# The Impact of Internal Structure Changes on the Damping Properties of 3D-Printed Composite Material
## 5 Comparison of Results
Figure 7: Comparison of damping coefficient of individual samples, 2 nd workplace: (a) variant 1; (b) variant 2.  
damping values in variant 2, glass-fiber-reinforced specimens have 51% lower values and Kevlar-reinforced specimens have 48% lower values compared to variant 1 (without circumferential fibers). Figure 8: Damping comparison between variant 1 (without circumferential fibers) and variant 2 (with circumferential fibers): (**a**) carbon reinforcement, first natural frequency; (**b**) carbon reinforcement, second natural frequency; (**c**) glass reinforcement, first natural frequency; (**d**) carbon reinforcement, second natural frequency; (**e**) Kevlar reinforcement, first natural frequency; (**f**) Kevlar reinforcement, second natural frequency. At the second workplace, the measuring devices indicated lower damping coefficient values for all materials and configurations, except for one case. In the carbon fiber reinforced specimens with the 5 th configuration (Figure 9a,b), we observed higher damping in both variants (with and without circumferential fibers). In other cases, the damping trends relative to individual configurations were similar to those observed in the measurements from the first workplace (Figure 9). This means that the lowest damping values are in configurations 1 and 5, i.e., specimens with longitudinal fibers. In the other configurations, we observed significantly higher values. Figure 9: Comparison of workplaces: (**a**) carbon reinforcement variant 1; (**b**) carbon reinforcement variant 2; (**c**) glass reinforcement variant 1; (**d**) glass reinforcement variant 2; (**e**) Kevlar reinforcement variant 1; (**f**) Kevlar reinforcement variant 2. The percentage differences in values between the workplaces are as follows. For specimens with carbon fiber reinforcement, the values from workplace 2 are on average 27% lower, for glass fiber reinforcement the values are on average 50% lower and for Kevlar reinforcement, the values are on average 51% lower than the values obtained from the first workplace. These discrepancies can be mainly attributed to the different weights of the accelerometers, as the weight ratio of the accelerometer to the specimen has a significant impact on the resonant frequencies according to findings in the paper by [PERSON] et al. [22]. The specific damping coefficient values for each specimen are shown in Tables 3 and 4. From the analysis results of the first natural frequency, it can be concluded that the lowest damping values are achieved with fiber orientations of 0\({}^{\circ}\) and 0\({}^{\circ}\),90\({}^{\circ}\) for all three materials. For carbon- and Kevlar-reinforced specimens, the maximum damping values are achieved with a fiber orientation of 45\({}^{\circ}\) and for glass-fiber-reinforced specimens, the maximum damping is at a fiber orientation of \(\pm\)45\({}^{\circ}\). Furthermore, the experiment indicates that the presence of longitudinally oriented fibers significantly reduces the ability to damp vibrations. This is also evidenced by the results of variant 2 specimens (with circumferential fibers), where almost all cases showed lower damping values compared to variant 1 (Figure 8). The damping values expressed from the second natural frequency show lower values compared to those derived from the first natural frequency. This observation suggests that the specimens exhibit a viscoelastic damping model, which is frequency dependent. Additionally, an interface damping model is also observed, which is dependent on the fiber orientation. These damping models are more pronounced in specimens reinforced with glass and Kevlar fibers, while in carbon-fiber-reinforced specimens the changes in damping are less evident, whether depending on fiber orientation, frequency dependence or the presence of circumferential fibers.