Push Pull Cyclic Fatigue Test of Sintered Silicon Nitride Ceramics at Elevated Temperatures.

Abstract

A specimen gripping device was newly developed for accurate evaluation of the axial cyclic fatigue strength of ceramics at elevated temperatures. The push-pull fatigue tests were successfully performed for the sintered silicon nitride ceramics in the temperature range from room temperature to 1200°C, using the closed-loop-type electrohydraulic test system equipped with this device. The cyclic fatigue strength decreased at 1000°C, compared with that at room temperature. Meanwhile, this showed a tendency to increase as test temperature rises from 1000°C to 1200°C through 1100°C in the long life range. As a result, the slope of a S-N curve decreased with increase in test temperature. The cyclic fatigue test increasing stress amplitude stepwise under stress ratio R=-1.0 at 1100°C and 1200°C, in which the stress level in the first step was below fatigue limit, raised fatigue strength far over the static tensile strength. Almost the same result was obtained from the fatigue test increasing mean stress at the fixed stress amplitude at 1200°C.