Evaluation of different lap-shear joint geometries for automotive applications

Adhesive bonding is used increasingly by the automotive industry to join structural components of metallic and composite materials. The most common joint configuration is the lap-shear joint, which has been investigated widely and several ideas have been proposed to improve its performance. For example, the introduction of fillets at the overlap ends or tapering of the substrates can reduce the peel stresses at the overlap end. Other approaches include the use of ‘reverse-bent’ substrates and ‘wavy joints’ to reduce peel stresses. This paper compares the stress distribution of the ‘reverse-bent’ and the ‘wavy joint’, with the stresses of the traditional lap-shear joint, using finite element analysis (FEA). A parametric study was carried out showing trends influencing stresses in the adhesive layer. Experimental tests were conducted to evaluate the assumptions used in, and the findings of, the FEA. The joint strength of ‘reverse-bent’ joints was found to be up to 40% higher compared to flat joints using various substrate materials, adhesives and overlap lengths.