Abstract
Microfracture processes of microcracking and crack propagation are simulated along with fracture strengths for 2-dimensional alumina polycrystals which have thermal anisotropy within a grain. Microcracks are generated by thermally induced residual stresses at a grain boundary. The stress concentration near the microcrack is calculated numerically by the body force method, and superposed on the preexisting residual stress. Stress intensity factors at the microcrack tip are also obtained by the method, and the location at which the next microfracture occurs is determined by the competition between microcracking and crack propagation in the new stress state. The microfracture stress increases with the progress of the fracture and decreases after maximum indicating a fracture strength. In many cases, the propagation of microcracks induces an unstable fracture. With decreasing grain size and increasing grain boundary toughness, the number of microfractures prior to the unstable state decreases, while the fracture strengths increase. For alumina of grain size 17.5 μm, when the fracture toughness of the grain boundary is 0.6 times that of the grain or greater, unstable fracture occurs prior to stable microcracking.
