## 2 Materials and Methods
### Impulse Excitation Test  
In this study, a GrindoSonic system (KU Leuven, Leuven, Belgium) enabled the non-destructive evaluation of both acoustic and vibration responses from samples subjected to impact testing. In order to identify the effect of defect size variation, the GrindoSonic MK7 device measured resonance frequencies and damping. The specimen's dynamic behavior during hammer excitation was observed in our investigation through a bending test. The configuration, including the placement of the hammer and the detectors, is depicted in Figures 2-4, which illustrate the method of analysis and sensor placement during the experiment. First, using two nodal supports, the beam was positioned on nodes 22.4% from either side of the part. In order to create vibrations, the setup consisted of tapping the samples with a steel hammer that had a 10 mm shaft ball diameter. Two detectors were used: one for acoustic signals and another for vibration signals. The steel hammer was applied at the center of the beam to ensure consistent excitation, while the vibration detector was placed at the intersection of the centered horizontal line and the nodal line to capture the vibrational response in the flexural mode. Its sensitivity to displacement in the direction of the black point detector makes it possible to identify a particular minimum vibrational amplitude at the nodal support shown in Figure 4. Simultaneously, the acoustic detector was positioned at the center end line of the beam no matter which side was chosen to record the generated sound waves and maximum vibration amplitude. This dual detection method enabled the analysis of both the acoustic and vibrational characteristics of the material. Six independent hammer taps were performed for each sample, and the FFT was obtained from the machine. Further, Table 4 describes the characteristics of the GrindoSonic machine, including its specifications and capabilities. After collecting data using both the acoustic and vibrational detectors, the frequency and damping responses of the samples were determined by data analysis. \begin{table}
\begin{tabular}{c c} \hline
**3D Printer** & **Anisoprint** \\ \hline Print volume & 297 mm \(\times\) 210 mm \(\times\) 140 mm \\ Control software & Aura version 2.5.8 \\ Minimum layer thickness & 0.06 mm \\ Nozzle diameter & 0.4 mm \\ Building plate temperature (\({}^{\circ}\)C) & 60 \\ Nozzle temperature (\({}^{\circ}\)C) & 265 \\ Print speed (mm/s) & 40 \\ Printing orientation & \(\pm 45^{\circ}\) \\ Layer thickness & First layer: 0.25 mm \\ Other layers: 0.1 mm \\ \hline \end{tabular}
\end{table} 
Table 2: Anisoprint machine specification and process parameters. \begin{table}
\begin{tabular}{c c c} \hline
**Test Case** & **No Defect/With Defect** & **Defect Dimensions** \\ \hline
1 & No defect & 3 mm \\
2 & With defect & 7 mm \\
3 & With defect & 5 mm \\
4 & With defect & 10 mm \\
5 & With defect & 10 mm \\ \hline \end{tabular}
\end{table} 
Table 3: Test case overview. The results of an impulse-tested fast Fourier transform (FFT) curve are presented in Figure 5. Using a vibration detector, this figure shows the experimental results for the frequency response of the bending mode of a ceramic reference beam. The ceramic reference bar is completely dry, free of defects, and in its original condition. Accordingly, the black curve represents the excitation's frequency response as computed using standard FFT approaches. Further, a fitted line is displayed through the plotted points on the red curve. Figure 4: Flexural vibrational mode: activation and monitoring. Figure 3: (**a**) Vibration bending test, (**b**) acoustic bending test for PA Smooth. Figure 2: Experimental setup for impulse excitation technique in flexion mode with (**a**) vibration detector, (**b**) acoustic detector. In this regard, the GrindoSonic system applies a Lorentzian function fitting using non-linear least-squares techniques. The variables \(\zeta\) and \(\Delta f\), representing damping and half-height width, respectively, were determined using this approach.