An extrinsic interface developed in an equilibrium based finite element formulation

The phenomenon of delamination in composite material is studied in the framework of hybrid equilibrium based formulation with extrinsic cohesive zone model. The hybrid equilibrium formulation is a stress based approaches defined in the class of statically admissible solutions. The formulation is based on the nine-node triangular element with quadratic stress field which implicitly satisfy the homogeneous equilibrium equations. The inter-element equilibrium condition and the boundary equilibrium condition are imposed by considering independent side displacement fields as interfacial Lagrangian variable, in a classical hybrid formulation. The hybrid equilibrium element formulation is coupled with an extrinsic interface, for which the interfacial separation is zero for a sound interface. The extrinsic interface is defined as a rigid-damage cohesive zone model (CZM) in the rigorous thermodynamic framework of damage mechanics and is defined as embedded interface at the hybrid equilibrium element sides.