Description of strain hardening behavior in neutron-irradiated fcc metals

This paper summarizes an investigation of the deformation hardening behavior of neutron-irradiated stainless steels and copper in terms of true stress(σ)-true strain(ε) curves. It is commonly accepted that the σ-ε curves are more informative for describing plastic flow, but there are few papers devoted to using the true curves for describing constitutive behavior of irradiated materials. This study uses previously published true and engineering curves for stainless steel and copper irradiated to different damage level. The most appropriate constitutive equation has been identified, and it is shown that for the strain range 0-0.6 the true curves can be well described by the Swift equation: σ = k(ε − ε0)0.5. The influence of irradiation on the parameters of the Swift equation is investigated in detail. It is found that in most cases the k-parameter of this equation is not changed significantly by irradiation. Since large data scatter was observed for the ε0-parameter, a modified Swift equation σ = k(ε − σ02/k2)0.5 was proposed and evaluated. This equation is based on the concept of an initial stress σ0, which is, in general, close to the yield stress. The relationships among k, ε0, and damage dose, influence of test temperature and grain size are discussed.