A New Finite Fracture Mechanics Approach for Assessing the Strength of Bonded Lap Joints

For the widespread use of adhesive joints an exact and reliable prediction of the strength is mandatory. In this work, a new approach to assess the strength of single lap joints is presented. The approach is based on the hybrid criterion as postulated by Leguillon in the framework of finite fracture mechanics. It strictly combines a consideration of an energy release balance and a fulfillment of a strength criterion. The present work is based on a simple model of the joint behavior and assumptions about crack initiation. From the stress distribution of the classical shear lag theory an incremental energy release rate is derived and is used to formulate the optimization problem of the failure load. The resulting predictions of critical failure loads are compared to experimental results of single lap joints. It is shown that the new approach is able to physically describe crack formation and the corresponding critical load within the framework and limitations of the underlying assumptions and simplifications. The work closes with a discussion of the limitations and an outlook on possible improvements of the underlying models and assumptions.