Influence of ground layer on proof testing effect in sintered silicon nitride

The effect of room temperature proof testing on high temperature static fatigue life was studied on sintered silicon nitride. The tests were conducted under four point bending. Two types of specimens were used; one was ground with a No. 800 diamond wheel in the longitudinal direction and the other was ground with a No. 200 in the perpendicular direction. The proof testing effect was clearly observed on the specimens ground with a No. 200 as the degradation in fatigue life arose during proof testing due to residual stress induced by grinding. On the specimens ground with a No. 800, however, the proof testing effect was not observed at all. This seems to result from the difference in fracture mechanism between fast fracture and static fatigue fracture at high temperature.