High temperature creep damage under biaxial loading: INCO 718 and 316 (17-12 SPH) steels

The respective influences of the Von-Mises equivalent stress and of the maximum principal stress on high temperature creep damage of two industrial alloys (Inconel 718 and 17-12 SPH stainless steel) are pointed out in a quantitative way through tensile-torsion biaxial tests. Through inversions of the shear component, the important part taken by the principal direction corresponding to the maximum principal stress is also shown. These results are supported by metallographic observations. Then, an anisotropic form of the damage variable D taking into account the experimental observations is proposed. (orig.)