Modeling the multiscale mechanics of flow localization-ductility loss in irradiation damaged bcc alloys

Multiscale processes control the true [σ(ε)] and engineering [s(e)] stress–strain behavior of alloys. Strain hardening in unirradiated bcc alloys is modeled as a competition between production and annihilation of stored dislocations. Large increases in yield stress (σy) following irradiation are accompanied by loss of uniform engineering strain (eu). All major features of the tensile test, including the effect of irradiation, can be modeled using finite element (FE) methods and a self-consistent σ(ε) that differs markedly from s(e). The irradiated σ(ε) reflect large increases in σy and reductions in strain hardening. The very low tensile eu following irradiation is due to enhanced continuum necking instabilities as a consequence of the intrinsic property changes. However, large elevations of σ(ε) persist up to very high strains. Homogeneous deformation constitutive and plasticity theory can be used in continuum FE modeling of irradiated alloys. On a mesoscopic scale, FE simulations indicate that the irradiated σ(ε) may be linked to an array of severely strain softening shear bands embedded in an irradiation hardened and strain hardening matrix.