Abstract
It is important to predict the S-N curves of ceramics under cyclic loading in their application to machine components. In order to study the cyclic fatigue characteristics of ceramics, the cyclic fatigue tests under 3-point bending were carried out at room temperature in air on the smooth specimens of sintered silicon nitride, partially stabilized zirconia and alumina as well as the precracked specimens of sintered silicon nitride with surface cracks introduced by Vickers hardness indentation. The effect of specimen geometry on the fatigue-life was also investigated by conducting ring compression tests under cyclic loading on the silicon nitride specimens at room temperature in air.
The effect of specimen geometry on the fatigue-life was found to be small for the endurance limit at 107 stress-cycles of the case investigated in this study. A large scatter was observed in the fatigue-life of the smooth specimens as compared with that of the pre-cracked specimens. The scatter in the fatigue-life on the smooth specimens may be explained from the scatter of the inherent flaw size in the specimens.
From the slow crack growth rate determined on the pre-cracked specimens, the S-N curves for the smooth specimens with different sizes of initial cracks were predicted. Furthermore, the S-N curves for the smooth specimens of the tested materials were predicted on the assumption that the distribution of flaw size of the specimens used for the fatigue tests were equal to that of the specimens for the static fracture tests.
