameters were estimated from the lifetime and the strength data obtained in the above tests. The results showed that the fibers fractured in a moment or a long-term period in the static loading tests, and the lifetime distributions predicted from the single time-dependent Weibull function were not in good agreement with the long-term lifetime data. The SEM observation for the fracture surfaces indicated that the cause of the long-term rupture was due to a creep damage, and completely different from that of the momentary fracture. Therefore, a mixed time-dependent Weibull function based on a mixed distribution model was proposed for evaluating again the lifetime data. It was clarified that, finally, the function proposed here was enough applicable for predicting the creep-rupture lifetime distribution of boron fibers.
