Hybrid equilibrium element with interelement interface for the analysis of delamination and crack propagation problems

This article proposes a formulation for the analysis of delamination and fracture propagation problems at the interelement interface, with perfect adhesion at the pre-failure condition and with linear softening at the post-failure regime. The proposed formulation is based on the hybrid equilibrium element (HEE) model, with stress fields which strongly verify the homogeneous equilibrium equations and interelement equilibrium equations. The HEE can easily model high-order stress fields and can implicitly model the initially rigid behavior of an extrinsic interface at the element sides. The interface model is defined as a function of the same degrees of freedom of the HEE (generalized stresses) and the pre- and post-failure behavior of the interface can be modeled without any additional degree of freedom. The proposed formulation is developed for a nine-node triangular HEE with quadratic stress fields. This article also proposes an extrinsic cohesive model, rigorously developed in the damage mechanics framework.