## 3 Results
### Aging Test and Absorption Model  
All of the specimens, treated according to IEC 60068, were controlled in weight according to ASTM D5229 to establish the trend of moisture diffusion in the material. In Figure 2, the water uptake results according to IEC 60068 of the present paper are compared to water uptake results according to ASTM D5229. The approach is the same, all of the data are collected at regular intervals for at least 400 h until the beginning of the asymptotic saturation. The difference is that ASTM D5229 provides a continuous spraying of distilled water on the specimen at 40 \({}^{\circ}\)C and 95%RH, whereas for the IEC 60068 the treatment is cyclic \(-20\) to 80 \({}^{\circ}\)C and 80 to 90%RH. The discrepancy of water uptake is appreciable between these two kinds of treatments, with the IEC 60068 the saturation is reached before. Diffusion is a thermally activated process so, once a certain activation energy threshold is exceeded, the process depends on the temperature at which the system is located. This can be modeled by the variation of the diffusion coefficient \(D\) according to the Arrhenius' law, in Equation (6):  
\[D=D_{0}\cdot exp^{(-\frac{\Delta E}{kT})} \tag{6}\] \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Test** & **Material** & \begin{tabular}{c} **Damping** \\ **Material** \\ \end{tabular} & **Test Specs** & \
\begin{tabular}{c} **Condition** \\ **before Test** \\ \end{tabular} &
\begin{tabular}{c} **N. of** \\ **Specimens** \\ \end{tabular} \\ \hline Absorption & T300/EP & Not Damped & IEC 60068 & untreated & 10 \\ T300/EP & HHZ & IEC 60068 & untreated & 10 \\ T300/EP & SUT & IEC 60068 & untreated & 10 \\ \hline Impact & T300/EP & Not Damped & 6 m/s & untreated \& aged & 6 \\ T300/EP & HHZ & 1.5 \& 6 m/s & untreated \& aged & 12 \\ T300/EP & SUT & 1.5 \& 6 m/s & untreated \& aged & 12 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Test configurations for T300/EP Composites and damped sandwiches. with \(D_{0}\) as the maximal diffusion coefficient (at infinite temperature; m\({}^{2}\)/s), \(\Delta\)E as activation energy for the diffusion process (J/mol), \(R\) as the universal gas constant and \(T\) as temperature (K). The ASTM D5229 thermal cycle keeps the temperature and humidity constant over time, therefore the total time of the duration of the diffusion process can be considered the sum of all of the hours of aging. In IEC 60068, on the other hand, the cycle is divided into three phases, two of which at 80 \({}^{\circ}\)C while the last at \(-\)20 \({}^{\circ}\)C. In this case it is correct to take into account only the hours in which the sample was subjected to 80 \({}^{\circ}\)C. It has been assumed that during freezing hours there is not enough energy to activate the diffusion process. Sandwiches with damping materials have the same behavior and the same moisture absorption, that is lower than the undamped composite. This can be due to the presence of the rubber, but the behavior has to be studied with further analysis. The diffusivity values for both the ASTM D5229 and IEC 60068 tests are reported in the Table 3. It can be seen that for the IEC 60068 not only the saturation is reached before the ASTM D5229, but also the coefficient of diffusivity is one order of magnitude greater. By comparing the data obtained with IEC 60068 and ASTM D5229 it is possible to obtain the activation energy of the diffusion process and the diffusion coefficient at infinite temperature for this kind of plastic-reinforced composite material. Plotting In(D) vs. 1/T, it was obtained constant \(D_{0}\) from the intercept and the value of \(\Delta\)E from the slope of the regression line, respectively. Thus, an activation energy equal to 237.3 J/mol and a maximal diffusion coefficient at infinite temperature of 6.2 m\({}^{2}\)/s is obtained, which would allow one to obtain a diffusion profile at different temperatures with the consequent saturation absorption time. Figure 2: Moisture uptake for T300/EP composites and damped sandwiches with error bars.