## 4 Discussion  
If the damage caused by the impact of slamming that occurs in the hulls of the GFRV vessels could be observed in the tests. These do evaluate the evolution of the energy that is being converted into damage inside the laminate.  
The insertion of a viscoelastic layer effectively mitigates the damage caused by the slamming phenomenon by reproducing the impacts under controlled laboratory conditions. The protection from the damage presented allows to absorb the dissipation of destructive energy, protecting the structure of the ship's hull and increasing its useful life. This brings a new perspective to the design of the ships and their scantlings, since the viscoelastic modification changes the way in which the stress concentrations are distributed in the hull of the boats. Comparing with the flexural stiffness values obtained along the scale of applied cycles, we observe in Figure 26 that over the \(5\times 10^{3}\), the unmodified and modified panels begin to distance in magnitude. The unmodified panel quickly gains flexural stiffness while the modified panel remains and does not change significantly.  
The panels impacted in pressure levels with values above and below the damage threshold calculated with the three-point flex test, marked an additional parameter to relate it to the maximum slamming pressure recommended by the ABS rules for the type of vessel selected.  
Figure 26: Comparison of the change in flexural stiffness during the slamming test with \(0.27\times 10^{5}\) cycles.  
Figure 25: Adhesion force obtained with the shear test.  
Visual observation of the damaged surface within the contact area with the cam served to calculate the percentage of damage. This is related to the stress values that exceeded the damage threshold, transformed into microcracks.  
The characterization by fluorescent penetrating inks, allowed us to physically observe how the damage does not propagate in the same way under the layers of the viscoelastic sheet, mixing this damage between the impact shock and the normal tension due to the flexion of the panel on the tensile side. Figure 27 shows two cut sections in the impact area already characterized by an unmodified and a modified panel, both impacted at 40 Joules. In the panel without modifying the interlaminar and intralaminar damages, they are linked, producing internal breaks in the laminate between layers 5 and 9 with important separations to the matrix. On the other hand, in the modified panel, the viscoelastic sheet protects the section of the laminate between layers 6 and 9, which correspond to those subsequent to the sheet. This means that it has returned the energy of damage and therefore little damage is observed on the underside, corresponding to microcracks and no delaminations.  
Figure 28 shows the same comparison, but for a test of 80 Joules. Damage to the unmodified panel is very severe and unusable. On the other hand, the damage for the modified panel is less. If there is delamination of layers 6 to 9 that correspond to the layers after the viscoelastic layer, but not in all the layers. Viscoelastic layer protected these layers from severe impact damage.  
According to these results, when comparing the absorbed energy calculations shown in Figure 29, there is a notable difference in the amount of energy for the same test at 30 Joules of impact. The modified panel absorbs little energy and returns it in a better way demonstrating protection.  
Figure 27: Comparison of the impact section for weight drop at 40 J characterized with fluorescent penetrating inks for unmodified panels (**a**) and modified panels (**b**).  
Figure 28: Comparison of the impact section for weight drop at 80 J characterized with fluorescent penetrating inks for unmodified panels (**a**) and modified panels (**b**).