Evaluation of fracture toughness for ceramics by chevron-notched compact specimen. Optimum shape design and application to elevated temperature test.

Fracture toughness tests conducted for hot-pressed silicon nitride, Si3N4, using chevron-notched compact specimens, with special attention paid to the fracture resistance curve (R-curve). Using the results at room temperature, optimum shape design was attemped for the simple fracture toughness test. Then, the validity of the specimens determined was confirmed at elevated temperatures (≤1160°C). The results obtained are summarized as follows. (1) The deeply chevron-notched specimen is judged to be the optimum shape from the view point of accuracy as well as of the simplicity of the test. (2) The resistance to stable crack growth is described as KR=KIC. (3) Within the temperature range tested, the fracture toughness, KIC, and the fracture resistance, KR, remain unchanged.