## 2 Materials and Methods  
The proposed energy absorbing method is based on the composite of porous materials and elastic polymer materials. The microscale structural representation of the proposed composite porous material modified by an elastic polymer fiber network is shown in Figure 2. The particles of the porous material are connected by the elastic polymer fiber, thereby forming the micro-network structure. This material design is based on the following two principles. First, mass of the porous material is much larger than that of the polymer, in order to maintain high porosity and achieve high energy absorption characteristics. Second, the network structure of the polymer has a binding effect on the porous material particles, so that the particles can recover to their initial state after the extreme impact. Therefore, the mass-ratio optimization of polymer and the formation of polymer network structure are the key to improve the energy absorption characteristics of composite materials in extreme multi-impact, which are discussed thoroughly in the following part of this paper. According to [PERSON] [26], activated carbon powder can be processed into thin film, which is a typical porous structure consisting of a large number of pores inside. Compared with foamed metal, the composite of porous carbon and elastic polymer is more easily realized in the process [27; 28]. EPDM (Ethylene-Propylene-Diene Monomer) rubber is a typical elastic polymer with good elasticity and stretching capability, which is applied in various fields [17]. Activated carbon and EPDM rubber are taken as an example in this study, as they are easier to mold. The activated carbon powder  
Figure 2: Schematic diagram of microscale structure change. (Hongsheng Activated Carbon Company, Guangzhou, China; \(\geq 140\) mL/g) is the basis porous material, and PVDF (Polyvinylidene Fluoride) (Arkema Chemical Co., France, Paris; 99%, HSV900) is used as binder to help activated carbon form the film [29]. In Reference [26], polymers can be stretched into the fibrous form under the shearing force and high temperature of the rubber mixing mill. In this paper, this method is adopted and the EPDM rubber (HMC Polymers Company Ltd., Bangkok, Thailand) is added to the porous material to improve the elasticity. The fabrication steps in Figure 3 are as follows. Step 1: Thoroughly mix the activated carbon powder and PVDF powder at a mass ratio of 85:15 in a ball mill (Shenzhen Mingruxiang Automation Equipment Co., Ltd., Shenzhen, China; MRX-ZQM1) for two hours. Step 2: Put the mixed powder into the rubber mixing mill (Dongguan Zhenggong Mechanical and Electrical Equipment Technology Co., Ltd., Dongguan, China; Eight-inch Double-roller Converter Speed-adjusting Mixer) under high-temperature conditions (150 \({}^{\circ}\)C) for two hours to produce a thin, pure activated carbon film (\(2.0\pm 0.1\) mm). The rotation speed of the front and back rollers are 4 r/min and 3.2 r/min, respectively. For the small speed difference, stress plays a major role in the process. Step 3: Put the thin film and EPDM rubber into the rubber mixing mill under high-temperature heating conditions (110 \({}^{\circ}\)C) for one hour, to produce the composite material film (2.0 \(\pm\) 0.1 mm). The rotation speed of the front and back rollers are 15 r/min and 12 r/min, respectively. The large speed difference can generate a high shear force on the surface of the film and EPDM rubber. According to the SEM (Scanning Electron Microscope) image, at a continuous shear force, the EPDM rubber is stretched to form a micro-network structure, which can wrap the activated carbon particles. Seven material ratios were prepared in this study. The M0 (0%) sample is a pure activated carbon film (regardless of the PVDF) without EPDM rubber, whereas the others are activated carbon films  
Figure 3: Schematic diagram of material preparation. with different mass ratios of EPDM rubber.