## 2 Materials and Methods  
A white-colour PLA filament, model Creality Ender Filament PLA (Shenzhen Creality 3D Technology Co., Ltd., Shenzhen, China), with a 1.75 mm diameter was used to print the specimens. It was done using a Creality CR-10 Smart Pro (Shenzhen Creality 3D Technology Co, Shenzhen, China) 3D FDM printer with a built volume of (X) \(\times\) (Y) \(\times\) (Z): 300 \(\times\) 300 \(\times\) 400 mm\({}^{3}\). The FDM parameters used in the manufacturing of specimens are given in Table 1.  
These parameters were set in the same manner to produce three circular specimens with different infill patterns, i.e., honeycomb (Figure 1a), stars (Figure 1b), and concentric (Figure 1c). At first, the model of a solid circular plate of thickness t = 3 mm and dimensions according to Figure 1 (in mm) was generated in Solidworks 2019 (Dassault Systemes, Paris, France). After transforming its PRT file into an STL file, the G-codes of the sliced models, containing the information about the printing parameters, infill pattern geometry, and dimensions (shown in the bottom left corners of Figure 1a-c), were generated in PrusaSlicer V2.6.1 (Prusa Research, Prague, Czech Republic). \begin{table}
\begin{tabular}{c c} \hline \hline
**Parameter** & **Value** \\ \hline Nozzle diameter & 0.4 mm \\ Layer height & 0.2 mm \\ Fill density & 15\% \\ Nozzle temperature & 205 \(\lx@math@degree\)C \\ Bed temperature & 50 \(\lx@math@degree\)C \\ Build orientation & flat \\ Top/bottom solid layers & 4/4 \\ Perimeters & 3 \\ Printing speed & 60 mm/s \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Parameters set for the manufacturing of specimens by Creality CR-10 Smart Pro printer. After the production of specimens (Figure 2a), their weights were measured with a precision digital XS balance, model BL 2002 (Giorgio Bormac s.r.l., Carpi, Italy), with a capacity of 2000 g, division of 0.01 g, and repeatability of 0.01 g (Figure 2b). Each specimen's weight was measured three times, whereby the scale was calibrated before each measurement. The average measured weights of the specimens are presented in Table 2.  
The specimen dimensions were determined according to the dimensions of the 3D printer's heated table and the requirement to clamp the specimens properly using a designed and manufactured fixture containing four through-holes (Figure 2c), allowing the \begin{table}
\begin{tabular}{c c} \hline \hline
**Infill Pattern** & **Weight (g)** \\ \hline Honeycomb & 151.55 \\ Star & 148.49 \\ Concentric & 148.42 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Measured weights of the analysed specimens. Figure 1: Schemes of specimens with part of the top surface showing the infill patterns: (**a**) honeycomb; (**b**) stars; (**c**) concentric. Figure 2: Experimental chain: (**a**) manufactured specimen; (**b**) digital balance; (**c**) unmounted specimen with the designed fixture put on the robust frame (modal shaker); (**d**) torque wrench with digital torque adaptor; (**e**) input module and modal hammer; (**f**) vibrometer with the specimen prepared for the analysis. bolt connection of the specimen to the robust frame (Figure 2c,f). Bolt tightening was done using a torque wrench with an applied digital torque adapter (Figure 2d). The excitation of the structure was realized using a Bruel & Kjaer 8206 (Hottinger Bruel & Kjaer A/S, Virum, Denmark) impact hammer with a plastic tip (Figure 2e). As all the specimens manufactured were made of plastic material, they were very light-weight. The mentioned impact hammer, with an output voltage sensitivity of 22.7 mV/N and full-scale force range compression of 220 N, is suitable for the implementation of impact-force measurements on small to medium structures. The application of a plastic tip allowed us to obtain optimal impulse shapes in the set frequency span. The use of conventional accelerometers to acquire specimens' responses was not possible due to their size, mass, and attachment method, which could cause undesirable mass loading or local stiffness changes.