1990 年 98 巻 1133 号 p. 98-103
AE parameters of β″-Al2O3 were measured during four point bending tests. Scanning electron micrographs of fractured surfaces revealed that fracture origins were divided into two classes: coarse grains and pores. Some cleavage steps were observed in the fractured coarse grains. Some micro-cracks, on the other hand, were observed around the fractured pores. AE behavior was classified into two different classes, which corresponded to different fracture origins. The KIC values were calculated from the sizes of the fracture origin of samples. Coarse-grain-originated fractures were well predicted by the linear fracture mechanics formula using KIC=1.7MPa√m, but no appropriate formula for pore-originated fractures were available. From the above results, it can be concluded that the fracture mechanisms of β″-Al2O3 differ according to the type of the defect. In coarse-grain-originated fracture, transgranular fracture occurred first, and then the final unstable fracture occurred at σc, while in pore-originated fracture, the “process zone” was made around a pore, and then the final unstable fracture occurred when micro-cracks grew up to the critical crack length.