## 2 Materials and Methods  
For this study two laminates were generated, one by autoclave (A) and the other by vacuum bag-only (VBO) as shown in Figure 3.  
Figure 2: Micrographs of laminates: (**a**) autoclave processing, and (**b**) vacuum bag-only (VBO) processing. Blue circles show voids in the VBO laminate. Since each solid presents resonances that can be expressed as a direct proportion to the speed of sound of the material that constitutes it, we can extrapolate from the study of the speed of sound to a simple geometry that allows analysis of the material with precision. The geometry used is the rectangular plate, since it allows for obtaining a great number of bending vibration modes. One way to express the resonances of a rectangular plate is [32]  
\[f_{n}=\frac{0.113h}{L^{2}}\ \sqrt{\frac{E}{\rho}}\ [2n+1] \tag{4}\]  
where \(h\) is the thickness, \(L\) is the length of the plate, \(E\) is the Young modulus, \(\rho\) is the density, and \(n\) is the number of nodes. To be able to cover a range equivalent to three octaves above and below the A3 reference (440 Hz), the frequency range of the study was focused such that 0 \(<\)\(f\)\(<\) 2000 Hz. For this, the plate dimensions must be adjusted using Equation (4), which defines the resonances for plates. The multipurpose CFRE system considered for this investigation was GG280T (Tenax HTA-3k)-DT806R-42 Fabric Laminate manufactured by an external company, (Magma Composites S.L, Alcaniz, Aragon, Spain) using prepreg plies supplied by Delta Preg Composites. DT806 is an epoxy resin with a glass transition temperature (Tg) of approximately 135 \({}^{\circ}\)C. GG280T is a 4/4 full carbon fabric, 3K high strength (HS) carbon fiber reinforcement having a density of 198 g/cm\({}^{2}\). Plates with dimensions of 220 \(\times\) 220 mm were manufactured by the vacuum bag-only and the autoclave method, layering three collinear plies to an approximate total thickness of 1.03 mm. Plate A was cured in an autoclave at 120 \({}^{\circ}\)C for 1 hour, without post-cure. The pressure was 4 atm for the autoclave plate (A), and atmospheric pressure was used for the VBO plate. The manufactured plates were afterwards cut down to 30 \(\times\) 200 mm plates, as shown in Figure 4.  
A total of five specimens (dimensions: 200 mm \(\times\) 30 mm \(\times\) 1.035 mm) were manufactured using three collinear layers, considering that the fiber directions were parallel to the sides of the rectangles that make up the specimen, as shown in the Figure 5.  
Properties provided by the manufacturer are shown in Table 1.  
In order to characterize the elastic and non-elastic properties of the specimens, a dynamic test was carried out using the vibration procedure under free conditions stipulated in ISO 6721-3 [45], as illustrated in Figure 6.  
Figure 3: (**a**) Autoclave and (**b**) VBO CFRE plates. Figure 4: Manufacturing process of CFRE specimens: (**a**) cutting of \(30\times 200\) mm specimens; (**b**) finished specimens; and (**c**) detailed visual comparison of the surface of autoclave and VBO top surfaces. Figure 5: Specimens (**a**) VBO and (**b**) autoclave. Figure 2:0 Experimental procedure for identifying resonance frequencies by external excitation [51]. \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline  & \multicolumn{3}{c}{**Young Modulus (GPa)**} & \multicolumn{3}{c}{**Poisson Ratio**} & \multicolumn{3}{c}{**Shear Modulus (GPa)**} \\ \hline
**Density (kg/m\({}^{3}\))** & **x** & **y** & **z** & **Xy** & **yz** & **xz** & **xy** & **yz** & **xz** \\ \hline
1420 & 35.9 & 35.9 & 6.9 & 0.04 & 0.34 & 0.34 & 11.5 & 2.7 & 2.7 \\ \hline \end{tabular}
\end{table} 
Table 1: Static mechanical properties of carbon fiber reinforced epoxy prepreg. In the second part of the study, the composite loss modulus \(E^{\prime}{}_{f}\) was obtained for each of the vibrational modes. To do this, the signal decrement of the oscillations in free conditions was analyzed for each of the resonances obtained.