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Friction and wear properties of combined surface modified carbon fabric reinforced

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Friction and wear properties of combined surface modified carbon fabric reinforced phenolic compositesXinrui Zhang a,b ,Xianqiang Pei a ,Qihua Wang a,*a State Key Laboratory of Solid Lubrication,Lanzhou Institute of Chemical Physics,Chinese Academy of Sciences,Lanzhou 730000,China bGraduate School,Chinese Academy of Sciences,Beijing 100039,Chinaa r t i c l e i n f o Article history:Received 27March 2008Received in revised form 31May 2008Accepted 12June 2008Available online 20June 2008Keywords:Carbon fabric composites Combined surface treatment Friction and wear Interfacial adhesiona b s t r a c tCarbon fabric (CF)was surface treated with silane-coupling agent modification,HNO 3oxida-tion,combined surface treatment,respectively.The friction and wear properties of the car-bon fabric reinforced phenolic composites (CFP),sliding against GCr15steel rings,were investigated on an M-2000model ring-on-block test rig.Experimental results revealed that combined surface treatment largely reduced the friction and wear of the CFP composites.Scanning electron microscope (SEM)investigation of the worn surfaces of the CFP composites showed that combined surface modified CFP composite had the strongest interfacial adhe-sion and the smoothest worn surface under given load and sliding rate.SEM and X-ray pho-toelectron spectroscopy (XPS)study of carbon fiber surface showed that the fiber surface became rougher and the oxygen concentration increased greatly after combined surface treatment,which improved the adhesion between the fiber and the phenolic resin matrix and hence to improve the friction–reduction and anti-wear properties of the CFP composite.Ó2008Elsevier Ltd.All rights reserved.1.IntroductionPolymers are finding wide acceptance in tribological applications because of their low friction against steel counterparts and the self-lubricating ability.Especially,polymer matrix composites reinforced with fibers have been widely accepted as tribo-materials and used on the components supposed to run without any external lubri-cants [1].Many researchers have made lots of attempts to understand the modifications in the tribological behav-iour of the polymers with the addition of fillers or fiber reinforcements [2,3].Many investigations have shown that the incorporation of fiber reinforcement improved the wear-resistance and reduced the coefficient of friction [4–9].This is attributed to a reduced ability of ploughing,tearing and other non-adhesive components of wear by the fibers,provided good interfacial adhesion between the matrix and the fiber reinforcement existed [5].Typical wear mechanisms of polymer matrix composites are:fiber breaking,fiber–matrix debonding and matrix fracture [10–15].Other important mechanisms are fiber pull out,matrix wear related to fiber movement,pealing of the matrix,shear deformation of the fibers and deformation of the edges of the wear track [16].Fabric reinforced polymer composites have high mechanical strength in both longitu-dinal and transverse directions.Another special feature of such reinforcement is their ability to drape or conform to curved surfaces without wrinkling [17].Carbon fabric (CF)reinforced composites are used in aircraft industries since more than five decades and this was initiated from trim tabs,rudders,spoilers,doors [18].However,when applied without previous surface mod-ification,the physical–chemical interaction between car-bon fibers and its reinforced matrix is not tough enough due to the inert surface property of carbon fibers,which will directly affect the degree of interfacial adhesion in the composite system.The lack of interfacial bonding lim-its load transfer capability from matrix to fiber.Typically,poorly adhered carbon fibers are pulled out of the matrix upon failure,thus limiting their reinforcement effect.Numerous methods concerning surface treatment,such as chemical method [19–22],electrochemical method0014-3057/$-see front matter Ó2008Elsevier Ltd.All rights reserved.doi:10.1016/j.eurpolymj.2008.06.013*Corresponding author.Tel.:+869314968180;fax:+869318277088.E-mail address:wangqh@ (Q.Wang).European Polymer Journal 44(2008)2551–2557Contents lists available at ScienceDirectEuropean Polymer Journaljournal homepage:www.elsevi e r.c o m /l o c a t e /e u r o p o l j[23–25],plasma treatment[26,27],etc.,have been devel-oped to increase the quantity of surface functional groups and thus enhance the ability to establish strong interac-tions betweenfibers and matrix.In this paper,silane-coupling agent modification,HNO3 oxidation and combined surface treatment was used to modify the carbonfibers surface,respectively.The friction and wear properties of the resulting modified carbon fabric composites were comparatively investigated with that of the unmodified carbon fabric composites.The present work is expected to understand the effect of combined sur-face modification technology.2.Experimental2.1.MaterialsIn the present study,the adhesive resin(204phenolic resin adhesive)was provided by Shanghai Xing-guang Chemical Plant of China.3-aminopropyltriethoxysilane (DB550)was provided by Diamond New Material Of Chem-ical Inc.of China.The reinforcements were PAN-based unmodified carbon fabric(supplied by Weihai Guangwei Group Co.Ltd.,China).The properties of the carbon fabric are shown in Table1.The commercial carbon fabric was dipped in acetone for24h,then cleaned ultrasonically in acetone for0.5h,finally,they were dried at100°C before used.2.2.Carbonfiber modificationThe cleaned carbon fabric was then modified in the fol-lowing ways:(1)Coupling agent treatment.The carbon fabric was immersed into the1wt%aqueous solution of DB550for1h,then dried at110°C for1h to cure the silane and simultaneously remove the excess of water.Finally, the carbon fabric was washed with dried toluene for 20min to eliminate the non-reacted fragments of silane.(2)HNO3oxidation.The carbon fabric was immersed intoa strong HNO3(65–68wt%)solution for4h,and then rinsed in distilled water and dried.(3)Combined surface treatment.The carbon fabric was treated by HNO3oxida-tion and coupling agent treatment in sequence as de-scribed in the above.2.3.Preparation of carbon fabric compositesThe carbon fabric(350Â250mm)was put into the phenolic resin solution and dipped ultrasonically for 10min,and then the fabric was put into an oven to evap-orate the solvent at40°C.The composite was prepared by dip-coating in the phenolic resin as the adhesive.A series of repetitive immersing and coating of the carbon fabric were performed to allow the generation of the composite coatings.Finally,the prepreg was cut into long pieces of 50Â30mm and put into the mould with plies orientations of[0°/0°].Thefinal target carbon fabric reinforced phenolic composites were obtained by heating the mould at180°C for3h.At the end of each run of heating sintering,the resulting specimens were cooled with the stove in air and then cut into preset sizes for friction and wear tests. In the following text,the composites were denoted as Composite U,A,B and C for the composites made of the unmodified carbon fabric and carbon fabric modified by coupling agent treatment,HNO3oxidation and combined surface treatment,respectively.2.4.Testing procedureAfter surface treatment,the carbonfibers samples were transferred in air to a VG Scientific ESCA LAB210spec-trometer for analysis of the surface elemental composi-tions by XPS.The XPS analysis was carried out using unmono-chromated Mg Ka X-radiation using Al/Mg dual anode at20KV under300W and the base pressure in the sample chamber was about10À7Pa.The morphologies of the treated and untreated carbonfibers were compared by SEM observation,before which the tested carbonfibers specimens were plated with gold coating to render them electrically conductive.The friction and wear behaviour of the carbon fabric composites sliding against stainless steel rings were evalu-ated on an M-2000model ring-on-block test rig(made by Jinan Testing Machine Factory,China).The contact techni-cal drawing is shown in Fig.1,The tested samples were Composite U,A,B and C in a size of30Â7Â2mm,while the counterpart were rings of GCr15stainless steels with a diameter of40mm.The chemical composition of the GCr15steel ring is shown in Table2.The tests were carried out at a linear velocity of0.431m/s under a load of200N to a period of120min.Before each test,the stainless steel ring and the composite block were polished to a roughness (Ra)of about0.3À/0.4l m.During the friction process,the block specimen was static and the steel ring was sliding against the block unidirectionally.The friction force was measured using a torque shaft equipped with strain gauges mounted on a vertical arm that carried the block,which was used to calculate the friction coefficient by taking into account the normal load applied.The width of the wear tracks was measured with a reading microscope to an accuracy of0.01mm.Then the specific wear rate(x)of the specimen was calculated from Eq.(1).Where B is the width of the specimen(mm),r is the semi diameter of the stainless steel ring(mm)and b is the width of the wear trace(mm),L is the sliding distance in meter,P is the load in Newton.The tests were repeated for three times,the wear tracks of the composite and stainless steel specimens were examined on a JSM-5600LV scanning electron micro-scope(SEM).In order to increase the resolution for the SEM observation,the tested composite specimens were plated with gold coating to render them electrically conductive.Table1The properties of the carbon fabricCarbon fabric PlainType PANTow1KEnd per inch(filament/10mm)1Pick per inch(filament/10mm)9.1Density(g/m2)25±5Thickness(mm)0.16±0.022552X.Zhang et al./European Polymer Journal44(2008)2551–2557x ¼B L ÃP p r 2180arcsin ðb 2r ÞÀb 2r ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffir 2Àb 22s 2435ðmm 3=N m Þð1Þ3.Results and discussion 3.1.Friction and wear propertiesThe friction coefficient and wear rate of Composite U,A,B and C sliding against GCr15stainless rings are compara-tively shown in Fig.2.It can be seen that the friction coef-ficient of the modified CFP composites (Composite A,B and C)decreased slightly as compared with that of CompositeU.Besides,the specific wear rate of the composite were in the following order:Composite C <Composite B <Com-posite A <Composite U.That is to say the surface modifica-tion of carbon fabric was favorable to improve the friction and wear behaviour of the composites.It is well worth not-ing that the wear rate of the composites decreased by 47%when the carbon fabric was modified by combined surface treatment (Composite C).The surface modification can im-proved the interfacial adhesion between the CF and the phenolic resin matrix and reduced the detachment of the CF from the phenolic resin matrix and prevented the for-mation of the third body,which resulted in producing pri-marily an adhesive wear mechanism.This mechanism is generally less dangerous than an abrasive one,resulting in a lower friction coefficient and wear rate [22].Fig.3shows the SEM morphologies of the worn surfaces of the composites made of various modified carbon fabric under dry sliding under 200N at a speed of 0.431m/s in a period of 120min.The sliding direction of the composites is marked with the white arrowhead.From Fig.3a,it can be seen that pronouncedly pulled out,even broken carbon fi-ber was on the worn surface of Composite U,which indi-cated that the CF performed very poor interface bonding with the phenolic resin matrix.The drop out of the CF from the phenolic resin matrix shifted the wear mechanisms from adhesive wear to abrasive wear.However,the worn surface of Composite A was relatively smoother (Fig.3b),and the phenomenon of pronounced carbon fiber pulling-out was abated.And for Composite B,only a few carbon fi-bers was pulled out or broken on the worn surface (Fig.3c).In particular,the worn surface of Composite C was the smoothest and little signs of carbon fiber damage were seen (Fig.3d),which conformed to the best wear-resis-tance of the composite.From the above,it is clear that the surface treatment of the CF can improve the adhesion between the CF and the phenolic resin matrix,which can transmit the load from the matrix to fibers efficiently and prevent the peeling off of the carbon fibers and resulted in better tribological behaviour.Fig.4shows the magnified SEM morphologies of the worn surfaces of the composites made of various modified carbon fabric.As shown in Fig.4a,the surface of carbon fi-bers is smooth and the carbon fibers were almost com-pletely separated from the matrix,with the fiber–adhesive interface gap to be significantly large,which indi-cated the adhesion between the CF and the phenolic resin matrix was poor and was consistent with the poorwear-Fig.1.The contact technical drawing for the friction couple.Table 2Chemical composition of the GCr15steel ring Chemical composition (wt%)CMn Si P S Cr 0.95–1.050.25–0.450.15–03560.02560.0251.40–1.65X.Zhang et al./European Polymer Journal 44(2008)2551–25572553resistance of Composite U.For Composite A and B,the car-bon fiber and the phenolic resin was still bonded to some extent after friction indicating that the bonding between the carbon fabric and the phenolic resin matrix was im-proved (Fig.4b and c),which was responsible for the slight increase of wear-resistance of the composite compared to the unmodified one.In the case of Composite C as seen from SEM,gap between the CF and the phenolic resin be-comes unnoticeable (Fig.4d),which indicated that com-bined surface treatment contributed to effectiveincreaseFig.3.SEM pictures of the worn surfaces of the composites made of various modified CF (a)composite U (b)composite A (c)composite B (d)compositeC.Fig.4.The magnified SEM morphologies of the worn surfaces of the composites made of various modified CF (a)composite U (b)composite A (c)composite B (d)composite C.2554X.Zhang et al./European Polymer Journal 44(2008)2551–2557in interfacial bonding between the CF and the phenolic re-sin and hence to significantly improve the tribological properties of the CFP composite.Fig.5shows the SEM morphologies of the transfer film on the surface of GCr15steel counterpart.For the steel counterpart friction against Composite U,a large amount of transferred wear debris was observed on the counter-part surface and the transfer film was thick and discontin-uous (Fig.5a),which corresponded to the poor wear-resistance of this composite.On the contrast,for the counterpart friction against composite made of carbon fabric by single surface modification,few wear debris was seen on the counterpart surface and the transfer film became thinner but still inhomogeneous (Fig.5b and c).Differently from the above transfer films,when friction against Composite C,a relative thin,uniform and compact transfer film was formed on the counterpart steel ring (Fig.5d).With the formation of the relative uniform and coherent transfer film,subsequent sliding occurred be-tween the surface of the CFP composites and the transfer film.Consequently,a lower friction coefficient and wear rate was reached.3.2.XPS and SEM analysis of the carbon fabric surfaces The elemental information got from the XPS spectra is shown in Table 3.It can be found that both the relative O concentration and the O/C ratios in the carbon fabric sur-face all increased after surface modification.It is worth noting that the combined surface treatment was themost effective in increasing the O concentration in the carbon fiber surface.The reason might be due to the fact that combined surface treatment can consolidate the ef-fect of HNO 3oxidation and can change the chemical composition of the fiber surface and introduce more ac-tive functional groups.The number of oxygen-containing groups of the untreated CF sample was attributed to the residual groups of the polymeric precursor,polyacryloni-trile and the polymeric sizing on the CF after washing in acetone.The curve fitting spectra of C1s of the untreated and treated CF are revealed in Fig.6.The main C1s peak is pre-sented at 285eV,which correspond to the graphitic link-age of carbon fiber.In addition,there are some peaks appeared at the higher binding energy positions compared with the main C1s peak and they correspond to different oxygen-containing groups.Each functional group gives rise to a signal in the XPS spectrum with a particular range of binding energies.Deconvolution of the C1s spectra of carbon fibers gave four peaks designated as peak 1(at 284.7–284.9eV as-signed to graphitic carbon),peak 2(at 285.9–286.3eV,car-bon bonded phenolic or alcoholic hydroxyls or ether oxygens),peak 3(at 287–287.4eV,Bridged structure)and peak 4(at 288.7–289eV,carbonyl carbon in ketones or carboxyl functions or ester groups).The fitting results of C1s of different samples are shown in Table 4.For the untreated CF sample,the mainly oxygen-containing groups on surface are A C A OH,A C A O A C.Also,a small amount of C @O and A COOR groups existed on the surface.When CF was treated,the content of A C A C AA decreased and more bridged structure and C @O,A C A OH,A C A O A C could be formed on the surface,especially modified by combined surface treatment.The increase in the oxygen-containing groups increased the polarity of the carbon fiber surface and thus enhanced the wettability of the CF with the phe-nolic resin matrix.Better wetting can improve the interfa-cial adhesion by providing a more intimate contact and increasing the thermodynamic work of adhesion or by reducing the number of interfacial defects,which led to better stress transfer from the matrix to the fiber materials [28].The SEM morphologies of the untreated and treated CF are shown in Fig.7.It can be observed remarkable differ-ences existed between the untreated and treated CF.The CF after DB550modification (Fig.7b)became smoother and the grooves were less obvious than the untreated CF (Fig.7a).Under the HNO 3oxidation,there appeared more defects,closely spaced grooves,protuberances on the sur-faces (Fig.7c).The etching effect can make the CF rougher,which can enhance the mechanical interlockingbetweenFig.5.SEM morphologies of the transfer films on the surface of GCr15steel counterpart (a)composite U (b)composite A (c)composite B (d)composite C.Table 3XPS surface elemental analysis data of untreated and treated CF SamplesC (%)O (%)N (%)O/C Pure CF 75.121.6 3.30.288CF/DB55067.226.1 6.70.388CF/HNO 369.723.8 6.50.34CF/HNO 3+DB55060.828.810.40.474X.Zhang et al./European Polymer Journal 44(2008)2551–25572555the CF and resin.The surface (Fig.7d)of the combined sur-face modified CF also became rougher,which resulted from the strong HNO 3etching.The rougher CF surface would provide a more contact between the carbon fibers and the phenolic resin matrix to ensure a significant level of van der Waals force,which enhanced the degree of mechanical contact between the fibers and polymer matrix and improved the interface physical adhesion between the fibers and polymer matrix [29].The adhesion between the CF and the phenolic resin matrix can be mainly improved by increasing the real con-tact between the CF and the phenolic resin and/or intro-ducing interfacial chemical reaction.The transition area formed between the fibers and the matrix can transmit load and prevent the propagation of crack.When the car-bon fibers were surface treated,the transition area formed would be improved.Especially,when the carbon fiber was treated with combined surface modification,the thickness of interphase formed was larger than those formed in the case of carbon fibers treated with coupling agent or HNO 3oxidation and hence to improve the adhesion be-tween the CF and the phenolic resin matrix.When thereis a strong adhesion between fibers and matrix,the fiber can bring more reinforcement,which played an important role on the tribological properties of CFP composites.Table 4Surface component analysis of C1s curve of different carbon fiber samples SamplesPeak 1Peak 2Peak 3Peak 4Pure CF 66.722.18 3.2CF/DB55061.725.49.6 3.3CF/HNO 359.226.89.8 4.2CF/HNO 3+DB55055.52316.15.4Fig.7.The SEM configurations of the untreated and treated CF(a)Pure CF (b)CF/DB550(c)CF/HNO 3(d)CF/HNO 3+DB550.2556X.Zhang et al./European Polymer Journal 44(2008)2551–25574.ConclusionsBoth coupling agent and HNO3oxidation can help im-prove the friction and wear behaviour of CF reinforced phe-nolic resin matrix composite,while combined surface treatment is the most effective to decrease the friction coefficient and wear rate of the composite.The worn sur-face morphology of the CFP composites with modifiedfiber exhibited better adhesive properties between thefiber and phenolic resin matrix,which was responsible for the improvement of the tribological properties of the composites.AcknowledgementsThe authors acknowledge thefinancial support of the Innovative Group Foundation from NSFC(Grant No. 50421502)and the National Natural Science Foundation of China(Grant No.50475128)and the important direction project for the knowledge innovative engineering of Chi-nese Academy of Sciences(Grant No.KGCX3-SYW-205). 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10. surface technology

10. surface technology

Friction dissipate energy, thus generating heat, which can have detrimental effects on an operation. Furthermore, because it impedes free movements at interfaces, friction can significantly affect the flow and deformation of materials in metalworking processes. However, friction is not always undesirable. Without friction, rolling metals, clamping workpieces on machines would be impossible.
defects
Several defects caused by and produced during component manufacturing can be responsible for inadequate surface integrity. The following are definitions of th emajor surface defects found in practice. • Cracks are external and internal separations with sharp outlines. • Craters are shallow depressions; •Inclusions are small, nonmetallic elements or compounds in the metal; •Metallurgical transformation involves microstructural changes caused by temperature and pressure cycling. • Plastic deformation is a severe surface deformation caused by high stresses due to friction, tool and die geometry, worn tools, and method of processing. • Residual stresses are surface stresses (tension and compression) cause by nonuniform deformation and temperature distribution; • Seams are surface defects resulting from overlapping of the material during processing.
碳纤维掺杂酚醛树脂

碳纤维掺杂酚醛树脂

Wear272 (2011) 43–49Contents lists available at ScienceDirectWearj o u r n a l h o m e p a g e:w w w.e l s e v i e r.c o m/l o c a t e/w e arEffect of the addition of carbonaceousfibers on the tribological behavior of a phenolic resin sliding against cast ironS.Betancourt a,∗,L.J.Cruz a,A.Toro ba New Materials Research Group,School of Engineering,Pontificia Bolivariana University,Circular1a N.70–01,Medellín,Colombiab Tribology and Surfaces Group,School of Materials Engineering,National University of Colombia,Cra80N.65-223,Medellín,Colombiaa r t i c l e i n f oArticle history:Received20January2011Received in revised form12July2011 Accepted22July2011Available online 30 July 2011Keywords:CarbonaceousfibersPhenolic resinCompositesSliding contactCast iron a b s t r a c tThe tribological behavior of novolac phenolic resin matrix composites reinforced with three kinds of carbonaceousfibers was studied in sliding contact against cast iron.Slow pyrolysis was used to obtain carbonaceousfibers from Colombian plantainfiber bundles(crops residues from Urabáregion).After the carbonization process the samples were heated up to either1200or1400◦C ensuring that many morphological aspects of the naturalfibers were retained.Then,novolac phenolic resin with HMTA as curing agent and the carbonaceousfibers were used to obtain a composite material by compression molding process.Samples with different type and volume fraction of carbonaceousfibers were prepared and tested in sliding contact against cast iron in a pin-on-disc wear testing machine.At the end of the tests,the worn surfaces and the debris were analyzed by SEM.A decrease in both friction coefficient and wear of composites was observed with the increase infiber volume fraction,which was associated to a beneficial effect of the detachment of carbonaceous material from the worn surface.Under the tested conditions,this material remains at the interface between the composite and the cast iron and helps reduce the shear resistance of the interface.On the other hand, surface fatigue and adhesion wear was identified as the dominant wear mechanism of the phenolic resin matrix.© 2011 Elsevier B.V. All rights reserved.1.IntroductionPyrolysis process transforms lignocellulosic materials into char-coal and slow heating rate pyrolysis gives rise to a porous carbon frame with the morphology derived from its precursor[1–3],which can be used to ceramic synthesis such as silicon carbide,alu-mina and titania[3].Typical lignocellulosic precursors of charcoal materials that retain morphological aspects of precursor are wood resources.Although non-wood plants are used to get carbon pow-ders and activated carbon,fibrous wastes from agricultural residues of edibles fruits from Musa species such as commercial plantain (Musa AAB,cv“Dominico Harton”)produced in Colombia have been used to get carbonaceousfibers[4–7].The sliding friction coefficients of some carbon-based materi-als,either amorphous or crystalline,are among the lowest for any solids.They are important ingredients of brake composite materi-als including different types such as graphite,coke,carbon black, and carbonfiber[8].Charcoal and carbonaceous substances,for instance,have good frictional characteristics even though they do not exhibit the basal slip properties of graphitic structures.∗Corresponding author.Tel.:+5744488388;fax:+5743544532.E-mail address:santiago.betancourt@.co(S.Betancourt).On the other hand,novolac phenolic resin is a common binder for resin-based friction materials[9].Tribological applications of phenolic resins are usually limited due to their relatively poor stability and wear resistance.Therefore,it is imperative to incorpo-rate various reinforcing andfilling constituents such as reinforcing fibers,abrasives,binders,fillers,and friction modifiers(solid lubri-cants)into phenolic resin-based friction composites with the purpose of increasing their stability and wear resistance[10–12].The type and relative amount of solid lubricants and abrasives in brake friction materials significantly affect the brake performance [13].Solid lubricants are added in relatively small amounts but they strongly affect wear resistance,stopping distance,friction stability and torque variation.Graphite and MoS2are frequently used in commercial brake linings and other chalcogenide compounds such as Sb2S3,ZnS,PbS,and Cu2S are often added for better brake per-formance.However,a few reports focused on the effect of solid lubricants on tribological properties of solidfilms coated on the metal substrates are available[14,15].Charcoal in particular has been reported as a potential replace-ment for graphite into composites for antifriction and antiwear applications as aluminum alloys applications[16,17],wood ceram-ics and in brake friction materials using carbonized coconut char powders[18].Nevertheless,it is rarely discussed in the literature the effect of charcoal materials on wear mechanisms acting on the0043-1648/$–see front matter© 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.wear.2011.07.01444S.Betancourt et al./Wear272 (2011) 43–49surfaces in contact.In this work,novolac phenolic resin matrix composites reinforced with three kinds of carbonaceousfibers and different volume fraction of reinforcement were prepared.Chem-ical composition and structural characteristics of carbonaceous fibers were studied.Tribological behavior of composites was tested in sliding contact against cast iron in a pin-on-disc wear testing machine.Worn surfaces were studied by SEM and wear mecha-nisms were identified.2.Materials and experimental methods2.1.MaterialsCarbonaceousfibers were obtained by pyrolysis of plantain fibers from leaf sheaths from Urabá,Colombia region.A mechani-cal extraction process for plantainfibers was used according to the method described in[19].The samples were further air-dried for at least24h and milled with a RETSCH SM100(Haan,Germany)to obtain a particle size smaller than5mm.Three types of carbonaceousfibers(T1000,T1200,T1400)were synthesized by slow pyrolysis performed in an electrical tube fur-nace MTI GSL1600-80X.T1000samples were heated from room temperature up to1000◦C,held at this temperature for90min and then cooled down to room temperature in N2atmosphere with99.9999%purity.T1200and T1400samples were initially treated under the same conditions used for T1000samples,and then submitted to a second thermal process at1200◦C and1400◦C, respectively.The heating(5◦C min−1)and cooling(−5◦C min−1) rates,as well as the nitrogenflow rate(200ml min−1),were the same for all the samples.Phenolic resin powder containing hexamethylenetetramine as curing agent was used as the matrix.Resin and carbonaceousfibers were molded by compression molding process.Previously,both components were mixed for5min by stirring them in a blender so as to improve the dispersion of the mixture.Contents of car-bonaceousfibers were2.5,5.0,7.5,10and12.5%(v/v)and phenolic resin was the balance.Fully mixed raw material was loaded into a 140mm diameter and3.5mm high steel mold and hot pressed at 200bar,165◦C for15min in a thermo hydraulic pressing machine.2.2.ExperimentalThe carbon,hydrogen,nitrogen and sulphur content of the car-bonaceousfiber bundles were determined using a LECO-CHNS-932 microanalyzer.Oxygen content was determined by means of a LECO-VTF-900furnace coupled to the microanalyzer.Ash content and moisture were determined for each carbon content in accor-dance with UNE32001and32002standards,respectively.For XRD analysis,carbonaceousfibers were ground to afine powder and the measurements were carried out in X’Pert Pro MPD,Panalytical, diffractometer operating at25mA and40kV,using Cu-Ka radiation.Table2Pin-on-disc testing conditions.Tribological test conditionsEnvironmental temperature25±2◦C Atmosphere Air–Relative speed1m s−1 Load15.11NTest distance1000m2.3.Tribological behaviorFriction and wear behavior of the phenolic resin and composites were evaluated by using a pin-on-disc tribometer.A cast iron brake disc(220mm in diameter and8mm in thickness)was adapted for the tests and the surfacefinishing wasfixed to circa Ra=0.5␮m in all the samples.Table1presents some of the most relevant metallurgical and chemical characteristics of cast iron disc.Phenolic and composite pins were glued to a metallic pin holder with conventional instant glue and machined by lathe turning to get thefinal dimensions shown in Fig.1a.The pin wasfixed to a rigid arm(Fig.1b)and put in contact with the surface of the disk in movement,while a normal load was applied by dead weights (Fig.1c).A general view of the equipment is shown in Fig.1d.All samples were tested under the same test conditions summarized in Table2and three replicas were obtained for each experimen-tal condition.Friction force was registered10times per second with the aid of a load cell connected to a data acquisition card and software Labview5.1provided by National Instruments under an educational contract.After each friction test,the pins were ultra-sonically cleaned in alcohol for5min,dried in air and weighed in an analytical balance Sartorius CPA225D with resolving power of 0.01mg.2.4.Surface examinationThe worn surfaces of disks and pins were examined by stere-omicroscopy(Nikon SMZ1500)and scanning electron microscopy (JEOL5910LV)in order to identify the main wear mechanisms act-ing during the tests.3.Results and discussionElemental composition offibers after pyrolysis process and sec-ond thermal treatment are shown in Table3.All samples have high amount of carbon as a consequence of carbonization of ligno-cellulosic compounds.A second thermal treatment increases the carbon content and reduces the amount of oxygen and hydrogen by volatilization.These changes are considered typical in carbon materials due to exposure to high temperature[20].Carbonaceuosfibers produced from plantainfibers bundles were crystallographically characterized by means of X-ray diffrac-Table1Metallurgical and chemical characteristics of cast iron disc.Nominal chemical composition(wt.%)C 3.65–3.85Sn Max.0.10 Si 2.15–2.795Cu Max.0.60 S Max.0.15Mo Max.0.10 P Max.0.10Ni Max.0.20 Mn0.5–0.9Fe Balance Cr Max.0.25Microstructure Graphite type:1–1A(sheets) Grain size:ASTM3–4 Pearlite:90%min.Ferrite:5%max. Cementite:5%max.Hardness170–217HBS.Betancourt et al./Wear272 (2011) 43–4945Fig.1.Details of positioning of the samples(a–c)and general aspect of pin-on-disc tribometer(d). tion as seen in Fig.2.All samples presented crystalline andamorphous phases associated to carbonaceous material and crys-tals of inorganic substances.Identification of diffraction angles andmineral substance is summarized in Table4as a function of car-bonization temperature.Table3Chemical composition of carbonaceousfibers measured by elemental analysis.Element(wt.%)SampleT1000T1200T1400Carbon66.6775.9180.12Hydrogen 1.37 1.21 1.29Nitrogen0.520.530.33Sulphur0.120.090.12Oxygen14.059.568.08Table4Crystallographic analysis of carbonaceousfibers(refer to Fig.2).Sample Peak2Â(◦)Mineral/chemical formulaT 1000a29.50Calcite/CaCO3b31.95Butschliite/K2Ca(CO3)2 c33.30d43.64T 1200e31.16Butschliite/K2Ca(CO3)2 f33.32g42.92T 1400h26.35Calciumcarbide/CaC2i32.65T1000samples show peaks corresponding to calcium and potas-sium crystals such as Calcite(CaCO3)and Butschliite(K2Ca2(CO3)3),the latter being a non-conventional phase found in wood ashesaccording to Winbo et al.[20].Amorphous region showsdiffuseFig.2.X-ray diffractograms of samples obtained by different processing parameters.Diffuse bands around2Â=26◦and44◦correspond to(002)and(100)planes of agraphite-like carbon structure.Peaks a to i are identified in Table4.46S.Betancourt et al./Wear 272 (2011) 43–49Fig.3.Friction force vs.testing time curves.Non-reinforced phenolic resin (a)and samples with 7.5%reinforcement content:T 1000(b),T 1200(c)and T 1400(d).bands at 2Â=26.5◦and 42.4◦,which correspond to typical crys-talline planes of non-graphitic carbon materials (002and 100,respectively)[21–23].Structural changes are observed in T 1200and T 1400samples due to the changes in thermal history.Calcite inorganic mineralpeak disappears and a slight shift of Butschliite peak is observed.Also,T 1400samples show a new crystalline phase identified as cal-cium carbide,which is not observed in T 1000and T 1200samples.Intensity of carbon 002and 100peaks increased for both sam-ples.Packing of basic structural unities (graphenes)along c axisisFig.4.Coefficient of friction (a)and wear rate (b)of phenolic resin and carbonaceous composites in pin-on-disc tests.S.Betancourt et al./Wear272 (2011) 43–4947Fig.5.Aspect of the worn surface of reinforcement-free resin.SEM.The arrows represent the sliding direction.a thermal activated process which occurs at temperatures higher to1000◦C[24].3.1.Friction coefficient and wear resistanceAfter a running-in period that lasted around100s for all the samples,a stable friction force was measured during testing of both phenolic and composite samples,as can be verified,for instance,in Fig.3where the friction force vs.testing time curves for non-reinforced phenolic resin samples and T1000,T1200and T1400 samples with7.5%of carbonaceousfiber content are shown.Results of the measurements of stable friction coefficient dur-ing pin-on-disc tests are shown in Fig.4.All composites exhibit an important reduction of friction coefficient as the carbon content is increased.The maximum relative reduction(near to40%)was observed for12.5%carbon content in T1200samples(Fig.4a). Fig.6.Aspect of the worn surface of composite pin.SEM.The arrows represent the sliding direction.48S.Betancourt et al./Wear 272 (2011) 43–49Fig.7.Aspect of the worn surface of grey iron disc SEM.Arrow represents sliding direction.Darker zones correspond to polymer adhered to the disc’s surface.The reduction in wear rate with the addition of carbonaceous fibers was much more dramatic,with relative variations up to 85%with respect to pure phenolic resin,as seen in Fig.4b.The results did not reveal statistical differences among the wear rates of samples T 1000with 2.5,5.0,and 7.5%of carbonaceous fibers.Similar results were obtained for T 1200composites with the same reinforcement content.According to friction coefficient and wear rate results,the addition of carbonaceous fibers to phenolic resin led to an improve-ment in tribological behavior due to significant reduction in wear rates while the friction coefficient values remained quite stable.This behavior can be attributed to the presence of graphite-like crystalline layers into the amorphous structure of carbonaceous material,which were detected by means of X-ray diffraction (see diffuse bands in diffractograms of Fig.2),as well as to the benefi-cial effect of the detachment of carbonaceous fibers that remain trapped between the composite and the cast iron during the tests.3.2.Examination of worn surfacesThe typical aspect of the worn surface of fiber-free phenolic resin samples is shown in Fig.5.Plastic deformation is observed up to some extent (Fig.5a and b)and evidences of fatigue-related wear mechanisms are clearly identified in Fig.5c where a parti-cle of material is about to be detached as a result of the joining of cracks that grew parallel to the contact surface.The character-istic pattern consisting of regularly spaced cracks perpendicular to the sliding direction (Fig.5d)has been previously observed in thermoset polymers sliding against smooth surfaces [25,26].These marks were systematically observed at the worn surface of the fiber-free samples and effectively denote the occurrence of fatigue-related phenomena.Crazing evidences can also be observed in Fig.5d,which are normally expected in polymers submitted to sliding wear conditions.In regards to composite samples,worn surface examination revealed a random distribution of carbonaceous fibers,with nopreferred orientation with respect to the sliding direction.Fig.6a shows a low magnification image of the surface of a typical sam-ple,where a number of features such as holes and incomplete carbonaceous fibers can be observed.Typical vascular plant mor-phology can be observed in carbonaceous fibers,Fig.6b and c,in a region where the fibers were broken and the inner part was exposed.Similarly to what was found in fiber-free pheno-lic resin samples,crazing and surface fatigue of the polymer are the dominant wear mechanisms,although some cracks were observed along the fibers as well.A fragment of broken fibers clearly shows the morphology of carbonaceous fibers which retain cellular features from precursor and evidences the fracture of carbonaceous material as one of the active wear mechanisms,Fig.6d.Regarding the analysis of the disc’s surface,evidences of adhe-sion of phenolic resin on the disc were found by SEM as shown in Fig.7.In Fig.7a,a slightly darker region that corresponds to the mark left by the fragments of matrix attached to the asperities of the surface of the disc during sliding contact can be observed.Accord-ing to the detailed examination of the worn surfaces,it can be said that initially the resin partially fills the valleys of the surface rough-ness of the disc and next it continues to accumulate in the whole contact area (Fig.7b–d).Therefore,two main wear mechanisms are active:adhesive wear and surface fatigue.A sequence of events occurring during sliding of composite sam-ples against cast iron is proposed according to the analysis of worn surfaces (Fig.8):once pin and disc surfaces are put in contact,stresses are produced by effect of the normal load and tangential forces during sliding.The main wear mechanisms of phenolic resin are adhesion and surface fatigue.On the other hand,once the car-bonaceous fibers get in contact with cast iron they crack and suffer brittle fracture.Some fragments remain at the interface between pin and disk so the carbonaceous material is crushed and a fine powder is formed.Then,a fine distribution of carbonaceous parti-cles is spread over the contact interface acting as a solid lubricant that provides the conditions for the stable friction coefficient and reduced wear rate observed in the experiments.S.Betancourt et al./Wear272 (2011) 43–4949Fig.8.Schematic of the sequence of events leading to wear of phenolic matrix composites reinforced with carbonaceousfibers in contact with cast iron.4.ConclusionsThe tribological behavior of phenolic resin composites rein-forced with carbonaceousfibers sliding against cast iron was studied.A reduction in wear rate of composites was observed with the increase in carbonaceousfiber volume fraction.Friction coef-ficient also showed a trend to reduce with the increase offiber volume fraction,although the measured values were close to those found in pure phenolic resin samples.Adhesion,surface fatigue and crazing were identified as the dominant wear mechanisms of the phenolic matrix while brittle fracture was the main cause of detachment of carbonaceousfibers.The analysis of the worn surfaces revealed that a signifi-cant amount of carbonaceous material removed from the matrix remained at the interface between the composite pins and metallic discs,which was associated to prevention of adhesive wear of the phenolic matrix and a possible function of carbonaceous material as a solid lubricant.References[1]C.Byrne,D.Nagle,Carbonization of wood for advanced materials applications,Carbon35(1997)259–266.[2]P.Greil,Biomorphous ceramics from lignocellulosics,J.Am.Ceram.Soc.21(2001)105–118.[3]H.Sieber,C.Hoffmann,A.Kaindl,P.Greil,Biomorphic cellular ceramics,Adv.Eng.Mater.2(2000)105–109.[4]S.Betancourt,Desarrollo de materiales compuestos de matriz fenólica conmateriales carbonosos sintetizados a partir de lasfibras vegetales obtenidas de la vena central de la hoja de plátano.Ph.D.Thesis.Universidad Pontificia Bolivariana,Medellín,2010.[5]C.R.Rambo,Materiais avanc¸ados inspirados na natureza:estruturas celulares,fibras e compósitos,Exacta9(2006)5–103.[6]C.Rambo,T.Andrade,T.Fey,H.Sieber,A.E.Martinelli,P.Greil,MicrocellularAl2O3ceramics from wood forfilter applications,J.Am.Ceram.Soc.91(2008) 852–859.[7]Z.Weiss,J.C.Crelling,G.Simha Martynkova,M.Valaskova,P.Filip,Identifica-tion of carbon forms and other phases in automotive brake composites using multiple analytical techniques,Carbon44(2006)792–798.[8]Y.Gewen,Y.Fengyuan,Mechanical and tribological properties of phenolicresin-based friction compositesfilled with several inorganicfillers,Wear262 (2007)121–129.[9]S.K.Rhee,M.G.Jacko,P.H.S.Tsang,The role of frictionfilm in friction,wear andnoise of automotive brakes,Wear146(1991)89–97.[10]S.J.Kim,H.Jang,Friction and wear of friction materials containing two differentphenolic resins reinforced with aramid pulp,Tribol.Int.146(2000)477–484.[11]P.Gopal,L.R.Dharani,F.D.Blum,Fade and wear characteristics of a glassfiberreinforced phenolic friction material,Wear174(1994)119–127.[12]M.H.Cho,J.J.S.J.Kim,H.Jang,Tribological properties of solid lubricants(graphite,Sb2S3,MoS2)for automotive brake friction materials,Wear260 (2006)855–860.[13]W.J.Bartz,J.Xu,Wear behavior and failure mechanism of bonded solid lubri-cants,Lub.Eng.43(1987)514–521.[14]M.N.Gardos,Synergistic effects of graphite on the friction and wear of MoS2films in air,Tribol.Trans.31(1988)214–227.[15]T.Wang,T.Fan,D.Zhang,G.Zhang,Fabrication and the wear behaviors ofthe carbon/aluminum composites based on wood templates,Carbon44(2006) 900–906.[16]T.P.Murali,S.V.Prasad,M.K.Surappa,P.K.Rohatgi,K.Gopinath,Friction andwear behaviour of aluminium alloy coconut shell char particulate composites, Wear80(1982)149–158.[17]M.Sutikno,P.Marwoto,S.Rustad,The mechanical properties of carbonizedcoconut char powder-based friction materials,Carbon48(2010)3616–3620.[18]D.Joseph,A.Oberlin,Oxidation of carbonaceous Matter I Elemental analysis(C,H,O)and IR spectrometry,Carbon21(1983)559–564.[19]P.Ganán,R.Zuluaga,A.Restrepo,bidi,Mondragon plantainfiber bun-dles isolated from Colombian agro-industrial residues,Bioresour.Technol.99 (2008)486–491.[20]C.Winbo,E.Rosen,M.Heimb,Thermal analytical study of the decompositionof K2Ca2(CO3)3,Acta Chem.Scand.(1998)431–434.[21]R.Franklin,Crystallite growth in graphitizing and non-graphitizing carbons,Proc.R.Soc.Lond.(1951)196–218.[22]X.Bourrat,in:H.Marsh,F.Rodríguez-Reinoso(Eds.),Science of Carbon Mate-rials,Ed.Universidad de Alicante,Alicante,2000,pp.1–90.[23]F.G.Emmerich,Evolution with heat treatment of crystallinity in carbons,Car-bon33(1995)1709–1715.[24]G.A.Zickler,T.Schoumlberl,O.Paris,Mechanical properties of pyrolysed wood:a nanoindentation study,Philos.Mag.86(2006)1373–2138.[25]B.Bhushan,Introduction to Tribology,John Wiley&Sons,New York,2002,p.406.[26]M.Terheci,Microscopic investigation on the origin of wear by surface fatiguein dry sliding,Mater.Charact.45(2000)1–15.。

FrictionandWearofMaterials2ndEdition：摩擦材料的磨损第二版

FrictionandWearofMaterials2ndEdition：摩擦材料的磨损第二版

BrochureMore information from /reports/2214513/Friction and Wear of Materials. 2nd EditionDescription:Friction and Wear of Materials Second Edition Written by one of the world's foremost authorities on friction, this classic book offers a lucid presentation of the theory of mechanical surface interactions as it applies tofriction, wear, adhesion, and boundary lubrication. To aid engineers in design decisions, Friction and Wear ofMaterials evaluates the properties of materials which, under specified conditions, cause one material tofunction better as a bearing material than another. Featured also are thorough treatments of lubricants andthe sizes and shapes of wear particles. This updated Second Edition includes new material on erosive wear,impact wear, and friction. Professor Rabinowicz's book will be especially welcomed by mechanical anddesign engineers, surface scientists, tribologists and others who design, produce and operate products,machines and equipment which involve friction and its effects.Contents:Material Properties That Influence Surface Interactions.Surface Interactions.Friction.Types of Wear.Adhesive Wear.Abrasive and Other Types of Wear.Lubrication.Adhesion.Appendix.Sample Problems.Index.Ordering:Order Online - /reports/2214513/Order by Fax - using the form belowOrder by Post - print the order form below and send toResearch and Markets,Guinness Centre,Taylors Lane,Dublin 8,Ireland.Fax Order FormTo place an order via fax simply print this form, fill in the information below and fax the completed form to 646-607-1907 (from USA) or +353-1-481-1716 (from Rest of World). If you have any questions please visit/contact/Order Information Please verify that the product information is correct.Product Format Please select the product format and quantity you require:* Shipping/Handling is only charged once per order.Contact InformationPlease enter all the information below in BLOCK CAPITALSProduct Name:Friction and Wear of Materials. 2nd Edition Web Address:/reports/2214513/Office Code:OC8DIMRRQTNTYS QuantityHard Copy (HardBack):EUR 147 + EUR 25 Shipping/HandlingTitle:MrMrsDrMissMsProf First Name:Last Name:Email Address: *Job Title:Organisation:Address:City:Postal / Zip Code:Country:Phone Number:Fax Number:* Please refrain from using free email accounts when ordering (e.g. Yahoo, Hotmail, AOL)Payment InformationPlease indicate the payment method you would like to use by selecting the appropriate box.Please fax this form to:(646) 607-1907 or (646) 964-6609 - From USA+353-1-481-1716 or +353-1-653-1571 - From Rest of WorldPay by credit card:American ExpressDiners ClubMaster CardVisa Cardholder's Name Cardholder's Signature Expiry Date Card Number CVV Number Issue Date(for Diners Club only)Pay by check:Please post the check, accompanied by this form, to:Research and Markets,Guinness Center,Taylors Lane,Dublin 8,Ireland.Pay by wire transfer:Please transfer funds to:Account number833 130 83Sort code98-53-30Swift codeULSBIE2D IBAN numberIE78ULSB98533083313083Bank Address Ulster Bank,27-35 Main Street,Blackrock,Co. Dublin,Ireland.If you have a Marketing Code please enter it below:Marketing Code:Please note that by ordering from Research and Markets you are agreeing to our Terms and Conditions at /info/terms.asp。

Chapter03IntroductiontoTribology机械零件设计英文全套教案课件

Chapter03IntroductiontoTribology机械零件设计英文全套教案课件

Five distinct forms of lubrication:
1. Hydrodynamic; 2. Hydrostatic; 3. Elastohydrodynamic; 4. Boundary; 5. Solid-film
Hydrodynamic Lubrication
The load-carrying surfaces of the bearing are separated by a relatively thick film of lubricant, so as to prevent metal-tometal contact.
The area of real contact between couples is proportional to the load; thus the frictional force should be proportional to the load.
Since the area of real contact is independent of the apparent surface area of the body, the friction should be independent of the apparent surface area.
Wear
In the same way as friction, wear of machinery is sometimes advantageous. The initial wear resulting in better mating of components (running-in), is evidently desirable.
By lubricating techniques By improving the bulk materials or metal surfaces