Abstract
Four-point bending tests of a gas pressure sintered silicon nitride were conducted using notched specimens with different notch shapes as well as smooth specimens of distinct sizes, and the effect of the specimen geometry on the bending strength was experimentally clarified. The mean strength in smooth specimens could be almost correlated with the effective volume, though the mean strength in notched specimens shifted toward the lower strength side compared with the relation for smooth specimens. From observation of fracture surface, no unique correlation of the strength with the effective volume was suggested to be ascribed to a difference in flaw morphology between smooth and notched specimens. To discuss the efficiency of the effective volume, a Monte Carlo simulation was also carried out by assuming the same distribution characteristics of cracks in a material. The simulated result revealed that the effect of the specimen geometry on the strength was explained by using the effective volume. The effective volume, however, was found to be inefficient because of a failure of the primitive assumption in the Weibull theory when the flaw density was extremely low in a material.
