Inelastic contact deformation of metal coated fibers

Metal matrix composites (MMCs) can be synthesized by aligning metal coated ceramic fibers in a shaped container and applying pressure at elevated temperatures. The high stresses created at the contacts between neighboring fibers cause inelastic matrix flow that fills interfiber voids, reduces interfiber separations and results in composite densification. The rate of densification depends on the contact's resistance to flow. Current contact mechanics models are unable to adequately predict this resistance because they do not account for tile effect of the (elastic) fiber. Closed-form solutions for contact stress-displacement rate and contact area-strain relationships are used to describe metal coated fiber blunting as a function of fiber volume fraction, matrix material non-linearity (i.e. creep stress exponent) and fiber packing geometry. The solutions contain two unknown coefficients (c and F) which are evaluated using the finite element method. A simple model for the consolidation of coated SiC fibers is developed in terms of the coefficients, c and F. The model indicates that materials with a low creep stress exponent are more difficult to densify as the fiber volume fraction increases whereas, perfectly plastic materials exhibit a relatively weak dependence on the fiber volume fraction. (C) 1997 Acta Metallurgica Inc.