PSI - Issue 77

Andrzej Katunin et al. / Procedia Structural Integrity 77 (2026) 18–25 Author name / Structural Integrity Procedia 00 (2026) 000–000

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experimentally for glass fiber-reinforced polymer (GFRP) plate-like structures with artificially introduced damage tested using SHVT technique. 2. Specimens and experiments The specimens for experimental studies were manufactured and supplied by Izo-Erg sp. z o.o. (Gliwice, Poland). 5-layered GFRP composite plates made of glass fabric and epoxy with the areal density of 200 g/m 2 , and spatial dimensions of 240×240 mm and thickness of 0.75 mm were machined using a 3-axis CNC milling machine equipped with a high-speed spindle (24K rpm) and positioning accuracy of 0.01 mm, to introduce artificial damage. The extrusions of 10%, 25%, and 50% of total thickness of the plates were performed in the square area of 50×50 mm positioned in the geometrical centers of the plates, which resulted in 3 damage scenarios with a damage depth of 0.08 mm, 0.19 mm, and 0.38 mm, respectively. The holes were drilled in upper and lower sides of the plates to fix them in the testing fixtures (see Fig. 1), reducing the testing area to 200×240 mm. The detailed description of the machining process, schemes with specific dimensions, and main material properties of the tested specimens can be found in (Amraei et al., 2025). Before testing, the specimens were covered with the silicone-based heat-resistant black matt coating from the Dragon Poland sp. z o.o. (Cracow, Poland) to ensure appropriate thermal emissivity for thermographic testing. The specimens were clamped in the upper and lower fixtures by bolts tightened with a constant torque using a torque wrench. The testing procedure is performed in two subsequent steps: first, the modal analysis was performed to determine the natural frequencies of vibration of the plates, and second, the loading with a harmonic signal representing the first natural frequency was performed, and the surface thermal response was registered. In each scenario, the tests were performed on the surfaces of the specimens, opposite to those where the artificial damage was introduced.

Fig. 1. The experimental setup (Amraei et al., 2025).

The loading for both steps was performed using the TIRA ® TV-51120 electrodynamic shaker (Schalkau, Germany) connected to the specimens’ upper fixture through the steel stinger and the PCB Piezotronics ® 208C02 piezoelectric force sensor (Depew, NJ, USA) for the acquisition of a reference signal for modal analysis. The signal from the force sensor was additionally amplified through the Brüel&Kjær Nexus 2693-0I4 amplifier (Nærum, Denmark), which was connected to the Polytec ® PSV-400 scanning laser Doppler vibrometer (SLDV) (Waldbronn, Germany) used for measurements of vibration velocity in the grid of 9×11 equidistant measurement points on the surface of the plate. For enhancement of focusing of a laser beam from SLDV, and, in consequence, quality of measurement signal, the reflective tape was stuck in the locations of the measurement points. Through the dedicated software of SLDV, the