Failure of Adhesive-Bonded Composite Single Lap Joints with Embedded Cracks

An experimental and analytical study is presented to investigate the effect of cracks embedded in continuous adherends near overlap ends on failure behavior of adhesive-bonded composite single lap joints. In the experimental part, the effects of the crack size and location on both failure loads and failure modes are illustrated. A nonlinear finite element analysis (FEA) is presented to demonstrate the effect of the cracks on the stress distribution in the adhesive layer. Based on the FEA results, an analytical model Is developed to study the effect of the cracks on the strengths of the jolnts. The energy release rates of modes I and II are calculated using both FEA and the present analytical model. Two failure criteria, one based on the critical energy release rate and the other based on the maximum stress, are used to predict the failure loads of the specimens. It is shown that there is a good correlation between the average measured failure loads and those predicted using FEA and the analytical models with the maximum-stress-based criterion. Based on the present results, it is concluded that short cracks at the chosen locations can cause larger reduction in the failure loads of adhesive-bonded single lap joints than long cracks.