# Research on Response Postures of Subway Train in Straight Line Collision
## 7 Conclusions  
This paper explores the response postures of subway trains under various collision scenarios. By establishing a finite element model of a six-car elastic-plastic subway train and a one-dimensional multi-body dynamics theoretical model, the energy absorption characteristics and collision response postures of the subway train were studied. Multiple accident modes were observed in the finite element simulations, among which:  
1. A one-dimensional theoretical model is proposed, in which the train car is regarded as a deformable body divided into three mass points, representing the front collision end, the middle passenger area, and the rear collision end, respectively. These mass points are connected by two springs to simulate the deformation of the train car. When the longitudinal collision speed is less than or equal to 25 km/h, the total energy absorption error of the theoretical model compared with the simulation results is less than 6.53%, and the velocity curve matches well. The coupler is simplified as a nonlinear spring, and the definition of stiffness in the force rise phase is particularly important for the accuracy of the velocity attenuation curve. 2. Except for oblique collisions, when the train collision speed exceeds 25 km/h, direct collisions between the ends of the carriages are unavoidable. At this point, the out-of-sync pitch and yaw motions, along with the plastic deformation at the ends, aggravate the vertical arch phenomenon of the train, which is extremely detrimental to the safety of passengers inside the train. A front-side impact can easily lead to lateral buckling, and as the collision speed increases, the degree of lateral buckling becomes more severe. However, when the collision speed reaches 45 km/h, the degree of lateral buckling decreases by a certain percentage, and the vertical arch increases, becoming the dominant response posture. In the simulation, the addition of anti-climbing devices between the carriages significantly reduced the maximum vertical displacement of the wheels. 3. In the case of an oblique collision, the lateral impact force causes the train's front to laterally shift and slide, which is the fundamental cause of rapid derailment of the front wheels. When the collision angle exceeds 10\({}^{\circ}\), the energy absorption efficiency of the coupler device can be reduced by up to 83.9%, and the train's front frame experiences direct impact, leading to rapid derailment. The post-impact behavior is extremely dangerous. For such scenarios, it is necessary to consider adding anti-derailment devices or installing lateral energy absorption devices on the wheels. * For train collisions at a switch, in the case of an angled head-on collision (25 km/h), the train fronts misalign and quickly derail. The energy-absorbing structures fail to operate as intended, and the moving train continues to derail and slide with a relatively high residual speed. More complex collision scenarios at switches require further study. For the various dangerous postures after a train derailment, such as vertical arch, lateral buckling, and overturning, it is necessary not only to take measures to prevent derailment from occurring, but also to implement protective measures to reduce the threat posed by the train's continued movement to the passengers inside--for example, optimizing the carriage stiffness to ensure survival and escape space for passengers. The failure of the weak bolt points in the train's front frame (which commonly occurs under conditions where the train impacts a rigid wall at 45 km/h) has minimal impact on the overall energy absorption of the train and its different parts, but it does pose a certain threat to the driver's survival space. This issue is not clearly addressed in the standards of various countries, and reinforcement measures need further in-depth research. Regarding subway train collision accidents, in most real-life cases, emergency braking is applied before a collision occurs.