On the 3D extension of failure models for adhesive joints under mixed-mode fracture conditions: LEBIM and CZM

Interface models for triggering damage events have been extensively used in many engineering applications due to their inherent versatility and relatively simple numerical implementations. Usually, the non-linear behavior of interfaces and thin adhesive joints between solids has been modeled using Cohesive Zone Models (CZMs) although other alternative models have been proposed as well. This is the case of the recently proposed Linear Elastic-Brittle Interface Model (LEBIM). The LEBIM is characterized by a linear constitutive law (traction-relative displacement relationship) in the undamaged state up to failure. Damage occurs when a material point reaches a critical energy release rate leading to an abrupt failure representation. Currently, from the numerical point of view, a great deal of research dealing with interface debonds and adhesive failure is still mainly focused on 2D models. The aim of the present investigation is to extend the LEBIM (originally proposed for 2D problems) for its applications to 3D problems under general fracture conditions and to examine its reliability against experimental data and cohesive-based interfaces pinpointing the main theoretical and numerical differences with respect to alternative methods. Thus, we focus our attention on addressing the main advantages of the proposed LEBIM over the nonlinear CZMs: (i) a simple interface law without the need of triggering a gradual stiffness degradation, (ii) a reliable accuracy in comparison with experimental results, endowing a clear identification of the crack front due to the preclusion of the fracture process zone concept, and (iii) a very high efficiency in terms of mesh requirements stemming from the absence of nonlinear cohesive crack representation. To show that 3D LEBIM is feasible it is implemented into the general purpose Finite Element Method (FEM) package ABAQUS through the user subroutine UMAT. Finally, special attention is given to the adequate treatment of the mixed mode fracture that may appear in complex 3D crack propagation cases.