Theoretical Calculation of Anisotropie Creep and Stress-Strain Behavior for a Class Of Metal-Matrix Composites

Abstract

A unified microcontinuum theory is developed to calculate the development of the anisotropic creep strain and the stress-strain relations under a constant strain rate for a class of metal-matrix composites from the constitutive equations of its constituent phases. Here, the ductile matrix is strengthened with aligned, identically shaped, spheroidal inclusions, which may be disc-like, spheres, or whiskers, so that at a given volume concentration, its anisotropic properties will further depend on the inclusion shape. The principle of stress transfer from the ductile matrix to the reinforcing inclusions is established for both creep and constant strain-rate processes. The theoretical analysis points to enhanced response with reinforcement along the axial direction with whiskers, but disc-reinforcement is far superior along the transverse direction. It is also found that the stress-strain curve of the dual-phase system can reach a saturation stress under a constant strain rate. The simple theory developed here is intended for the low volume concentration and small creep strain range, and it is demonstrated that, within this range, the theoretical predictions for the development of creep strain of a Borsic/aluminum system and for the stress-strain curves of a silicon carbide/aluminum system are in close accord with the experimental observations.