Prediction of crack initiation and propagation of adhesive lap joints using an energy failure criterion

In a previous paper, the present authors have pointed out limitations of some fracture mechanics parameters and shown that the vectorial J-integral can be applied to adhesive joints. Here, problems concerning the practical application of the vectorial J-integral are discussed and a more suitable failure criterion has been proposed, based on a specific strain energy criterion. The specific energy is not so sensitive to the size of the integration zone since it is ‘averaged’ over the volume of the zone. This criterion has been used to model the crack initiation and propagation in single lap joints with a brittle adhesive and a ductile adhesive. The effect of the shrinkage thermal stresses, adhesive fillet, surface preparation and type of adherends (aluminium and steel) were studied. The predicted failure loads and crack patterns are in very good agreement with the experimental results. One of the major conclusions is that the predictions can explain well the experimental scatter band that is always present in single lap joints due to the difficulty of controlling the adhesive fillet.