Comparison of methods to determine the fracture toughness of three glass-ceramics at elevated temperatures

Two standardized methods for measuring K-Ic in ceramics are compared for us e at high temperatures (precracked beam and surface crack in flexure). Resu lts from a third technique involving the measurement of cracks around Vicke rs indentations are also presented. Three dental glass-ceramics, differing primarily in microstructure, were used as model materials in this study, Th ey emphasized the importance of microstructure in determining high-temperat ure K-Ic values and the challenges in measuring them. The measured fracture toughnesses decreased with temperature and increased with imbedded grain s ize for all three methods.