Evaluating the Conditions When Warm Pre-stressing does not Produce a Benefit in Apparent Toughness

Warm pre-stressing (WPS) is the process of subjecting a pre-cracked component to a load cycle at a temperature higher than subsequent operating temperatures. This process is widely acknowledged as being able to enhance the load to fracture, especially in ferritic steels which exhibit lower shelf cleavage fracture. Although accurate estimates of the toughness distributions can be obtained, the accuracy of WPS predictions may be limited by the sample size. It can be argued that the experiments conducted to date are devised to show that the WPS enhancement is always successful, however there are circumstances when a specimen might fail prematurely during the WPS path. Focus is drawn on predicting the number of prematurely failed specimens at different temperatures and pre-load levels.