On the elastic-plastic boundary conditions in strain-gradient plasticity theory

In rate-independent strain gradient plasticity theories, boundary conditions regarding plastic strain or its gradient must be imposed at the interface between plastic and elastic regions inside the body. Previous studies have attempted to define these conditions based on physical considerations, but the issue remains unresolved. This study analyzes a pure bending problem numerically using a visco-plasticity model with a nearly zero viscosity parameter to detect appropriate boundary conditions for rate-independent cases. It is confirmed that, prior to full yielding over the thickness of bent specimen, the analytical solution assuming a zero plastic strain gradient at the internal interface shows good agreement with the numerical results.