DAMAGE DUE TO FRACTURE OF BRITTLE REINFORCEMENTS IN A DUCTILE MATRIX

A micromechanical model is developed for brittle particle reinforced metal matrix composites sustaining damage. A composite with uniformly distributed damage is modelled by a three-phase damage cell consisting of a cracked particle in a cylindrical matrix cell embedded in an undamaged composite cylinder. The fraction of broken particles to all particles is taken as the ratio of the broken-particle/matrix cell volume to the whole damage cell volume. Systematic analysis is carried out for aligned spherical and cylindrical particles in an elastic-perfectly plastic matrix subject to tensile loading normal to the plane of particle cracks. The influence of damage evolution paths on the composite stress-strain behavior is investigated. Results are given for the effects of damaged particle percentage, total particle volume fraction and particle shape on the overall composite limit flow behavior. Significant reduction in composite limit flow stress may occur if most of the particles are broken. For composite with spherical reinforcement, the reduction is found to be linearly dependent on the percentage of damaged particles.