## 3 Results
### Recoverability Analysis: Polymer Fiber Network Enhances Elasticity
As shown in Region 1, when the mass ratio of the EPDM rubber is less than 10%, the recovery coefficients of the samples increase rapidly with increasing EPDM rubber content. Hence, the restorability of the composite material improves clearly by the addition of EPDM rubber during the multiple loading processes, which is consistent with the result that the attenuation coefficient of the multi-impact decreases rapidly with increasing EPDM content. Furthermore, the buffering performances of the composite materials improve with increasing EPDM content. When the mass ratio of the EPDM rubber is over 10%, the recovery coefficients of the samples increase slowly and tend to stabilize. This result is consistent with the result that the attenuation coefficient decreases slightly and the decrease in the buffering coefficient is small during the multi-impact process for an EPDM rubber mass ratio of over 10%. To study the effect of the microstructure on the restorability, three typical samples, M0 (without EPDM rubber), M2 (10% EPDM rubber), and M6 (40% EPDM rubber), are selected for the scanning electron microscopy (SEM) tests. Figure 9a presents the SEM image of M0 (0%). Clearly, the activated carbon film is a porous material composed of activated carbon particles and pores in the microscopic state. The pores are clearly visible at \(10,000\times\) magnification and will be compressed and deformed during an impact process. Figure 9b presents the SEM image of the M2 (10%) sample. The added EPDM rubber exists in the form of fibers under the action of a shearing force, and the activated carbon particles are connected to each other by the EPDM rubber fiber, thereby forming a micro-network envelope structure. This structure will lead to an increase in the elastic ability of the composite material based on the plastic deformation ability. Hence, M2 can exhibit a better buffering effect in the multi-impact process. First, the SEM image verifies that the composite of the activated carbon and EPDM rubber exhibits the characteristics of the proposed structure. Second, it explains the reason of the improvement of the recovery coefficient. Moreover, Figure 9c shows the SEM image of M6 (40%). When the mass ratio of the EPDM rubber reaches 40%, the activated carbon particles are completely covered by rubber, and the pores are filled up with rubber. The pores are barely visible at \(10,000\times\) magnification. In addition, the elastic deformation capacity is greatly improved. Therefore, the attenuation coefficient of M6 (40%) changes slightly during the multi-impact process. As the EPDM network exhibits a fiber structure, the elasticity modulus can be determined based on an empirical equation proposed in [32; 33; 34; 35]. \[\frac{E}{E_{m}}=\frac{1+\xi\eta\varphi_{f}}{1-\eta\varphi_{f}} \tag{4}\]  
\[\eta=\frac{(E_{f}/E_{m})-1}{(E_{f}/E_{m})+\xi}. \tag{5}\]  
Figure 9: (**a-c**) SEM images of pure activated carbon film, activated carbon film containing 10% EPDM rubber, and activated carbon film containing 40% EPDM rubber, respectively. Here, \(E\) represents the elasticity modulus of the composite material; \(E_{m}\) the elasticity modulus of the pure activated carbon film; \(E_{f}\) the elasticity modulus of the fiber; \(\xi\) a non-negative value, which represents the fiber reinforcement effect and depends on the geometry, arrangement, and loading conditions of the fibers; and \(\varphi_{f}\) is the fiber volume fraction. For \(\xi=0\):  
\[\eta=1-\frac{E_{m}}{E_{f}}. \tag{6}\]  
Therefore, Equation (4) becomes:  
\[\frac{1}{E}=\frac{\varphi_{f}}{E_{f}}+\frac{1-\varphi_{f}}{E_{m}}. \tag{7}\]  
The strain \(\varepsilon\) can be determined as follows:  
Figure 7:0  
When \(\xi\rightarrow\infty\), \(\eta\to 0\):  
Figure 7:1  
and  
Figure 7:2  
Consequently, the strain \(\varepsilon\) is expressed as follows:  
Figure 7:3  
Based on the quasi-static compression mechanical test, \(E_{m}=29\)MPa\(a\) and \(E_{f}=78\)MPa\(a\).