STRAIN GRADIENTS AND CONTINUUM MODELING OF SIZE EFFECT IN METAL-MATRIX COMPOSITES

Constitutive modeling for the particle size effect on the strength of particulate-reinforced metal matrix composites is investigated. The ap proach is based on a gradient-dependent theory of plasticity that inco rporates strain gradients into the expression of the flow stress of ma trix materials, and a finite unit cell technique that is used to calcu late the overall flow properties of composites. It is shown that the s train gradient term introduces a spatial length scale in the constitut ive equations for composites, and the dependence of the flow stress on the particle size/spacing can be obtained. Moreover, a nondimensional analysis along with the numerical result yields an explicit relation for the strain gradient coefficient in terms of particle size, strain, and yield stress. Typical results for aluminum matrix composites with ellipsoidal particles are calculated and compare well with data measu red experimentally.