Cyclic fatigue degradation is contemplated in polycrystalline ceramics exhibiting grain bridging as the principle toughening mechanism. A frictional-wear mechanism based on repetitive sliding wear degradation of frictional grain bridges is discussed. A micromechanical model is developed which provides an insight into the effects of salient mechanical and microstructural variables such as wear rate at the grain/matrix interface and initial residual stress of bridging grains, on fatigue-crack growth behavior. Results of the analysis are compared to experimentally observed fatigue-crack growth rates in coarse grained alumina and silicon nitride.

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