## 3 Results
### Vertical Weight Drop Tests for Modified Panels with Viscoelastic Layer  
The tests for vertical drop in weight were carried out in different energy ranges, varying the impactor weight and height as seen in Table 4. This in order to observe results for low energy and high energy tests. Figure 17: Modified panel K impacted at \(1\times 10^{3}\) cycles with 343 kN/m\({}^{2}\) slamming pressure. Figure 18: Evolution of flexural stiffness in modified panel F up to \(0.27\times 10^{5}\) impact cycles with P = 343 kN/m\({}^{2}\). The tests carried out on the panels with a viscoelastic layer with impact energies for weight drop of 20 and 40 Joules are shown in Figure 19. The impact of 20 Joules presents little damage on the surface with little failure of adhesion with the laminate matrix. In contrast, in the 40 Joules panel, the damage is much greater and there is a complete cradle separating the viscoelastic lamina with the matrix. The impact is punctual and there is a noticeable difference with the high energy slamming test. The vertical weight drop tests obtained similar results for the low energy case. Over 30 Joules the data obtained is applicable for a comparison. The modified panels were treated in the same way with fluorescent penetrating inks to assess the type of damage. During the cut, the viscoelastic sheet came off. This is seen in Figure 20. It should be noted that the viscoelastic layer came off due to the oil cut. The sections were 2 mm thick and despite the slow cutting speed, this affected their adherence. The cutting speed was very slow and oiled, to prevent fragments of composite material from sticking to the sections and showing erroneous results under fluorescent light. It can be seen in the cross sections that the impacted laminate layers before the viscoelastic layer have damage to the matrix and fiber. The layers after this have little delamination. The matrix shows few vertical breaks and the ladder joints are not clearly visible. Delamination do not take a lateral direction due to the orientation of the layers but appear intermittently and hardly visible. All sections \begin{table}
\begin{tabular}{c c c} \hline \hline
**Impact (J)** & **Deformation Maximum (\(\upmu\)m/m)** & **\# of Rebounds** \\ \hline
20 & 252 & 1 \\
40 & 655 & 1 \\
80 & 991 & 1 \\
120 & 1040 & 3 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Conditions of the vertical weight drop tests on panels modified with viscoelastic layer. Figure 19: Impact tests for gravity weight drop of 30 and 40 J of energy to modified panels. Figure 20: Characterization with penetrating ink to panels impacted at 40 J and 80 J.  
exposed to ultraviolet light show the same behavior. Vertical impact is similar to a fatigue event shown in slamming trials. According to the results of the accelerometer and the use of the respective formulation, the behavior of the panel during the impact at 40 and 80 Joules is observed in Figures 21 and 22. It is observed that the impactor breaks layers 1, 2 and 3, and then experiences a decrease in force. This means that the impact force is damped by the viscoelastic layer. The impactor breaks the next layers, from the decreased force causing less damage. Depending on the impact force, the impactor does more or less damage to layer 9 on which it has bounced. Both results, the presence of the viscoelastic sheet is fully identified. At the 80 Joules high-energy impact, the layers broke at similar time intervals, until the interference of the viscoelastic layer. The acceleration curve is clearly marked as it affects the impactor and protects subsequent layers. The energy absorbed by the modified panels for impacts of 30, 40, 80 and 120 Joules is shown in Figure 23. It is observed that the panels maintain their capacity to absorb impact energy, which indicates that the damage does not increase proportionally as which increases the impact energy. This is indicative of less damage to the matrix, which accumulates the kinetic energy imposed by the impactor.