Bending fatigue tests of sintered silicon nitride at room temperature.

Abstract

For strength design of ceramic parts, static bending fatigue tests, namely delayed failure tests, and cyclic bending fatigue tests were carried out at room temperature on smooth specimens, hourglass type specimens and notched specimens of sintered Si3N4. (1) Cyclic bending fatigue strength (maximum stress) at stress ratio R=-1 is lower than static bending fatigue strength. It is considered that this is due to the effect of cyclic stress rather than the effect of compressive stress in alternating stress and the difference of effective volume. (2) Both static bending strength and rotating bending fatigue strength of a notched specimen reduced almost at the rate of a stress concentration factor. (3) In case of cyclic fatigue, the mark made by rubbing against each other was observed on the fracture surface of some specimens.