Strain gradient crystal plasticity: size-dependent deformation of bicrystals

The role of the grain boundary in influencing the deformation of a bicrysta l is explored using a rate-dependent crystal formulation of the Fleck-Hutch inson strain gradient plasticity theory. The physical basis of the theory i s the elevated strengthening of a slip system due to geometrically necessar y dislocations, associated with spatial gradients of slip. The theory is im plemented within the finite element framework and is used to study the defo rmation of a bicrystal under in-plane shear loading. Contrary to classical scale-independent crystal plasticity theories, the strain gradient theory p redicts that the deformation state depends strongly upon grain size. Strain gradient effects are pronounced within a narrow layer at the grain boundar y of a bicrystal, and a significant grain-size dependence of the yield stre ngth is predicted. (C) 1999 Elsevier Science Ltd. All rights reserved.