A Fractographic Study of Damage Mechanisms in Short-Fiber Metal Matrix Composites

Abstract

A general constitutive theory is formulated for a short-fiber metal matrix composite. The constitutive theory is based on continuum mechanics with constraints provided by fracture mechanics and thermodynamics. The basic premise of the constitutive theory is that load-induced microstructural damage associated with the inclusion of the fibers in the metal matrix results in a loss of material stiffness. The concept of the damage-dependent constitutive theory was evaluated by an experimental investigation of the microstructural damage in an Aluminum 6016-T6 matrix with silicon carbide (SiC) whiskers. The primary objective of the investigation was the identification of microstructural damage such as voids or cracks that were associated with the presence of the SiC whiskers. The results of the experimental investigation include measured reductions in the elastic modulus of tension specimens which were loaded beyond yield and unloaded. Also, there was an associated change in the extent of the microstructural damage. These results lead to the conclusion that the effect of microstructural damage must be included in the constitutive relationship in order to fully describe the behavior of a metal matrix composite.