## 4 Structural Crashworthiness  
### Influence of Connecting Diaphragm Thickness  
Connecting diaphragms can constrain bending modes, and connecting diaphragms are capable of constraining the buckling modes, allowing the energy-absorbing structure to undergo sequential progressive buckling, thereby enhancing its energy absorption capacity. Due to the limited size of individual aluminum honeycomb cells, they cannot meet the substantial energy absorption requirements of subway vehicles during a collision. Moreover, increasing the size of a single honeycomb cell can easily lead to instability during the collision, resulting in a less-than-ideal deformation pattern. Therefore, multiple aluminum honeycomb cells are used in series, with the spacing between honeycombs as shown in Figure 3, and connecting diaphragms are inserted in between them. This combined arrangement significantly increases the energy absorption capability of the honeycombs. The role of the connecting diaphragms is to prevent adjacent honeycomb blocks from interlocking, which could deteriorate the energy absorption effect, ensuring a more stable and orderly deformation process. Consequently, the thickness of the connecting diaphragms has a significant impact on the energy absorption outcomes of the entire aluminum honeycomb anti-climb device. Variable thicknesses of the connecting diaphragms, denoted as tI, are selected with values of 2, 3, 4, 5, and 6 mm. The impact force and energy absorption are calculated for each connecting diaphragm thickness. Figure 4 presents the collision force-displacement curves and energy absorption-displacement curves for different connecting diaphragm thicknesses. Figure 4: (**a**) Collision force–displacement curves for different connecting diaphragm thicknesses; (**b**) Energy absorption–displacement curves for different connecting diaphragm thicknesses. From Figure 4a, it can be observed that different connecting diaphragm thicknesses have a significant impact on the impact force of the anti-climb energy-absorbing device, while having a smaller effect on the initial peak force. In the initial stage, except for the connecting diaphragm with a thickness of 2 mm, which shows a distinct difference, the impact force and initial peak force for the other thickness parameters remain consistent. This indicates that the connecting diaphragm thickness does not significantly affect the initial peak force of the anti-climb energy-absorbing device. However, after the initial stage, it is found that different connecting diaphragm thicknesses have a more pronounced effect on the maximum impact force peak value. Especially for the 5 mm thickness, the maximum peak force approaches 1000 kN, which is significantly higher than the initial peak force, and the maximum peak force also increases with the increase in connecting diaphragm thickness. Therefore, when designing the partition walls for the anti-climb energy-absorbing device, it is necessary to consider the impact of the connecting diaphragm on the peak force, aiming to reduce the connecting diaphragm thickness as much as possible while ensuring the energy absorption effect of the device. Figure 4b shows that in the initial stage, the energy absorption does not change with the connecting diaphragm thickness and has a minor effect on energy absorption. As the compression displacement increases, there is a certain fluctuation in the energy absorption. When the connecting diaphragm thickness is 4 mm, the energy absorption is the greatest. After the compression displacement exceeds 443 mm, the anti-climb energy-absorbing device with a 5 mm connecting diaphragm thickness has the highest energy absorption. At a compression displacement of 538 mm, there is a trend that the energy absorption increases with the increase in connecting diaphragm thickness, with the energy absorption of the 6 mm connecting diaphragm being 7.5% higher than that of the 3 mm partition wall.