606 Beneficial Effect of Compressive Loading on Fatigue Strength of Silicon Nitride Ceramics at High Temperature

概要

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Silicon nitride ceramic is one of the most useful materials for high temperature mechanical structure. Therefore, an improvement of fatigue properties of silicon nitride ceramics is very important in a point of engineering view. In this study, fatigue crack propagation behavior of silicon nitride ceramics at high temperature was observed and crack opening behavior was also analyzed by using the digital image correlation method (DICM). It was found that the fatigue strength under a negative stress ratio, R<0,had a significantly higher value than that under zero and/or positive stress ratio. From the results of the DICM analysis, the crack tip opening displacement under R<0 was found to be smaller than that under R=0. These results imply that the stress shielding effect in silicon nitride ceramics was enhanced by the compressive loading, and this beneficial effect might strongly affected the improvement of the high temperature fatigue strength
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