EFFECTIVE PLASTIC RESPONSE OF 2-PHASE COMPOSITES

Finite element analyses of the overall stress-strain response of metal-matrix composites are carried out using axisymmetric and plane strain unit cell formulations. The metal matrix is characterized as an isotropically hardening elastic-plastic solid and the ceramic reinforcement is taken to be isotropic elastic. Perfect bonding between the matrix and the reinforcement is assumed. The focus is on the effects of reinforcement shape, size and spatial distribution. Under monotonic loading, the stress-carrying capacity in the plastic range increases in the following order for the reinforcement shapes considered: double-cone --> sphere --> truncated cylinder --> unit cylinder --> whisker. The extent of the Bauschinger effect under reversed loading increases in the same order for particle reinforced composites. The effects of reinforcement size and distribution are analyzed by considering a plane strain model with two sizes of reinforcing particles. For certain distributions, it is found that the smaller family of particles plays virtually no role in affecting the stress-strain response. Thermal residual stresses are also considered and their effects are seen to persist far into the plastic range. The predicted plastic stress-strain behavior can be rationalized in terms of the evolution of matrix field quantities and, in particular, in terms of the effect of the constraint on plastic flow.