A finite fracture mechanics approach to brittle failure of adhesive lap joints

In this work a Finite Fracture Mechanics approach for predicting the load causing delamination along an interface of adhesive lap joints is presented. Beside the fact that the procedure used is general, the details are given for double lap joint and balanced single lap joint configurations. For both geometries the failure load is predicted and compared with the solution given by other approaches such as the Linear Elastic Fracture Mechanics and Maximum Shear Stress Criterion. Regarding the double lap joint, a comparison with the the widely-spread Cohesive Crack Model has been performed and the results found are almost coincident. This ensures that, for the study of the critical load, the used approach gives reliable predictions and, due to his simpleness, is advantageous respect to the more complex Cohesive Crack Model. The predictions have been validated also against experimental results for both geometries. A particular focus has been performed on the two different hypothesis that crack can propagate from one or from both sides of the adhesive region. This investigation shows interesting results especially for what concerns the Double Lap Joint configuration, where the predicted critical load for allowing crack propagation on both sides is lower than the one predicted by assuming that the crack propagates only on side. Moreover, the discontinuity between those two predictions depends on the symmetry of the considered geometry. For the Single Lap Joint instead this different hypothesis are not influencing the results. The failure behaviour described by the combination of stress and energy criterion, which allows to have an agreement with experimental results and effects of geometrical parameters, requires only basic failure parameters and can be computed on a personal computer.