Finite Element Analysis Of Wheel-Rail Dynamic Response Caused By Wheel Polygonization

With the large-scale operation of China's high-speed railway,the wheel polygonization of high-speed trains has become increasingly prominent,which has become one of the research difficulties in the field of wheel-rail relationship,and it also attracted much attention but difficult to solve thoroughly in the railway industry at present.Wheel-rail impact caused by wheel polygonization will cause damage to wheel-rail system and abnormal vibration of car body,resulting in a series of high/low frequency of impact noise and rolling noise,which seriously affects the service life of vehicle-track system component and ride comfort of high speed train.Futhermore,it even causes hidden dangers to train operation safety in some extreme cases.In this study,the finite element simulation method is adopted,to explore the mechanical response of wheel-rail impact and the damage rule to wheel-rail system caused by wheel polygonization.The main contents and results include the following aspects:(1)A three-dimensional finite element model of wheel-rail rolling contact is established,and the geometrical nonlinearity,material nonlinearity and contact nonlinearity of the wheel-rail dynamic contact are considered.A finite element simulation method of wheel-rail dynamic contact is developed to describe the real wheel polygonization,i.e.,the geometric irregularity of the polygonal wheel was simplified into the displacement irregularity of the perfect wheel in rolling contact in the geometry modelling,which has been demonstrated to be an effective research method for solving rolling contact problem between polygonal wheel and rail.(2)Based on the above models and methods,the explicit finite element analysis(FEA)is adopted to investigate the wheel-rail impact response induced by wheel polygonization,including the vertical wheel-rail contact force,contact pressure and stress/strain state in the time domain.Besides,the differences of the impact responses caused by periodic and non-periodic polygonal wheels are compared,and influences of train speed and polygonal order of wheel on the dynamic wheel-rail response are discussed,respectixely.The results indicate that the polygonal wheels have seriously influenced the contact state of wheel-rail system;the dynamic wheel-rail contact force induced by wheel polygonization is sensitive to the variation of wheel radial deviation,and larger variation rate and magnitude of radial deviation will lead to larger contact force;and among the order range studied in this paper,the maximum wheel-rail contact force,maximum von Mises equivalent stress,maximum longitudinal stress and maximum plastic strain are all elevated with the increase of the order of periodic polygonal wheel.(3)Considering the strain-rate effect of wheel/rail materials,the wheel-rail rolling contact behavior under the condition of wheel polygonization is studied,and the influence of strain rate on wheel-rail contact pressure,vertical contact force and stress/strain state between wheel and rail are discussed,respectively.The results indicate that the strain-rate hardening effect of wheel-rail materials can significantly increase the von Mises equivalent stress and inhibit the plastic deformation between wheel and rail.(4)Using the random function and uniform distribution,the randomly irregular displacement excitation between polygonal wheel and rail is generated based on the software MATLAB.By means of the above-mentioned finite element model of wheel-rail dynamic contact,the wheel-rail impact response caused by randomized wheel polygonization is studied,and influences of train speed and polygonal order of wheel on wheel-rail vertical contact force and Mises equivalent stress of wheel tread are analyzed.The results indicate that,during the whole wheel-rail rolling contact process,the maximum wheel-rail contact stress on wheel tread shows a periodic trend of increasing first and then decreasing.(5)On the base of the dynamic wheel-rail rolling contact finite element simulation results,the effect of wheel polygonization on additional load of axle and fatigue life of wheel is studied.The additional load coefficient of axle is obtained and the fatigue life of wheel is predicted under the condition of wheel polygonization.The results indicate that,with the increasing of train speed,the additional load coefficient of axle shows an increasing trend,and for a given speed condition,the higher the order of periodic polygonal wheel,the greater the additional load coefficient of axle.In addition,the wheel polygonization will lead to the decreasing of fatigue life for wheel rim and hub.The wheel-rail rolling contact behavior and damage rule to the wheel-rail system induced by wheel polygonization are systematically investigated in this study,and influences of some key parameters on wheel-rail impact mechanical responses caused by wheel polygonization are also expounded,which can provide some theoretical and technical support for the optimal design of wheel-rail system and the safety operation of high-speed train.