## 2 Materials and Methods
### Testing Procedure  
Rectangular samples with the size of 60 \(\times\) 10 mm\({}^{2}\) were extracted by the hybrid laminates for dynamic mechanical analysis (DMA), one sample from each laminate. Isothermal tests (by Netzsch DMA 242C) were performed in 3-point bending configuration for 5 min at room temperature (25 \({}^{\circ}\)C) with the frequency of 10 Hz and the span-length of 40 mm. Neat samples of elastomers (soft and rigid) and CFR laminate (3-ply) were extracted for comparison from the hybrid composites The final value of storage modulus (E') and loss factor (tg 8) were used for comparison. After DMA testing, the same hybrid specimens were used for quasi-static bending tests by the universal material testing machine (Insight 5 by MTS). The same 3-point bending configuration of DMA was adopted, with the span-length of 40 mm, at the rate of 1 mm/min up to 1 mm of maximum displacement and at room temperature (25 \({}^{\circ}\)C, 40% RH). The elastic modulus (E) was extracted from quasi-static bending tests to be compared \begin{table}
\begin{tabular}{c c c} \hline \hline
**Hybrid Laminate** & **Thickness, mm** & **Density, g/cm\({}^{3}\)** \\ \hline _Rigid elastomer_ & & \\ C3-E1-C3 & 2.88 & 1.26 \\ C3-E2-C3 & 4.79 & 1.23 \\ C1-E1-C2-E1-C2-E1-C1 & 5.86 & 1.15 \\ C1-E1-C4-E1-C1 & 4.35 & 1.19 \\ C2-E1-C2-E1-C2 & 4.36 & 1.18 \\ E1-C6-E1 & 4.35 & 1.18 \\ _Soft elastomer_ & & \\ C3-E1-C3 & 4.28 & 1.28 \\ C3-E2-C3 & 7.87 & 1.20 \\ C1-E1-C2-E1-C2-E1-C1 & 9.89 & 1.20 \\ C1-E1-C4-E1-C1 & 4 & 1.28 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Thickness and density of molded hybrid composite laminates. with E'. In fact, differences are expected because of the effect of the loading conditions (cyclic and quasi-static) and the adopted elasticity range. DMA tests analyze samples in a micro-range (up to 120 \(\upmu\)m), whereas quasi-static bending tests use a large displacement range (up to 1 mm). Rubbers and elastomers are particularly sensitive to the elastic range of testing, being more rigid at low displacements. For dynamic testing in the universal material testing machine, larger size samples were extracted (150 \(\times\) 30 mm\({}^{2}\)), 4 samples from each laminate. One of these samples, for each type, was used for cyclic bending tests. In this dynamic test, 10 loading-unloading cycles were repeated by applying a maximum displacement of 10 mm at the testing rate of 10 mm/min, with an initial pre-load of 0.5 N and a span length of 120 mm at room temperature (25 \({}^{\circ}\)C, 40% RH). The testing setup details are depicted in Figure 4a, for the quasi-static test. Inversion occurred at the maximum displacement and at the pre-load. Figure 5 shows a typical cyclic bending test in terms of load-time and stress-strain curves. A small decrease in the load peak is observed during cycling (Figure 5a), primarily after the first cycle, and rarely in the last cycles. The stress-strain curve (Figure 5b) shows the typical hysteresis of damping, the area of which is the evaluation of the energy loss in that loading-unloading cycle. Figure 4: Testing setup details for quasi-static tests (**a**) and for dynamic free oscillation tests (**b**). Figure 3: Cross-section of hybrid laminates and details of such interfaces. The last test was performed to evaluate the behavior of the hybrid samples under free oscillations. Single cantilever configuration was used considering a span length of 120 mm and the maximum displacement of 30 mm. The tests were conducted at room temperature (25 \({}^{\circ}\)C, 40% RH). The free end was fixed by a metal wire to the testing machine cross-head to apply the initial inflection. An accelerometer was placed on the bottom surface of the sample at the same end. By cutting the wire, it was possible to measure the acceleration damping over time. As shown in Figure 4b, acceleration data were acquired by using a mono-axial accelerometer fixed on the free end. A vibration meter PCE-VT-2800, with resolution of 0.1 m/s\({}^{2}\) and accuracy of \(\pm\) 5%, was used with the acquisition rate at 160 Hz.