外文翻译--振动故障分析中的微动磨损轴模拟器 英文版.pdf

Keywords:FailureanalysisFrettingwearsimulatorVibratingshaftHightemperatureandhighpressurewaterFracturesurfaceminethefailureinitiationandfailuremode.Itwasfoundthatthefailurehadinitiatedataofthesenuclearfuelrods,whichhavethefollowingdimensions；9.5mmouterdiameter,0.6mmwallthicknessandabouta4mlength.BecauseoftheFIVphenomenonbyaprimarycoolant,theseslenderfuelrodscouldeasilyvibrate,thustheyaresupportedbyseveralspacergridstructuresasshowninFig.1.Eachcellofaspacergridstructureconsistsoftwospringsandfourdimples.Therefore,anuclearfuelrodissupportedbyacertainamountofspringforce,whichdependsonthespringshapeanditsstiffness.UnderahightemperatureinanoperatingNPPcondition,however,thecontactforcebetweenthefuel1350-6307/$-seefrontmatterC2112008ElsevierLtd.Allrightsreserved.*Correspondingauthor.Tel.:+8242688761；fax:+82428630565.E-mailaddress:leeyhkaeri.re.kr(Y.-H.Lee).EngineeringFailureAnalysis16(2009)12381244ContentslistsavailableatScienceDirectEngineeringFailureAnalysisdoi:10.1016/j.engfailanal.2008.08.013temperature(C24320C176C),pressurizedwater(C2415MPa)andradioactiveenvironment.Thisconditioninevitablyresultsinmaterialdegradationssuchasacorrosion,fatigue,irradiationembrittlement,creep,etc.duringtheiroperation.Anothersevereconditionfordegradingstructuralmaterialsisknownasaflow-inducedvibration(FIV)ofrelativelyslenderstructuresduetotherapidflowvelocityofprimaryandsecondarycoolants,whichresultsinfrettingdamagesbetweentheseslenderstructuresandtheirsupportingstructures.ThesekindsoffrettingdamageshavebeenexperiencedinthemajorcomponentsofNPPssuchasthenuclearfuelrods,steamgenerator(SG)tubesandcontrolrods1.Amongthesecomponents,inourlaboratory,thefrettingwearphenomenonofnuclearfuelrodshasbeeninvestigatedinordertoexamineanddevelopafret-tingwearmechanismandadefect-freefuelassembly(FA),respectively.Generally,aFAconsistsof16C216or17C2171.IntroductionThefailurephenomenaofmechanicalfrequentlyinvariousindustries.Onecontactregionbetweenthevibratingshaftandthefuelrodholderjigandafatiguecrackwaspropagatedalthoughitwasdifficulttoproveitconclusivelyduetotheheavilyoxi-dizedfracturesurface.Nearthefailurelocations,however,thethreadholewassubjectedtoarepeatedloadingduetothefactthatthespecimenholderjighadacircularmotionforsimulatingavibrationmotion.Thissuggeststhatthevibratingshaftfailureresultedfromcorrosionfatiguephenomenonbecausethefrettingtesthadbeenperformedathightemperature(C24320C176C)andpressurizeddistilledwater(C2415MPa)conditions.Inthispaper,thereasonsforthisfailureandthefracturemechanismsarerevealedanddiscussedbyusingtheOMandSEMresultsofthefailuresurfaceandthestressanalysisofthecontactregionsbetweenthevibratingshaftandthespecimenholderjig.Finally,theaboveresultswereappliedtoadesignchangeofthevibratingshaft.C2112008ElsevierLtd.Allrightsreserved.structuresbymaterialdegradationsinextremeenvironmentshavebeenreportedexamples,isinnuclearpowerplants(NPPs).Generally,NPPsoperateinahighFailureanalysisofavibratingshaftinafrettingwearsimulatorYoung-HoLee*,Jae-YongKim,Hyung-KyuKimKoreaAtomicEnergyResearchInstitute,150Dukjin-dong,Yuseong-gu,Daejeon305-353,RepublicofKoreaarticleinfoArticlehistory:Received11July2008Accepted1August2008Availableonline15August2008abstractRecently,afrettingwearsimulatorwasdevelopedinordertoevaluatethefrettingwearbehaviorofnuclearcomponentsinhightemperatureandhighpressure(HTHP)watercon-ditions.After500htests,however,twovibratingshaftsamongfourwerefractured,whichwereconnectedtoaspecimenholderjigbyusingabolt.Thefracturesurfacewasexaminedusingbothanopticalmicroscope(OM)andascanningelectronmicroscope(SEM)todeter-journalhomepage:www.elsevier.com/locate/engfailanalY.-H.Leeetal./EngineeringFailureAnalysis16(2009)123812441239rodandspring/dimpleisgraduallydecreasedduetoaspringrelaxation.Inaddition,thespringstiffnessisalsograduallyincreasedbecauseofanirradiationembrittlementofaspacergridspring/dimple.Eventhoughacertainamountofspringforceisexertedonthefuelrodatitsinitialoperation,arelativelysmallslipamplitudeonthecontactsurfaceisunavoidableunderasevereFIVcondition.Consequently,thecontactforceisgraduallydecreasedandfinally,agapisopenedup.ThisFig.1.Theschematicviewofanuclearfuelassemblythatconsistsof16C216or17C217fuelrodsandseveralspacergridassembly.meansthatthefrettingwearmodecouldbechangedfromaslidingweartoanimpactingwearwithincreasingoperatingtime.Anotherimportantpointisthatthevibrationcharacteristicsofanuclearfuelrodalsochangedduetoacontactconditionchangeofafuelrod.Therefore,itisquitedifficulttoexaminethefrettingwearmechanismofanuclearfuelrodinNPPoperatingconditions.Averticaltypeofafrettingweartester(FRETONUS,FRTttingTesterOfNUclearSystems)foraHTHPwaterconditionwasdevelopedinordertoevaluatethefrettingwearbehaviorofnuclearcomponents2.After500htests,however,twovibrat-ingshaftsamongfourwerefractured,whichwereconnectedtoaspecimenholderjigbyusingaboltasshowninFig.2.ItisFig.2.Schematicviewsoftheassemblingmethodbetweenthevibratingshaftandrodspecimenholderjigandthefracturedvibratingshaftafter500htestsathightemperatureandpressurizedwatercondition.essentialtoevaluatethereasonfortheirfailureandtoimprovethevibratingshaftdesigntoconfirmthereliabilityofthefrettingweartesterforalongexperiment.Inthisstudy,thereasonsforthefailureandthefracturemechanismsarerevealedanddiscussedbyusingtheOMandSEMresultsofthefracturesurface,measurementofthemicro-vickershardnessandthestressanalysisofthevibratingshaft.Finally,theaboveresultswereappliedtoadesignchangeofthevibratingshaft.2.Fracturesurfaceanalysis2.1.OMobservationThevibratingshaftismadeofaconventionalhigh-carbonmartensiticstainlesssteel(SUS440C)andthismaterialiswidelyusedastoolsorbladesforuseinrelativelycorrosiveatmospheres3.ThechemicalcompositionandmechanicalpropertiesarelistedinTable.1.Fig.3showstheOMresultofthefracturesurfaceforthevibratingshaft.DuetotheHTHPwatercondition,thefracturesurfacewasheavilyoxidizedanditwasdifficulttoobtainmetallographicproofbyusingtheOMobservation.However,itisexpectedthatthefailurewasinitiatedatacontactregionbetweenthevibratingshaftandthefuelrodholderjigbecausethesetwopartswasassembledbyusingaboltasshowninFig.2.Duringthefrettingweartests,fourvibratingshaftswerereciprocatedintheiraxialdirectionwitharangeof±200lm,afrequencyof30C176Hzandasinusoidalmotionbytwoelectro-magneticactuatorsthatwerearrayedatanangleof90o.TogenerateacircularmotionofthefuelrodspecimenwhichisregardedasaconservativesimulationofanactualfuelrodvibrationinoperatingNPPs,thephasedifferenceofthesinusoidalwaveformfortheshakesignalsoftwoactuatorsissetto90oasshowninFig.4.Whenthefuelrodspecimenisvibratedwithacircularmotion,thecontactregionofthevibratingshaftswiththefuelrodholderjigisexpectedtoexperiencefatigueloads.Generally,striationtracesthataredistinctproofforafatiguefailurecouldbefoundeasilyonafracturesurface,ifthestructuralmaterialsarefracturedunderthefatigueloadingconditions.However,theoxi-dizedfracturesurfaceofthevibratingshaftwasexaminedbyusingSEMwithoutanycleaningsbecausethestriationtracescouldbeexpectedtoremovebytheoxideremovalprocess(i.e.acidcleaning).2.2.HardnessvariationBeforetheSEMobservation,itisnecessarytoexaminethemechanicalpropertychangesofthevibratingshaft,becauseitwasexposedtotheHTHPwaterconditionduring500htests.So,amicro-vickershardnessofthefracturedvibratingshaft1240Y.-H.Leeetal./EngineeringFailureAnalysis16(2009)12381244wasmeasuredanditsresultisshowninFig.5.Itisapparentthatthemicro-vickershardnessvalueincreasedaccordingtotheexposedtemperatureforthevibratingshaft.ThisresultcorrespondswellwiththetemperingtemperatureeffectTable1Chemicalcompositionsandmechanicalproperties(roomtemperature)ofaconventionalhigh-carbonmartensiticstainlesssteel(SUS440C)4CMnSiPSCrMoFeChemicalcompositions(wt%)1.01.01.00.040.03170.75Bal.YieldstrengthTensilestrengthElongationElasticmodulusDensityPoissonsratioMechanicalproperties1280MPa1750MPa4%200GPa7.8g/cm30.3Fig.3.OMresultofthefracturesurfaceforthevibratingshaft:arrowsindicatetheexpectedcrackinitiationregion.Y.-H.Leeetal./EngineeringFailureAnalysis16(2009)123812441241Fig.4.Actuatingmechanismofthefuelrodbyusingtwoelectro-magneticactuatorsinFRETONUS:notethatthefuelrodmotionsarechangeablebyadjustingvibrationamplitudesandphasedifferencebetweentwoactuators.onthemechanicalpropertiesofSUS440C4.Inthisstudy,thehighercarbonmartensiticstainlesssteelislikelytoretainalargeamountofuntransformedaustenite.Itisthoughtthatadelayedtransformationmayoccurastemperaturefluctuationsinseveralfrettingweartestsbecausethe500htestsatabout320C176Cdidnothaveanegligibleeffectonthestressrelievingofthevibratingshaftmaterial.Inaddition,itispossiblethatsomelossinductilitymayresultfromahydrogenembrittlementthatisanimportantconcerninmartensiticstainlesssteelsinaheat-treatingatmospherecontaininghydrogenintheformofdistilledwater.2.3.SEMresultsFig.6showsthemorphologyofthefracturesurfacebyusingSEM.Itisapparentthatthefracturesurfacewasalmostcov-eredwithoxidesanditisdifficulttodetectevidenceofafatiguefailuresuchasstriationtraces.Fromacarefulinspectionoftheresults,however,weakstriationtracesappearednearalateraloutersurface.Also,acrackpropagationtracewasfoundatthecontactregionbetweenthevibratingshaftandthefuelrodholderjigeventhoughitscharacteristiccouldnotbedefinedduetothesevereoxidationintheHTHPwatercondition.Oneoftheinterestingresultsisthatanimpactingwearscarappearedinthefracturesurfaceofthevibratingshaft.Thisresultmeansthattheimpactingwearbetweenthetwofracturedsurfacesisgeneratedafterafracturebecausethefracturedvibratingshaftiscontinuouslyreciprocatedbyanelectro-mag-neticactuatorregardlessoftheshaftfailure.So,itisexpectedthatthefatiguestriationtraceshaddisappearedandwerecov-eredbytheimpactingwearmotionandbytheweardebriswithasevereoxidation,respectively.Consequently,thevibratingshaftfailureisexpectedtobeinitiatedbyacontactfatigueatthecontactregionandthenthecontactforceexertedbyaboltFig.5.Measurementresultofthemicro-vickershardnessaccordingtotheexposedtemperatureforthevibratingshaft.