Frictional-magnetic Coupling Behavior And Mechanism Of Magnetic Conductive Brake Pair

Tribological researches have indicated that the magnetic field possesses some influences on the friction and wear behavior of materials,and the influence degree increases with the increasing of permeability of materials.For ferromagnetic materials,friction can also induce magnetization.Therefore,when the brake pair comprising ferromagnetic brake disc materials operates under a magnetic field,the coupling effect between friction and magnetic field on friction interface objectively existes.However,little attention has been currently paid to frictional-magnetic coupling interaction on friction interface under a magnetic field.In addition,the investigations on magnetic field tribology and tribomagnetization have mainly focused on metal/metal friction pairs,but organic/metal brake pairs are rarely involved.Consequently,the research on frictional-magnetic coupling behavior and mechanism of brake pair has great theoretical values and practical significances for enriching the contents of tribological research and developing the friction braking technology controlled by the magnetic field.This thesis aimed at automotive disc brake engineering background.The magnetic conductive organic friction pad and HT250 brake disc were utilized to compose the magnetic conductive brake pair,and its frictional-magnetic coupling behavior and mechanism were investigated.Firstly,permalloy was chosen as filler to manufacture the magnetic conductive organic friction pad.The structure of automotive disc brake was improved to form the magnetic conductive brake pair.Based on the self-made automotive disc brake simulated braking test-bed,a magnetic field applying device was set up,and the hardware and software of measurement system were also upgraded to build a frictional-magnetic coupling test device based on the magnetic conductive brake pair.Secondly,simulated braking tests were implemented not only under the alternating magnetic field with different magnetic induction intensities and frequencies but also different initial braking velocities and braking pressures to investigate the frictional-magnetic coupling behavior of magnetic conductive brake pair.Thirdly,the methods of OM,SEM,EDS and BSE were applied to carry out microanalysis tests on the wear morphology,elemental composition,wear debris and ferro-nickel wear particles of the worn surface of magnetic conductive organic friction pads,and the frictionalmagnetic coupling mechanism of magnetic conductive brake pair was revealed.The results showed that: 1)The magnetic field can promote wear debris refining,oxidation reaction and formation of friction layer on the worn surface of magnetic conductive organic friction pads.2)Under the certain magnetic field frequency,with the increasing of magnetic induction intensity,the main wear forms are transformed from cutting wear and abrasive wear without magnetic field to three-body wear with magnetic field,and the friction coefficient and its stability coefficient increase with the increasing of actual contact area of brake pair.3)Under the certain magnetic induction intensity,with the increasing of magnetic field frequency,the main wear forms of the friction pad surfaces under different magnetic field frequencies are all three-body wear.However,the regulation mechanism of the third body is converted from S3,4M3 model with low magnetic field frequency to S4,5M4 model with high magnetic field frequency.The wear resistance of the friction pads increase at first and then decrease.As a result,the friction coefficient and its stability coefficient also increase at first and then decrease.4)Initial braking velocity mainly increases the friction surface temperature,accordingly the tribo-magnetization is weakened.The braking pressure mainly increases the friction and wear of friction surface,accordingly the tribo-magnetization is promoted.5)External magnetic field can promote the aggregation of ferromagnetic particles on the friction surface,and more ferromagnetic particles are involved in friction and wear.Meanwhile,the formation of ferromagnetic materials such as Fe₂O₃,Fe₃O₄ are also promoted.As a result,the tribo-magnetization can be further enhanced after the ferromagnetic materials are magnetized.