The Effect Of The Contact Pattern On The Disk Temperature Field And Friction Coefficient

During the high-speed train braking process,the complete contact between brake disc and pad makes the contact pressure be evenly distributed.Thus it can make the wear and temperature uniformity.But in the actual braking process,due to the deviation of machining and assembly accuracy,and the replacement of brake pads,there will always be local contact.Local contact will inevitably lead to the stress concentration and local temperature.Thereby speeding up the wear of the brake disc and resulting in brake disc failure.Therefore,it is significant to study the influence of the friction pairs on the temperature field of the brake disc and friction properties.Combined with simulation method and expereriment test,the effects of different contact patterns on the brake disc temperature field are investigated.Through the observation of the surface morphology on the brake pad after the braking,the reason of the change in friction coefficient is analyzed.The result shows that:(1)The effect of local contact on temperature distribution and peak temperature is obvious.Under complete contact pattern,the energy distribution is uniform,the peak temperature and the temperature gradient is low.Under the local contact pattern,with the change of the location in contact place,the temperature distribution changes.The both sides of the contact pattern will keep balance between heating and heat dissipating.Thus it makes the surface temperature distribution uniformity,the peak temperature is low.When the contact area is limited in the middle,inside and outside,the degree of concentration of high heat is improved,peak temperature is higher 20%~30% than complete contact pattern.(2)The expereriment shows that the maximum difference in the peak temperature at different contact patterns increases with the increasing of the initial braking speed and pressure.Under the condition of 50km/h,the peak temperature of the middle contact pattern is 92.8 ?,it is higher 25? than the both sides contact pattern.When the initial braking speed increases to 200km/h,the maximum difference between the peak temperature is about 100 ?;In the high speed conditions,the effect of braking pressure on the maximum difference is larger.In the 200km/h condition,the maximum difference of peak temperature between 0.5MPa,0.75 MPa and 1 MPa is 68 ? and 114.6 ? and 141.7 ?.(3)When the local contact area is concentrated on the large friction radius,the large contact arc and the contact center of the brake pad,the temperature distribution of the disk and the peak temperature will be increased.The reason is that these areas are high friction power and poor heat dissipation area.(4)In simulation,the stress of the contact surface is uniform and the stress distribution is uneven.The difference between the simulation results and the expereriment results is inconsistent.Under the condition of low velocity and low pressure,the contact pressure of the friction expereriment is poor.When the brake pressure exceeds 0.75 MPa,the speed is more than 200km/h,the contact pressure is uniform,and the simulation results and the expereriment results have good consistency.(5)The contact pattern also affects the friction coefficient.The friction coefficient is the highest in the complete contact state.At low speed condition,the friction coefficient increases with the increasing of brake pressure.At high speed condition,the friction coefficient decreases with the increasing of brake pressure.The high temperature caused by local contact makes the friction coefficient decrease.