The Impact Mechanical Response And Damage Rule Of The Wheel-rail System With A Wheel Flat

The wheel-rail interaction is an important research topic in the field of high-speed railway engineering.As a common type of wheel/rail failure,wheel flat is normally caused by the slipping or sliding of the wheel on the rail under the condition of a sudden lock of the vehicle during the braking process or the condition of a low adhesion(a local reduction of the wheelrail adhesion force).With the continuous increase of the running speed of high-speed trains,the wheel flat impacts circularly against the rail,resulting in the significantly larger dynamic periodic impact force than the corresponding quasi-static wheel load,which may result in severe damages to wheel-rail components and even inducing the wheel/rail failure.Besides,a serious rolling noise caused by the wheel flat affects greatly the comfortableness for passengers.In this study,the finite element simulation method is adopted,combining with partly experimental investigations and theoretical analyses,to explore the wheel-rail impact response and damage rule induced by a wheel flat.The main contents and results include the following aspects:(1)Quasi-static and dynamic mechanical performance tests on D1 railway wheel steel are conducted,and the stress-strain response curves of the wheel rim steel at different strain rates are obtained.Dynamic constitutive relations are established based on Cowper-Symonds empirical formula accordingly.(2)Based on the Hertz contact theory,a theoretical analysis of the wheel-rail impact is conducted,and the impact process of the wheel flat is described detailly.The results indicate that the wheel-rail impact force first increases and then decreases to a stable value with the increasing train speed,and the peak value is reached at the critical velocity;the wheel-rail impact force increases with the increasing flat length and axle load,respectively;the wheel-rail impact force decreases with the increasing wheel radius.(3)The three-dimensional wheel-rail rolling contact finite element model is built based on the real geometrical configuration of the wheel flat,and geometric nonlinearity,material nonlinearity and contact nonlinearity of the wheel-rail dynamic contact are considered.(4)Simulation analysis of the wheel-rail impact response induced by a wheel flat is conducted.Influences of train speed,flat length,axle load,strain-rate effect of wheel/rail materials and braking thermal stress on the wheel-rail impact response are discussed,repectively.The results indicate that the the maximum vertical wheel-rail impact force induced by a wheel flat is 2.6~4.4 times greater than the corresponding quasi-static value;the wheelrail impact response is found to be sensitive to the train speed,flat length and axle load.Both the vertical wheel-rail impact force and maximum XY shear stress are revealed to be insensitive to the strain-rate effect of wheel/rail materials;however,the maximum von-Mises equivalent stress and the maximum shear stress are increased when the strain-rate effect is considered,and the maximum equivalent plastic strain is also decreased.With the braking thermal stress considered,the maximum vertical wheel-rail impact force,maximum von-Mises equivalent stress and maximum XY shear stress are decreased significantly,and the maximum equivalent plastic strain is increased correspondingly.(5)On the base of the contact pressure and von-Mises equivalent stress distribtuiton of the wheel and rail during the moment of point B of the wheel flat impacts against the rail,the corresponding influences of strain-rate effect of wheel/rail materials,braking thermal stress,train speed,flat length and axle load are discussed,respectively.The results indicate that contact patches of contact pressures and von-Mises equivalent stresses of the wheel and rail are presented as irregular elliptical shape,and they are only dependent on the flat length.Strainrate effect of wheel/rail materials has almost no influence on both contact pressures and vonMises equivalent stresses of the wheel and rail,and it has little influence on contact patch sizes(i.e.,maximum sizes in the X-direction and Z-direction)of the wheel and rail.The braking thermal stress,train speed,flat length and axle load all have signicantly influences on the maximum contact pressures,maximum von-Mises equivalent stresses and contact patch sizes of the wheel and rail.The wheel-rail impact response induced by a wheel flat and the damage rule are investigated in this study,and influnences of some key parameters on the wheel-rail impact response are clarified.These findings are helpful to guide the safety design and maintenance of the wheel-rail system.