Design Of Brake Friction Materials Based On Graphene-polymer Composites Applied In Trains

At present,with the improvement of economic conditions and the increase of the number and speed of trains,trains have become an indispensable means of transportation in life.However,trains also bring a series of safety risks caused by brake system failure.Firstly,a detailed introduction of the research history of brake friction materials is presented,characteristics,and their influences on the environment.Secondly,graphene polymer composites were introduced.Graphene has shown unique properties and introduced new challenges to light materials applicable in different areas.Graphene added to the polymer has brought materials with marvelous properties in mechanical,electrical,thermal,and related to conductivity.Different methods were discovered to produce good graphene-polymer nanocomposites.This paper summarized those methods,as well as discussed the properties of graphene combined with different kinds of polymers.Furthermore,the different factors affecting graphene reinforced polymer nanocomposites were also studied.In the end,the challenges and future perspectives for graphene-polymer nanocomposites were considered.During our study,we used Polyimide as an excellent polymer matrix material that has excellent mechanical properties,high-temperature resistance,and excellent corrosion resistance,and is considered as a potential material.However,because of its poor wear resistance,it cannot be widely used as a friction material.Graphene oxide is a kind of graphene derivative with rich oxygen-containing functional groups.It has a unique twodimensional nanolamellar structure,excellent mechanical properties,good thermal properties,especially good water solubility,and can be well dispersed in the aqueous phase of the polymer matrix.Therefore,it can be used as a new type of ideal filler to add to the polymer matrix,expecting to improve all aspects of the performance of the polymer matrix,including improving the friction characteristics.In this project,graphene oxide was prepared by chemical dispersion method;graphene oxide and hexagonal boron(G0/h-BN)were prepared and mixed with polyimide(PI)by the In-situ method.The structure of GO/h-BN/PI composites was characterized by infrared spectroscopy and X-ray diffraction,and the dispersion state was analyzed by a scanning electron microscope(SEM).The friction and wear properties of polyimide graphene oxide with hexagonal born nitride composites under dry sliding were studied by an MM-200 friction and wear tester.The worn surface morphology was investigated by optical microscope,and the friction and wear mechanism of the composites was revealed as well as compressive and thermal properties.Tribological properties show that GO sheet and h-BN particles have an obvious synergistic effect in the tribological performance test.0.8% GO/h-BN contents at 200 N load showed the lowest friction coefficient.Consequently the addition of GO/h-BN decrease dramatically the friction coefficient as well as wear rate compared to pure PI.The wear mechanism surface of the unfilled PI is rough;GO/PI has some pits with cracks,while GO/h-BN/PI surface is smooth which tends to have good tribological properties.The compressive strength of pure PI film is 94MPa.When the content of h-BN is 1wt%,the compressive strength of the composite film prepared by in-situ polymerization is 103MPa.Besides,the compressive strength of 1wt%GO and 1wt%G0/h-BN composite film prepared by in-situ polymerization is slightly higher than that of pure PI which is 120MPa and 140MPa respectively.Their compressive modulus is corresponding to 1.2GPa(PI),1.38GPa(h-BN/PI),1.8GPa(G0/PI),and 2.62GPa(GO/hBN/PI).Thermal properties results show that the addition of GO/h-BN improves the thermal stability and thermal decomposition properties of polyimide.Pure PI showed thermal stability corresponding to Ts and Tmax which are 352.6?and 650?respectively while the addition of 1wt%GO/h-BN into PI composites correspond to 422.6?and 701.8?respectively.All those experimental analyses showed 0.8%wt GO/h-BN introduced into PI as promising potential material to be used for brake friction materials.Finally,simulations using ABAQUS software were conducted,for the comparative study of ordinary brake disc which is composed of steel discs & rib and Non-asbestos organic brake pad and that composed with GO/h-BN/PI brake pad.After proper simplification of the brake model,the thermal structure coupling analysis model of the brake is established,this only includes the brake discs,rib,and brake pad.The boundary conditions were applied,meshing was also designed,and the pressure was applied on both sides of the brake pad.It is found that the mechanical and tribological properties of the GO/h-BN/PI composite brake disc showed a good impact on simulation final results.The thermal-structure analysis was then used with coupling to determine the working strain,von mises stress and temperature to check which material is ideal to be used in designing friction parts applied in trains.Comparatively,GO/hBN/PI composite brake disc produces good stress and working strain.Results also showed a less temperature distribution during rotating.A simulation result shows also GO/h-BN/PI composite material as a preferable candidate for designing brake friction materials with incredible properties.