Prediction of fracture toughness in ductile-to-brittle transition region using combined CDM and Beremin models

Scatter of fracture toughness in the ductile-to-brittle transition (DTB) region for ferritic steels may show a dependence on the specimen geometry constraint. Consequently, this can be a source of uncertainty in transferring fracture data from one test geometry to other configurations. In this work, the modified Beremin model (MBM) for cleavage and the Bonora damage model (BDM) for ductile tearing, were combined to account for the two failure mechanisms competing in the DTB and to predict fracture toughness scatter band with temperature. The model was validated predicting the scatter in the fracture toughness data of A533B steel for SEB specimens with shallow and deep crack. Present model predictions were compared with master curve results. For the MBM, a more physical definition for the process zone was introduced and the temperature dependence of the reference stress σu was described by the sum of athermal and thermally activated stress contributions. Results indicate that ductile crack growth occurring before fracture, which is predicted by the ductile damage model, has a relevant effect on the computed probability of brittle fracture. The proposed combined model is able to accurately account for the loss of constraint occurring in different specimen geometries confirming the geometry transferability of model parameters.