Performance degradation of structural steels in nuclear environments results from the formation of a high number density of nanometre-scale defects. The defects observed in copper-based alloys were composed of vacancy clusters in the form of stacking fault tetrahedra and/or prismatic dislocation loops that impede the motion of dislocations. The mechanical behaviour of irradiated Cu alloys exhibits increased yield strength, decreased total strain to failure and decreased work hardening as compared to their unirradiated behaviour. Above certain critical defect concentrations (neutron doses), the mechanical behaviour exhibits distinct upper yield points. The formulation of an internal state variable model for the mechanical behaviour of such materials subject to these (irradiation) environments was described here. This model was developed within a multiscale materials-modelling framework, in which molecular dynamics simulations of dislocation-radiation defect interactions guided the final coarse-grained continuum model. The plasticity model includes mechanisms for dislocation density growth and multiplication and for irradiation defect density evolution with dislocation interaction. The general behaviour of the constitutive (homogeneous material point) model showed that as the defect density increased, the initial yield point increased and the initial strain hardening decreased. The final coarse-grained model was implemented into a finite element framework and used to simulate the behaviour of tensile specimens with varying levels of irradiation-induced material damage. The simulation results compare favourably with the experimentally observed mechanical behaviour of irradiated materials.

Dislocation Density-Based Constitutive Model for the Mechanical Behaviour of Irradiated Cu. A.Arsenlis, B.D.Wirth, M.Rhee: Philosophical Magazine, 2004, 84[34], 3617-35