Prediction of Temperature Dependence of Fracture Toughness as a Function of Neutron Fluence for Pressure-Vessel Steels by Using the Unified Curve Method

Abstract

Using the Unified Curve method as proposed by the authors earlier and a probabilistic model based on the local approach and physical background of the influence of impurities and carbide size on the local strength of material, a method has been elaborated for predicting a variation of the temperature dependence of fracture toughness with neutron fluence. The results calculated by this method are compared to the available experimental data.Keywords: fracture toughness, Unified Curve method, Master Curve method, probabilistic model, local criterion, neutron fluence, pressure vessel.Introduction. The authors have developed a new engineering method whereby the temperature dependence of fracture toughness for pressure vessel (PV) steels is predicted from the results of fracture toughness testing of specimens at one or several temperatures [1]. The method is similar to the widely accepted Master Curve method [2-5] but, unlike the latter, it allows for a change in shape of the K T Jc ( ) curve depending on the degree of embrittlement of material. It is called the Unified Curve method. It was demonstrated earlier [1] that the Master Curve method is a particular case of the Unified Curve method.Here are the basic principles of the Unified Curve method. 1. The temperature dependence of fracture toughness of ferrite-pearlite structural steels with a fracture probability P f = 0 5. for specimens of thickness B = 25 mm can be represented by a single relationship