## 2 Materials and Methods
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Temperature**} & \multicolumn{5}{c}{**Young’s Modulus [GPa]**} \\ \cline{2-6}  & **T300/EP** & **SUT** & **HHZ** &
\begin{tabular}{c} **Sandwich** \\ **T300/EP + SUT** \\ \end{tabular} & **Sandwich** \\ \hline \(-\)20 \({}^{\circ}\)C & 28 & 2 & 7 & 33 & 35 \\ +20 \({}^{\circ}\)C & 28 & 1 & 2 & 23 & 33 \\ +60 \({}^{\circ}\)C & 28 & 1 & 1 & 13 & 25 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Young’s Modulus averaged values for the composite laminate, for the pure damping layers and for the Sandwich laminates with SUT and HHZ at temperature of \(-\)20, 20, and 60 \({}^{\circ}\)C in untreated conditions. The impact tests were carried out in first analysis on the untreated material and subsequently on the specimens aged for 750 h. No intermediate tests were performed due to the small number of specimens that can be inserted into the aging machine. The aging has been carried out using an Angelantoni Challenge 250 Climatic Chamber. To simulate the behavior of the damping materials at different stages of life, it has been defined an aging cycle according to IEC 60068 standard [26]. The choice of this standard cycle is due to the specific application of these materials for Automotive sector. Output results are the average of at least three tests. The aging cycle used is reported in Figure 1, it has a duration of about 24 h, so each aging step of 250 h lasts for about 11 days. Specimens are exposed to different temperatures (\(-\)30 to +80 \({}^{\circ}\)C) at different stages of relative humidity (80 to 90% RH). For the different aging steps, the same specimens have been used. During freeze aging phase (blue dashed line), the relative humidity was not controlled as set by the IEC 60068 standard. The type of aging was chosen according to the final use of the component: an automotive industrial standard was used for this component. According to the IEC 60068 standard, aging method is composed by three cycles of 8 h each: two hot/wet cycles between 25-80 \({}^{\circ}\)C/90-80%RH and one cold cycle without humidity control. The alternation between cold and hot cycles is necessary to evaluate the variation of properties due to the formations of solid particles cooling the liquids. In fact, in each cycle there is a first phase of absorption of moisture during standstill at 80 \({}^{\circ}\)C and a subsequent ice formation at \(-\)30 \({}^{\circ}\)C. This alternation of environmental conditions could be modified the material in a technological condition that is no longer acceptable for its purpose. This is a factor of considerable importance for the design of energy absorption structures. In the steady period at room temperature of the aging treatment, all of the specimens were dried and weighed using an analytic balance (with accuracy \(\pm\) 0.0001 g), according to the ASTM D5229 [34], with the same methodology adopted in [35]. The increasing mass of water were normalized using Equation (4). \[M_{f}=\frac{w_{f}-w_{i}}{w_{i}}\cdot 100\% \tag{4}\]  
where: \(M_{f}\) is the moisture mass uptake, \(w_{f}\) is the final mass, and \(w_{i}\) is the initial mass of the specimen. Figure 1: Controlled temperature and humidity diagram for the aging cycle IEC 60068. The graph of relative moisture uptake in function of time was plotted for all of the configurations, damped and undamped. The coefficient of diffusivity, explained in the Fick's Second Law, was calculated in the initial linear zone using the Equation (5). \[D_{z}=\pi\left(\frac{l}{4M_{eq}}\right)^{2}\left(\frac{w_{f}-w_{i}}{\sqrt{t_{f} -\sqrt{t_{i}}}}\right)^{2} \tag{5}\]  
where: \(D_{z}\) is the coefficient of diffusivity in z-direction (thickness), \(M_{eq}\) is the moisture mass uptake at equilibrium, \(l\) is the specimen thickness, \(t_{f}\) is the final time, and \(t_{f}\) is the initial time. This is an important value to quantify the level of water saturation of the specimen.