## 3 Results and Discussion  
The Results Section comprises five sections. The first describes the visual assessment of printed samples with the naked eye. The second presents data from X-ray radiography, used to detect the internal defects created in the analyzed parts. The third one emphasizes the mass measurement of each defective printed part. The fourth covers the results obtained by the acoustic detector, in the form of frequency peaks, amplitude, and damping. The fifth sub-section presents the vibration measured by the vibration detector, also including the frequency peaks, damping, and amplitude values associated with each defect. * Visual inspection  
All parts were examined with the naked eye before being tested. No major visible defects were observed. In addition, the presence of lines on the sides of samples indicates the interfaces between each printed layer, identified as traces of printed layers, as shown in Figure 6. However, defect-free parts show no traces for any printed layer. X-ray inspection  
Figure 7 displays the radiographic image of the beams, with and without defects, illustrating the defects that have been detected. Simply visible are all defects ranging in square dimensions from 3 to 10 mm, with a depth of 0.25 mm. The dimensions and the square structure of the defects can be precisely ascertained. Nevertheless, a single hole is seen in parts that are free of defects, whereas two holes are found in parts that have 7 mm defects. In addition, a delamination is visible in the side view of the 7 and 10 mm defective components. Nonetheless, due to the 45\({}^{\circ}\) printing angle of the parts, a defect printing line indicates the direction of printing. The systematic defect is likely caused by the 45\({}^{\circ}\) print direction, where the head always starts near the edge, creating a visible direction mark at the same spot with each layer. Mass Characterization  
The masses obtained for each defect size are listed in Table 5. A highly accurate VWR model M254 Ai-M electronic balance (BEL Engineering SRL, Monza, Italy), capable of holding up to 250 g of material, was used to measure the mass of each sample (see Figure 8). Its accuracy is 0.0001 g. With standard deviations less than 0.5, the measured masses show consistent values for many measurements. A slight variation in mass is observed when comparing defective and non-defective samples. Among the parts tested, the sample with the 3 mm internal defect has the highest mass (23.648 g), while the parts without internal defects have the lowest mass (23.408 g). As shown in Figure 9, a slight increase in mass is due to local hardening at the edges of the defects during printing. Figure 6: Side view of printed samples showing layer deposition traces. Figure 7: \(Cont.\)  
Figure 8: Sample mass measurement. Figure 7: X-ray scans of beams: front and side views of samples with (**a**) no defects and (**b**) 3 mm, (**c**) 5 mm, (**d**) 7 mm, and (**e**) 10 mm defects. \begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline
**Defect** & \multirow{2}{*}{**Defect-Free**} & \multirow{2}{*}{**3 mm**} & \multirow{2}{*}{**5 mm**} & \multirow{2}{*}{**7 mm**} & \multirow{2}{*}{**10 mm**} \\
**Size** & & & & & & & & & \\ \hline \multirow{2}{*}{**Average**} & **Standard** & \multirow{2}{*}{**Average**} & **Standard** & \multirow{2}{*}{**Average**} & **Standard** & \multirow{2}{*}{**Average**} & **Standard** & \multirow{2}{*}{**Average**} & **Standard** \\  & & **Deviation** & & & & & & & & & \\ \hline Mass (g) & 23.408 & 0.028 & 23.648 & 0.056 & 23.585 & 0.457 & 23.647 & 0.057 & 23.644 & 0.049 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Measured masses for each defect size. Figure 9: Local hardening in defective 3 mm samples (X-ray image). Acoustic detector  
Table 6 shows the mean values for maximum frequency and damping extracted from the FFT curves. The mean values represent the average of six taps of three samples from each fault situation. As can be seen, the maximum frequency is minimal in cases where there is no defect.