This paper reviews the reported literature on dissimilar (non-matched adherend) adhesively bonded joints (ABJs), currently used bonding processes, and the mechanisms by which these types of joints fail when subjected to structural loading and environmental conditions. Additionally, approaches to improve the performance of dissimilar ABJs, through geometrical and material modifications, are also discussed. Many studies have reported on the strength and failure behaviours of adhesively bonded joints, but of those, few have reported on the performance of dissimilar ABJs. Unlike matched ABJs, the absence of accepted design approaches for dissimilar ABJs arises from their inherent inhomogeneity, which introduces complexities in load transfer mechanisms, in the distribution of stresses through the joint, and in the mechanisms by which the joint ultimately fails. Several authors have proposed approaches to improve the performance of adhesively bonded joints, variously through geometrical or material modification means, but there remains unmet research needs to better understand novel dissimilar ABJ designs.
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.
Stress distributions at interfaces of adhesive lap joints have been widely studied to optimize overall structural strength. However, these studies focussed mainly on the mechanics of adhesive layers. In this paper, a novel concept for a double lap adhesive joint is proposed by introducing a slot in its inner adherend. Numerical simulations employing a finite-element method are used to validate the proposed concept. The results show that the introduction of the slots can smooth the stress distributions along the edges of the interfaces between adhesive and adherend and reduce stress concentration near the cutoff ends of the joint. The results also show that the height of the slots has significant effects on alternating the interfacial stresses. Thus, the proposed concept provides a promising way to optimize double lap adhesive joints for enhanced strength with reduced weight.
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