PSI - Issue 77

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

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as a resin-hardener-water mixture consisting of 68 wt% Prefere 14J021 resin, 14 wt% Prefere 24J662 hardener, and the balance water, which was applied using a Black Bros 22-D glue roller. The veneer stacks were hot-pressed with the contact pressure of 2.2 MPa applied for 15 min at the temperature of 140 °C using an INFOR PM84 veneer panel press. For the reinforcement, 1 mm-thick Ti/Zr-coated EN AW-6016-T4 aluminum alloy sheets with dimensions of 420 mm × 420 mm and 200 mm × 50 mm were cut using a SafanDarley M-Shear 205-6 TS200 hydraulic guillotine. Young’s modulus, yield strength, ultimate tensile strength (UTS), and strain to fracture of the aluminum alloy are 71 GPa, 120 MPa, 234 MPa, and 27 %, respectively. For bonding the aluminum alloy and the plywood, three different adhesives were used: (i) Prefere 24J662 phenol formaldehyde (PF), (ii) Kiilto PL 250 two-component polyurethane (PUR), and (iii) Penosil Epoxy Fix&Coat 507 two-component epoxy (EP). Prior to bonding, the aluminum alloy sheet surfaces were only cleaned using acetone without any other surface treatment. For producing the PF-bonded aluminum-wood composites, about 160 g/m 2 of adhesive was applied between the plywood and the 420 mm × 420 mm aluminum alloy sheet on top. The stack was again hot-pressed with identical parameters used for laminating the plywood. After curing, the stack was cut into samples with dimensions of 200 mm × 50 mm using a conventional circular saw. For producing PUR- and EP-bonded samples, the plywood was cut into 200 mm × 50 mm samples. About 400 g/m 2 of adhesive was applied between the plywood and the aluminum alloy sheets on top. The samples were cold-pressed at 0.1 MPa for about 6 hours at room temperature. The total thickness of the aluminum-wood composites was 4.4±0.1 mm. The density of the aluminum alloy was 2.70 g/m 3 , and the density of the plywood (consisting of the birch veneers and the PF adhesive layers) at the moisture content of about 8 % was 0.92 g/cm 3 . In addition, 2 mm- and 4 mm-thick aluminum alloy sheets with dimensions of 200 mm × 50 mm were also prepared, which were weight- or thickness-equivalent to the aluminum wood composites. The mass of the PF-, PUR-, and EP-bonded aluminum-wood composites and 2 mm- and 4 mm thick aluminum alloys was determined with 58.6±0.8 g, 61.4±0.3 g, 61.2±0.4 g, 54.0±0.5 g, and 107.1±0.1 g.

Fig. 1. Schematic illustration of aluminum-wood composites in the two stacking orders: (a) perpendicular (P), and (b) longitudinal (L) with wood fiber orientations (grey full lines) perpendicular (90°) and parallel (0°) to the rolling direction (dashed arrow) of the aluminum alloy sheet. The adhesive layers are not explicitly shown. (c) Photo of the stacked wood veneers with every second layer coated with adhesive. 2.2. Experimental procedure Quasi-static three-point bending tests were performed using a ZwickRoell Z100 uniaxial testing machine, which was equipped with a 100 kN load cell. The test setup is shown in Figure 2 (a,b). The tests were conducted according to the ÖNORM EN 310 standard (Österreichisches Normungsinstitut, 2005). The punch radius and the support roll radius were 15 mm and 7.5 mm, respectively, with a span distance of 150 mm between the rolls. Tests were carried out with a testing speed of 10 mm/min and were terminated when the maximum bending force decreased by 30 %. To prevent tensile-induced fracture of the plywood, the aluminum-wood composites were positioned with the aluminum alloy sheet on the outer bending radius, contacting the support rolls. Bending force-displacement curves were recorded and evaluated using the testXpert III software. Energy uptake was evaluated up to a displacement of 50 mm for all samples except for the EP-bonded samples, for which the curves terminated earlier.