AE Analysis of Fracture Mechanisms of Beta-Alumina during Four Point Bending Test

Abstract

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 K_IC 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 K_IC=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.