Abstract
A model to predict the process of embrittlement, deformation and fracture of reactor pressure vessel steels subject to neutron irradiation is proposed. In order to describe the fracture process under unirradiated condition, the notion of effective stress and the hypothesis of strain equivalence of damage mechanics are first incorporated into a viscoplastic constitutive equation with isotropic hardening. The damage state of the material is represented by a scalar damage variable D, and the evolution equation of D is modeled by postulating that the damage rate D is specified as a function of plastic strain εp and its rate εp. The material is assumed to fracture when D attains to its critical value Dc. The effect of neutron irradiation is represented by expressing the material constants of the constitutive and evolution equations as functions of neutron fluence Φ. The resulting constitutive equations of elastic-plastic damage under neutron irradiation are applied to describe the irradiation embrittlement of a low alloy steel ASTM A533B cl. 1 for the pressure vessel use of light-water reactors. The increase of yield stress and tensile stress as well as the decrease of fracture strain and fracture energy due to neutron irradiation can be described by the proposed model.
