Research On Multi-Scale Wear Mechanism Of Brake Disc Surface Based On Coupling Of Friction-Thermal-Wear

The disc brake is a key component to ensure the safe operation of rail trains.When the disc brake of rail trains brakes under high-speed and heavy load conditions,the interaction of multiple physical phenomena such as friction,heat,and wear make the surface of the brake disc prone to problems such as uneven friction heat distribution and abnormal wear in the friction contact area,resulting in reduced braking efficiency and reliability of the brake,seriously affecting the operational safety of rail trains.Only studying the surface wear of brake discs at the macroscopic,mesoscopic or microscopic scale alone cannot reveal the mechanism and action of brake disc surface wear.Therefore,it is of great significance to conduct research on the multi-scale wear mechanism of brake disc surfaces based on the coupling of friction-heat-wear,and predict the wear laws and wear life of brake discs.In this paper,the three scale of macro-meso-micro scales are organically combined,and the simulation analysis model of material damage on the micro wear surface of the friction pair and the micro wear calculation and analysis model for the fractal rough surface of the friction pair are established.The time-varying wear iterative calculation method of the fractal rough surface of the friction pair,the surface wear analysis method of the brake disc under the coupling of friction-heat-wear and the brake disc wear life prediction method based on multi-scale wear calculation are proposed.The prediction system for the wear life of the brake disc of the track train disc brake has been designed.The main research content and achievements are as follows:(1)A simulation analysis model for material damage on the micro surface of friction pairs is established to address the material destruction and damage issues that occur during the wear process.The micro material damage criteria are established and the micro surface friction materials are characterized using discrete element.The discrete element simulation model of sliding friction surface damage is established by using the particle flow circulation method with boundary remapping feature,and the variation law of interface clearance and sliding friction coefficient caused by sliding friction surface damage is obtained.(2)A micro wear calculation and analysis model for fractal rough surfaces of friction pairs is established to address the wear phenomenon generated during the mutual friction process between real rough surfaces.The elastic-plastic deformation and stress state of micro convex peaks under a single peak contact state during the friction process are analyzed,and the elastic-plastic deformation criterion of micro convex peaks is obtained.A fractal rough surface wear calculation model is established,and the effects of wear coefficient and fractal parameters on surface wear amount and wear rate are analyzed.The wear calculation model was validated through the pin-on-disc friction and wear tests,and the influence of friction parameters on surface wear volume and volume wear rate was obtained.(3)Considering the surface morphology characteristics of friction pairs changing with time during the wear process,an iterative calculation method for time-varying wear of fractal rough surfaces is proposed.Considering the peak wear and indentation phenomena that occur on rough surfaces under different frictional contact states,a time-varying wear calculation model for worn surfaces and a compensation wear calculation model for non-worn surfaces are established.The relationship between instantaneous wear and dynamic changes in rough surface morphology is comprehensively described.The continuous rough surface is subjected to microelement processing using image digitization,and the dynamic changes in wear depth and surface morphology of the rough surface are simulated.The influence of friction parameters on the stability and quality of the worn surface is obtained.(4)A method for analyzing the uneven wear of the brake disc surface during the braking process of the brake friction pair under the coupling effect of friction heat wear is proposed.By analyzing the heat generation and dissipation mechanism of the brake friction pair surface,a heat transfer equation for the brake disc surface is established.Based on the constitutive model of brake friction materials and the evaluation criteria for shear failure of friction interfaces,a finite element model of brake disc surface wear under the coupling effect of the friction-heat-wear is established,and the distribution cloud maps of brake disc surface wear during the braking process are obtained.The thermal wear results of the brake disc surface were verified through disc brake friction and wear tests.The influence of braking parameters on the surface wear of brake discs and the variation pattern of wear stability are obtained.(5)A method for predicting the wear life of brake discs based on multi-scale wear calculation is proposed to address the issue of disc brake disc surface failure due to wear to limit.A process for predicting the wear life of brake discs based on multi-scale wear calculation has been established.A neural network prediction model is established to train the prediction model based on simulated wear results,and a brake disc wear life prediction model is established.A wear life prediction system for track train disc brakes has been designed,achieving visual prediction of the wear life of train brake discs.This article reveals the multi-scale wear mechanism of the brake disc surface under the coupling effect of the friction-heat-wear,predicts the distribution laws and life of the brake disc surface wear,provides a theoretical basis for the design and manufacturing of brake discs and provides a new approach for the research of friction and wear of friction pairs.