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

Multiscale processes control the true [sigma(epsilon)] 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 (sigma(y)) following irradiation are accompanied by loss of uniform engineering strain (e(u)). All major features of the tensile test, including the effect of irradiation, can be modeled using finite element (FE) methods and a self-consistent sigma(epsilon) that differs markedly from s(e). The irradiated sigma(epsilon) reflect large increases in sigma(y) and reductions in strain hardening. The very low tensile e(u) following irradiation is due to enhanced continuum necking instabilities as a consequence of the intrinsic property changes. However, large elevations of sigma(epsilon) 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 sigma(epsilon) may be linked to an array of severely strain softening shear bands embedded in an irradiation hardened and strain hardening matrix. (C) 2002 Elsevier Science B.V. All rights reserved.