Micromechanics versus macromechanics: a combined approach for metal matrixcomposite constitutive modelling

The cyclic constitutive behaviour description of lone fibre metal matrix co mposites needs to take into account viscoplasticity of the matrix, damage o f the constituents and interfaces, manufacture residual stresses and damage deactivation effects. In order to incorporate in the model the main consti tuent characteristics and the composite parameters (volume fractions, fibre shape and arrangements) a combined approach is proposed, i.e. that of usin g a micromechanics-based analysis for the thermo-elastoviscoplasticity of t he composite with damaging effects when the damage is active (i.e. when the microcracks are open). The developed model is based on transformation fiel d analysis and on the effective stress-effective strain space within the co ntinuum damage mechanics of the constituents. The particularization to a tw o-phase material permits an explanation of the macroscopic constitutive ope rators of the composite. The obtained macroscopic model is then formulated in such a way as to describe the damage deactivation effects that take plac e under cyclic conditions for compressive-like loadings. The formalism is e xtended from that developed previously for elastic brittle ceramic matrix c omposites, taking into account the possible deactivation for a given (or va rying) non-zero strain. The deactivation criterion ensures the continuity o f the stress-strain response for any multiaxial loadings. The proposed mode l is then applied to a SiC/Ti metal matrix composite, with unidirectional l ong fibres. (C) Elsevier, Paris.