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1、TribologyLetters,Vol.17,No.2,August2004(ó2004)337Amethodforthemeasurementofhydrodynamicoil?lmsusingultrasonicre?ectiona,abR.S.Dwyer-Joyce,P.HarperandB.W.DrinkwateraDepartmentofMechanicalEngineering,MappinStreet,UniversityofShe?eld,She?eldS13JD,UKbDepartmentofMechanica
2、lEngineering,UniversityWalk,UniversityofBristol,BristolBS81TR,UKReceived23November,2003;accepted23January,2004Themeasurementofthethicknessofanoil?lminalubricatedcomponentisessentialinformationforperformancemoni-toringandcontrol.Inthiswork,anewmethodforoil?lmthicknessmeas
3、urement,basedonthere?ectionofultrasound,isevaluatedforusein?uid?lmjournalbearingapplications.Anultrasonicwavewillbepartiallyre?ectedwhenitstrikesathinlayerbetweentwosolidmedia.Theproportionofthewavere?ecteddependsonthethicknessofthelayeranditsacousticproperties.Asimplequ
4、asi-staticspringmodelshowshowthere?ectiondependsonthesti?nessofthelayeralone.Thismethodhasbeen?rstevaluatedusing?atplatesseparatedbya?lmofoil,andthenusedinthemeasurementofoil?lmsinahydrody-namicjournalbearing.Atransducerismountedontheoutsideofthejournalandapulsepropagate
5、dthroughtheshell.Thepulseisre?ectedbackattheoil?lmandreceivedbythesametransducer.Theamplitudeofthere?ectedwaveisprocessedinthefrequencydomain.Thespringmodelisthenusedtodeterminetheoil?lmsti?nessthatcanbereadilyconvertedto?lmthickness.Whilstthere?ectedamplitudeofthewaveis
6、dependentonthefrequencycomponent,themeasured?lmthicknessisnot;thisindicatesthatthequasi-staticassumptionholds.Measurementsofthelubricant?lmgeneratedinasimplejournalbear-inghavebeentakenoverarangeofloadsandspeeds.Theresultsarecomparedwithpredictionsfromclassicalhydrodynam
7、iclubricationtheory.Thetechniquehasalsobeenusedtomeasureoil?lmthicknessduringtransientloadingevents.Theresponsetimeisrapidand?lmthicknessvariationduetostepchangesinloadandoilfeedpressurecanbeclearlyobserved.KEYWORDS:oil?lmmeasurement,journalbearings,hydrodynamic,?uid?lmb
8、earings,ultrasound,lubrication,?lmthick-ness1.IntroductionUltrasoundisroutinelyusedfordefectdetectionin
