The influence of notching and mixed-adhesives at the bonding area on the strength and stress distribution of dissimilar single-lap joints

With the rapid development of new engineering materials, multi-material structures are now widely used to achieve desired performances instead of conventional ones. The increased use of dissimilar adherends such as composites and metals for joining structural parts in aerospace, maritime and civil and transport structures in the past decades make it essential to find methods to improve the performance of this type of joints due to the potential for lightweight products. The first aim of this research is to minimise peak stress concentration by introducing notches in the bonding area to increase the performance of single-lap joints with epoxy adhesive. This is done by utilising the finite element method (FEA) in Abaqus® software to model a series of single lap joints (SLJ) with various notch designs to find the optimum. Experimental tests are carried out to verify the designs.

The optimal design is used then to model various SLJs with mono-adhesive and mixed-adhesives to optimise single-lap joints with dissimilar adherends. The novel geometrical modification reduces peak stresses significantly in the joints with dissimilar adherends, which leads to smaller asymmetric stress distribution along bond-line. The experimental results show significant improvement in the dissimilar joint strength. Compared with using a single material as the adhesive, it is found that using both epoxy and polyurethane as adhesive offers a higher failure load. This can be explained as the polyurethane adhesive provides more uniform stress distribution by transferring stress concentration to the interior part of the overlap length.