Interfacial Matrix Stresses in Composites Due to Misfitting Cylindrical Constituents

Abstract

The constituent phases in composite materials of all types can induce local residual stress due to their differing mechanical responses. Changes in thermal, mechanical, or chemical states, encountered in processing or service applications, will generate these stress fields. Analytical solutions to isolated spherical or cylindrical inclusions exist, but the interaction of stress fields among neighboring constituents has not been examined in detail. The present study examined the matrix stress fields at the interface between the matrix and hexagonal arrays of misfitting cylinders. Stresses were analyzed using the photoelastic method, wherein the matrix was the photoelastic material. As the nearest-neighbor cylindrical inclusions first approach each other, there is a tendency for both radial compression and tensile hoop stress components to increase beyond values predicted for single, isolated inclusions. At nearest-neighbor separations less than 40% of the cylindrical inclusion diameter, however, the contact pressure between reinforcement and matrix decreases. At the same time, the tensile hoop component in creases markedly, less so in the hexagonal array than for two inclusions. The physical positioning and arraying of the reinforcement will clearly determine the local stress in duced by processing, which, in turn, will influence composite response and service endurance.