# Research on Response Postures of Subway Train in Straight Line Collision
## 4 Train-Train Collision  
### Frontal Collision  
As shown in Figure 12, under the collision conditions specified by EN 15227 for C-II class railway vehicles (i.e., subway trains), the primary energy-absorbing components are the coupler buffer devices on the moving train set and the stationary train set. Figure 13 illustrates the energy absorption process of the coupler buffer device between carriages of the moving train set under above condition. It can be seen that energy absorption by the coupler buffer device ends at 0.8 s, and the energy absorption starts sequentially, with the energy absorption values decreasing from the front to the rear. The energy absorbed by the carriages is primarily recoverable elastic strain energy, accounting for only 4.9% to 7% of the total energy absorption of the coupler buffer devices. The energy absorption of the front aluminum alloy frame accounts for only 1.47% of the energy absorbed by the front coupler buffer device, and similarly, there is essentially no plastic deformation. It can be concluded that under the collision condition specified by EN 15227, the aluminum alloy frame at the front of the train and all carriages essentially do not undergo plastic  
Figure 11: Carriages and couplers number. deformation. The impact energy is entirely absorbed by the coupler buffer devices, and there is no damage to the train. By extracting the vertical (Y-direction) displacement of the wheelsets of the moving and stationary train sets, it is found that the maximum vertical relative displacement between the wheel and rail for the moving train set is 2.5 mm, while for the stationary train set it is 12 mm. According to EN 15227, the requirement for the climbing control of railway vehicles is that the lift of the wheelset relative to the track surface should not exceed 75% of the flange height [21]. The maximum vertical displacement for both train sets is below this value, indicating that the subway model meets the standard requirements  
When the relative collision speed increases, energy absorption values of each part at 36 km/h and 45 km/h are shown in Figure 12. The energy dissipation is basically completed by the coupler buffer device at relative collision speed of 25 km/h and 36 km/h, and there is basically no plastic deformation or little plastic deformation of the carriage. As the impact velocity increases to 45 km/h, the energy absorption value of the aluminum alloy front frame increases significantly, the degree of plastic deformation increases. The distance from the top of the wheel flange to the track surface for this train model is 22 mm. That is, when the vertical relative displacement between the wheel and rail exceeds 22 mm, the wheel loses its constraint from the track at that moment. The maximum vertical displacement of each wheelset at different collision speeds is shown in Figure 14. During the relative collision speeds between 25 km/h and 45 km/h, only a few wheelsets of the moving and stationary trains experienced a brief derailment phenomenon (i.e., the wheels briefly lifted off the track, with the vertical relative displacement between the wheel and  
Figure 12: Energy absorption of subway train under different velocity. The blue rectangular prism represents the moving train, the red cylinder represents the stationary train, the blue circle represents the derailment of a carriage of the moving train, and the red triangle represents the derailment of a carriage of the stationary train. The aluminum alloy front frame is numbered as 0. Figure 13: Energy absorption history curves of coupler buffer device in 25 km/h head-on collision condition. rail exceeding 22 mm, but eventually returning to the track surface. The briefly derailed carriage is shown in Figure 7. No derailment or climbing phenomena occurred. It can be seen that in the above collision speed range of the six-car subway train model, the impact energy absorption is mainly completed by the train body and buffer device in front of the fourth carriage, without derailment and other accident risks.