## 3 Results
### Energy Absorption Analysis: Small-Scale Pores Contribute Most to the Buffering Ability  
The porosity analysis tests are conducted with a mercury porosimeter analyzer (Quantachrome Instrument; Poremaster GT60) to analyze the influence of the internal microstructure of the composite material on the energy absorption characteristics. The results are shown in Figure 11. According to Figure 11a, the porosities of the four samples M0 (0%), M2 (10%), M4 (20%), and M6 (40%) are 50.678%, 45.608%, 32.62%, and 14.236%, respectively. Hence, the inner pores can be compressed during the impact process in order to reduce the overload acting on the protected parts and realize the buffering effect. In addition, the energy absorption characteristics are closely related to the porosity. The higher the porosity, the stronger are the energy absorption characteristics. According to the overall trend, the porosity of the samples decreases with increasing EPDM rubber proportion, which is consistent with the result that the buffering coefficient of the single impact process decreases gradually in Figure 5b. The porosity volume of the pure activated carbon film (M0 (0%)) is larger than the half sample volume, which is consistent with the fact (Figure 9a) that the pure activated carbon film consists of activated carbon particles and many pores. When the EPDM rubber proportion increases to 40%, the porosity decreases sharply. This is reflected in Figure 9c, in which the pores are barely visible at \(10,000\times\) magnification. Regarding the local change trend, compared with that of M0 (0%), although the EPDM mass ratio of M2 (10%) is increased by 10%, the porosity decreases only by 5.07%. By contrast, the porosity of M4 (20%) decreases by 12.988% with respect to that of M2 (10%), despite the 10% mass ratio increase of EPDM rubber. This is consistent with the result that the buffering coefficient of M2 (10%) decreases slightly compared with that of M0 (0%), whereas the buffering coefficient of M4 (20%) decreases dramatically compared with that of M2 (10%) during the single impact process. Figure 11: (**a**) Porosity of test materials containing different mass ratios of EPDM rubber; (**b**) Pore size distribution; (**c**) Pore volumes of test materials containing different proportions of EPDM; (**d**) Relationship between buffering ratio and pore volume (size \(<\) 1 \(\upmu\)m). The pore size distributions of the four test samples are shown in Figure 11b. The \(x\)-axis represents the pore diameter (\(\mu\)m; logarithmic form). Based on the large pore size span, the \(y\)-axis is the differential of the logarithm of the pore volume with respect to the pore diameter (cm\({}^{3}\)/g), according to the BjH algorithm. Furthermore, the pore sizes of the samples decrease with increasing EPDM rubber proportion, in particular for M4 (20%) and M6 (40%). The pore size distribution of M2 (10%) is similar to that of M0 (0%), whereas the pore size distributions of M4 (20%) and M6 (40%) are quite different from that of M0. By integrating the pore size distribution of each sample, the pore volume is divided into two parts by taking the pore size 1 \(\mu\)m as the limit, as shown in Figure 11c. This step is necessary for analyzing the effect of the increasing EPDM proportion on the pore size of the activated carbon film. According to Figure 11c, compared with that of M0 (0%), the reduction (0.1608 mL/g) in the small-scale pore volume (size \(<\) 1 \(\mu\)m) of M2 (10%) is slightly higher than the reduction (0.1309 mL/g) in the large-scale pore volume (size \(>\) 1 \(\mu\)m). However, the large-scale pore volume (size \(>\) 1 \(\mu\)m) of M4 (20%) basically does not change compared with that of M2 (10%), whereas the small-scale pore volume (size \(<\) 1 \(\mu\)m) of M4 (20%) decreases greatly, from 0.4108 to 0.0949 mL/g.