Probabilistic model for fracture toughness prediction based on the new local fracture criteria

The stochastic nature of various critical parameters controlling cleavage fracture of nuclear pressure vessel steels has been analyzed. On the basis of the performed analysis the local criterion for cleavage fracture proposed by authors has been modified into a probabilistic statement. The probabilistic model for fracture toughness prediction has been elaborated on the basis of the modified local criterion for cleavage fracture, the ductile fracture criterion proposed by authors earlier and the approximated solution for problems relating to the stress-strain state near the crack tip. This probabilistic model allows one to predict the dependence of KIC on temperature for any given probability of brittle fracture; to describe the effect of the specimen thickness on KIC; and to determine the scatter band for the brittle to ductile transition temperature. The connection of parameters determining the scatter of KIC with material properties has been analyzed. Comparison of experimental and calculated results has been performed as applied to a 2.5Cr-Mo-V nuclear pressure vessel steel. The proposed probabilistic model has been shown to describe the lower and upper envelopes for a large number of experimental data.