Cyclic Fatigue of Silicon Nitrides and a Whisker-Reinforced Silicon Nitride
Cyclic stresses derived from mechanical loads or temperature changes are common in engines. Compression-tension cycling is recently found to degradate the mechanical properties of common engineering ceramic materials. In this study, the cyclic fatigue behaviour of sintered and hot-pressed silicon nitride is compared to the behaviour of SiC-whisker- reinforced silicon nitride. Alternating cyclic testing, R=−1, was done by using modified four-point bending arrangement. Cycling resulted in clear degradation of mechanical properties in all materials studied. The composite structure had different behaviour as compared to the monolithic materials showing a bimodal behaviour with little degradation at low cycle area but increased degradation at high cycle area. The results of the test are presented and the behaviour is interpreted and discussed based on the results of fractographic analysis.
Unable to display preview. Download preview PDF.