Effects of crack tip blunting and residual stress on a warm pre-stressed crack specimen

Warm pre-stressing is a frequently used procedure for improving the load bearing capacity of cracked specimens through applying a preload in a temperature higher than the service temperature. Preloading a cracked specimen in upper shelf zone can produce a region of compressive residual stress around the crack tip. It can also blunt the crack tip after unloading. The crack tip blunting and the residual stress are two major mechanisms suggested for justifying the improvement in load bearing capacity of cracked specimens. In this paper finite element analysis and some theoretical models are used to study the effects of these two mechanisms. It is shown that both crack tip blunting and residual stress contribute in warm pre-stressing effects but it is the level of preload that determines which mechanism is more influential in the warm pre-stressing procedure.