Failure analysis of high-temperature composites. Ph.D. Thesis
A micromechanics analytical model is developed for predicting the failure modes in fiber reinforced ceramic matrix composite laminates at high temperatures. The model is also modified to facilitate the study of interface debonding and/or frictional slipping in a bimaterial system. The consistent shear lag theory is used in representing the constitutive relations. The governing equations are solved satisfying the boundary conditions appropriate to the damage mode by making use of an eigenvalue technique. The failure modes are predicted based on point stress failure criterion. For composites with weak fibers but strong fiber/matrix interfaces, the crack will propagate in a self-similar mode. For those with relatively weak fiber/matrix interfaces, interface debonding and frictional slipping will occur and a secondary crack away from the original crack plane will be initiated. For strong fiber composites, the crack will propagate in the matrix at the crack tip forming fiber bridged matrix cracking, and when the interface friction is high, the bridging fibers at the crack center will break and cause a catastrophic crack extension. The difference between the thermal expansion coefficients of fibers and matrix can alter the stress distribution. Thermal stresses make the crack surfaces zigzag but remain closed. Higher matrix thermal expansion coefficient can help to lower the longitudinal stress in matrix and transverse normal stress on the fiber/matrix interfaces. Both stresses and strain energy release rate vary linearly with thermal mismatch.
- Research Organization:
- Missouri Univ., Rolla, MO (United States). Dept. of Ceramic Engineering
- OSTI ID:
- 147189
- Resource Relation:
- Other Information: TH: Ph.D. Thesis; PBD: 1993
- Country of Publication:
- United States
- Language:
- English
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