THEORETICAL CALCULATION OF ANISOTROPIC CREEP AND STRESS-STRAIN BEHAVIOR FOR A CLASS OF METAL-MATRIX COMPOSITES

A unified microcontinuum theory is developed to calculate the developm ent of the anisotropic creep strain and the stress-strain relations un der a constant strain rate for a class of metal-matrix composites from the constitutive equations of its constituent phases. Here, the ducti le 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 t he ductile matrix to the reinforcing inclusions is established for bot h creep and constant strain-rate processes. The theoretical analysis p oints to enhanced response with reinforcement along the axial directio n with whiskers, but disc-reinforcement is far superior along the tran sverse direction. It is also found that the stress-strain curve of the dual-phase system can reach a saturation stress under a constant stra in rate. The simple theory developed here is intended for the low volu me concentration and small creep strain range, and it is demonstrated that, within this range, the theoretical predictions for the developme nt of creep strain of a Borsic/aluminum system and for the stress-stra in curves of a silicon carbide/aluminum system are in close accord wit h the experimental observations.