边界润滑，Stribeck curves，BoundaryLubrication

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1、1BoundaryLubricationDefinition:Campbell[1]"Boundarylubricationislubricationbyaliquidunderconditionswherethesolidsurfacesaresoclosetogetherthatappreciablecontactbetweenopposingasperitiesispossible.Thefrictionandwearinboundarylubricationaredeterminedpredominantlybyinteracti

2、onbetweenthesolidsandbetweenthesolidsandtheliquid.Thebulkflowpropertiesoftheliquidplaylittleornopartinthefrictionandwearbehavior."StribeckCurve2Characteristics•Liquid-solidinteractions•Contactbetweenasperities−Increasedfriction−Wear•Friction&weardeterminedbypropertiesofso

3、lidsurfacesaswellaspropertiesoflubricant•Shearofthinsurfacefilms−Lubricantfilms<100nmthick−Severaltohundredsofmoleculesthick−Solidorliquid−“Lubricantstarved”contact•Loadsharing−Asperity-asperitycontacts−LubricantpressuresgeneratedbySqueezefilmsSliding•"Oiliness"ofsurfac

4、esdeterminesfriction−Lubricantfilmthickness<100nmthick3ExamplesEngines:Pistonrings&liner@TDC&BDCBiologicaloSynovialjoints,e.g.,kneewithsynovialfluidoTeeth/salivaduringchewingOiledgunbarrel&bulletStartup&shutdownofequipment:oEnginesoBearingsoCamsLubricatedmetalcutting

5、ormachining4ProtectiveFilms•Chemicalinteractionsform(protective)films−Surfaceabsorption−Surfacereactions•Diamondlike(protective)films−Verylow(dry)frictionµ≈0.001−Chemicallyinert,veryhard−AliErdemir:"Near-FrictionlessCarbon…….ultra-hardcoatingmanytimesslickerthanTeflon."−H

6、ydrogenatedcarbonbondedtosurface,unreactive.•Designofprotectiveboundaryfilms(hydrocarbons)−Filmabsorbstosurface−Bodiesdon'ttouch−Classofoiladditivesforbondingtosurfaces(surfactants)5GREASESMOLECULARDYNAMICSOFFILMSFLOWTHROUGHROUGHSURFACESADHESIONOFLUBRICANTGOODBOUNDARYLUBR

7、ICANTS6BOUNDARYLUBRICATEDCONTACTMODELS•Roughsurfacescontact:•AsperityforcesPisupportload@discretepoints•Hydrodynamicfluidpressurespfluidsupportloadelsewhere7•TotalloadsupportP=ΣasperitiesPi+ ∫areapfluiddA∞≈⌠N⌡Pi(z)F(z)dzd+ ∫ApfluiddANotes:•RealcontactareaAreal<

8、contactarea.Thus∫(A-Areal)pfluiddA≈∫ApfluiddA•Manyasperitiesofmanyheights,thus∞⌠ΣasperitiesPi≈N⌡