Dynamic fracture toughness and microstructural fracture mechanisms in ceramics

The dynamic fracture toughness of ceramics was evaluated by the strain-gage method, the applicability of which was demonstrated by the two-dimensional dynamic finite element method. Five kinds of ceramics were tested: Al{sub 2}O{sub 3}, ZrO{sub 2} (TZP), Si{sub 3}N{sub 4}, SiC, and sialon. The fracture toughness of Al{sub 2}O{sub 3} and TZP increased with increasing loading rate, while that of the others remained almost constant. For Al{sub 2}O{sub 3}, the increased toughness was explained by microcracking and branching near the precrack tip. In TZP, on the other hand, transformation to the monoclinic phase contributed to the increased toughness. 15 refs.