HIGH-TEMPERATURE DEGRADATION OF STRUCTURAL COMPOSITES

Ceramic matrix composites are being developed to improve the toughness of ceramics in structural applications. Modest success has been experienced in manufacturing ceramic matrix composites for which it is possible to double the room temperature toughness while still retaining the high strength of the untoughened material. As many of these new composites are expected to be used at high temperatures, their mechanical behavior at both high and low temperature must be characterized. In this paper, creep and creep rupture of both particulate and whisker reinforced ceramic matrix composites are discussed. Principal findings of experimental investigations on these materials indicate: (1) resistance to creep deformation is greater in compression than in tension; (2) the creep rupture lifetime follows a Monkman-Grant behavior in which the lifetime can be expressed as a power function of the steady state creep rate; (3) the principal mechanism of failure in creep is interfacial cavitation. Cavities nucleate at interfaces and then grow into full facet cavities. Failure occurs either by the growth or the linkage of these cavities to form critical size cracks in the composite.