Comparison of Global and Local Approaches to Predicting Warm Pre-Stress Effect on Cleavage Fracture of Ferritic Steels

Potentially both global and local approaches may be used to predicting the effect of loading history on cleavage fracture toughness distribution of ferritic steels. In this paper the dramatic increase in the apparent lower shelf fracture toughness of A533B steel following warm pre-stressing (WPS) has been predicted using these approaches. Extensive experimental evidence suggesting significant enhancement in fracture toughness of ferritic steels within the lower shelf temperatures following WPS are used to verify and compare the applicability and the extent of validity of the models. The global approach is based on the distribution of toughness data described by Wallin statistical model in conjunction with the Chell model for WPS effect. The local approach on the other hand is a Beremin type model that uses the Weibull stress to predict the WPS effect. Weibull stresses would essentially reflect the WPS effect on redistribution of stress-state around the crack tip. Predictions for apparent toughness using the two approaches are discussed in the light of the suggestion that residual stresses are the main cause of the enhancement, at least for the material and geometry used in this study.