# The Impact of Internal Structure Changes on the Damping Properties of 3D-Printed Composite Material
## 5 Comparison of Results  
For comparison, specimens with five different configurations of reinforcement fiber orientations for three material compositions were used. The first series of specimens is reinforced with carbon fibers, the second series is reinforced with glass fibers, and the third series is reinforced with Kevlar fibers. The same fiber arrangement configurations are used in each series. The first configuration has fibers arranged longitudinally, the second configuration has fibers oriented transversely at a 45\({}^{\circ}\) angle to the longitudinal axis, the third configuration has fibers oriented perpendicularly, the fourth configuration has fibers oriented alternately at \(\pm\)45\({}^{\circ}\) and the fifth configuration has fibers arranged alternately in the longitudinal and perpendicular directions. The damping results varied depending on the examined specimen variants and their structural configurations, the type of reinforcement material used and the type of measuring equipment. From a material perspective, the glass-reinforced specimens achieved the second highest damping values (0.232) and the lowest values were obtained by the carbon-reinforced specimens (0.087) (Figures 5-7). The highest damping coefficient values were achieved by the Kevlar-reinforced specimens (0.249) in the 45\({}^{\circ}\) configuration, except in the case of the second natural frequency of variant 1 (Figure 6a) and variant 2 from the second workplace (Figure 7b), where the maximum damping values were obtained by the glass-reinforced specimens. From a structural configuration perspective, the damping coefficient values for the first variant (without circumferential fibers) for the first natural frequency of the series of carbon-fiber-reinforced specimens ranged from 0.023 (5 th configuration) to 0.087 (2 nd configuration), representing an increase of 278%. The damping values for the second natural frequency were on average 24% lower than the damping values for the first natural frequencies. The maximum damping value in this case is, in both variants, in the 90\({}^{\circ}\) configuration. For variant 1, the maximum damping value is 0.073 (Figure 6a), and for variant 2, the maximum damping value is 0.046 (Figure 6b). Figure 5: Comparison of damping coefficient of individual samples, 1 st natural frequency: (**a**) variant 1; (**b**) variant 2. The damping coefficient values for the series of glass-fiber-reinforced specimens ranged from 0.066 (5 th configuration) to 0.232 (4 th configuration), representing an increase of 251%. The damping values for the second natural frequency were on average 42% lower than the damping values for the first natural frequencies. The maximum damping value in this case is in the 45\({}^{\circ}\) variant 1 configuration (0.134) (Figure 6a) and in the \(\pm\)45\({}^{\circ}\) variant 2 configuration (0.054) (Figure 6b). The damping coefficient values for the series of Kevlar-fiber-reinforced specimens ranged from 0.045 (1 st configuration) to 0.249 (2 nd configuration), representing an increase of 453%. The damping values for the second natural frequency were on average 56% lower than the damping values for the first natural frequencies. The maximum damping value in this case is in the 45\({}^{\circ}\) variant 1 configuration (0.09) (Figure 6a) and in the \(\pm\)45\({}^{\circ}\) variant 2 configuration (0.072) (Figure 6b). By comparing the specimens of variant 1 and variant 2, for the first natural frequency, we found that the average damping values are significantly lower in variant 2 (specimens with circumferential fibers) (Figure 8a,c,e). For the second natural frequency, the difference in values is smaller, but there is still a significant decrease in damping in the second variant (Figure 8b,d,f). Carbon-fiber-reinforced specimens have on average 28% lower  
Figure 6: Comparison of damping coefficient of individual samples, 2 nd natural frequency: (a) variant 1; (b) variant 2.