COMPARISON OF DISCRETE DISLOCATION AND CONTINUUM PLASTICITY PREDICTIONS FOR A COMPOSITE-MATERIAL

A two-dimensional model composite with elastic reinforcements in a cry stalline matrix subject to macroscopic shear is analyzed using both di screte dislocation plasticity and conventional continuum slip crystal plasticity. In the discrete dislocation formulation, the dislocations are modeled as line defects in a linear elastic medium. At each stage of loading, superposition is used to represent the solution in terms o f the infinite medium solution for the discrete dislocations and a com plimentary solution that enforces the boundary conditions, which is no n-singular and obtained from a linear elastic, finite element solution . The lattice resistance to dislocation motion, dislocation nucleation , and dislocation annihilation are incorporated into the formulation t hrough a set of constitutive rules. Obstacles leading to possible disl ocation pile-ups are also accounted for. Results are presented for mat erials with a single slip system. A reinforcement size effect is exhib ited by the discrete dislocation-based analysis whereas the continuum slip results are size independent. The discrete dislocation results ha ve higher average reinforcement stress levels than do the correspondin g continuum slip calculations. Averaging of stress fields over windows of increasing size is used to gain insight into the transition from d iscrete dislocation-controlled to continuum behavior. (C) 1997 Acta Me tallurgica Inc.