Torsional fatigue tests of sintered silicon nitride at room temperature.

Abstract

For strength design of ceramic parts, static, static fatigue and cyclic fatigue torsional tests were carried out at room temperature on smooth specimens and notched specimens of sintered Si3N4. (1) The cyclic fatigue strength (maximum principal stress) at stress ratio R=0 was lower than the static fatigue strength. This was due to the effect of cyclic stress. The cyclic fatigue strength at stress ratio R=-1 was lower than that at R=0. This difference was almost equal to the difference in strength calculated from the effective volume. In this case, the effective volume of R=-1 is twice as much as that of R=0. (2) In the case of a gentle notch, both static torsional strength and cyclic torsional strength increased unlike in the case of static plane bending and rotating bending respectively. This can be accounted for by the difference in the effective volume.