| Constant speed test and inertia test which could simulate the process of actual braking test are used by the main methods for automobile brake friction material performance test.The former can give the friction and wear properties of material under a certain speed brake with the different braking parameters as well as the environmental change; The latter tend to research the properties of actual braking process.Due to the experiment methods used are different,there are some difference between the friction coefficient and the worn surface morphology,while the present research focus on single test, it’s necessary to carry out a more detailed comparison between the two methods.In this work,two representative resin matrix brake friction materials and one commercial brake lining material were selected as the research object.Friction and wear properties of friction pairs matching different materials at different loads^ speeds under dry and water conditions were tested on MMS-2A abrasion tester.By taking one type of Volkswagen for reference,friction and wear properties of the brake materials under the condition of continuous braking in simulating the actual driving were tested on MM-1000Ⅱ inertia tester.By obtaining the tribology performance of different braking materials in special working conditions, the friction and wear properties of the resin matrix friction braking material and the effect of working condition and braking parameters were analyzed, the friction and wear mechanisms in the braking process were clarified.The experimental results showed that the average of friction coefficient of automotive brake materials in aqueous media environment would fall to 60% of the dry friction, a significant drop from high-speed and heavy condition.Impact of braking parameters on tribological properties in dry conditions was not the same as that in wet, even contrary.The micrograph of worn suface and the analysis of the surface composition under different working environment indicated that the main wear mechanism of the resin matrix in dry friction was adhesive wear and abrasive wear; in the aqueous media environment,adsorbed water film formed in the friction pair changed the frictional contact state and played a important role in lubrication,the cooling effect of water reduced the friction heat and material transfer,inhibited the production of the rubbing films,thus the adhesion wear would reduced. Water soaking would caused the expansion and cracking of the brake material,thereby led to the reduction of strength of which affect the friction performance.The date of inertia experiment showed that the friction performance was more volatile than constant speed test,speed and braking might work together in a synergistic manner.Generally the higher driving speed and braking pressure,the higher temperature of friction interface,and the friction state was more complicated and unstable.Braking in high-speed would accelerate the shear rate on the surface of the materials and cause the thermal stress and shear stress,the wear pattern of friction material was thermal wear and fatigue abrasion, accompany with adhesion abrasion; the rubbing films would repeated the process of forming-damaging-regenerating under the effect of brake pressure,there is usually a critical pressure value could improve the capability of brake material in braking process.Grey cast iron which used as brake disc matched with resin matrix friction materials could get more stable friction coefficient and lower wear rate. |
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