Effective Elastoplastic Behavior of a Class of Two-Phase Composites with a Polycrystal-Like Microstructure

Abstract

A micromechanical theory is developed to determine the overall elastoplastic response of a two-phase composite with dual ductile phases. The microstructure of the two-phase system is of the inclusion/matrix type, where spheroidal inclusions are first aligned and clustered together, forming a packet, and then these packets are packed together with random orientations, with a final structure akin to that of a polycrystalline aggregate. The yielding process of the inclusions and the matrix in this case is intimately related to the orientation of the inclusions in each packet; it takes place sequentially from one to another upon continuous loading. The influence of inclusion shape, concentration, and whether the hard or the soft phase takes the position of the matrix, is examined in light of this sequential yielding process. It is found that when the matrix is the soft phase in each packet, disc-shaped inclusions generally give a superior reinforcement, whereas with a hard matrix spherical inclusions provide the least weakening effect. A microstress analysis on the sequential yielding process of the colonies indicates that, when the matrix is the soft phase, prolate inclusions with symmetric axis pointing towards the loading direction (the pole projection) tend to yield first, but that with oblate inclusions it starts from those whose symmetric axes are perpendicular to the tensile axis (pointing to the equator). The influence of the plasticity of inclusions on the ductility of the two-phase system is further demonstrated in light of elastic inclusions.