Fracture toughness of SiC, Si3N4, and sialon ceramics using controlled surface flaws

Knoop and Vickers indentation cracks have frequently been used as model 'precracks' in ceramic bend specimens for fracture toughness (K-1c) determination. Indentation residual stress reduces the measured K-1c but can be removed or accounted for by grinding, annealing, or modelling. Values of K-1c are obtained for four materials using Vickers indentations and an improved stress intensity factor. Methods for residual stress removal or incorporation are compared, and the most reliable stress removal alternative is identified for each material. (C) 1996 The Institute of Materials.