PLASTICITY OF ISOTROPIC COMPOSITES WITH RANDOMLY ORIENTED AND PACKETED INCLUSIONS

Based on an energy approach, the nonlinear elastoplastic behavior of a two-phase, isotropic composite with two kinds of inclusion morphologi es are determined as a function of inclusion shape at the low concentr ation range. Both types of morphology involve the three-dimensional ra ndomly oriented spheroidal inclusions, but one is homogeneously disper sed, resulting in an ordinary two-phase composite, and the other posse sses a packeted structure in a form similar to a polycrystalline arran gement. The overall elastoplastic response of these two kinds of compo site is found to be strongly dependent upon the inclusion shape and th eir morphological arrangement. Disc-shaped inclusions generally give a superior reinforcing effect, but when the inclusions become very stif f or totally rigid, needle-shaped inclusions tend to be more effective . In line with the known elastic behavior, the overall elastoplastic r esponse of an ordinary two-phase composite is markedly stiffer than th at of the packeted composite at a given inclusion shape and concentrat ion. The theory is finally compared with the finite-element calculatio ns of a particle-reinforced composite and of a packeted one with oblat e and prolate inclusions, and also with some experimental data for a s ilicon-carbide/aluminium system. In both cases, reasonable agreement i s found in the comparison.