Damage mechanics approach for predicting high-temperature crack growth under mixed-mode loading conditions

Recent studies of the factors that control high-temperature crack growth under mixed-mode loading conditions are reviewed. In particular, measurements of crack growth direction and crack growth rate in specially designed specimens under mode I, mode II and mixed-mode loading conditions are discussed. Attempts have been made with the aid of finite element results to determine how both the crack path and the crack growth rate are influenced by the nature of loading. Discrepancies as to the ability of the von Mises equivalent stress in correlating the experimental data have been observed. A damage mechanics approach is proposed that brings mixed-mode crack growth data into better agreement when plotted against an effective value of C∗. This approach is also shown to correlate mixed-mode stress field calculations with reported observations of crack growth direction. The results demonstrate the importance of addressing damage mechanics ahead of the crack tip for accurate predictions of high-temperature crack growth under mixed-mode loading conditions.