Theoretical and experimental considerations in representing macroscale flow/damage surfaces for metal matrix composites

This report shows how robust, multiaxial, constitutive models for advanced materials can be formulated by using micromechanics to address theoretical and experimental issues. An analytical micromechanical model that includes viscoplastic matrix response, as well as fiber-matrix debonding, is used to predict the multiaxial response of metal matrix composites in terms of macro* flow/damage surfaces at room and elevated temperatures. Macro flow/damage surfaces (i.e. debonding envelopes, matrix threshold surfaces, macro 'yield' surfaces, surfaces of constant inelastic strain rate, and surfaces of constant dissipation rate) are determined for a silicon carbide/titanium composite in three stress spaces. The flow/damage surfaces are shown to have their centers offset from the origin by residual stresses and their shape altered by debonding. The normality condition is shown to be reasonably well satisfied for macro surfaces of constant dissipation rate in the presence of fiber-matrix debonding. These results indicate which types of flow/damage surfaces should be characterized and what loadings must be applied to obtain the most meaningful experimental data for guiding theoretical model development and verification.