Energy-absorbing Structure Study And Safety Evaluation Of High-speed Trains Meeting In Open Air

With the rapid development of high-speed trains in China, the problem of railway safety has been paid more and more attention. Especially when an accident of high-speed trains crash happens, the personal injuries and property losses are immeasurable. The developed countries in Europe and America started a lot of researches on vehicle collision in1990s. The Ministry of Railways in China also with some universities established high-speed EMU importing, absorbing and re-innovating research group. Earlier studies show that when a high-speed train has a collision, the head of the train first participate in the impact process. The force goes along the draft sill, and then go into the side beams which form a force conductive structure. At the same time, because the collision brings an impulsive load, the stress wave caused by the collision will pass behind with refraction and transmission many times. Due to a complex structure of a train inside, stress wave propagation is very complex. When a high-speed train travels properly, stiffness of structures is needed which should meet the requirements of the technical specification. When the collision happens, in order to reduce the loss, protect the passive safety, it is necessary to study and design the energy-absorbing structure for the high speed trains according to its own characteristics. Ideal energy-absorbing structure should be located in the front and the back of a carbody, deform plastically in the controllable deformation area, absorb the impact energy, ensure no serious damage in the passenger region, and not produce impact force too large in the crash, which may be beyond the limit human body can stand. In this thesis, with the experimental investigation, under the premise that the original vehicle structure can not be changed much, we add a thin-walled circle tube filled with aluminum foam as the energy-absorbing structure. Through the finite element simulation, we have done analysis on crashworthiness of trains both before and after improved and get the conclusion that the new added structure in the energy absorbing area has good advantage of absorbing energy, which provides theoretical guidance for production of vehicles.When high-speed trains meet in the open air, there will be a moving load pressure wave generated between two trains. The wavelength, amplitude and other physical characteristics of the transient load wave are decided by the meeting speed, the line spacing, the geometry of the train head and other factors. Some researches show that the meeting pressure wave will influence the safety and stability of travelling high-speed trains. In this paper we adopt the method of multi-body dynamics to establish the middle carbody of high-speed trains, and simplify the mobile load wave as the force and moment acting on the train. By comparing the body swing, lateral wheel-rail forces, derailment coefficients, rate of wheel load reduction and other safety indicators of the trains at the same speed when travelling alone and meeting in the open air, we can find out that the pressure pulse caused by trains meeting in the open air has some impact on the travelling safety of the high-speed trains.In this thesis, a finite element model of a head carriage is established. We simulated the situations that the head-car body of the train crashes a rigid wall at10m/s and20m/s (equivalent to a train at72km/h and144km/h crashing a same still train). Because the running speed of the train is less than200km/h usually, the crash speed is sufficient to meet the safety requirements. When the train starting or braking, the coupler will absorb some energy which is small compared with the impact energy of the system, and drop in a short period of time, so it has little influence on the crashworthiness analysis. We ignore the influence of the coupler in the impact events. A period of300ms used in this simulation. According to the crashworthiness analysis, we can get the energy absorption curve of the draft sill, the impact force and the trains damage.When a crash occurs, the energy-absorbing parts of the original structure, mainly deform in Euler buckling mode, which is not conducive to the energy absorption and the buffer of impact force through the numerical simulation. Therefore, according to the experiment and based on the actual situation that we can only make some local improvements of the vehicle design and the train can not be extended, we put forward four improvement schemes. We change the main part of the draft sill to rounded square tube from the original square tube and add some energy-absorbing tubes in coaxial position. Through the numerical calculation, we got the energy absorption curves of draft sills and the rigid wall counter-force curves of the four schemes at2crash speeds, compared the energy absorption performance of the four improvement schemes and found out the deformation mode and energy absorption law of the main energy-absorbing structure under the four schemes. Finally, the results show that the energy-absorbing structure in the best improvement scheme can make the energy absorption improve322%, the peak of the counter-force reduce12%, relative to the original design at lOm/s; make the energy absorption improve288%, the peak of the counter-force reduce36%, at20m/s, which has significant effects.Dynamic response of a carriage under excitations with high speed, low interference track spectrum of German together with the air pressure pulses generated as high-speed trains passing each other at six constant velocities (250～500km/h) are simulated with a multi-body dynamics method. The variations of DOFs (horizontal movement, roll angle and yaw angle), lateral wheel-rail force, derailment coefficient and rate of wheel load reduction with time when two carriages meet in the open air are obtained and compared with the results of a single train travelling at the same speed. Results show that all safety indexes are allowed except the rate of wheel load reduction. Among them the lateral wheel-rail force and derailment coefficient meet the safety standards well, while the horizontal movement and yaw angle are much larger than those in the single train case. The rate of wheel load reduction at a speed over400km/h is obviously affected by the air pressure pulses. According to the safety standard for the rate of wheel load reduction in Europe and United States, the corresponding standard of China seems conservative and should be relaxed properly, with limitation of overtime as a complement. Thus, the influence of pressure pulses should be considered in the train safety evaluation.