The Influence Of Friction Temperature On The Braking Performance Of Copper-based Friction Materials During Braking

The significant feature of high-speed train braking is that the friction surface temperature rises sharply,which changes the morphological characteristics of the third body between the brake disc and the brake pads,and affects the friction performance.Therefore,clarifying the relationship between friction temperature,third body and friction coefficient will help understand the friction performance of brake materials.In this paper,for copper-based powder metallurgy friction materials,using 1:1 test bench and scale-down test bench,respectively,braking test in the range of braking speed50～300km/h and braking pressure 0.28～0.56 MPa combined with surface topography analysis,Discussed the relationship between friction temperature and friction coefficient during braking,and got the main conclusions as follows:(1)With the increase of the initial braking speed,the maximum temperature of the disk surface of the scaled-down parking test and the 1:1 parking test both increased significantly,but the change trend of the average friction coefficient of the material was different.When the maximum temperature of the scaled parking test and the 1:1 parking test surface increased from 60°C to about 350°C,the average friction coefficient generally showed a decreasing trend.When the maximum temperature of the disc surface exceeds 350℃,the average friction coefficient generally increases.The reason is that the friction temperature increases,the third body on the surface softens,the fluidity increases,and the friction coefficient decreases.(2)The scaled-down parking test and 1:1 parking test brake,as the test progresses,the changes in the average radial temperature of the disc surface and the instantaneous friction coefficient are consistent.The radial average temperature of the disk surface increases,and the instantaneous friction coefficient also increases.At low speed,the increase rate of the instantaneous friction coefficient is higher than the average temperature increase rate of the disk surface;when it exceeds 200km/h,the increase rate of the instantaneous friction coefficient is lower than the average temperature increase rate of the disk surface.(3)During the 1:1 continuous braking process,the maximum temperature of the disc surface affects the relationship between the friction temperature,the third body and the friction coefficient.When the maximum temperature of the disk surface is lower than 350℃,the instantaneous friction coefficient increases with the increase of the maximum temperature.The reason is that the temperature change of the disk surface has no obvious influence on the third body of the hard particles covered by the friction surface;when the maximum temperature of the disk surface is higher than 350 At ℃,the instantaneous coefficient of friction decreases with the increase of temperature.This is due to the increased fluidity of the third body caused by high temperature,which acts as a fluid lubrication and reduces the coefficient of friction.