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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Pendulum impact bending tests were carried out using an instrumented Otto Wolpert-Werke pendulum hammer. The maximum impact energy of the hammer was 150 J. The hammer head had a semi-cylindrical striking edge with a radius of 15 mm. The setup of the impact tests, Figure 2 (c,d), was adapted to the setup of the three-point bending tests, Figure 2 (a,b). Accordingly, the radius of the supports was 7.5 mm, and the clear width was 150 mm. Bending force-displacement curves were determined using a rotative position transducer PR-65-E-0-103 (Gefran, Provaglio D´iseo, Italy) mounted on the hammer axis located at the backside of the device. The rotation angle signal was sampled at 20 kHz and filtered with a low-pass Butterworth filter CFC 100. To obtain the angular velocity and the angular acceleration, the signal was differentiated twice. Reference tests with and without inserted samples were performed to obtain the acceleration signal of an empty pendulum swing. Subsequently, the difference between angular acceleration signals (with and without sample) has been calculated. The differentiated angular acceleration was then multiplied by the moment of inertia of the pendulum hammer to receive the momentum. Through dividing the momentum curve by the length of the pendulum rod, the force profile was calculated. The final force-displacement curve was obtained by calculating the displacement from the rotation angle multiplied with the length of the pendulum rod. Plausibility was verified by integrating the curve to obtain absorbed energy and comparing it with the trailing pointer reading. The apparatus exhibited frictional losses of 0.85 J, as determined by releasing the hammer in the absence of a test sample. The impact velocity of the hammer head, calculated using energy conservation principles at the midpoint of the striking edge, was 5.50 m/s. The effect of the impact side was assessed by testing PF-bonded samples with impact applied to either the wood or the aluminum face. The quasi-static and impact bending strength σ was calculated from the maximum bending force F max , the span distance L , the sample width b , and the sample thickness d : σ = 3 F max L 2 b d 2 (1)

Fig. 2. (a,c) Schematic illustrations and (b,d) photos of the testing setups used for (a,b) quasi-static three-point bending and (c,d) pendulum impact bending of aluminum-wood composites. Dimensions are given in mm.