The experimental and numerical analysis of the adhesively bonded three-step-lap joints with different step lengths

Adhesive bonding is one of the most used joining methods for bonding composite or different types of materials. The joint type commonly used in adhesive bonding is the single lap joint (SLJ) type. However, in adhesively bonded joins, peel stress occurs due to the eccentric loading, which causes damage to the ends of the overlap area. Different types of joints are used to reduce these peel stresses. One of these joint types is the step-lap joint type obtained by creating steps in the overlap area. In this study, mechanical properties of the single lap joint (SLJ), one-step lap joint (OSLJ) and three-step lap joint (TSLJ) with five different step lengths subjected to tensile loading were examined experimentally and numerically by keeping the bonding area same for all samples examined. In this experimental study, AA2024-T3 aluminum alloy was used as the adherend and DP460, a structural adhesive with two components, was used as the adhesive. In addition, the progress of the crack in the overlap area was observed with a high-speed camera. As a result, the TLSJ type was found to carry more load than other joint types. Also, the change in the step length in the three-step lap joint type had a significant effect on the failure load of the joint. When the failure loads obtained in the experiments and the numerical analysis were examined, it was concluded that their results were quite compatible with each other when the cohesive zone model was used in the numerical analysis. Another result obtained from the study is the optimum length of the first step created at the ends of the overlap area in the three-step lap joint.