| There are many inland mountainous areas in our country,and heavy duty trains running on long downhill road need periodic braking to slow down.Therefore,bright white organization will appear at the tread position of train wheels,which is called white layer organization in academic circles.White layer will accelerate the generation of tread cracks,and tread peeling will occur under the alternating stress between wheel and rail,which seriously affects the stability of train operation.Therefore,it is very important for train running safety to study the mechanism of white layer on tread and avoid white layerIn this Paper,the finite element model of wheel is established by Abaqus software,and the physical and mechanical property Parameters of CL60 steel are calculated by hot compression test and JMat Pro software.Based on Hertz contact theory and function transition relationship,the mechanical load and heat flux of brake shoe and track on tread were calculated,and the influence of heat convection heat radiation on wheel temperature field was considered.Fortran subroutine was written for the secondary development of Abaqus software,and the mechanical load and heat flow load were carried out by rotating load method.The temperature field,stress and strain field of the wheel under different braking conditions were obtained by simulation,and the quantitative functional relationship between the maximum tread temperature and axle load,speed reduction and slope was fitted.Secondly,according to the simulation analysis results under emergency braking conditions,an isothermal cooling experiment was set up,and the critical cooling rate of martensitic transformation was determined to be between 15-17.5℃/s.Then a thermodynamic coupling test was set up to simulate the temperature field and plastic deformation of the tread during the braking process of the train,and the microstructure of the sample after hot compression was observed with a microscope.It was found that no martensite tissue was produced in 9 groups.The plastic deformation only changes the spacing of the pearlite lamellae and has no obvious effect on the martensitic transformation.Based on the theory of recrystallization dynamics,the grain refinement degree in the braking process of wheel tread was explored.Firstly,a Python subroutine based on JMAK model was written for the secondary development of Abaqus to read the temperature field stress field of wheel tread,so as to calculate the real-time grain diameter of wheel tread.According to the grain size,the initial region and shape of nanocrystalline white layer are determined.Considering the influence of tread wear during periodic braking,the final shape and position of tread white layer are determined. |
