Study On The Influence Of Environmental Humidity On The Friction And Wear Performance Of Brake Materials For High-speed Railways

The brake pair(brake disc and brake pad)of high-speed trains is an important component of the braking system and a guarantee of safe train operation.The quality of its friction and braking performance is a key factor determining whether the train operates safely.With the rapid development of China’s high-speed rail industry and the complex geographical environment issues in China,this study focuses on the direction of environmental humidity and changing the initial temperature of brake discs.It is of great significance to study the friction and wear performance of the brake disc/pad of high-speed trains and ensure the safe running of high-speed trains operating in high humidity environments.Using a self developed multifunctional friction and wear testing machine,the friction and wear properties of high-speed railway brake disc(disc specimen)and brake pad(pin specimen)materials at different initial disc temperatures(20 ℃,100 ℃,200 ℃)and different ambient humidity(55%,95%)were studied in this paper;At the same time,under the condition that the initial temperature of the disc is 200 ℃ and the ambient humidity is 95% constant,wear tests were conducted on the contact pressure(0.5MPa,1.0MPa,1.5MPa)and sliding speed(0.5m/s,0.7m/s,0.9m/s).The experimental results were studied and analyzed from four aspects: friction coefficient,wear rate,surface morphology,and disk surface temperature.The main contents are as follows:(1)To study the effect of environmental humidity on the friction and wear performance of high-speed train brake materials,wear tests were conducted with different environmental humidity(55%,95%).The conclusion is as follows: the friction coefficient of high-speed train brake materials under the condition of environmental humidity of 55% is greater than that under the condition of environmental humidity of 95%.Under the condition of environmental humidity of 55%,the overall damage of the brake pads is more severe than that of the brake discs;When the ambient humidity is 95%,the overall damage of the brake disc is greater than that of the brake pad.As the environmental humidity increases from 55% to 95%,the wear mechanism of the brake pair material shifts from abrasive wear and severe adhesive wear to abrasive wear,lighter adhesive wear,and fatigue wear.(2)In order to study the effect of initial disc temperature on the friction and wear performance of high-speed train braking materials under certain environmental humidity(55%,95%),wear tests were conducted with different initial disc temperatures(20 ℃,100 ℃,200 ℃).The conclusion is as follows: under the condition of 55% environmental humidity,the change in disc temperature has little effect on the friction coefficient,but under the condition of 95%environmental humidity,when the initial disc temperature is 20 ℃ and 200 ℃,The average friction coefficient is about 0.58,and when the initial temperature of the disk surface is 100 ℃,the average friction coefficient is about 0.39.(3)The wear tests of brake materials under different contact pressures(0.5MPa,1.0MPa,1.5MPa)with an initial disc temperature of 200 ℃ and an ambient humidity of 95% were studied.The conclusions are as follows: With the increase of contact pressure,the average friction coefficient first decreases and then increases,and the overall friction coefficient fluctuates sharply under low contact pressure(0.5MPa),The fluctuation of friction coefficient under high contact pressure(1.0MPa,1.5MPa)is relatively stable.With the increase of contact pressure,the wear rate of the brake disc/pad friction material presents a gradual upward trend,and the damage mechanism of the brake pair friction material gradually changes from abrasive wear and adhesive wear to three types of mixed wear: abrasive wear,adhesive wear,and fatigue wear.With the increase of contact pressure,the maximum equilibrium temperature of the brake disc material tends to increase,but the rate of increase gradually decreases.(4)The wear tests of brake materials at different sliding speeds(0.5 m/s,0.7 m/s,0.9 m/s)with an initial disc temperature of 200 ℃ and an ambient humidity of 95% were studied.The conclusions are as follows: As the sliding speed increases,the friction coefficient generally maintains a trend of first increasing,then decreasing,and then slightly increasing,but their overall fluctuation is not significant,and the friction coefficient at high sliding speed is smaller than that at low sliding speed.As the sliding speed increases,the brake disc wear gradually decreases,while the brake pad wear rate presents a trend of first decreasing and then increasing,and the difference in wear rate between the brake pad and the brake disc becomes increasingly large.