FINITE ELEMENT ANALYSIS ON THE MECHANICAL BEHAVIOUR OF ADHESIVE LAP JOINTS

Adhesive lap joints for structural purposes are well known in many sectors of Engineering, above all in the Aeronautical and Mechanical fields, mainly due to the strong reduction of both time and construction cost given by their use. Other benefits are represented by the resistance to corrosion and fatigue as well as the toughness with regard to the fracture. In recent years, adhesive lap joints are going to diffuse themselves also in the field of Civil Engineering, in particular regarding the applications of FRP (Fiber Reinforced Polymer) structural members. The modern theoretical approaches in studying the mechanical behaviour of adhesive lap joints refers to Fracture Mechanics and follows two main lines: the first one is based on the classical Griffith criterion (Linear Elastic Fracture Mechanics), while the second one is based on appropriate models of interfacial laws (cohesive constitutive laws) between adherents and adhesive. The main limit of the first line is represented by the hypothesis of linear elastic behaviour required to adherents and adhesive up to the fracture. In fact, when dealing with adhesive lap joints made of FRP, the aforementioned hypothesis is certainly satisfied by the adherents, but it is certainly not appropriate for the adhesive. A theoretical and numerical analysis on the equilibrium problem of FRP adhesive lap joints, has been recently developed using cohesive interfacial laws [14-15]. In particular, bilinear interfacial laws have been considered, composed of a linear elastic branch followed by a decreasing range, linear too, which corresponds to a softening behaviour of the adhesive. No shear deformability as well as no coupling between extensional and flexure behaviour of the adherents have been taken into account. Furthermore, only a pseudo-interaction between fracture modes I and II has been considered, by using the Hutchinson and Suo fracture criterion [4]. The aim of the present paper is to extend the above mentioned analysis accounting for the shear deformability of the adherents and the coupling between extensional and flexure equilibrium problems. The numerical results, obtained via finite element simulations, are compared with those available in literature