EFFECT OF DEFECT SIZE AND NOTCH ROOT RADIUS ON FRACTURE STRENGTH OF ENGINEERING CERAMICS.

Abstract

The strength of sintered silicon nitride and hot-pressed silicon carbide specimens with various small defects was obtained by four-point flexural tests. The relationship between the strength and equivalent crack length a//e for surface roughness, semicircular cracks and edge notches was almost the same. The fracture toughness of specimens with large defects was higher. This means that conventional linear fracture mechanics gives unsafe estimates for components with small defects. The relationship between the ratio of the equivalent crack length and grain size, and the ratio of critical stress intensity factors for small and large defects was identical. The strength, effect of grain diameter and effect of notch root radius on fracture strength are explained by a granular fracture model.