A Research On Contact Model And Thermal-Mechanical Coupling Of Wheel-Rail Sliding Contact Considering Wear

Wheel-rail sliding contact is a common contact state when train starts or brakes and the wheel-rail abrasion caused by sliding contact is a typical type of damage on wheel-rail.The abrasion increases the contact force,deteriorates the train's operating environment,and shortens the service life of train-track structure.In the process of the sliding contact,the wear,contact stress and friction heat on the wheel-rail contact interface change dramatically,affect each other and form a strong coupling relationship.How to distribute the friction heat generated on wheel-rail contact surface between wheel and rail is a significant research content.And it is very important to determine the partition of friction heat and further clarify the coupling relationship among wear,contact stress and friction heat.This dissertation mainly analyzes the thermal-mechanical coupling phenomenon on the contact interface during the wheel-rail sliding contact process by means of experimental research,numerical calculation and theoretical analysis.The main research work and achievements are as follows.(1)A wear-dependent wheel-rail contact model is established and based on this model,the thermal-mechanical coupling equation for wheel-rail sliding contact is deduced.(2)The experimental equipment adopted and its motion principle are introduced in detail,the geometric and thermal-mechanical parameters of the experimental specimen are listed,and the other test devices used in the experiment are also introduced.(3)The finite element model calculating the wheel-rail wear during sliding contact is established,the influence of wheel-rail wear on the contact stress is analyzed,and the unknown parameters in the wear-dependent contact model are determined.The results show that with the increase of load and sliding speed,the maximum contact stress decreases gradually,and the contact stress becomes more even.As to three-dimensional wheel-rail contact,when the depth of wear is less than 1mm,the contact surface remains elliptical shape,the inner side of the wheel-rail contact patch is more likely to be worn,and the change of contact stress between wheel and rail is the same as that of the plane wear model.The results also show that the stress uniformity index increases with the growth of wear depth.(4)The temperature of contact region during wheel-rail sliding contact is obtained through experiment and numerical calculation,the partition of friction heat between wheel and rail is calculated,and the heat transfer mechanism on the contact interface is discussed in detail.The results show that there are three stages of the temperature time history curves of different measuring points on wheel-rail.At the same depth,the temperature of points of wheel is higher than that on the rail.The reason is related to the size and heat transfer of the contact surface.At the same time,the calculation results show that the friction heat on the sliding contact surface is not evenly distributed between the wheel and rail,and the friction heat entering the rail is more than that entering the wheel.With the increase of load,sliding speed and contact time,the heat partition entering the wheel tends to increase.And the temperature of wheel-rail contact area is high when not considering the wear.(5)A three-dimensional thermal-mechanical direct coupling finite element model of wheel-rail sliding friction is established.The temperature-dependent mechanical and thermal parameters are employed to analyze the temperature,stress and strain of wheel-rail.At the same time,the results are compared with that without considering friction heat.The calculation results suggest that with the increase of sliding distance,the temperature of the nodes on the wheel contact surface is always on the rise,while the temperature curve of the node on the rail has three obvious stages.The contact surface temperature of wheel and rail is very high,but the influence depth of temperature is less than 3mm.Compared with the calculation results without considering the friction heat,it can be found that the Mises stress caused by temperature can reach 59% of the maximum Mises stress.The friction stress between wheel and rail and the tangential strain of rail surface are closely related to the vertical load,sliding speed and friction heat.(6)The damage of the wheel-rail contact surface under different contact condition is experimentally studied,and the damage causes are analyzed from the microscopic perspective combining mechanical and thermal effects.The results show that there are obvious grooves on the wheel contact surface during sliding contact.At the same time,there are a lot of micro particles adhering to the rail surface.And on the rail surface,the various types of damage can be seen,especially the cracks.Moreover,the results show that sliding friction heat has a significant effect on wheel and rail damage.In this dissertation,the partition of sliding friction heat between wheel and rail is analyzed by experiment and numerical simulation.The coupling relationship among wear,contact stress and friction heat during wheel-rail sliding contact is studied in detail.And the friction heat conduction process and transfer mechanism are researched in detail.The calculation method adopted in this dissertation is feasible and the calculation result is reliable.And the methods and results can provide reference for further analysis of fatigue damage and similar problem in the process of wheel-rail contact.