Dynamic Fracture Toughness of Ceramics

Abstract

The dynamic fracture toughness of ceramics was evaluated by the strain gage method over a wide range of loading rates with using testing machines conventional Instron-type and newly developed drop-weight type. The validity of the method was demonstrated by the 2-dimensional dynamic finite element method. Six kinds of ceramics were tested: fine and coarse grained alumina, tetragonal zirconia polycrystal (TZP), silicon nitride, silicon carbide and sialon. All the specimens were precracked before testing by the bridge indentation method. The fracture toughness of alumina and TZP increased with increasing loading rate, while that of others remained almost constant. For alumina, the increased toughness has been explained by microcracking and branching near the precrack tip. In TZP, on the other hand, both slow crack growth and transformation to monoclinic phase contributed to the increased toughness.