セラミックスの室温・高温曲げ強度特性と破壊起点形態の関係

抄録

Four-point bending tests were conducted on smooth and Vickers indentation notched specimens of Al₂O₃ and Si₃N₄ ceramics at room and elevated temperatures. The effects of surface polishing and grinding on the flexural strength of the smooth specimens of Al₂O₃ ceramics were studied at room temperature at first. And the detailed observation of fracture surface of the smooth specimens by a scanning electron microscope was carried out in order to specify the defect morphology as the fracture site and to study the relation between defect size and flexural strength at room and elevated temperatures. The fracture toughness evaluation by the indentation strength (IS) method was also studied on two kinds of ceramics at room and elevated temperatures for the Vickers indentation notched specimens under different load conditions. Then, by introducing the assumed equivalent crack length, the general evaluation of the relation between strength and crack size (defect size) for the smooth and notched specimens of two kind of ceramics were tried at room and elevated temperatures under the conditions of this study.