Mechanical performance of adhesive-bonded aluminum–wood single lap joints under quasi-static and cyclic tensile loading

The demand for sustainable lightweight materials that replace non-renewable materials is steadily increasing. Therefore, the present study investigates the mechanical performance of aluminum-wood single lap joints (SLJ) of 4.5 mm-thick beech plywood and commercial 1.5 mm-thick EN AW-6016-T4 aluminum alloy sheets bonded using different adhesive types. Plywood consisting of 1.5 mm-thick beech veneers with stacking orders of 0°/90°/0° and 90°/0°/90° to the uniaxial loading direction was used. After adhesive curing, the quasi-static uniaxial tensile shear strength (TSS) and the displacement to failure of the SLJ were determined. Additionally, the fatigue behavior of selected SLJ was investigated, and the macroscopic fracture behavior was qualitatively analyzed. Cyanoacrylate-based, polychloroprene-based and emulsion polymer isocyanate adhesives may be unsuitable for bonding untreated aluminum alloy sheets to plywood, as they achieved minimal TSS due to adhesive failure at the adhesive-substrate interface. In contrast, SLJ bonded with epoxy and polyurethane adhesives showed the best mechanical performance, as their mean TSS was about 7 MPa and their mean energy absorption was almost 19 J for the veneer stacking order of 0°/90°/0°. However, lower TSS and cyclic load bearing capacity were achieved for the veneer stacking order of 90°/0°/90°. The stacking order-related difference in the TSS was even more significant for SLJ showing a brittle failure behavior. Increasing the number of veneer layers with the fiber orientation parallel to the loading direction improves the bending stiffness of the plywood and, thus, the mechanical performance of SLJ increases.