Molecular dynamics analysis and experimental study on fretting wear mechanism of variable gauge bogie
[Objective]As global trade integration accelerates,the frequency of transnational cargo transportation has surged,spotlighting the development of railways as a crucial objective for various countries.Railways offer the advantages of low cost and high transportation capacity.However,the efficiency of goods transportation is hampered by the disparities in track gauges between countries.Among the numerous proposed solutions,the variable gauge bogie can efficiently solve this problem.However,in practical applications,micro-fretting wear between wheels and axles of variable gauge vehicles can lead to connection relaxation and failure,posing potential safety hazards.Although experimental results have demonstrated that surface treatment technology can effectively reduce friction and wear between wheels and axles,the underlying micro-wear reduction mechanism remains poorly understood.[Methods]This study uses the molecular dynamics method to develop a three-dimensional micro-fretting wear model for bogie wheels and axles.This study aims to elucidate the wear reduction mechanism of surface treatment technology from a microscopic perspective and provides experimental validation.The micro-canonical ensemble,also known as the NVE ensemble,was selected to stimulate the working conditions between the wheel and axle,ensuring that the system was isolated from external energy and particle exchanges.The embedded atom model is suitable for intermetallic molecular dynamics simulation.In this study,EAM was used for relaxation processing to accurately characterize the interactions between atoms within the alloy in a stable state.Meanwhile,the Lennard-Jones(LJ)potential,known for its simple structure and computational efficiency,was applied to calculate the interaction force between the wheel and axle interfaces with high precision.Therefore,the LJ potential plays a crucial role in the present study,representing the complex interface interactions.[Results]The results show that under contact stress,a slight protrusion contact occurs between the two surfaces of the wheel axle,leading to deformation and adhesion.When these surfaces are separated,the adhesion material from the protrusions is detached by shear force,causing micro-motion wear.To explore solutions,two molecular dynamics models of surface treatment processes were developed:one involving coating with MoS2 and the other ion nitriding.The calculations reveal that both surface treatment processes significantly reduce wear,as evidenced by a lower average friction coefficient.Further analysis of the temporal variation in lateral and longitudinal forces uncovers that the wear reduction effect of these surface treatment processes stems primarily from a decrease in lateral force.In addition,it was found that the friction coefficient of the MoS2 coating model decreases with an increasing load.Conversely,the friction coefficient of the ion nitriding model decreases with an increased amount of nitriding.To ensure the accuracy of these simulation results,experiments were conducted using the WTM-2E controllable atmosphere micro friction and wear tester.[Conclusions]Experimental and simulation results demonstrate that MoS2 coating and ion nitriding treatments effectively enhance lubrication and reduce wear.These treatments improve the processing performance of components,extend their service life,and minimize potential safety hazards.The application of molecular dynamics simulation in analyzing micro-motion wear offers significant educational value,particularly in the context of courses on Friction Wear and Lubrication.It provides students with a tangible understanding of how micro-motion affects the macroscopic performance of materials and components.
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