PSI - Issue 77

Eva Graf et al. / Procedia Structural Integrity 77 (2026) 331–338 Graf et al. / Structural Integrity Procedia 00 (2026) 000–000

337

7

of wood . In general, since only one sample was tested for each configuration and no direct force measurement was carried out under impact loading, the results should be considered rather indicative than conclusive. L-stacked PF-bonded composite absorbed about 8 % and 11 % higher impact energy than the P-stacked composite impacted on the wood and aluminum side, respectively, and the maximum bending force was only 7 % higher. As illustrated in Figure 6 (a), comparing the composites after the impact test reveals that debonding between the aluminum alloy and the plywood occurred in the forming zone of all samples tested. Regardless of the stacking order of the composite, the maximum bending force was strongly influenced by the location of the impact. Samples impacted on the wood side showed about 70 % higher maximum bending force than samples impacted on the aluminum alloy side, because the aluminum alloy sheet placed at the tension zone of the composite was able to absorb the critical tensile strain during bending. In contrast, when the composite was impacted on the aluminum alloy side, the wood exhibited brittle fracture, as illustrated in Figure 6 (b). The L-stacked PF-bonded composite impacted on the wood side achieved nearly three times higher maximum force and impact energy absorption than the 2 mm-thick aluminum alloy with comparable mass. The 4 mm-thick aluminum alloy exhibited approximately 1.5 times higher maximum forces than the composite; however, its mass is about twice as high as that of the composite. A detailed work on the impact performance of aluminum-wood composites compared to well-established lightweight materials (e.g., aluminum alloys) is an ongoing work (Graf et al., 2025). Fig. 6. Microscope images after pendulum impact bending of PF-bonded aluminum-wood composites (a) in L- stacked configuration impacted on the wood side, and (b) in P-stacked configuration impacted on the aluminum side. 4. Conclusions This work investigated the performance of adhesive-bonded aluminum-wood composites consisting of nine layers of 0.5 mm-thick birch veneers reinforced with a single 1 mm-thick EN AW-6016-T4 aluminum alloy sheet, which were exposed to quasi-static three-point bending and pendulum impact loadings. Three different adhesives, (i) phenol formaldehyde (PF, (ii) two-component polyurethane (PUR) and (iii) two-component epoxy (EP), were tested for bonding between the aluminum alloy and the plywood. Based on the results, the following conclusions can be drawn: • Using thin veneers for plywood manufacturing seemingly decreased the scattering of the mechanical properties of the composites. • In quasi-static bending, the PF and PUR adhesives demonstrated stable bonding, while the EP adhesive caused significant debonding. Impact bending led to local debonding in the forming zone of all samples. • Longitudinal stacked PF- and PUR-bonded aluminum-wood composites showed high maximum bending force, bendability, and energy absorption without exhibiting brittle failure under both load conditions. • The lightweight potential of PF- and PUR-bonded composites was evident, as they exceeded aluminum alloy sheets of comparable mass in both maximum force and energy absorption. • The beneficial performance was only achieved if the composite was loaded from the wood side, as the aluminum alloy sheet located in the tension zone absorbed the critical tensile strain and prevented premature brittle failure of the veneers. Acknowledgements The authors gratefully acknowledge the support of the ERASMUS+ Mobility Program of the European Union for providing scholarships that enabled the international mobility of two authors, and the Estonian Research Council grant