Damaging mechanisms and constitutive modeling of metal-matrix composites

The overall mechanical behavior of metal-matrix composites beyond the elastic threshold is often hypothesized to be dominated by metal ductility. However, the progressive loss of elastic stiffness for repeated loading-unloading cycles, which has been evidenced by the output of some mechanical testing, rather suggests quasi-brittle response typical of ceramics. The consequences of these alternative assumptions are discussed in this contribution on the basis of the results of simulated indentation tests, which induce significant triaxial stress states. The possibility of identifying the actual failure mode of these materials by combined experimental and computational work is assesses with specific reference to the predictive capacity of constitutive models implemented in widely available computer codes.