Research On Fatigue Crack Initiation And Propagation Mechanism Of Heavy Duty Train During Long Downhill Braking Process

With the increase of freight train transportation capacity,the axle load increases and the friction between wheel and rail is intensified.Besides,I have traveled over mountainous areas in railway more often,and the railway ramps are slow,so I need to go through quite a long distance when going downhill.Therefore,constant braking is needed in this process.In the process of periodic braking,friction between brake shoe and wheel generates a lot of heat,which causes the temperature to rise,and material properties of wheel will change with temperature.With the increase of temperature,wheel tread is prone to fatigue damage under the variable load of rail and brake shoe.In order to obtain the fatigue life of train under long and downhill cycle braking conditions,the mechanical parameters of wheel steel CL60 at different temperatures were measured by high temperature creep testing machine.The obtained mechanical parameters were set in the finite element software Abaqus,and the mechanical load of the rail and brake shoe was applied to the wheel with the subroutine.The heat generation between the wheel and brake shoe was calculated with the function relation,and the heat flux density between the wheel and brake shoe,the contact heat transfer of the wheel rail,the convective heat transfer of the wheel and air and the heat radiation were set.The results of temperature and stress distribution were obtained by finite element method after7 consecutive braking times.The fracture energy of the material at different temperatures was obtained by using the stress-strain curves obtained by tensile fracture test,and the critical elongation of the material at different temperatures was calculated.Two-and three-dimensional models of near-field dynamics were established using the finite element results as external loads.The depth direction of wheel tread and the process of crack initiation and propagation on the tread surface were obtained.The equivalent principal stress was obtained by finite element method.The damage and crack initiation life of wheel tread were calculated by local stress-strain analysis method and Miner damage accumulation method.Combined with the crack length obtained by two-dimensional near-field dynamics,the propagation life of the crack is obtained by using Paris crack propagation rate calculation method.