Micromechanical modeling of damage in periodic composites using strain gradient plasticity

Damage evolution at the fiber matrix interface in Metal Matrix Composites (MMCs) is studied using strain gradient theory of plasticity. The study includes the rate independent formulation of energetic strain gradient plasticity for the matrix, purely elastic model for the fiber and cohesive zone model for the fiber–matrix interface. For the micro structure, free energy holds both elastic strains and plastic strain gradients. Due to the gradient theory, higher order boundary conditions must be considered. A unit cell with a circular elastic fiber is studied by the numerical finite element cell model under simple shear and transverse uniaxial tension using plane strain and periodic boundary conditions. The result of the overall response curve, effective plastic strain, effective stress and higher order stress distributions are shown. The effect of the material length scale, maximum stress carried by the interface and the work of separation per unit interface area on the composites overall behavior are investigated. The results are compared with those for strong interface.

► In MMCs, the particle size does not affect the elastic response but it enhances the hardening.
► With lower particle size, the plastic strain is significantly suppressed at the crack tip.
► By increasing the maximum stress carried by the interface in the debonding is postponed.