Prediction of Creep Crack Initiation Under Transient Stress Conditions

A method to predict the time for creep crack initiation (CCI) from a stationary crack tip is presented. The method is relevant to situations where small scale yield or widespread plasticity conditions prevail on initial loading. Initiation is considered to occur at the attainment of a critical creep strain at a small distance from the crack tip. The model proposed here considers the integrated effects of creep strain accumulation as the stress distribution changes from that on initial loading (controlled by J) to the steady state creep stress distribution (controlled by C*). Material properties are chosen to represent Type 316H stainless steel at 550°C and plane strain conditions are considered. For the conditions examined, the CCI times predicted are significantly shorter times than those predicted using a steady state creep model.