ai-aerospace/ams_data_full_2000-2020 huggingface dataset:
7000_[]Non-coated Block .""" u6000--ti_Coated Block 5000 •_4000 0 i "m=3000 ,-2000_._;__-_._-_ tu1000 .. 0 Movic Surftech Hohman Teer-Ti CSEM-Ti CSEM-AI TypeofSputtered MoS2Coating Figure14.Average endurance lifefordifferent sputtered MoS2films(obtained fromvarious vendors andtestedindrynitrogen) onablock-on-ring Tribometer. Block-on RingBlockWearRate Thevariation ofblockwearratesfortheBlock-on-Ring testsaregiveninTable3andtheaverages in Figure15.Thelowestwearratewasobtained withtheCSEM-TI Blockslidingagainst theCSEM-Ti coating (0.7+0.3X10-18m3/m).Thesecond lowestwaswiththenon-coated blockslidingagainst the Hohman coating (1.2+1.0 X10-18m3/m)andthenextlowest wasobtained withthenon-coated blocksliding against theMoviccoating (2.0+1.0 X10-18m3/m).ThecoatedCSEM-Ti blockslidingagainst theMoviccoatedringincreased theblockwearratealmost2ordersofmagnitude ,compared tothenoncoatedblock.Thenon-coated blockslidingagainst theCSEM-Ti coating alsohadaveryhighwearrate. Block-on RinqSurface Morphology TheMoviccoatings produced verythin,continuous transfer filmsontheblocksandverythin,flowing layersofmaterial ontherings.Figure16givesphotomicrographs ofthetransfer filrnsonthenon-coated blockandthefilmremaining ontheringafter1200kcofsliding. Thewearprocess ontheringappears to bebyverythinlayerdelamination. Figure17givesphotomicrographs oftheHohman testspecimens after 3700kcofsliding. Theblockshowsverythin,continuous transfer andthematerial ontheringappears to bethicker thanthatfoundwiththeMoviccoating (Figure 16)butitalsoseems tobewearing by delamination. "-"45 n  40 x35 E ou30 E"---25 .= 20n15 10 u5o m0 Movic Surftech Hohman Teer-Ti CSEM-Ti TypeofSputtered MoS_CoatingCSEM-AI Figure15.Blockwearratefor440Cstainless steelblocks sliding ondifferent sputtered MoS2 films(obtained fromvarious vendors) andtestedindrynitrogen onablock-on-ring Tribometer. NASA/CP--2002-211506 315
Wear...................... contact !i_.'i_:___'_"/_-_ _:_'_; areawithvery, _.__,_._=___'/_ thin Transfer 11210jJ.m Block Contact AreaThin layer delamination 50tJ.rn Ring Contact Area Figure16.Photomicrographs ofthewearsurfaces ona440CblockandaMoviccoated ring after1200kcofsliding inadrynitrogen atmosphere onaBlock-on-Ring Tribometer. _Wear contact area _'withverythintransferEdgeof Thinlayer ! wearcontact delamination _J Block Contact Area 100!1m RingContact Area 10_m Figure 17.Photomicrographs ofthewearsurfaces ofa440Cuncoated blockandaHohman coated ringafter3700kcinadrynitrogen onaBlock-on-Ring Tribometer. Build-up of_j I debris Ininletarea_ IWearcontact area_'_]i, • )* , 100/_m BlockContact Area Figure 18.Photomicrographs_ii_tStriati°ns in Iii!;_llt_ slidngdrection ,t:!iif?!i )lgiii!l   501tm RingContact Area ofthewear surfaces ona440CCSEM-Ti coated blockanda CSEM-Ti coated ringafter3150kcofsliding ina drynitrogen atmosphere onaBlock-on-Ring Tribometer.::;,Fracture of ":CSEM-Ti Film Edgeof wear contact 50#m Figure 19.Photomicrograph ofthewear surface onaCSEM-Ti coated ringafter0.2 kcofsliding inadrynitrogen atmosphere against and uncoated block. NASA/C P--2002-211506 316
3.Farr,J.P.G.,"Molybdenum DisulfideasaLubricant:AReviewoftheFundamental Knowledge," Wear,10,(1967)442-452. 4.Spalvins,T.,"Lubrication withSputteredMoS2Films,NASATMX67832(1971) 5.Spalvins,T.,"Deposition ofMoS2 FilmsbyPhysical Sputtering andTheirLubrication Properties in Vacuum," ASLETrans., 12(1969), 36-43. 6.Loewenthal, S.H.,Chou,R.G.,Hopple, G.B.andWenger, W.L.,"Evaluation ofIon-Sputtered Molydenum Disulfide Bearings forSpacecraft Gimbals," Tribology Trans., 37,3(1994), 505-515. 7.Hopple, G.B.andLoewenthal, S.H.,"Development, Testing andCharacterization ofMoS2 Film Bearings," Surface andCoatings Technology, 68/69(1994), 398-406. 8.DeGee,A.W.J., Salomon, G.,andZaat,J.H.,"Mechano-Chemical Factors inMoS2Film Lubrication," Wear,7(1964), 87-101. 9.DeGee,A.W.J., Begelinger, A.andSalomon, G.,"Influence oftheAtmosphere ontheEndurance ofSomeSolidLubricants Compared atConstant LayerThickness," Proc.Inst.Mech.Engr.,183, Pt3,I,(1968), 18-27. 10.Gansheimer, J.,"Review ofChemical Reactions ofSolidLubricants duringFriction," ASLETrans., 15,4(1972), 244-251. 11.Pritchard, C.,andMidgley, J.W.,"TheEffectofHumidity ontheFriction andLifeofUnbonded Molybdenum Disulfide Films"Wear, 13,(1969), 39-50. 12.Peterson, M.B.,andJohnson, R.L.,"Friction andWearInvestigation ofMolybdenum Disulfide. IEffectofMoisture," NACATN3055(1953). 13.Fusaro, R.L.,"Lubrication andFailure Mechanisms ofMolybdenum Disulfide FilmsI-Effectof Atmosphere," NASATP-1343 (1978). 14.Singer, I.L.,Fayeulle, S.,andEhni,P.D.,"WearBehavior ofTriode-Sputtered MoS2Coatings in DrySlidingContact withSteelandCeramics," Wear,195,(1996), 7-20. 15.Miyoshi, K.,andPepper, S.V.,"Properties DataforOpening theGalileo's Partially Unfurled Main Antenna," NASATM105355 (1992). 16.Stupp,B.C.,"Synergistic EffectsofMetalsCo-Sputtered withMoS2," ThinSolidFilms,84(1981), 257-266. 17.Hilton,M.R.,Bauer,B.,Didziulis, S.V.,Dugger, M.T.Keem,J.M.andScholhamer, J.,"Structural andTribological Studies ofMoS2 SolidLubricant FilmsHaving Tailored MetaI-Multilayer Nanostructures," Surf.andCoat.Tech,53(1993), 13-23. 18.Zabinski, J.S.,Donley, M.S.,Walck, S.D.,Schneider, T.R.,andMcDevitt, N.T.,"TheEffects of Dopants ontheChemistry andTribology ofSputter-Deposited MoS2Films,"Tribology Trans., 38, 4,(1995), 894-904. 19.Teer,D.G.,Hampshire, J.,Fox,V.,andBellido-Gonzalez, V.,"TheTribological Properties MoS2/Metal Composite Coatings Deposited byClosed FieldMagnetron Sputtering," Surface and Coatings Technology, 94-5,(1997), 572-577. 20.Aharonov, R.andLoBiondo, N.,"TheInfluence ofTemperature andHumidity onWearofMoS2 andMoSTFilms,"Proceedings oftheInternational Conference ofMetallurgical Coatings andThin Films,(April2001). 21.Fusaro, R.L.,"HowtoEvaluate SolidLubricant FilmsUsingaPin-on-Disk Tribometer," Lubr. Eng.,43,5,(1986), 330-338. 22.Fusaro, Robert L.,"Mechanisms ofLubrication andWearofaBonded Solid-Lubricant Film," ASLETrans., 24,2(1981)191-204. NASA/CP--2002-211506 318
SpaceBallBearing LoadCapacity withDryLubrication A.Borrien*, J.B.Mondier* andE.Conde* Abstract Stainless steelballbearings arewidelyusedinspacemechanisms eitherwitharigidorasoftaxial preload. Thedynamic behavior ofthesecomponents duringlaunchvibrations ishighlydependent onthe non-linear stiffness oftheball-races contact andthemodalresponse ofthesuspended mass.Therefore, theprediction ofthecontact stressinthebearings requires acareful analysis ofallthestructural parts aroundthebearings. Thisanalysis mustbedoneoveralargefrequency bandwidth because therandom vibration spectrum induced bythelauncher environment generates mechanical disturbances upto2000 Hz.Thecalculated stressisthencompared tothetheoretical limitgivenbytheISO76standard, taking intoaccount asafetymargin. Theaimofthisstudywastodetermine themaximum allowable stressinthe[_/1oS2drycoated ball bearings toprevent anydegradation thatcouldbeevidenced through thefrictiontorquebehavior orthe binocular inspection ofthecoatedpieces. Twenty rigidlypreloaded ballbearing pairsweretestedtoinvestigate thispoint.Inordertorelyonthe experimental results, wedecided nottouseashakerfittedwithanaccelerometer sensorthatwouldhave required adouble integration forthedisplacement estimation. Wepreferred apulling machine witha redundant loadcellandaninductive displacement sensor. Bydoingthis,wegotadirectmeasurement of theaxialstrokeofthebearing rings,adirectmeasurement oftheloadapplied tothebearings, andwe avoidanydynamic resonance inthetestbenchthanks toa20-Hzlowfrequency loadsinecycle.The effectofcumulated surface fatiguewastakenintoaccount bydoingthesamenumber ofcyclesasin800 Hzoscillations duringtwominutes. Analysis ofthebearing contact stresswasperformed through theCNESsoftware named RBS2.The effectoftheinitialpreload onthegapping amplitude inthebearing wasalsocomputed aswellastheballracesfrictiontorque. Thefirstlessonlearned isthattheHertzian theoryusedinRBS2givesincorrect valuesofthecontact stressinthecaseofaverysmalldifference between theballandtheraceradiiofcurvature. Athreshold wasclearlypointed outtoensurethevalidity oftheresults. Thesecond lessonisrelated tothegeometrical internal shapeofthebearing thatcouldlimititsload capacity toavaluethatislowerthantheallowable stressbecause thecontact areaisnotentirely located intheraceway. Thethirdlessonisrelatedtothescattering ofthebearing manufactured radialgap.Wefounddifferences between thetheoretical axialdisplacement underloadandthemeasured one.Themeasurement ofthis radialgapisthusessential tocompare thepredictions tothetestresults. Thepaperwillpresent theexperimental stresslimitthatisobserved previous totheraceindentation onset,andtheeffectoftheseindentations onthefrictiontorque. Theeffectofthegapping amplitude on thepost-vibration frictiontorqueisalsodiscussed. Inspected hardware showstheMoS2coating aspects inthecontact areas. *CNES,Toulouse, France Proceedings ofthe36thAerospace Mechanisms Symposium, GlennResearch Center,May15-17,2002 NASA/CP--2002-211506 319
Figures1and2showaphotoandacrosssectionofthetestbench:Oncethebearingpairwasattached tothepullingmachine,afirsttestwasperformedtomeasurethepreload.Atthebeginningofmotion,the bearingstiffnesswasrelatedtothepreloadedpairuntiltheloadreached2.7timesthepreload.Afterthat time,theslopeofthestiffnesscurveischangedbecauseoneofthebearingswasoffloaded.Plottingthe slopechangeonthecurvegivestheoffloadingeffortandthenthepreloadvalue.Allthemeasurements doneforatheoretical600Npreloadshowedapreloadvaluebetween530Nand660N. Figure1.TestBenchview Figure2.TestBenchcrosssection Theeffectofinternal geometry (firstcampaign) Afirstsetofballbearings wasprocured forthetestsaftersomepreliminary calculations. Thebearings hadtobelargeenough tomaketheringsandballsobservation easier,andnottoolargetoavoidany stiffness limitation ofthetestbenchitself.A37-mm external diameter bearing fromtheADRCompany waschosen. Fortheinternal geometry, itwasdecided toachieve different conformities fortheinnerand outerraceinordertoinvestigate theeffectoftheHertzian ellipsesizeonthecontact pressure evaluation. Amicroscope observation oftheraceswouldconfirm thepresence ofmarksincaseofplastic deformation. Themaincharacteristics ofthebearing pairaredescribed inTable1. NASA/C P--2002-211506 321
Table1.Bearing characteristics ADRrefW61904H Outside diameter (mm) Borediameter (mm) Balldiameter (mm) Contact angle(o) Nominal Preload (N) Outerraceconformity Innerraceconformity Number ofballs Bearing width(mm) Lubrication37 20 4.762 15° 600(+100) 1.12 1.06 14 MoS2(ADRprocess ) TheRBS2software wasusedtoestimate therelative axialdisplacement between theinternal and external ringofthebearing underagivenaxialload.Thesevalueswerecompared withthecomputation ofthePalmgren formula (Table2). Table2:Bearing axialdisplacement computation Axialload(N) 4350Axialdisplacement I.R./O.R. RBS2Software (pm) 48 8400 75 9600 81 11720 91 14820 111Axialdisplacement I.R./O.R. Palmgren (IJm) 44 78 87 100 120 Thevaluesareverysimilarandthisallowsustobeconfident inthepredicted displacement calculation. Themaximum axialloadapplied tothebearing arrangement toreach4200MPaonthetwoball/races contacts wasalsocalculated usingtheRBS2software. Theresultisabout8400N, whichinduces 4199 MPaontheinnerringcontact and4256MPaontheouterringcontact. Thesteeldamage onbothrings wouldnormally occurforaloadexceeding 8400N. Forthisfirstcampaign, awiderangeofaxialloadswasapplied tothebearings todamage themand makeeasiertheobservation oftheringsplasticdeformation. Table3summarizes themainresults. Table3.Bearing plastic deformation versus axialload. Axialload(N) 2170 84OO 11720 19760Computed Max Pressure (MPa) 2880 42O0 4600 5300Computed Axial displacement (pm) 27 75 91 111Measured axial displacement (pm) 22 60 90 120Depthof deformation (IJm) Harris 1,7 3,3 9,4Depthof deformation (pm) observation NASA/CP--2002-211506 322
Thedataindicatesthatevenwitha5300MPaaxiallimitload,thatrepresents morethantwotimesthe theoretical, thereisnoevidenceofanydamageontheraceways.Thephotooftheinnerandouterringof testn°6(19760N)showssuccession ofMoS2accumulation spotswithoutanymarkonthesteelitself. Figure3showsthesensordisplacement obtainedatlowfrequency(4Hz)afterthecalibrationsequence. Thecurveisnotapuresineduetothehystereticbehaviourofthecontact.Themicroscope inspectionof thedifferentbearingelementsshowsthepresenceofMoS2 oneachballtogether withdrawnlinesthat indicates arotation oftheballsduringthegapping period.SomeMoS2 transfer occurred alsobetween the ballsandthecagethatisvisibleonthecagepockets aspect. Figure4showstheaspectoftheballand cageaftervibration. Itwasthendecided toapplyaveryhighloadtoonebearing pairtomakeaballindentation onthe raceways andtoinspect thelubricant presence aftertest.Thechosen loadwas80,000N. Inthatcase,the calculation leadstoaverywidemarkontherings.Theobservation confirmed thesemarksandclearly indicated thatthecontact areahasmovedtotheedgeoftheringraceway, gettingatruncated ellipse. deplacements (miillimetres) 1.28 1.26 1.24 1.22 1.2 1.18 1.16 1.14 1.12 ........ : 0 200 400 600 800 1000 Figure3:Inductive sensor displacement (mm) Figure4:Innerandouterringaspect after19760Naxialload NASA/CP--2002-211506 323
Figure5:Ballandcageaspects aftertest Whydon'tweseeanymarksat5300MPa? Thesteelhardness hasbeenchecked andconfirms the 60HRcto61HRc valuewithaverygoodhomogeneity fromonebearing toanother. So,theabsence of indentation isobviously linkedtoafalseestimation ofthemaximum pressure. Everyone knowsthatwhen thecontact areabecomes largecompared tothecontact piecesdiameter, asitisthecaseforexample in aballandsocketjoint,thereismorethanonecontact pointandthepressure distribution ishighly dependant onthemicro-geometrical deviations ofthesurfaces. Inthiscase,theHertzcalculation isno longerrealistic. Atthisstage,welookedintothecontact ellipsesizecompared totheballsize.Thisratio between theellipselengthandtheballradiusiswelldescribed bytheangle13. Thesineofthemaximum halfcontact angle1_/2between theballandtheraceisdefined byhalfthe lengthofthemajoraxisofthecontact ellipseAdivided bytheballradiusRb(Figure 6) 2 Figure6.Ellipse angle_definition Foragivenmajoraxislength, thatmeansforagivenellipseangleI}between aballandtheraces,a computation madewiththeRBS2software givesthevalues inTable4fortheHertzian pressure fora givenaxialloadasafunction oftheball/ring conformity. NASA/CP--2002-211506 324
Table4:Effectoftheellipsesize 13=40° InnerRing OuterRing Conform. Axialload (N)Hertz. Press. (MPa)Axialload (N)Hertz. Press (MPa) 1.06 4185 3335 4480 2980 1.08 5640 3940 6240 3245 1.10 7610 4500 8485 4065 1.12 9330 5010 10360 4535 1.14 11480 5480 12745 4975 1.16 13170 5925 14730 5390 1.20 17020 6730 17680 6140 1.22 1.2413=35° InnerRing OuterRing Axialload (N)Hertz. Press (MPa)Axialload (N)Hertz. Press. (MPa) 4720 3985 5175 3585 5910 4430 6580 4005 7090 4850 7910 4390 8340 5240 9330 4755 10790 5960 12145 5430 12015 6290 13585 5740 13245 6605 14975 6035 Thesecalculations showthatfora1.12conformity, thedamage oftheouterringshouldoccurat8500N. Thesameconformity leadstoalowervaluefortheinnerring(5900N). Thisisthereason whythe manufacturers oftenchoose alowerconformity fortheinnerringtobetterbalance thebearing resistance. Withaconformity of1.06ontheinnerring,weobserve thattheellipselengthbecomes quickly veryhigh astheloadincreases. For8500N, the13angleisgreater than40°onthetworings.Figure7showsthe evolution ofthecontact pressure andtheellipseangleasafunction ofthebearing axialload: 60OO 5OOO 4000ADR W61904 ballbearing inner curvature ratio=0,53 outer curvature ratio=0,56 2OOO 1000 0 1000/ I/ /f / /, / / 2000S f / IfI1I / JII / ............. 19 3000 4000 5000 6000 7000 8000 9000 10000 11000 1200044 39 34 29---- IRHertzstress ----ORHertzstress --- IRcontact extent ---ORcontact extent Axialload(N) Figure7.Maximum contact pressure andellipse angleevolution NASA/CP--2002-211506 325
Theellipseanglecurve(_)indicatesthatforapressureof4200MPa,theinnerandouteranglesare greaterthan35°.Thisleadsustobecarefulaboutthepressurecalculationforsuchalargeangle. Modification oftheinternal geometry (second campaign) Inordertoimprove ourunderstanding onthecontact pressure behavior, wedecided tochange theinner ringconformity togetasignificant increase ofthecontact pressure foragivenload.Thenewconformity ischosen at1.15fortheinnerringwhiletheouteroneisunchanged. Thebearing manufacturer sentusa newsetofbearings withthisgeometry. Thecontact pressure computation withRBS2givestheaxialload corresponding to4200MPaforthetwocontacts. Fortheinnerringcontact, thevalueisabout4000Nand fortheouterringcontact, thevaluebecomes 7400Ninstead of8500N. Thelossofloadcapacity isvery important ontheinnerringcontact, butitisalsosignificant ontheouterringcontact. Thisisduetothe change inthebearing contact angle.Thenewvaluesofthe_angleare28°fortheinnercontact and35° fortheoutercontact. Thecontact pressure andellipseangleevolution asafunction oftheaxialloadare depicted ontheFigure8.Anewtestcampaign wasdonewiththepullingmachine. Themainresultsare presented inTable5: These results areveryinteresting because theyshowaverygoodcorrelation withthetheoretical pressure limit.Figure9,relatedtothebearing pairn°18,pointsoutthesteelmarksontheinnerringand theMoS2accumulation aroundthecontact pointsontheouterring. 6000 500O 4000 3000 2000 1000ADR W61904 ballbearing inner curvature ratio=0,575 outer curvature ratio=0,56 -i............. !...._I-__"_--_-_-.......... i ,_...i,- .........../../- _ '<"_ .... /1 0 19 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 11000 1200044 39--- IRHertzstress ---ORHertzstress -- IRcontact extent ---ORcontact extent Axialload(N) Figure8:max.contact pressure andellipse angleevolution aftermodification NASA/CP--2002-211506 326
Table5.Bearings marksaftermodification Bearing pair number 20 10 11Axialload(N) 2050 3900 425O 4250 50OOInnercontact pressure (MPa) 35OO 4200 4300 4300 4500Outercontact pressure (MPa) 2900 3500 365O 365O 3800Innercontact marks None None Yes Onlyone Yes 18 5400 4600 3900 Yes 13 6000 4700 4000 Yes+OuterRing Note:"Yes"meansthere_sasteelmarkatmostofballraceway contacts. • i InnerRing OuterRing Figure9.Bearing n°18,innerandouterringsaspect Theopticalaspectofthebearings rings,evenifitlooksquiteunambiguous isnotenough tobeconfident onthesteelindentation. Itwasthendecided tochecktheraceways surface through aroundness "Talyrond" measurement. Thismeasurement isnotaffected bytheMoS2presence anditallowssensing theraceways onseveral parallel trackstoquantify thedepthandthewidthofthesteelmarks. Forthis test,thebearing n°13waschosen andtheresultsforbothinnerandouterringsaredepicted onthe Figure10.Theballnumber iseasilyvisibleonthiscurveanditisalsoclearthatthedepthmarksarenot similarallaround therings,whichindicates adifference intheloadrepartition between theballs.Inthe caseofthisbearing, theindents depthonthemeasured ringisbetween 1pmand1.5pm(seeFig9). Compared totheballdiameter, thisisgreater thanDb/10000, thatconfirms theapplication ofalocal pressure greater than4200MPa. NASA/CP--2002-211506 327
,13 ......:.,-..... -.:,-,:_;_ ;J-.-_ t':_'_:_"":."_+-2;"'_ m-..i.....--".................. I-" ......._.......-.-..... I ,......... L__ L,""._- ........ i,_,__....... _..-r. ,4... ..... _ _ i -.- ",_ i ....: iI bi •J' ....-_,,. •..:_• /,.,, • . ! --.._. >/- Figure10.Bearing n°13,"Talyrond" measurements TheFriction Torque Behavior Theaimofthispartwastoquantify thefrictiontorqueinstabilities afterthehighcontact stresses induced bythealternative axialload.Thetorqueofeachbearing pairwasmeasured atlowspeedunderthe600Naxialpreload beforeandafterthepullingmachine test.Theexternal ringsaredrivenbyamotorwhile theinneronesarecoupled toatorquemeter. Thefrictiontorqueaverage valuebeforetestisabout20 mNmwithsomevariation fromonebearing toanother. Inallcases,thepost-test frictiontorqueisnoisier. ThisisduetotheMoS2 particles pushed outside the contact zoneandlyingontheraceways. Whenthecontact pressure becomes high,several frictiontorque spikesappear. Thesespikesareduetoaringofparticle accumulation around eachcontact zone.There are14ballsinthebearings thatwouldnormally induce14spikedisturbances ontheraceway revolution. Infact,thetorque measurement ismadeoveronerevolution oftheexternal ringandthenumber of spikescorresponds tothetotalanglecovered byoneballdivided bytheangular distance between two balls. Thecalculation givesavalueof7.6fortheinnerringand6.4fortheouterring.Thepicture n°11 corresponding to4200MPa contact, showsclearlyabout6spikesforoneCWandCCWrevolution. The distinction between theinternal andexternal ringspikesisnoteasy,butsometimes, twospikesarevery closetoeachother,indicates thatthephenomenon doesaffectthetworings. , t:;'::,:Tt................... '........... i c_. ,:_-,s ,.,......,llI I iIill,!,_!lI'',I''_, Figure11.Friction torque measurement beforetest NASA/CP--2002-211506 328
I _^,_GES, 8.O00V I0. OOV IO.OnV OFFSETS, 3.ov o.ov o.ov TOTALTIME, ;_.IOM PO._T-T_IC, O.O5 TRIGGER, NAN .,.._._~.._ , ,i, i,ltII!":- ' I '--_'.'t .:-: !- i . 1 ':........."_....i";....._-:Ilt.I_:;:'i ::.....:.....F:.-.:l__- ,i,',i<; , tl'1t,,, i Figure12.Friction torque measurement aftertest(4200MPa) Arunning-in testmadeononebearing pairshowsthattheamplitude ofthespikesdecreases alotafter several thousands ofrevolutions. Thisrunning- inphaseisnecessary tocleantheraceways fromall particles andtosmooth theringsaccumulation ofMoS2. Somemoretestsshould bedoneonthedamaged bearings tochecktheinfluence ofpossible interference between thesteelmarksandtheballraceways underthenominal preload. Unfortunately, we didnothaveenough timetoperform thesetestsin2001. Thegapping influence (ThirdCampaign) Alotofthingshavebeensaidontheinfluence ofgapping amplitude onthebearing internal shocks and theassociated degradation ofsolidlubricant coatings andinsomecases,thesteelsurfaces. Therelatedinvestigation wasperformed withthesametypeofbearing byusingdifferent strutlengths to tunethebearing pairpreload. Doingthat,thepreload rangewasvarying from80Nto1200N, andthe bearing gapping becomes smaller asthepreload increases. Thedifferent testsperformed aredepicted on theTable6. Table6.Pulling machine results fordifferent preload values Bearing n° Pre-load (N) Contact Axialload (N)Gapping Steel marks pressure(MPa) amplitude (pm)obse_ation 12 80 4200 3900 85 Yes 14 300 3500 2050 46 None 17 3OO 4200 39OO 72 Several 15 300 4300 4250 76 Yes 19 300 4500 5000 84 Yes 20 600 4200 3900 59 None 7 600 4500 5000 71 Yes 1200 4250 16 48 4300 Yes NASA/CP--2002-211506 329