Monte Carlo simulation of creep failure in a 0°/90° plain weave SiC/SiC composite lamina

A Monte Carlo model of the effects of fiber creep in a 0°/90° plain weave ceramic-grade Nicalon reinforced SiC composite has been developed. Creep degradation of fibers was predicted to result in stress dependent premature failure of woven ceramic matrix composites, and that premature failure was modeled using a power-law. A power-law exponent of 3.1 ± 0.1 was predicted. The power-law exponent was predicted to be independent of initial crack size for crack length to specimen width ratios of 0.02, 0.10, 0.25, and 0.50. The power-law exponent was also predicted to be independent of the matrix to fiber strength ratio for ratios from 0.25 to 1.0. Premature failure in the 90° (transverse) tows resulted in premature failure of the composite for low values of the matrix to fiber strength ratio (less than 0.75), and decreased creep life was predicted for decreased matrix to fiber strength ratio. For a matrix to fiber strength ratio of 1.0, the creep life of the woven composite was predicted to be equivalent to a unidirectional composite. At small initial crack lengths, a 10% improvement in the creep life was predicted for a reduction in the matrix to fiber strength ratio from 1.0 to 0.75. This improvement was related to the formation of microcracks in the 90° tows and shielding of the macrocrack tip from accelerated creep damage. This improvement in the predicted creep life at a matrix to fiber strength ratio of 0.75 was predicted to be independent of applied stress. However, improvement of the creep life was not predicted to occur for larger values of initial crack length.