Impact Characteristics Of Metro Trains Coupler And Draft Gears And Its Effect On Derailment Behavior

The metro train has become the first choice for citizens to travel because of its advantages such as convenience,fast speed and large load bearing.However,the global metro train accidents are common,among which the derailment accidents caused by the coupler and draft gear should not be underestimated.Therefore,a certain type of metro train coupler and draft gear is taken as the research object in this thesis.A detailed finite element model is established to accurately simulate the axial and motion characteristics.On this basis,a four-train finite element model of metro train is established.The collision characteristics of the coupler under different working conditions and its influence on the derailment are studied in depth.It is of great significance to further analyze the characteristics of the coupler in the collision and help to improve the passive safety performance of metro trains.Firstly,the finite element models of the clay buffer and the crushing tube are established.On this basis,the detailed finite element models of automatic and semi-permanent coupler and draft gears are established.In view of the axial characteristics of the coupler and draft gear,the energy absorption characteristics of the buffer,the tube and the failure characteristics of the overload protection device are considered.According to its motion characteristics,nodding and yaw motion are mainly considered.Based on this,five working conditions are designed to verify the validity of the finite element model of the coupler.Secondly,based on the finite element models of automatic and semi-permanent coupler and draft gears,a four-train collision finite element model is established.According to the axial characteristics,five speed conditions of low-speed collision(8 km/h,15 km/h)and mediumspeed collision(25 km/h,36 km/h,48 km/h)are designed.According to the motion characteristics,the vertical height difference and lateral offset of the active and the passive vehicle are set as 0 mm,20 mm,40 mm and 60 mm,respectively,at the initial impact speed of25 km/h.The effects of three single variables,as mentioned above,on the action process and motion attitude of the coupler and on the derailment behavior of the train are studied respectively.According to the analysis,the impact characteristics of coupler and draft gear are analyzed,and the laws are as follows:(1)The action process of coupler is related to the corresponding interface force.(2)Due to the impact of the buffer,the active and passive crushing tubes of the head car acted one after another.And the utilization rate of the tube is affected by the failure sequence of the coupler and draft gear.(3)The motion characteristics are related to its force and stroke.In low-speed collision,the higher the collision speed is,the more violent the coupler will be.In medium-speed collision,it is just the opposite.(4)The nodding and yaw angle of the coupler will increase due to the vertical height difference.With the increase of the vertical height difference,the nodding motion becomes more intense,while the yaw motion becomes vice versa.(5)The larger the lateral offset,the more intense the nodding and yaw motion of the coupler.However,when the lateral offset is more than 40 mm,the motion degree of coupler is weakenedFinally,the derailment behavior is studied by comparing the derailment coefficients under different collision boundary conditions in this thesis.The results are as follows:(1)The derailment risk is the result of the combined action of the force borne by the coupler at both ends of the vehicle and the motion attitude.(2)During the action time of the head coupler retarder,in low-speed collision,the higher the speed,the greater the risk of derailment.But in mediumspeed collision,the opposite is true.When the collision speed is 15 km/h,the risk of derailment is the highest.(3)During the action time of the head coupler retarder,the vertical height difference between the opposite and passive trains will increase the risk of derailment.However,with the increase of it,the risk of derailment becomes smaller.(4)During the action time of the head coupler retarder,the risk of derailment increases with the increase of lateral offset of the main and passive trains,and decreases when the lateral offset is greater than 40 mm.