Research On The Tribological Performance Of Resin-based Brake Materials Based On Long Downhill Condition

When the automobile apply the brake during the long downhill condition,the working situation of its brake system will become more severe,as a consequence,the brake performance will decline,or even failure and then cause safety accidents.While the research status both at home and abroad focus on establishing mathematical model and conducting computer simulation,so it is necessary to make an intensive study on the friction and wear properties and mechanism of brake materials under the long downhill condition by inertia simulation experiment platform.In this paper,a sort of CaSO₄ whiskers reinforced resin-based composite friction materials which were developed by our own research team and a kind of commercially available brake material were selected as the research objects.Based on the long downhill conditions,the effect of friction time,braking frequency and braking pressure on tribological properties of two kinds of brake materials were tested on CHASE and MM-1000 II friction tester,respectively.With the purpose to summarize the change rules of friction and wear properties of resin-based brake materials under the long downhill working conditions,and then analysis the friction and wear mechanisms and the key influence factors to its tribological properties.The experimental results show that the friction surface temperature of brake materials showed the change process from sharp heating to temperature stability to slow heating with the increasing of friction time,and then appeared the heat fading phenomenon,as a result,the friction coefficient decreased and fluctuated obviously,and the braking stability became worse as well as with the brake noise and vibration,and the wear rate increased;While,with the increasing of braking frequency,the rise of friction surface temperature of brake materials was smaller for the friction have proceeded the sufficient heat exchange,therefore,the friction coefficient changed smoothly and showed the reliable braking.However,it was easy to form the micro cracks on the surface or sub surface due to the dual action of thermal cycle impact stress and interfacial frictional shear resistance,and then caused fatigue wear.The friction and wear properties of brake materials showed more sensitive to braking velocity than initial braking temperature,so the fluctuation of friction coefficient was extended with the increasing of braking velocity,besides,the surface friction temperature raised too.Furthermore,the braking time showed a diminishing linear relationship with braking pressure,while the friction power absorption of brake materials showed an increasing linear relationship with it.The greater the braking pressure,the more serious the friction torque curve of dithering phenomenon,and the worse the braking stability would become,nevertheless,the increase of braking pressure was beneficial to the formation of friction film on the friction surface in a certain range,so as to reduce the wear rate.The effect of different braking conditions on the tribological properties of resin-based friction materials under the long downhill working conditions are mainly reflected in the temperature rise and stress state of friction surface.During the braking process,the friction surface temperature will rise for the friction heat generating large amounts of heat and accumulate on it,when the temperature exceeds a certain range,it will cause the matrix softening,viscous flow and thermal decomposition,and the adhesion effect with the dual disc will reinforced,besides,the metal components in material system will occur oxidation reaction too.In addition,with the action of interface impact stress and friction shear resistance,the wear surface morphology characteristics will changed,and part of the materials will fall off and at the material defects or stress concentration points will form the crack sources,thus affecting the structure and properties of each element in material system and weaken its synergistic effect between each other,as a result,all of those will change the friction and wear properties of brake materials and decline brake performance.