Creep Crack Growth under Non-Steady-State Conditions

The problem of characterizing crack growth under small scale creep and transition conditions is of great practical significance. This paper defines a crack tip parameter C_t for characterizing creep crack growth behavior under wide range creep conditions from small scale creep to steady-state creep. Under steady-state creep conditions, C_t is shown to reduce to the familiar C∗-integral. The physical basis for the C_t parameter is also provided. Wide range creep crack growth data on A470 Class 8 steel using two specimen geometries were obtained and correlated with the C_t parameter in the temperature regime of 482 to 538°C. The levels of creep deformation in the various specimens tested to obtain the crack growth rate data ranged from small scale creep to essentially steady-state creep conditions.