Fracture toughness evaluation of mullite with respect to slow crack growth.

Abstract

Sometimes in ceramics remarkable slow crack growth appears even at room temperature and in air. The evaluation of fracture toughness in such a case is one of the most important problems for the development and practical use of ceramics.This paper deals with the case of mullite. Two kinds of mullite were tested by using the precracked and chevron-notched specimens at room temperature and in air. Especially in the chevron-notched specimens, remarkable slow crack growth was detected. The compliance method obtained from the notch mouth opening displacement gave the slow crack growth quantatively and the acoustic emission measurement indicated that qualitatively. The fracture toughness obtained from the three point bending tests was evaluated from the viewpoint of the material resistance against slow crack growth.