Effect of fretting amplitudes on fretting wear behavior of steel wires in coal mines

MININGScienceDirectSCIENCE ANDTECHNOLOGYELSEVIERMining Science and Technology 20(2010)0803-0808www.elsevier.com/locate/jcumtEffect of fretting amplitudes on fretting wearbehavior of steel wires in coal minesSHEN Yan, ZHANG Dekun, GE ShirongSchool of Materials Science and Engineering, China University of Mining Technology, Xuzhou 221116, ChinaAbstract: Given that fretting wear causes failure in steel wires, we carried out tangential fretting wear tests of steel wires on aelf-made fretting wear test rig under contact loads of 9 and 29 N and fretting amplitudes ranging from 5 to 180 um. We observedmorphologies of fretted steel wire surfaces on an S-3000N scanning electron microscope in order to analyze fretting wear mecha-nisms. The results show that the fretting regime of steel wires transforms from partial slip regime into mixed fretting regime andgross slip regime with an increase in fretting amplitudes under a given contact load. In partial slip regime, the friction coefficienthas a relatively low value. Four stages can be defined in mixed fretting and gross slip regimes. the fretting wear of steel wires in-creases obviously with increases in fretting amplitudes, Fretting scars present a typical morphology of annularity, showing sligdamage in partial slip regime. However, wear clearly increases in mixed fretting regime where wear mechanism is a combination ofplastic deformation, abrasive wear and oxidative wear. In gross slip regime, more severe degradation is present than in the otherregimes. The main fretting wear mechanisms of steel wires are abrasive wear, surface fatigue and friction oxidationKeywords: steel wires; fretting wear, fretting amplitude; fretting regime; wear mechanism1 Introductionmum disulfide bonded solid lubricating coating underradial and tangential fretting conditions and discovSteel ropes are important components of hoist ered that fretting damage of the coating was stronglyequipment in coalmines and are used to connect the dependent on the displacement amplitude. Young et alhoister with a hoisting container. Their intensity and examined the effect of a current load on the frettinglife span are directly related to the security of the corrosion behavior of tin coated- brass contacts athoister and mine production. Fretting wear occursvarious current loads. Zhang and his coworkersbetween strands and steel wires in hoisting ropes. It revealed the impact of loads, cycles and amplitudesreduces the fatigue strength and accelerates fatiguethe friction coefficient, wear depth and fatigue lifefracture failure of steel wires-2]. Therefore, reducing of steel wires in coalmines02. These scientists havethe fatigue damage of steel wires is a good way to presented some damage models and views from theprolong the service life of steel ropes and a key meas- different perspectives of material, fracture mechanicsure to ensure their reliable useand so on. However, they have seldom systematicallyFretting is te movement of small amplitude (mi: mechanisms of steel opea in ceos min es by frettingonly affected by material parameters such as strength, map theory In our study, we explored the tangentialmodulus of elasticity and plasticity, but is also closely fretting wear characteristics of steel wires and therelated to experimental parameters such as displace- impact of fretting amplitude on fretting damage underment,load, frequency, stiffness, contact mode, rough- different amplitudes for a given contact loadness and fretting cycles. Zhu and his coworkersinvestigated the fretting wear and kinetic behavior of 2 Experimentalmicro-arc oxidation coating and aluminum alloy substrates under different fretting amplitudes and drySteel wires(cold drawn, high-quality carbon struc-friction conditions. They also studied molybde- turalcontact ropes wereused中国煤化工 e diameter of theReceived 31 March 2010, accepted 1steeCorresponding author. Tel: 86516 83591918CNMHGcopOSLon DyE-mailaddress:dkzhang@cumt.edu.cns are shown in Table 2doi:10.106/s16745264(09)602854Mining Science and Technologyw20N6Table 1 Chemical composition of wire specimens (% 3 Results and discussionomposition FeMn siPercentage98.710.390.020010.870001<00013.1 Fretting running- regime characteristicsUnder a given contact load of 9 N, the evolution ofTable 2 Mechanical properties of wire specimensFrD curves as a function of the number of cycles atYieldMaterialGe, ity Hardness the different displacement amplitudes are shown inFig. 1. According to the variation of FrD-N curvesSteel wire m 1. 60we observed three fretting running regimes, i. e,par365tial slip regime (straight line), mixed fretting regime(elliptic)and gross slip regime( quasi-rectangular).We carried out fretting wear tests between steel When Fn=9 N, D=5 um, all FrD curves show thewires on self-made fretting wear equipment and fixed shape of a quasi-closed line; the only adhesive was intwo wires in the form of a cross on the holders and the center of the contact zone and micro-slip occurredaligned them at 90 to each other The following at the contact edge( Fig. 1a). The imposed amplitudemajor test parameters were chosen: fretting ampli- was essentially accommodated by elastic deformationtudes of 5, 30, 65, 90, 150, 180 um; contact loads of of the surface layer. The friction force was small and9 and 29 N; frequency of 1.2 Hz and the number of steady. Therefore, fretting occurred in partial slip re-cycles varied from I to 1.3x10" cycles at room tem- gime under this conditionperatureIn contrast, for D=180 um, all FrD curves are opena computer recorded the variety of friction forces as quasi-rectangular, a characteristic of gross slip re-and fretting amplitudes in the fretting process, so we gimes(Fig. Ic). Relative slip took place between thecould assure fretting wear characteristics on the basis contact surfaces. The deformation between the conof friction logs, i.e., evolution of tangential force(Fs),tact surfaces was elastic-plastic deformation and plasdisplacement amplitude(D), and the number of cytic deformation. as a result, wear was severe.cles(N)3]. After the fretting wear tests, the lengthFor D=65 um, a mixed fretting regime appearedand width of wear scars were measured by an optical where the shapes of the fretting looop were composmicroscope with a video imaging device in order to of quasi-rectangular loops(100cycles), straight linescalculate the maximum worn depth, applied to char- (1000 cycles) and elliptical loops( thousands of cyacterize the fretting wear loss"2. We examined mor- cles). The shape of lines and elliptical loops changedphologies of fretting scars and wear debris with an often, but became finally stabilized as elliptical loopsS-3000N Scanning Electron Microscope (SEM) and At the same time the friction force increased with theanalyzed the damage to the steel wiresincrease in the number of cycles(Fig. Ib)(a)D=5(b)D=65mFig. I Evolution of FrD curves with fretting cycles under different displacement amplitudes(Fn=9N)Table 3 shows the distribution of fretting regimes parent tendency in friction logs of steel wires develof steel wires according to the variety of FrD curves, oped, i.e., fretting regimes varied from partial slipwhen displacement amplitude increased from 5 to regime to mixed fretting regime and to gross slip re-80 um at the imposed contact loads of 9 and 29 N. gime with an increase in displacement amplitudes,shown in Table 3, partial slip regimes occurred demonstrating that slin between the contact surfacesunder large loads for a given displacement amplitude occur中国煤化工 mplitude(e.g, D=30 um)or in small displacement amplitudesnplitude imposedfor a given contact load; in contrast, gross slip regime theCNMHGrsed with an in-an, and mixed fretting regime developed between crease in contact load. When the contact load inthem. Given certain imposed contact loads, an ap- creased from 9 to 29 N, the width of the partial slSHEN Yan et alEffect of fretting amplitudes on fretting wear behavior of steel wires in coal mineszone increased and the amplitude in mixed fretting load was low, the variation at the rapid increase stageregime and gross slip regime was relatively postwas gentle and lasted for a long series of cycles, buted, i.e., slip between contact wires became less the results were reversed when the contact load wasjuent and the running regime went from gross slip high. Friction coefficients in the stable stage deand mixed slip to partial slipcreased with an increase of contact loadsTable 3 Distribution of fretting regimes of steel wireAccording to the tests, the curve of friction coeffiunder different fretting amplitudes and loadscient in mixed fretting and gross slip regime presented more complex processes of evolution, whereFR(Nfriction coefficients of steel wires became larger and306590150180MM Sstage, an ascending stage, a descending stage andstable stage. In the initial running- in stage, frictionNote: Pis partial slip regime; M is mixed fretting regime; S is slip regime. coefficients were low owing to the protection of anatural pollution'film above the sample surfaces. In3.2 Analysis of friction coefficientthe ascending stage, rapid elimination of the surfaceFriction coefficients were also quite different at the film increased adhesion and abrasion during thevarious fretting regimes. Fig. 2 shows the evolution steel-to-steel contact, causing the friction coefficientof friction coefficient as a function of fretting cycles to increase. During the descending part of the curve,when the displacement amplitude increases from 5 tocontinuous surface hardening and a change of surface180 um at the imposed contact loads of 9 and 29 N. layer structure increased the brittleness of the mate-When D=5 um, friction coefficients were low and rial, inducing metallic particles to detach and groundremained essentially steady state values, at only 0.13 and then form oxidative third-bodies4. On one handfor Fn=9 N and 0.05 for Fn=29N. For D-30 Hm, the these third-bodies could take part in load-carrying: onevolution processes of friction coefficients varied the other hand, they could inhibit adhesion of matewith the fretting cycles; only three stages can be ob- rial, so friction coefficients were reduced. During theserved in partial slip regimes, i.e., a running-in, ast stage, as a balance between continuous formationrapid increase and a stable stage at both levels of the and ejection of debris was obtained, the friction coefcontact load. The initial running-in stage lasted for ficient approached a steady value. In addition, at thisabout the first 50 cycles, after which the friction coef. relatively stable stage, friction coefficients increasedficient increased slowly and gradually to a stable state with an increase of displacement amplitudes in partial(friction coefficients in this stable state were aboutslireached a maximum during mixed fret0.40 for F=9 N and 0. 19 for Fr=29 N). Friction coef- tingand then decreased slowly with a furtherficients significantly increased with successive in- increase in displacement amplitudes in gross slip recreases in displacement amplitudes. When the contact三°01CycleCyo(a)F=9NFig. 2 Variation of the friction coefficient as a function of fretting cycles under two different contact loads3.3 Fretting wear mechanismcondition that the relative movement was largely acFig. 3 exhibits traces of fretting wear scars at dif. commodated by elastic deformation of the contactferent displacement amplitudes from optical mor-interface. Hence the friction coefficients remained atphologies at low magnification. As seen in Fig. 3the scar presents a typical morphology of annularity,(dept中国煤化工 y slight damagest, less than 3 um.where the micro-slip occurred at the contact edge and showCNMHG in displacementthe sticking occurred at the center of the contact zoneplituues, uit lletung luuveu up into the mixed andin the partial slip regime. This can be attributed to thegross slip regimes. The worn surface became coveredVoL 20 No 6with a red-brown oxide as a result of oxidation during posed load of 29 N, the depth of wear scars was lar-the fretting wear test. The fretting scars became rather ger and more pronounced in the corresponding relarge showing evident loss of material due to the plas- gions(Fig. 4b). It can be seen that the depth of weartic deformation flow and severe detachment of parti- scars increased with increases in displacement am-cles(Figs. 3b, 3c), resulting in a significant increaseplitudes and contact loadsin the depth of wear scars(Fig. 4a). Under the im-(a)D=30 um(b)D=90m(c)D=150mFig 3 Optical photographs of traces of wear under different displacement amplitudes, Fr=29 N(upper566590150180(a)F,=9NFig 4 Depth of wear scars of steel wiresThe SEM morphologies of fretting scars are quite Moreover, plowing action(Fig. 5e)occurred owing todissimilar for the various fretting regimes, as seen in the gross sliding of third-body particles and fatigueFig. 5. With Fn=9, 29 N and D=30 um(the fretting striation formed in virtue of surface fatigue(Fig. 5frunning in partial slip regime), wear scars show typi- X-ray energy spectrum analysis showed an evidentcal annularity. Hardly any adhesive wear occurred in oxygen peak and more oxygen at the contact zone,the center of the contact zone and micro-slip and which was covered with a thick layer of oxidativeslight wear damage occurred at the contact edge, debris( Fig. 3c), proof that steel wires oxidize in thewhere material had accumulated owing to plastic de- fretting wear process(Fig. 6c). Therefore, more seformation along the sliding direction(Figs. Sa, 5b). vere degradation occurred in gross slip regime than inMoreover, there was hardly any oxidation between other regimes, which presented the main wearthe steel wires, shown in Fig. 6a. In other words, the mechanisms as abrasive wear, oxidative wear andoverall damage was slightsurface fatigueIn the mixed fretting regime, for instance, whenFig. 7 shows SEM photographs of fretting debris ofFr=29 N and D=90 and 150 um, we observed traces steel wires. The fretting time was short and plasticof strong plastic deformation and micro cracks in the deformation occurred mainly in the contact zone incontact zone as well as plows and detachments of the mixed fretting regime, i. e, not all material wasparticles on the edge region from the fretting scars completely pulled off and only a small amount of(Figs 5c, 5d)where a certain amount of oxygendebris was found in the contact zone(Fig. 7a). withdetected( Fig. 6b). This indicated that plastic defor- the increase of displacement amplitudes, materialmation, abrasive wear and oxidative wear were the the contact zone slipped and formed a large amountmain wear mechanismsof中国煤化工ofpanIn gross slip regime, more severe detachment of clessized flakes(Figparticles occurred at the center of the contact zone 7c)CNMHGcontacts betweenand a thick debris layer was formed from the oxida- two samplestion of detached metal particles on the contact zoneSHEN Yan et alEffect of fretting amplitudes on fretting wear behavior of steel wires in coal mines(a)Partial slip regime. D=30 um, F-=9N (b)Partial slip regime, D-30 um. F. 29N (c)Mixed fretting regime. D=90 um. F- 9N( d)In mixed fretting regime, D=150 um, F==29N (e) Gross slip regime. D=150 um, Fr=9N (f Gross slip regime. D=180 um, Fr=gNFig. 5 SEM photographs of fretting wear regions of steel wire under different running regimesAtomic percentage O024681012l41646810121416i8681012141618Energy (kev)Energy (keV(a)D-s um, F:9N(b)D=65m,F=9N(c)D=180pm,F=9NFig 6 X-ray energy spectrum analysis of traces of wear of steel wires(a)D=90 um, F+gNb)D=150m,F=9N(c)D=180 um, Fr=29 NFig. 7 SEM photographs of fretting debris of steel wires4 Conclusionsogy of annularity, composed of slight wear at the contact edge and hardly any adhesive wear at the contact1)Given certain imposed contact loads, fretting re- center and slight damage in the partial slip regime.imes varied from partial slip regimes to mixed fret- However, wear clearly increased in mixed frettingting regimes, then to gross slip regime with an in- regime where the wear mechanism was a combina-crease in displacement amplitude; when constant dis- tion of plastic deformation, abrasion and oxidativeplacement amplitudes were imposed, the variation wear. In slip regime, more severe degradation ocwith the increase of normal loads was reversedcurred, where abrasive wear, surface fatigue and fric2)In partial slip regimes, friction coefficients pre- tion oxidation were the main fretting wear mechasented relatively low values. In mixed fretting and nisms of steel wiresslip regimes, four stages could be defined. The friction coefficient in the steady stage increased in the Ack中国煤化工to a maximum in the mixed fret-ting regimeen decreased in the gross slip re-CNMHported by the Nagime with increases in displacement amplitudetional Natural Science Foundation of China(No3)The fretting scars presented a typical morphol- 50875252): the Program for New Century ExcellentMining science and TechnoVol 20 No 6Talents in Universities (No. NCET-06-0479)and thetive study on radial and tangential fretting damage ofNatural Science Foundation of Jiangsu Provincemolybdenum disulfide bonded solid lubrication coating(NoBK2008005)Tribology, 2002, 22(1): 14-18. 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