INELASTIC DEFORMATION OF METAL MATRIX COMPOSITES - PLASTICITY AND DAMAGE MECHANISMS

The deformation mechanisms of a (Ti 15-3)-SCS6 (SiC fibre) metal matrix composite (MMC) were investigated using a combination of mechanical measurements and microstructural analysis. The objectives were to evaluate the contributions of plasticity and damage to the overall inelastic response, and the sequence in which those mechanisms operated. Inelastic deformation of the 0-degrees MMC was dominated by plasticity of the matrix. Reaction-zone cracks and grain boundaries were found to be important sites for dislocation and slip-band nucleation. Inelastic deformation of the 90-degrees composite occurred by both damage and plasticity. This lay-up system had a characteristic three-stage deformation behaviour: stages I, II, and III. Inelastic deformation in stage II was dominated by damage; however, microyielding of the matrix also occurred in this stage. In stage III, plasticity became largely concentrated in intense shear bands between fibres, and this led to shear crack initiation and failure. The predictions of continuum elastic plastic models were compared with the experimental data. The importance of rigorously validating constitutive models using a combination of mechanical measurements and microstructural analysis is pointed out.