Study On Wear Of Brake Disc/pad And Friction Braking Behavior Of Emu In Low Temperature Environment

The brake disc and pad are basic components for ensuring the operation safety of high-speed train.The friction braking behaviors between the brake disc and pad has important significance for train safety operation.With the operation of Harbin-Dalian high-speed railway,China’s high-speed trains have officially started the period to the development of Alpine high-speed railway.Low temperature environment brings serious problems such as unstable braking friction performance,abnormal wear,etc.which brings great hidden danger to the braking safety of trains.Therefore,the study of the friction behavior of disc brake interface in low temperature has great significance to ensure the reliability of high-speed braking systems.Firstly,the effects of ambient temperature and contact conditions on the wear properties of brake disc/pad materials were studied using a pin-on-disc testing rig,and the evolution of wear and damage of brake disc/pad materials under different ambient temperatures and contact conditions was revealed.Then,a MM-1000 high-speed friction braking machine was used to simulate the braking performance of disc brake materials of high-speed train in low temperature environment.The effects of initial braking speed,braking pressure and ambient temperature on friction and braking performance were studied.The main conclusions are as follows:(1)In the range of-30～20℃,during the continuous contact test,with the increased of ambient temperature,the wear rate first increased and then decreased.The fall off and particle breakage decreased on the brake pad sample surface,and the area of the third body increased.The fatigue pitting on the surface of the disc sample first increased and then gradually lighted.In the intermittent contact test,the average friction coefficient and wear rate were relatively high at 0℃ and-10℃,and the pits,scratches and furrows on the sample surface increased.(2)In the range of 0.5～1.5MPa,with the increased of contact pressure,the fluctuation of friction coefficient decreased,the wear rate increased,the area of the third body decreased,and the number and area of the falling pits increased.At an ambient temperature of-20℃,the surface damage of the disc sample except for furrows,adhesive particles and the third body,and the fatigue pitting damage increased with contact pressure.At a normal temperature of 20℃,the massive shedding and furrow phenomenon on the surface of the disc specimen increased.(3)In the range of 0.3～0.7m/s,with the increased of sliding speed,the fluctuation of friction coefficient and the wear rate decreased,and the growth rate of wear rate of disc specimen was greater than that of brake pad specimen.The area of the third body formed of the brake pad sample increased,and the area of the shedding pit decreased.The surface furrow and adhesive particles on the surface of the disc sample decreased,the area of the third body increased.(4)In the braking process,within the-30～20 ℃,with the decreased of the ambient temperature,the braking distance and the wear rate of the brake pad sample increased and then decreased.The surface peeling and breakage of the brake pad samples increased,and the area of third body decreased.The surface temperature rise of the sample and the wear rate of the brake pad sample at an ambient temperature of 20℃ were lower than at-30～0℃.(5)Under the ambient temperature of-20℃,at the initial braking speed range of80～110km/h,the average friction coefficient increased with the increased of initial braking speed.The graphite particles on the surface of brake pad sample decreased significantly,and the area of third body increased.Under the braking pressure range of 0.8～1.2MPa,with the increased of the braking pressure,the average friction coefficient decreased;the graphite particles on the surface of the brake pad samples,shedding and breakage increased.