CopyrightbyInternationalOCSCOWorldPress.Allrightsreserved.2006VOLUME18ISSUE1-2SeptemberOctober2006ofAchievementsinMaterialsandManufacturingEngineeringShortpaper127PropertiesandapplicationofmagnetorheologicalfluidsM.Kciuka,*R.TurczynbaDivisionofNanocrystallineandFunctionalMaterialsandSustainablePro-ecologicalTechnologies,InstituteofEngineeringMaterialsandBiomaterials,SilesianUniversityofTechnology,ul.Konarskiego18a,44-100Gliwice,PolandbDepartmentofPhysicalChemistryandTechnologyofPolymers,SilesianUniversityofTechnologyul.MarcinaStrzody9,44-100Gliwice,Poland*Correspondingauthor:E-mailaddress:monika.kciukpolsl.plReceived15.03.2006；acceptedinrevisedform30.04.2006MaterialsAbstrActPurpose:Thispaperpresentsbasicpropertiesofthemagnetorheologicalfluids(MR)andtheirdevelopmentinrecentyears.Avarietyofstillgrowingpracticalapplicationsinmechanicaldevicesarepresented.Design/methodology/approach:Thetheoreticalresearchresultsofthepropertiesandapplicationsobtainedinthepastdecadesandprogressedinrecentyearsarereviewed.Findings:Itisveryclearlyandwellunderstoodfromthepresentedpaperthatreplacementofthetraditionaldeviceswithactive,smartsystembetteradaptedtotheenvironmentstimulusarenecessary.ManyofthemwillincludeMRfluidsasactivecomponent.Researchlimitations/implications:MRfluidswithexcellentpropertiescanbeappliedinvariousfieldsofcivilengineering,safetyengineering,transportationandlifescience.Theyofferanoutstandingcapabilityofactivecontrolofmechanicalproperties.Practicalimplications:Averyusefulmaterialfortheengineersengagedinthedesignofbrakes,dampers,clutchesandshockabsorberssystems.Originality/value:Thisarticledescribesanup-to-dateMRmaterialsdevelopmentandtheirapplicationincivilengineering.Theadvantageofthesmartsystemsovernowadayssolutionsbecomesthedirectionoftheresearchesanddesigningof21stcenturydevices.Keywords:Smartmaterials；Magnetorheologicalmaterials；Magneticproperties；Shearstress1.IntroductionScienceandtechnologyhavemadeamazingdevelopmentsinthedesignofelectronicsandmachineryusingstandardmaterials,whichdonothaveparticularlyspecialproperties(i.e.steel,aluminum,gold).Imaginetherangeofpossibilities,whichexistforspecialmaterialsthathavepropertiesscientistscanmanipulate.Somesuchmaterialshavetheabilitytochangeshapeorsizesimplybyaddingalittlebitofheat,ortochangefromaliquidtoasolidalmostinstantlywhennearamagnet；thesematerialsarecalledsmartmaterials.Smartmaterialshaveoneormorepropertiesthatcanbedramaticallyaltered.Mosteverydaymaterialshavephysicalproperties,whichcannotbesignificantlyaltered；forexampleifoilisheateditwillbecomealittlethinner,whereasasmartmaterialwithvariablemayturnfromaliquidstatewhichflowseasilytoasolid.Eachindividualtypeofsmartmaterialhasadifferentpropertywhichcanbesignificantlyaltered,suchasviscosity,volumeorconductivity.Thepropertythatcanbealtereddetermineswhattypeofapplicationsthesmartmaterialcanbeusedfor1.IntroductionShortpaper128JournalofAchievementsinMaterialsandManufacturingEngineeringM.Kciuk,R.TurczynVolume18Issue1-2SeptemberOctober2006Varietiesofsmartmaterialsalreadyexist,andarebeingresearchedextensively.Theseincludepiezoelectricmaterials,magnetorheostaticmaterials,electrorheostaticmaterials,andshapememoryalloys.Someeverydayitemsarealreadyincorporatingsmartmaterials(coffeepots,cars,glasses)andthenumberofapplicationsforthemisgrowingsteadily.Magnetorheologicalmaterials(fluids)(MR)areaclassofsmartmaterialswhoserheologicalproperties(e.g.viscosity)mayberapidlyvariedbyapplyingamagneticfield.Underinfluenceofmagneticfieldthesuspendedmagneticparticlesinteracttoformastructurethatresistssheardeformationorflow.Thischangeinthematerialappearsasarapidincreaseinapparentviscosityorinthedevelopmentofasemisolidstate.AdvancesintheapplicationofMRmaterialsareparalleltothedevelopmentofnew,moresophisticatedMRmaterialswithbetterpropertiesandstability.ManysmartsystemsandstructureswouldbenefitfromthechangeinviscosityorothermaterialpropertiesofMR.Nowadays,theseapplicationsincludebrakes,dampers,clutchesandshockabsorberssystems.2.PropertiesofmagnetorheologicalfluidsTypicalmagnetorheologicalfluidsarethesuspensionsofmicronsized,magnetizableparticles(mainlyiron)suspendedinanappropriatecarrierliquidsuchasmineraloil,syntheticoil,waterorethyleneglycol.Thecarrierfluidservesasadispersedmediumandensuresthehomogeneityofparticlesinthefluid.Avarietyofadditives(stabilizersandsurfactants)areusedtopreventgravitationalsettlingandpromotestableparticlessuspension,enhancelubricityandchangeinitialviscosityoftheMRfluids.Thestabilizersservetokeeptheparticlessuspendedinthefluid,whilstthesurfactantsareadsorbedonthesurfaceofthemagneticparticlestoenhancethepolarizationinducedinthesuspendedparticlesupontheapplicationofamagneticfield.Table1.SummaryofthepropertiesofMRfluids1PropertyTypicalvalueInitialviscosity0,20,3Pas(at25oC)Density34g/cm3Magneticfieldstrength150250kA/mYieldpoint2o50100kPaReactiontimefewmillisecondsTypicalsupplyvoltageandcurrentintensity225V,12AWorktemperature-50do150oCTypically,thediameterofthemagnetizableparticlesrangefrom3to5microns.FunctionalMRfluidsmaybemadewithlargerparticles,however,stablesuspensionofparticlesbecomesincreasinglymoredifficultasthesizeincreases.Commercialquantitiesofrelativelyinexpensivecarbonylironaregenerallylimitedtosizesgreaterthan1or2microns.Smallerparticlesthatareeasiertosuspendcouldbeused2,3,butthemanufactureofsuchparticlesisdifficult.Significantlysmallerferromagneticparticlesaregenerallyonlyavailableasoxides,suchaspigmentscommonlyfoundinmagneticrecordingmedia.MRfluidsmadefromsuchpigmentparticlesarequitestablebecausetheparticlesaretypicallyonly30nanometersindiameter.However,becauseoftheirlowersaturationmagnetization,fluidsmadefromtheseparticlesaregenerallylimitedinstrengthtoabout5kPaandhavealargeplasticviscosityduetothelargesurfacearea.Mainparametersofthesefluidsarepresentedintable1.Intheabsenceofanappliedfield,MRfluidsarereasonablywellapproximatedasNewtonianliquids.FormostengineeringapplicationsasimpleBinghamplasticmodeliseffectiveatdescribingtheessential,field-dependentfluidcharacteristics.ABinghamplasticisanon-Newtonianfluidwhoseyieldstressmustbeexceededbeforeflowcanbegin4.Thereafter,therate-of-shearvs.shearstresscurveislinear.Inthismodel,thetotalyieldstressisgivenby(1):JKWW)(Ho(1)where:oW-yieldstresscausedbyappliedmagneticfield,PaH-magneticfieldstrength,A/mJ-shearrate,s-1K-plasticviscosity,PasLotsofmodern,complexmodelsofmagnetorheologicalfluidsaredeveloped5,6.Normally,MRfluidsarefreeflowingliquidshavingaconsistencysimilartothatofmotoroil(Fig.1).Fig.1.MRfluidmodelwithoutoutermagneticfield(1carrierliquid,2suspendedmagnetizableparticles)However,inthepresenceofanappliedmagneticfield,theironparticlesacquireadipolemomentalignedwiththeexternalfieldwhichcausesparticlestoformlinearchainsalignedtothemagneticfield,asshowninFig.2.Thisphenomenoncansolidifythesuspendedironparticlesandrestrictthefluidmovement.Consequently,yieldstrengthisdevelopedwithinthefluid.Thedegreeofchangeisrelatedtothemagnitudeoftheappliedmagneticfield,andcanoccurinafewmilliseconds.2.Propertiesofmagnetorheologicalfluids129MaterialsPropertiesandapplicationofmagnetorheologicalfluidsTypicalmagnetorheologicalmaterialscanachieveyieldstrengthsupto50100kPaatmagneticfieldstrengthofabout150250kA/m.Itwasfoundthatwallroughnessoncontactwiththefluidisimportantforyieldstrengths,especiallyinlowmagneticfields.Forlowstrainspriortoyield,theshearmodulusofaMRfluidalsoshowsaverylargeincreaseinanappliedmagneticfield.MRmaterialseventuallyreachasaturationpointwhereincreasesofmagneticfieldstrengthdonotincreasetheyieldstrengthoftheMRmaterial.Thisphenomenontypicallyoccursaround300kA/m.TheeffectofmagneticsaturationonthestrengthofMRmaterialscanbestudiedbyusingfiniteelementanalysis.Fig.2.MRfluidmodelintheoutermagneticfieldTheMReffectisimmediatelyreversibleifthemagneticfieldisreducedorremoved.Responsetimesof6.5mshavebeenrecorded.MRmaterialsthathavebeenalreadydevelopedarestableintemperaturerangesfrom50to150qC.Thereareslightchangesinthevolumefractionandhenceslightreductionsintheyieldstrengthatthesetemperatures,buttheyaresmall.AlsosizeandsizedistributionofthesuspendedparticlesaffectthechangeinpropertiesoftheMRfluidwhenplacedinamagneticfield.Magnetorheologicalmaterialsexhibitsomeadvantagesovertypicalelectrorheologicalmaterials.Incontrasttoelectror-heologicalmaterials,MRfluidsaremoreusefulbecausethechangeintheirrheologicalpropertiesislarge,largerthatinERfluids,soanincreaseofyieldstressare20-50timesstronger.UnlikeERmaterials,theyarealsolesssensitivetomoistureandcontaminants,andthusMRmaterialsarecandidatesforuseindirtyorcontaminatedenvironments.TheyarealsounaffectedbythesurfacechemistryofsurfactantsasERmaterialsare.Thepower(50W)andvoltage(1224V)requirementsforMRmaterialsactivationarerelativelysmallcomparedwithERmaterials.3.ApplicationofmagnetorheologicalfluidsBecausethestateofMRmaterialscanbecontrolledbythestrengthofanappliedmagneticfield,itisusefulinapplicationswherevariableperformanceisdesired.Microprocessors,sensortechnologiesandincreasingelectroniccontentandprocessingspeedshavecreatedreal-timecontrolpossibilitiesofsmartsystemsusedMRdevices.BeginningofthecommercializationofMRtechnologywasyear1995anduseofrotarybrakesinaerobicexerciseequipment.Fromthismomentapplicationofmagneto-rheologicalmaterialtechnologyinreal-worldsystemshasgrownsteadily.Duringthepastfewyearsanumberofcommerciallyavailableproducts(ornearcommercialization)havebeendeveloped,e.g.7-14:xlinearMRdampersforreal-timeactivevibrationalcontrolsystemsinheavydutytrucks,xlinearandrotarybrakesforlow-cost,accurate,positionalandvelocitycontrolofpneumaticactuatorsystems,xrotarybrakestoprovidetactileforce-feedbackinsteer-by-wiresystems,xlineardampersforreal-timegaitcontrolinadvancedprostheticdevices,xadjustablereal-timecontrolledshockabsorbersforautomobiles,xMRspongedampersforwashingmachines,xmagnetorheologicalfluidpolishingtools,xverylargeMRfluiddampersforseismicdamagemitigationincivilengineeringstructures,xlargeMRfluiddamperstocontrolwind-inducedvibrationsincable-stayedbridges.TheMRbrakeoperatesinadirect-shearmode,shearingtheMRfluidfillingthegapbetweenthetwosurfaces(housingandrotor)movingwithrespecttooneanother.Rotorisfixedtotheshaft,whichisplacedinbearingsandcanrotateinrelationtohousing.ResistancetorqueintheMRbrakedependsonviscosityoftheMRfluidthatcanbechangedbymagneticfield.MRbrakeallowsforcontinuouscontroloftorque.Whenthereisnomagneticfieldthetorqueiscausedbyviscosityofcarrierliquid,bearingsandseals.MRbrakeisespeciallywellsuitedforavarietyofapplicationsincludingpneumaticactuatorcontrol,precisiontensioncontrolandhapticforcefeedbackinapplicationssuchassteer-by-wire15.MRclutchsimilartoMRbrakeoperatesinadirect-shearmodeandtransferstorquebetweeninputandoutputshaft.TherearetwomaintypesconstructionsofMRclutch:cylindricalandfrontal.InthecylindricalmodelMRfluidworksbetweentwocylindricalsurfacesandinfrontalMRfluidfillsgapbetweentwodiscs.Duringworkmagneticfieldproducedbycoilsincreasesviscosityoffluidandcausestransferoftorqueforminputtooutputshaft.Usefultorqueisavailableafter2-3millisecondsfromstimulation1.MRdampersaresemi-activedevicesthatcontainmagnetorheologicalfluids.Afterapplicationofamagneticfieldthefluidchangesfromliquidtosemi-solidstateinfewmilliseconds,sotheresultisaninfinitelyvariable,controllabledampercapableoflargedampingforces.MRdampersofferanattractivesolutiontoenergyabsorptioninmechanicalsystemsandstructuresandcanbeconsideredas“fail-safe”devices.magneticfieldcarrierliquidmagnetizableparticles3.ApplicationofmagnetorheologicalfluidsShortpaper130READINGDIRECT:JournalofAchievementsinMaterialsandManufacturingEngineeringVolume18Issue1-2SeptemberOctober20064.ConclusionsScienceandtechnologyinthe21stcenturywillrelyheavilyonthedevelopmentofnewmaterialsthatareexpectedtorespondtotheenvironmentalchangesandmanifesttheirownfunctionsaccordingtotheoptimumconditions.Thedevelopmentofsmartmaterialswillundoubtedlybeanessentialtaskinmanyfieldsofscienceandtechnologysuchasinformationscience,microelectronics,computerscience,medicaltreatment,lifescience,energy,transportation,safetyengineeringandmilitarytechnologies.Materialsdevelopmentinthefuture,therefore,shouldbedirectedtowardcreationofhyperfunctionalmaterialswhichsurpassevenbiologicalorganinsomeaspects.Thecurrentmaterialsresearchistodevelopvariouspathwaysthatwillleadthemoderntechnologytowardthesmartsystem.Thesefluidscanreversiblyandinstantaneouslychangefromafree-flowingliquidtoasemi-solidwithcontrollableyieldstrengthwhenexposedtoamagneticfield.Intheabsenceofanappliedfield,MRfluidsarereasonablywellapproximatedasNewtonianliquids.Formostengineeringapplications,asimpleBinghamplasticmodeliseffectiveindescribingtheessential,field-dependentfluidcharacteristics.MRtechnologyhasmovedoutofthelaboratoryandintoviablecommercialapplicationsforadiversespectrumofproducts.Applicationsincludeautomotiveprimarysuspensions,truckseatsystems,control-by-wire/tactile-feedbackdevices,pneumaticcontrol,seismicmitigationandhumanprosthetics.Incontrasttoconventionalelectro-mechanicalsolutions,MRtechnologyoffers:xReal-time,continuouslyvariablecontrolofxDampingxMotionandpositioncontrolxLockingxHapticfeedbackxHighdissipativeforceindependentofvelocityxGreaterenergydensityxSimpledesign(fewornomovingparts)xQuickresponsetime(10milliseconds)xConsistentefficacyacrossextremetemperaturevariations(rangeof140Cto130C)xMinimalpowerusage(typically12V,1Ampmaxcurrent；fail-safetobatterybackup,whichcanfail-safetopassivedampingmode)xInherentsystemstability(noactiveforcesgenerated)xMRfluidscanbeoperateddirectlyfromlow-voltagepowersupplies.MRtechnologycanprovideflexible,reliablecontrolcapabilitiesindesigns.References1A.awniczak,Electro-andMagnetorheologicalFluidsandtheirApplicationsinEngineering,Pozna1999(inPolish)2S.P.Rwei,H.Y.Lee,S.D.Yoo,L.Y.Wang,J.G.Lin,MagnetorheologicalcharacteristicsofaqueoussuspensionsthatcontainFe3O4nanoparticles,ColloidPolymerScience283(2005),125312583C.Holm,J.-J.Weis,Thestructureofferrofluids:Astatusreport,CurrentOpinioninColloid&InterfaceScience10(2005),1331404D.A.Siginer,AdvancesintheFlowandRheologyofNon-NewtonianFluids,Elsevier,19995K.C.Chen,C.S.Yeh,Amixturemodelformagneto-rheologicalmaterials,ContinuumMechanicsandThermodynamics,15(2002),4955106L.Zhou,W.Wen,P.Sheng:GroundStatesofMagnetorheo-logicalFluids,PhysicalReviewL