Stress-Strain response of irradiated material using dislocation dynamics modelling

Abstract

Irradiation of materials by energetic particles causes significant degradation of the mechanical properties, most notably an increased yield stress and decreased ductility, thus limiting lifetime of materials used in nuclear reactors. Effect of irradiation on materials is to produce vacancies and self-interstitial atoms, and stacking fault tetrahedra. These defect clusters form loops around existing dislocations, leading to their decoration and immobilization. These microstructural features ultimately lead to radiation hardening in most of the materials. An attempt is made to understand these phenomena using discrete dislocation dynamics (DD) modelling. The plastic flow is represented by collective motion of a large number of edge dislocations. The dislocation fields are specified by continuum elasticity theory. Since the elastic fields act infinite in medium, corrections for boundaries are specified by a complementary problem, which consists of solving a linear elastic boundary value problem through finite element method. The dislocation phenomenon like annihilation, generation and pinning of dislocations by obstacles are incorporated in the model. Irradiation effects are modelled by assuming that a fraction of total dislocations are locked by irradiation induced defects. These dislocations get unlocked when stress on them exceeds a threshold value. The stress-strain response of an irradiated material as a function of density of Frank -Read sources and obstacles density and irradiation fluence is studied.