A comparison of failure predictions by strength and fracture mechanics techniques

Predictions of lifetime under load were made for five ceramic materials using strength and fracture mechanics techniques. The double-torsion technique was used to obtain fracture mechanics data, while the stressing-rate technique was used to obtain strength data. An error analysis based on the error propagation law was performed to determine confidence limits for the failure predictions. Agreement of lifetime predictions by the stressing-rate and fracture mechanics techniques were obtained for only two of the materials. The implications of these results with regard to microstructural effects on crack propagation and design applications are discussed.