The Self-Equilibrated Back-Stresses Induce Compensation between Hardening and Softening : Micromechanical and Microstructural Features

To satisfy the mesoscopic stress equilibrium and strain compatibility requirements, the slip activities are regulated not solely via the local stress, but also by the stresses in neighboring medium. The resolved back stress on slip systems is a fundamentally constitutive component of the crystal plasticity theory. Physically the back stress can dynamically induce either hardening or softening effects to adjust the dislocation hardening of slip systems, whereas the sum of the stresses resulting in the back stress in the representative volume element is zero. The self-equilibrated back stresses induce compensation between hardening and softening. In comparison with cases without the back stresses, the back-stress hardening suppresses certain slip activities, while the back-stress softening triggers excess dislocations.A two-phase brass is studied. The back stress makes the hard phase deform smaller and the soft phase deform more than those without the back stresses. More homogeneous lattice strain and higher yield stress than those without the back stresses are obtained. The back stress has limited effects on the evolution of the critical resolved shear stress and crystallographic texture. However, it is a major cause for the banded structures featuring sharp crystallographic contrast that are not parallel with the slip planes. Tests indicate that the back stress induces a serrated behavior at early deformation and suppresses certain dislocations for the back-stress hardened matrix, then at some locations the back stress changes the slip activities and induces some geometrically necessary bands, which is parallel to the macroscopic axes