Application of Coupled Damage and Beremin Model to Ductile-Brittle Transition Temperature Region Considering Constraint Effect

Abstract

For nuclear safety, fracture evaluation of reactor pressure vessels (RPV) under neutron irradiation is key issue. Fracture toughness from a CT specimen is used as a material constant for fracture evaluation, but it is well known that it has a large constraint, which causes lower toughness than that of flawed structures, such as a RPV with a surface flaw. In ductile to brittle transition temperature (DBTT) region ferritic steel which is material of RPV has a large scatter and it becomes important to know the accurate scatter of an irradiated material because of less margin of RPV’s integrity after a long term operation. In this paper to establish a more precise fracture evaluation method in DBTT region for an irradiated RPV with a postulated surface flaw, a coupled model of damage mechanics for ductile fracture and Beremin model for cleavage fracture was applied for correction of the effect of a small ductile growth on the stress-strain field. To confirm the validity of the method, as the first trial, fracture tests using CT specimens were performed in several temperature conditions. The temperature dependence of the parameters of Beremin models were investigated as well.