High-temperature crack growth in 304 stainless steel under mixed-mode loading conditions

High-temperature crack growth experiments have been conducted with 304 stainless steel specimens under mode I, mode II, and mixed-mode conditions. Crack growth rate and direction data for three different mixed-mode loadings have been analyzed to investigate the factors that control crack growth under mixed-mode conditions. The value of C* was calculated for mode mixities ranging from pure tensile to pure shear loading at the crack tip using a reference stress approach. Effective values of C* based on a damage mechanics approach were then calculated in an attempt to determine the multiaxial stress parameter that most accurately characterizes the stresses driving crack tip damage. The hydrostatic stress was found to be the stress parameter that best correlates the crack growth rate data for mode I, mode II, and mixed-mode loading conditions. The angle of growth for the mode I and mixed-mode conditions appears to be governed by both the maximum principal stress and the hydrostatic stress. However, the lack of tensile loads for mode II loading results in crack growth that is nearly collinear with the notch corresponding to the position of the maximum effective stress. Overall, the present results indicate that the hydrostatic stress is the most valid multiaxial stress parameter for predicting high-temperature crack growth in the present material under mixed-mode conditions.