Process zone size fracture criterion for ceramics.

Abstract

Ceramics are typically brittle materials. However, fracture toughness of ceramics is variable with flaw size and also notch root radius. Generally, a process zone is formed ahead of the crack or notch tip. Numerous microcracks or phase transformations are formed in the process zone. The following are the main results obtained in this paper. Formation stress of process zone is equal to fracture stress or static fatigue limit stress of plain specimen. A new failure criterion based on process zone size is proposed. Based on the process zone size failure criterion, calculated failure stress as a function of crack size or notch root radius shows a very good agreement with experimented failure stress. Calculated process zone size is about 5 times the average grain diameter.