Coupled Inelasticity and Damage Model for Metal Matrix Composites

Multiaxial constitutive models to describe fully coupled inelastic deformation and damage of unidirectional fiber-reinforced metal matrix composites are developed from a phenomenological point of view. A damage-coupled kinematic hardening model for transversely isotropic materials is first formulated in the invariant form on the basis of the internal variable approach. An isotropic hardening model coupled with damage is then constructed by assuming a particular representation of the kinematic hardening variable. The extent of composite damage is described using a scalar variable, and a different damage growth rate depending on the orientation of composite is considered through a fourth-rank anisotropic tensor. The rates of damage and hardening are affected by the magnitudes of the relevant internal variables, respectively, so that a full coupling between inelasticity and damage can be predicted. An analytical expression for the creep rupture time under a constant stress condition can be derived from the isotropic hardening model. This expression of the creep life depends on both the time when the minimum creep rate is attained and the degree of damage at that instant. Numerical simulations have been performed to elucidate the characteristics of the present formulation.