Prediction of fracture in the transition regime: Application to an A533B pressure vessel steel

In order to model the fracture behaviour of pressure vessel steels in the transition regime, a new model has been developped in 1991 at EDF R&D Division in the framework of local approach to fracture. This approach couples the damage mechanics model developped by Rousselier which is accounting for ductile propagation of a crack, and the Beremin's model based on Weibull's statistics which stands for cleavage. It is possible to predict, by this coupled approach, safe lower bound transition curves for a temperature range up to RTNDT+50 degrees C. It has been shown that the predictions of the model agree well with the experimental data, both in terms of fracture toughness at cleavage instability and the amount of pre-cleavage tearing. Those predicted curves have also been compared to the ASME design curve, and substantial safety margins have been exhibited.