DISFRAC Testing and Results

A theoretical, multi-scale model to predict the fracture toughness of ferritic steels in the ductile-to-brittle fracture mode transition temperature region has been implemented into the DISlocation-based FRACture (DISFRAC) computer code to permit fracture safety assessments of ferritic structures. The theoretical basis of this model provides a means of predicting fracture behavior outside of the ranges of data currently used in deriving empirically-based models and should provide a means of improving the understanding of fracture behavior in the fracture mode transition region. Testing has been conducted to verify the model behavior as coded into DISFRAC_V2 and to validate the code predictions against trends observed in mechanical test data. Sensitivity studies were also conducted to identify the models and parameters having the greatest effect on the predicted results. The DISFRAC model was found to be most sensitive to the definition of a “specimen size” relative to the number of particles considered. Specimen size had a large effect, both on the temperature-dependence observed across the range of predicted fracture toughness as well as on the range of K_Jc values simulated at each test temperature. This sensitivity of K_Jc to specimen size needs more study to ensure definition of an appropriate specimen size based strongly on the particles most relevant to the fracture process.