Structural tuning of single-lap joints with thin-walled inserts and nanomodified adhesives for superior flexural performance

This study investigates the enhancement of bending performance in single-lap joints (SLJs) through the integration of thin-walled metallic inserts and nanostructure-reinforced adhesives. The experimental and numerical work focused on evaluating the influence of carboxyl-functionalized carbon nanotubes (CNT-COOH) added to a structural epoxy adhesive (DP460), as well as the role of thin-walled AA2024-T3 aluminum alloy and carbon fiber fabric reinforced composite inserts embedded within the joint’s overlap region. The bonded adherends were also fabricated from AA2024-T3 aluminum alloy, a commonly used material in lightweight structural applications. Insert lengths were varied systematically (25, 22, 19, 16, 13, and 10 mm) to assess their contribution to load transfer efficiency under four-point bending. While the addition of 1 wt% CNT-COOH alone enhanced the joint’s maximum bending moment by around 10 %, its impact became far more pronounced when used with reinforcement inserts. Specifically, thin-walled aluminum inserts boosted the moment capacity by up to 93.1 %, and composite inserts led to even greater improvements—reaching as high as 128.1 %. The combination of CNT-COOH-enhanced adhesive and strategically placed thin-walled inserts delivered the highest structural gains. A finite element model was developed to investigate failure mechanisms, revealing that the buckling behavior and flexural stiffness of the thin-walled inserts significantly influenced joint performance.