常圧焼結窒化ケイ素の平滑材および切欠材の1000℃での静的疲労強度

抄録

The static fatigue strength of both smooth and notched bars of sintered Si₃N₄ was investigated experimentally under four-point bending at 1000°C. The static fatigue strength of the notched bars was greater than that of the smooth bars when they were evaluated for the maximum elastic stress value. It was shown that the static fatigue strength of the notched bars can be estimated from that of the smooth bars by the combined theories of the Weibull distribution of the strength and slow-crack-growth (SCG). But it should be noted that the results obtained by the theory are very sensitive to the material constants. The observations of fracture surfaces revealed that there is a very rough region in the fracture surface, which is thought to be formed by SCG accompanying creep deformation and crack initiations at grain boundaries, and is a characteristic feature in the static fatigue failure at high temperature.