EFFECT OF WAVY GRAIN BOUNDARY ON CREEP FRACTURE BEHAVIOUR IN ASTROLOY ALLOY

By comparing the measurement and the prediction of the creep crack initiation life at the sharp notch root, it is demonstrated that the creep J~*-integral is the effective parameter controlling the asymptotic field at the tip of the notch (and so the crack). Accordingly, a combined analysis on the linear damage model and the HRR singularity is carried out and an expression for the creep crack growth rate is derived as:da/dt=Ba k/n+1 D(x_0)J~* kn/n+1which is in good agreement with the experimental results of material with smooth and wavy grain boundaries. A microscopic mechanism of the creep damage in the material with the wavy grain boundaries has been discussed from the view point of the cavity formation along the grain boundary.