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1、TribologyLetters,Vol.17,No.2,August2004(Ó2004)337Amethodforthemeasurementofhydrodynamicoilfilmsusingultrasonicreflectiona,abR.S.Dwyer-Joyce,P.HarperandB.W.DrinkwateraDepartmentofMechanicalEngineering,MappinStreet,UniversityofSheffield,SheffieldS13JD,UKbDepartmentofMechanica
2、lEngineering,UniversityWalk,UniversityofBristol,BristolBS81TR,UKReceived23November,2003;accepted23January,2004Themeasurementofthethicknessofanoilfilminalubricatedcomponentisessentialinformationforperformancemoni-toringandcontrol.Inthiswork,anewmethodforoilfilmthicknessmeas
3、urement,basedonthereflectionofultrasound,isevaluatedforuseinfluidfilmjournalbearingapplications.Anultrasonicwavewillbepartiallyreflectedwhenitstrikesathinlayerbetweentwosolidmedia.Theproportionofthewavereflecteddependsonthethicknessofthelayeranditsacousticproperties.Asimplequ
4、asi-staticspringmodelshowshowthereflectiondependsonthestiffnessofthelayeralone.Thismethodhasbeenfirstevaluatedusingflatplatesseparatedbyafilmofoil,andthenusedinthemeasurementofoilfilmsinahydrody-namicjournalbearing.Atransducerismountedontheoutsideofthejournalandapulsepropagate
5、dthroughtheshell.Thepulseisreflectedbackattheoilfilmandreceivedbythesametransducer.Theamplitudeofthereflectedwaveisprocessedinthefrequencydomain.Thespringmodelisthenusedtodeterminetheoilfilmstiffnessthatcanbereadilyconvertedtofilmthickness.Whilstthereflectedamplitudeofthewaveis
6、dependentonthefrequencycomponent,themeasuredfilmthicknessisnot;thisindicatesthatthequasi-staticassumptionholds.Measurementsofthelubricantfilmgeneratedinasimplejournalbear-inghavebeentakenoverarangeofloadsandspeeds.Theresultsarecomparedwithpredictionsfromclassicalhydrodynam
7、iclubricationtheory.Thetechniquehasalsobeenusedtomeasureoilfilmthicknessduringtransientloadingevents.Theresponsetimeisrapidandfilmthicknessvariationduetostepchangesinloadandoilfeedpressurecanbeclearlyobserved.KEYWORDS:oilfilmmeasurement,journalbearings,hydrodynamic,fluidfilmb
8、earings,ultrasound,lubrication,filmthick-ness1.IntroductionUltrasoundisroutinelyusedfordefectdetectionin
