Abstract
Crack propagation behavior in a gas pressure sintered silicon nitride was investigated under static and cyclic loading at room temperature to clarify the cycling effect. All the testing was conducted in 3-point bending for specimens with artificial flaws introduced by indentation on the center of the mirror finished tensile surfaces. Crack propagation occurred under cyclic loading with maximum applied stress below the applied stress with which crack propagation stagnated under static loading, showing clearly that crack propagation velocity under cyclic loading was higher than that under static loading. Although intergranular crack propagation with crack-bridging was observed in both cases under static and cyclic loading, crack-bridgings, that were observed after static loading, were found to be fractured by the subsequent cyclic loading. It was thought that crack shielding force by crack-bridging, which is effective for restraining crack propagation under static loading, was decreased by cyclic loading and consequently crack propagated faster under cyclic loading than under static loading.
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