Prediction of fracture behaviour of structural steels using temperature-dependent local approach

Proper design of pressure boundary elements for pipes, vessels, etc., taking the risk of service-related material degradation into account, is conditioned by understanding of their thermal behaviour. The approach applied here correlates the probability of failure with the stress distribution in front of the crack front. Although the occurrence of a failure is predicted from local stress, a priori in the so-called Weibull stress, effects such as loss of constraint are included. The local approach methodology is a powerful tool for predicting component life. The need for careful and accurate determination of stress/strain in the considered body is essential. The principle is based on the assumption that there is a small but finite volume of material that contains a set of evenly distributed defects. The problem of failure is reduced to finding a critical defect. The considerations follow the assumption of initiation by the rupture of a brittle particle, or the so-called critical cell. It is shown that the effect of plastic strain and temperature are controlling factors for local parameters determination. Accounting temperature and strain dependence into critical volume gives rise to the invariance of parameters of the Weibull distribution. The study has been done on two steels, cast manganese steel for containers for spent nuclear fuel and reactor steel (RPV).