Strain gradient crystal plasticity: size-dependent deformation of bicrystals

The role of the grain boundary in influencing the deformation of a bicrystal is explored using a rate-dependent crystal formulation of the Fleck-Hutchinson strain gradient plasticity theory. The physical basis of the theory is the elevated strengthening of a slip system due to geometrically necessary dislocations, associated with spatial gradients of slip. The theory is implemented within the finite element framework and is used to study the deformation of a bicrystal under in-plane shear loading. Contrary to classical scale-independent crystal plasticity theories, the strain gradient theory predicts that the deformation state depends strongly upon grain size. Strain gradient effects are pronounced within a narrow layer at the grain boundary of a bicrystal, and a significant grain-size dependence of the yield strength is predicted. (C) 1999 Elsevier Science Ltd. All rights reserved.