Evaluation of the Local Fracture Toughness of Toughened Ceramic Composites Based on In-situ Observation of Microscoic Crack Extension

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The influence of elastic msmatch or thermal expansion mismatch between dispersed particle and matrix on fracture toughness of toughened ceramic composites was formulated by the equivalent inclusion method.This theory was verified with experimental results of particle-dispersed polycrystalline mullite. Microscopic crack extension in polycrystalline alumina was in-situ observed with secondary electron microscope equipped with bending test fixture. It indicated that the microscopic crack extenson was explained with markov process. Byconsidering the relation-ship between fracture toughness and fraction of transgranular fracture, the local fracture toughnesses ( fracture toughness for transgranular fracture and that for intergranular fracture ) of particle-dispersed polycrystalline magnesia were quantitatively evaluated.