Prediction of fracture toughness of a reactor pressure vessel steel in the ductile-to-brittle transition region based on a probabilistic cohesive zone model approach

The availability of irradiated material for the fracture-mechanical characterization of reactor pressure vessel steels in the context of surveillance programs is severely limited. Additional efforts are necessary to reduce the amount of material required for the determination of the reference temperature based on the Master Curve methodology. The objective of this study is the further development of a method for identifying the parameters of a cohesive zone model to simulate the fracture-mechanical behavior within the ductile-to-brittle transition region. A novel approach is proposed where statistically distributed numerical fracture toughness values are obtained by means of random spatial distributions of cohesive elements with either brittle or ductile fracture properties throughout the cohesive zone. Thereby, a numerical reference temperature is determined based on the ASTM E1921 standard and compared to the reference temperature obtained from tests on miniaturized CT specimens. It is shown that with the presented approach the reference temperature of a reactor pressure vessel steel can be predicted with high accuracy. Less material is required for the calibration of the model parameters than for an experimental determination of the reference temperature. Further development of the model is required to accurately predict the experimentally observed fracture toughness scatter within the transition region.