1989 年 38 巻 426 号 p. 261-267
Fracture toughness of sintered silicon nitride was evaluated at room temperature, 1000 and 1200°C using the technique of single edge precracked beam method or bridge indentation method. It was observed that the geometry of precrack developed from five Vicker's indents satisfied the requirements of the standard test method for plane strain fracture toughness of metallic materials (ASTM E 399-83). The scatter of the fracture toughness obtained by this testing method was small compared with that of tensile strength for the same material in the temperature range from room temperature to 1200°C, and the Weibull shape parameter was in the range from 21.09 to 60.72. The mean value of fracture toughness obtained at 1000°C was nearly equal to that obtained at room temperature, and the value decreased when the temperature exceeded 1000°C. Furthermore, a slow crack growth was observed at the precrack front on the fracture surfaces at 1000 and 1200°C.