ai-aerospace/ams_data_full_2000-2020 huggingface dataset:
Disassembly andInspection Uponcompletion of144,263,692 cycles,thestationwasdisassembled. Photographs weretaken throughout thedisassembly andinspection process. Samples werealsogathered duringthedisassembly. Amajority ofthebearing analysis wasperformed at5140/Tribology andSurface Science BranchofGlen Research Center. Figure4presents theteststationpriortodisassembly. Thedrivemotor,beltandtestconnector had previously beenremoved. I | Figure4-TestStation IIIPriortoDisassembly Thecomplete shaftandallbearing components wereremoved fromtheteststationandtransported toaflow bench. Uponinspection ofthetestassembly, oilwasseenonthelowerflywheel andaringabovetheslip ring(seeFigures 5and6). 307
Topandbottombearingassemblies showeddrydebrisandwornraces,ballsandretainers.Thetopbearing assemblyalsoshowedsilverdebrisfromslipringwear(seeFigures11through15). Figure 11-LowerBearing Pair,InnerRaceClamp/Housing andOuterRaceClamp/Housing (Notetheblackdebrisintheouterraceclamp/housing andonthebackground cloth) Figure 12-LowerBearing Pair (Notetheblackdebrisonthebearings andonthebackground cloth) 311
Figure 19-Middle Bearing Pair Figure20-CleanBallsfromMiddle Bearing (Notetheshinyfinish) Results Photographs clearlyshowthatthetopandbottombearing assemblies weredryandworn.Damage ofthe ballsandraceswereobserved. X-rayphotoelectron spectroscopy (XPS)analyses, performed atGlenn Research Center, indicated thepresence ofcarbon, iron,chromium, oxygen andfluorine (anartifact). Themiddlebearing assembly wasseentobewelllubricated andwearwasminimal. Theoilwasonly slightlydiscolored. MicroFouriertransform infrared(Micro-FTIR) analysis ofthreeballs,performed atGlenn Research Center, yieldedthenormalsignature forundegraded Pennzane lubricant. Scanning electron microscope (SEM)analyses, alsoperformed atGlennResearch Center, yielded thenormalsteelsubstrate elements. Conclusion Successful accelerated lifetestingofflightbearings withtheflightlubricant intheboundary lubrication regimeatelevated temperature wasaccomplished earlyintheprogram. Thistestresultdemonstrated that theflightlubricant wouldperform successfully intheflightscanmechanism. Basedoncurrentinformation, itislikelythattheelevated temperatures observed at88millionrevolutions (wellbeyond thespecified mechanism lifeof57millionrevolutions) wereactually higherthanrecorded (due todelaminated PRTsand/orheatercontrolfailure)anddrovelubricant fromthebearing pairs.Telemetry PRTdelamination waslikelycaused bystresses created fromthedifference inthermal expansion ofthe PRTandtheberyllium-copper mounting plate.Thesmaller sizeofthecontrolPRTsresulted inlowerbondlinestresses anddidnotcausedelamination. Analysis oftheheatercontrolcircuitrevealed cyclingofa relaynearitsspecified life.Anintermittently stuckrelaycouldhavecaused thetemperature excursion seen at88millionrevolutions. Theconclusion ofanalyses performed atGlenResearch Centerwasthatlossofoil intheupperbearing pairwasprobably caused byanextended (i.e.,4week)temperature excursion ofmore than90°C.Theupperandlowerbearing pairswereprobably heatedbeyond thetemperature ofthemiddle pair.Without theheatermalfunction, thetestcouldhaveproceeded considerably longer. 315
Twoadditionallifeteststations,onewith60millionaccumulated revolutions(noheaters)andonewith200 millionaccumulated revolutionscontinuetorun.Thequalification model(QM),with48millionaccumulated cycles,alsocontinuestorun.Currentmeasurements (directlycorresponding totorque)oftheQM performedmonthlyhaveshowna29%increaseoverlife.Investigation ofanengineering model(EM),with severalhundredthousandrevolutions, andtheQM,with46millionrevolutions, byNASAGoddardSpace FlightCenterhasshownabeginningoflifeandendoflifetorquemarginofgreaterthan20.Marginonphase lock(closedloopcontrol)forbothunitswasdetermined tobe200%.Thebeginningoflifetorque,measured withtheEM,was0.066N-m(9.4oz-in).Thenearendoflifetorque,measuredwiththeQM,was0.086N-m (12.2oz-in).Thisrepresented a30%increaseintorqueoverthe46millionrevolutionlifeoftheunit.The bearingandlubricationsystemselectedforthescannerhasproventoexceedtheliferequirements ofthe MODISprogram. Lessons Learned Criteria fordetermination offailureshouldbesetandfollowed priortotheinitiation oftest.Hadthetestbeen terminated after57millionrevolutions orassoonasthetorquespikeswereobserved, itislikelythatresults moresimilartotheactualmission wouldhavebeenachieved. Configuration andmaterials usedintestingshouldmatchtheproduction hardware ascloselyaspossible. Inthiscase,itisfortunate thatthequalification unit(identical totheflightunits)wasaddedtothelifetesting inJanuary, 1995andhasaccumulated over48millionrevolutions. Recenttestingofthequalification unit indicated performance withinspecification. Without thequalification unit,integrity ofproduction hardware couldbequestioned. Asmalfunctioning testequipment wasthelikelycauseoflubrication lossintwoofthethreebearing pairs tested,the"keepitsimple" theorycertainly applies. Theaddition ofheaters wasoflittlebenefittothetest. Thebearings wereoperating inaboundary layerlubrication regimewithout heaters. Tolifetestaspacemechanism, aflightmechanism shouldbetestedratherthanthebearings alone. Acknowledgements W.Jones,GlennResearch Center. J.Uber,S.Cicchelli, M.Roberto andRajeevSharma, NASAGoddard SpaceFlightCenter. A.DeForrest, Raytheon Systems Company, SantaBarbara Remote Sensing. L.Alegre, S.Natvipada, D.Owens, T.Phan,P.Tokeshi andH.Tsui,MoogSMD. References 1.Jones,William R.,"MODIS ScanMirrorBearing LifeTestAnalysis", Letterdated8/19/99 (Glen Research Center). 2.Uber,Joanne M,"MODIS LifeTestStation IIIThermistors", Letterdated8/18/99 (NASAGoddard Space FlightCenter) 3.Sharma, Rajeev, "Scanner Report", dated11/4/99 (NASAGoddard SpaceFlightCenter) 316
A B C Figure1.Schematic ofalatchmechanism asthetabpassesthrough thecams Thissimplelatchisdesigned foroperation withtheCOFwithincertainlimits,yetthedevicemayrequire carefulscrutinyifthesurfaces areallowedtooxidize,collectadsorbed contaminants, oracquirelubricants fromsomeotherregionofthesampleintheproximity ofthehigh-friction contact. Forexample, ifasolid lubricant isappliedtotheslidingsurfaces, theCOFmaybegreaterthanspecified bythemanufacturer ifit isnotburnished orifithasoxidized. Similarly, theCOFofthemetallicinterface maybelessthan expected ifthesurfacehasoxidized orifcontaminants arepresent. TheCOFofthemetalinterface may alsobelowerthanexpected ifthelubricant filmhadtransferred tothecleanmetalsurfaces duringtesting. Furthermore, bothinterfaces willexhibitdifferences between theCOFmeasured inairandinvacuum. Toinvestigate theanomalous performance ofasimilarmechanism, wehaveconducted aseriesoftests todetermine frictioncoefficients ofcommon materials inavarietyofdifferent conditions. Wedirectly measured frictionforcesbetween oxidized metalandsolidlubricated surfaces asafunctionoftimeand loadinairandinvacuum. Wemonitored thetransferoflubricant acrossaweartrackandtheeffectithad ontheCOF.Wealsoinvestigated theeffectofthinlayersofthinoilfilmsonthesurfaces ofthese materials. Theresultsofthesemeasurements arereported below. Experimental TestSamples Thematerials usedforthetribological testsincluded thefollowing: 4.76mm.-diam, grade5bearingballs madeof440Cstainless steel;14mm.-diam superalloy diskswitha0.41I_m.surfacefinish;superalloy diskscoatedwithabondedfilmofMoS2;andsuperalloy diskswithhalfofthesurfacecoatedwiththe solidlubricant (seeFigure2).Priortothetribological tests,thebearingballswerecleanedultrasonically inethylacetate. Toreproduce thesurfacetreatment protocol usedonanactuallatch,theunlubricated superalloy diskswerewipedwithclean-room wiperssoakedinethylacetate. Theuncoated portionofthe half-lubricated diskswasalsocleanedwithanethylacetate-soaked wiper.Thecompletely solid lubricated diskswereusedasreceived, withoutburnishing. Figure2.Schematic ofthehalf-solid-lubricated sample 318
Thesurfaceofthesuperalloymaterial,MP35N,wasdetermined byx-rayphotoelectron spectroscopy (XPS)tobecomposedofNi,Co,Cr,andMo.Thesolidlubricant,Everlube620C,wascomposedof MoS2inaphenolic binder.Fortheoilcontamination tests,asolutionofBray880oilwasprepared in heptane. Thedilutions werecalculated suchthattheresidualoilleftbehindfroma20_1aliquotwould coatthesubstrate surfacewithaspecified average filmthickness afterthesolventevaporated. For example, the60-nm-thick filmwascreatedfromasolutionwithaconcentration of0.453mg/ml.Thefilm thickness valuesinvestigated werenominally 15,30,and60nm. FrictionForceMeasurements Thedeviceusedtomeasure frictioncoefficients forthisworkiscalledtheultrahigh vacuum(UHV) tribometer. Thistribometer isacustomball-on-disk devicethatishousedinanion-pumped vacuum chamber, enabling measurements tobeobtained atpressures aslowas1x10-9Torr.Inthepresent study,thebasepressure andoperating pressure ofthetribometer were1-2x10.8Ton'.Testswerealso performed afterthetribometer hadbeenventedwithlaboratory air.Boththesampledisksandballscould betransferred toandfromthetestpositions underUHVconditions. Thetribometer's vacuum chamber is directlyconnected toasurfaceanalysis system,enabling chemical analysis withx-rayphotoelectron spectroscopy (XPS)tobeconducted onbothballanddisksamples aftertestwithoutexposing the samples toair. Aschematic oftheUHVtribometer isprovided inFigure3.Themainelements ofthisinstrument arethe rotatingdiskandthestationary ball.Anexternal motorthroughaferrofluidic feed-through drivesthe rotatingdisk.Thestationary ballismounted onanarmthatpossesses orthogonal flexures instrumented withstraingagestomeasure boththeloadandfrictional forces.Thetribometer isloadedbymanually movingmicrometers thatpositionthearmsuchthattheballcontacts thedisk.Oncecontactismade,the loadiscontrolled bythemicrometers andmeasured bythestraingagesontheloadflexurethatwere calibrated beforethetests.Testswererunatvariousdurations, conditions ofload,andspeeds. UHVchamber tosurface a% s,sr-- , chamber _ _ i.I____-...._ II XYZtranslation  stage-positions I-_ U'1 andloadspin motor IIL__J  toionpump _C_----optical encoderLoadand frictionstrain gageoutputs computer Figure3.Schematic representation oftheball-on-disk UHVtribometer Straingagedataobtained fromthetribometer arerecorded viamicrocomputer. Thistaskisdonewiththe useofageneral-purpose analog-to-digital interface boardandacustomacquisition program writteninthe LabView programming environment. Thefrictioncoefficients ofthecleanandsolidlubricated surfaces weredetermined byvaryingtheloads fromapproximately 0.2-6N.Thisrangewasselected toproduce theexpected rangeofcontactstresses between thelatchparts-up to1.38GPamaximum Hertz.ian contactstress.Thecalculated contact 319
stressesareappropriate fortheunlubricated parts.Thepresence ofthemorecompliant solidlubricant filmcouldincrease theeffective contactareaandthusdecrease thestress. Tomeasure thesteadystateCOF,thediskwasrotatedatanominally constant speedofapproximately 150rpmwhiletheloadwasincreased incrementally. Somespeedfluctuations wereevidentinthe experiments, butprevious workhadshownthatsuchfluctuations havelittleimpactonthefriction measured bythetribometer. Datawerecollected digitallyatarateof15Hz,andthetimespentateach toadwasapproximately 45s. Tomeasure theCOFasafunctionoftimeduringtheinitialwearoftheinterfaces, samples weretestedin adifferent fashion. Fortheseexperiments, wefocused onobtaining dataataparticular load(nominally either3.0or-0.3N)atamuchhighercollection rateof250Hz.Datawerecollected forapproximately 1 min.Astheresultswillshow,theseconditions wereadequate tocapturethedesiredfrictionbehavior. Surfacechemical analysis wasperformed onselected samples todocument thesurfacecomposition of thesolidlubricant, thesuperalloy, andthelubricant transferfilmsformedonthehalf-lubricated disks.The XPSusedwasaSurfaceScience Instruments X-100smallspotspectrometer, witha300I_mx-rayspot toexamine thecomposition ofthewearareascreatedbythetests. UtilityoftheSurfaceAnalysis Facility Figure4isshownasanexample ofthebenefitprovided bylocatingsurfacespectroscopic probeswithin thechamber thathousesthetribometer. Inthisfigure,thefrictioncoefficient versustimeisplottedduring testingofaTiC-coated ballagainsta440Csurface. Theloadwasincreased anddecreased incrementally whilethefrictionforcewasmeasured. Thenegative frictionlevelreported issimplya functionofthedirection ofthedeflection ofthestraingageflexure. Attimet=290s,wefoundthatthe frictiondecreased suddenly. Inadditiontothedecrease intheCOF,theamountofscatterinthedatadue tostick-slip motionofthefixturehaddecreased. Whenthesesurfaces wereobserved intheXPSit becameapparent thatasmallamountofcopperwasactingasalubricant intheweartrack.TheXPS spectrum showninFigure5,ofthe440Csurfaceafterthefrictionmeasurement, showsthepresence 4 2 0.0- 0....'to  _2z (1.5) I -10 0.0 100.0 200.0 300.0 400.0 500.0 600.0 Time(s) Figure4.Friction coefficient vs.timewhileatitanium-carbide coated ballwasheldinaslidingcontact againsta440Cdisk 320
ofcopperintheweartrack.Evidently, asmallamountofcopperwastransferred tothediskbyan unknown mechanism fromourtestfixturecomponents thataremadeofcopper. Thisillustrates the importance ofhavingasurfacesensitive technique available tocharacterize andmonitorthechemical integrityofthesurfaces L_o,=</_- I"" v I-gJM<"=v o .Q V ¢J) e" Cm I 1000L.. v '_ I i.__m I ' I ' I ' I ' 800 600 400 200 0 Bi'K:lingEne'gy(eV) Figure5.Photoelectron spectrum ofthe440Csurface after contamination withcopperduringtribological testing Results andAnalysis Contactbetween oxidized 440Candasuperalloy Therawdatafromoneofthevacuum testsoftheclean,unlubricated 440C/superalloy pairarepresented inFigure6.Thesedatashowboththeloadandthefrictionchannels fromthetest.Thedatashowthe expected trendofincreasing frictional forceinresponse totheincreasing loadforce.Thedataalsoshow thehighnoiselevelobtained inthesetests,whichresultsfromthesmallsizesofthetestdiskrequired in thisinstrument andtheerraticfrictionbehavior oftendisplayed inunlubricated systems. Thisbehavior is duetothestick-slip motionthatoccursinsuchcontacts. Itismoreinstructive topresentthedatainadifferent format,whichisdoneintheplotinFigure7.Inthis plot,wehavetakentheaverage recorded frictionobtained atagivenloadandplotteditagainstthe average recorded load.Inthisform,thedataclearlyshowthelineardependence ofthefrictionforceon theappliedload,withtheslopeofthelinerepresenting theaverage frictioncoefficient forthematerial combination, tnthisparticular experiment, theaverage frictioncoefficient wasdetermined tobe0.76. Similarexperiments wereperformed usingtheunlubricated materials testedinair,andthe440C/Solidlube/superalloy material combination testedinbothvacuumandair.Atleasttwoexperiments foreach testcondition wereperformed. Theaverage frictioncoefficients obtained arepresented inTable1. 321
6.0" 4.0" Zv (1) PO LL2.00.0_ (2.0)- (4.0)- (6.0)- 0--Friction .....o....Load J i t 200 400 600 800 Time(s) Figure6.Rawdatashowing thefrictionforceandloadforcevs.timeduring theslidingcontact between a440Cballandsuperalloy disk 6.0 5,0" 4.08 ,_3.0" LL _O_2.0- (1) 1.00.0_ (1.0) o.o 21o 41o 61oy=0.764x+0.028r2=0.996 8.0 Average Load(N) Figure7.Averaged frictiondatafromFigure5plottedvs.applied load Table1.Avera_eFriction Coefficients ofClean440Cvs.superallo: MP35NSample Vacuum, initialVacuum, steadystateAir,initial Clean 0.37 0.74 0.20 Solid-lube Coated 0.18 0.024 -- aThisvaluevariedwithloadbetween 0.17and0.06.,Air,steadystate 0.56 0.08" 322
Thefrictioncoefficient obtained fromtheunlubricated samples inairaveraged 0.56,whichissignificantly lowerthanthatobtained undervacuum. Thisphenomenon isoftenobserved forunlubricated metals, because reaction withthelaboratory airformssurface oxidesthatusually havelowerfrictionthanthe baremetalsthatareexposed undervacuum afterthesurface oxidewearsaway.1Alargeamount ofwear debriswasobserved aroundthecontact pathduringandafterthetestsinair,someofwhichwere collected andanalyzed withXPStodetermine composition. Wefoundthedebristobecomposed entirely ofmetallic oxidesofthesuperalloy. Thisfindingisconsistent previous work,4whichhasshownthatoxide layersquicklyreforminthepresence ofatmospheric gasesandacttolowerthefriction. Thetimedependent COFduringtheinitialwearoftheunlubricated 440C/superalloy contact inairis showninFigure8.Inthisfigure,wherethedatawerecollected muchmorerapidlythanisshownin Figure6,theload(diamonds) andCOF(solidline)areplottedasafunction oftime.Thefriction coefficient wasobtained bydividing thefrictionforceresultsbytheloadforceresults. Thefluctuation in theloadchannel resultsfromthesample disknotbeingcompletely flat(because ofsystem run-out, disk variations, andsample mounting). Whilethisoscillation wastoosmalltoaffecttheCOFmeasurement, it provides aconvenient measure forcounting thenumber ofrevolutions. Thisfigurereveals thatforthe firstrevolution theCOFwasapproximately 0.2;lessthanhalfofthesteadystateCOFbetween theclean metalsinair(0.56).Witheachofthefirstthreesuccessive rotations thesurface composition was changing toastateofhigherCOFuntilasteadystateaverage valuewasachieved. (0.25) 0 Figure8.3 I I I I I I I I 0 123456789 Time(s) TheCOFandloadvs.timeduringtheinitialrun-inof 440Candsuperalloy inair,_ Zv O _.1 1 Whenthispairofmaterials wastestedinvacuum, theinitialandsteadystatefrictionvalueswereboth measurably larger.Thisexperiment, notshownhere,beganwithanaverage COFof0.37forthefirst revolution, andincreased to0.74afterapproximately 10revolutions. Thissuggests adifference inthe surface composition atthebeginning ofthetest,possibly duetofeweradsorbed contaminants invacuum, andadifference inthesteadystatecomposition, asonlythesurface exposed toaircontinued tooxidize aftertheinitialoxidelayerhadbeenwornaway. 323
Contactbetween 440CandabondedfilmofMoSzlubricant Thevacuumtestsofthesolid-lube coatedspecimens resulted inverylowsteadystatefriction coefficients, averaging 0.024.Thelubricant withinthesolid-lube coatingisMoS2,whichisanexcellent vacuumlubricant. Thetestsofsolid-lube conducted in-airwerecharacterized byvadable performance, asindicated inTable1.Wefoundthatthisvariability isnotduetoarun-inburnishing processthatsolid lubricated systems usuallydisplay,butisrelatedtoload.Thedependence oftheCOFontheapplied loadhasbeenobserved formanysolidlubricant systems2,including MoS2.3Theeffecthasbeen explained byaload-dependent shearstrength basedonHertzian contactmechanics. Fortheball-onflat geometry, thefrictioncoefficient shoulddependontheload(L)asL"(1/3),andourdatashowaL-°39 dependence. TheCOFvariedfromalow-load (0.7N)valueof0.17,toahigh-load (6.2N)valueof0.06. Forcomparison withourresults,ahandbook reportsthein-airfrictioncoefficient forthesolid-lube as <0.10.3Following testsineitherairorvacuum, atrackwasplainlyevidentonalldisks,butthecoating didnotappeartobewornthroughtothesuperalloy disks,consistent withthelowfrictionmeasured during thetests. Thedifference between steadystateaverage frictioncoefficients inairandinvacuum isconsistent with previous studies5,whichshowedthereactionofMoS2inatmospheric gasestoproduce oxideswithlesser lubricating capability. Testswereperformed todetermine thefrictioncoefficient ofthesolid-lubricant beforeburnishing andthe numberofcyclesrequired toachieveasteadystatevalueoftheCOF.Figure9showsthattheinitial frictioncoefficient averaged 0.18,andquicklyfelltoasteadystateaverage of0.04afterapproximately fourrevolutions. XPSspectraoftheunburnished surfaceshowedonlycarbonandoxygenwithinthe escapedepthofthephotoelectrons (3-5nm);noMoS2wasdetected onthissurface. Weconclude that thislubricant-depleted layerwaswornawaywithinthefirstfewcycles,revealing subsurface MoS2crystals thatwereimbedded inthebinder,whichsubsequently loweredtheCOF.Thisconclusion wassupported byXPSspectraoftheweartrackaftertesting,whichshowedthepresence ofmolybdenum andsulfur. tO _E O O tOmw O t,.,.. LL1.00 0.75 0.50 0.25 0.00 (0.25). 3.5 01234562.52.0 1.5 1.0 0.5 0.0 789ZV "O O _J Time(s) Figure9.TheCOFandloadvs.timeduringtheinitialrun-inof440C andEverlube 620Cinvacuum 324
Lubricant Transfer Studies Toinvestigate therateoftransferoflubricant alongtheweartrackfromoneregionofasampleto another, weperformed aseriesoftestsinwhicha440Cballwasheldinslidingcontactwithoneofthe half-solid-lube-coated samples performed atthe3Nloadundervacuum. Infigure10,theloadchannelis presented alongwiththefrictioncoefficient, whichwasobtained bydividingthefrictionforceresultsby theloadforceresults.Again,weobserved aperiodicoscillation intheappliedload.Theloadfluctuation doesnotaccountforthefrictionvariation observed, astheloadforthisandothersimilartestsvariedat mostby+5%,whilethefrictionchanges weremuchgreateranddidnotfollowthesameshapeasthe loadchannel. Inthistest,theballwasinitiallypositioned onthelubricated halfofthesampleandthe motorwasstarted. .-- (DO (b cO "5 u_0.50 4 0.25 0.00 (0.25) (0.5o) (0.75)Friction Coefficient --o......Load(N) 2I | I I 0 3 4 5 6 7 Time(s)ZV 2"o O __1 Figure10.PlotoftheCOFandnormalloadatthestartofatestofa half-solid-lube-coated superalloy diskagainsta440CballIn vacuum. Thediskbeganrotating justpriortothe3smark, asindicated bythefrictionmeasurement. Manyinteresting observations canbemadefromthesedata.Duringthefirstfewrevolutions, the transition fromthelubricated sideofthesampletotheunlubricated sideisplainlyevidentbythestep changes ofthefrictioncoefficient. Theinitialfrictioncoefficient oscillates about0.1onthelubricated side ofthedisk,andincreases abruptly toapproximately 0.25-0.40 ontheunlubricated sideduringthefirst revolution. Inthesecondrevolution, thefrictionmeasured onthelubricated sideissomewhat higher, between 0.1and0.15.Theaverage (-0.35)andmaximum (-0.55)frictioncoefficients onthe unlubricated sideofthediskalsoincrease onthesecondrevolution, presumably because surfacelayers havebeenremoved. Bythethirdrevolution, theunlubricated sideofthediskisshowing atrendof achieving highermaximum frictionlevelsbutisspending shortertimeperiodsatthesehigherlevels.The dataclearlyshowthattheduration ofthetimespentbythesampleathigherfrictionlevelsgrowsshorter witheachsuccessive revolution. Aftersevencyclesonthissample,thefrictioncoefficient hasdecreased ontheunlubricated sideofthedisk,reaching valuesrangingfrom0.1to0.35bytheninthcycle. 325