Crack onset and propagation in composite materials using Finite Fracture Mechanics on elastic interfaces

A method for the prediction of crack onset and propagation along an interface in a fibre-reinforced composite system is developed. The method is based on the Linear Elastic-(Perfectly) Brittle Interface Model (LEBIM) and a coupled stress and energy criterion of the Finite Fracture Mechanics (FFM). Models similar to LEBIM, also called weak or imperfect interface models, are frequently applied to describe the behaviour of adhesively bonded joints. In the present paper the interface is modelled by a continuous distribution of linear elastic-brittle springs where the normal and tangential stresses across the undamaged interface are, respectively, proportional to the relative normal and tangential displacements. The interface failure criterion applied takes into account the variation of the fracture toughness with the fracture mode mixity. In the present work a 2D collocational boundary element method (BEM) code is used to analyse debond onset and propagation at a fibre embedded in a matrix subjected to remote uniaxial transverse tension. One of the advantages of the method proposed here by applying the FFM criterion to the LEBIM is that we are able to make independent the two governing parameters of the model (critical stress and fracture toughness of the interface), which are related by an equation in the original LEBIM formulation. It seems that the predictions provided by FFM with LEBIM are quite similar to those obtained by the well-known Cohesive Crack Model (CCM). The advantage of the present method with respect to the CCM is evident, since a troublesome nonlinear analysis due to the softening can be avoided. (C) 2014 Elsevier Ltd.