Aspects of cyclic fatigue-crack propagation in monolithic and composite ceramics are described, with emphasis on the role of cyclic loading in degrading toughening, or crack-tip shielding, mechanisms in the crack wake. Specific example is given for grain-bridging ceramics, such as Al2O3, Si3N4, where fatigue cracks are modeled to proceed by a degradation of such bridging through progressive wear of sliding grain/matrix interfaces. It is concluded that cyclic fatigue in ceramics is conceptually distinct from metal fatigue and is driven primarily by such a cycle-dependent suppression of shielding.
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