Crack Propagation and Arrest Behavior in Sintered Silicon Nitride under Static Fatigue at Elevated Temperature

Abstract

Crack growth behavior from an artificial defect in sintered silicon nitride was measured under static fatigue at room and at elevated temperatures. The static fatigue strength decreased with an increase of the time and approached a constant value over 10³ to 10⁴ s, which was defined as the static fatigue limit. The static fatigue crack growth rate, which did not bear a close relation to the stress intensity factor, decreased at the first stage and increased at the second stage for the broken specimen. For the un-broken specimen, it decreased monotonically, then arrested at the second stage. This confirmed the existence of a static fatigue limit. The crack at the 1 000°C in the air was similar to the behavior in the vacuum. On the other hand, the static fatigue limit in the humid air decreased to the 70% of the short time strength. However, the static fatigue limit in the vacuum did not decrease at room temperature.