偏心控制的多轴疲劳试验机研究外文翻译.docx
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偏心控制的多轴疲劳试验机研究外文翻译.docx
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偏心控制的多轴疲劳试验机研究外文翻译
毕业设计(外文翻译)
英文题目DevelopmentofaDeflection
ControlledMultlaxlalFatigue
TestingMaching
中文题目偏心控制的多轴疲劳试验机设计
系(院)机电工程系
专业机械设计制造及其自动化
学生姓名
学号
指导教师
职称
二〇一六年三月
DevelopmentofaDeflectionControlledMultlaxlalFatigueTestingMaching
Thispaperdiscussesthedevelopmentofamultiaxialfatiguetestigmachine.Thedeflectioncontrolledeccentricdisktypetestingmachineproducesmode
mode
orcombinationofboth,ofcracksurfacedisplacementsonroundorflatspecimens.Theseloadingsarenecessaryforresearchoncomplexmultiaxialstresseswhicharecommoninengineeringpractice,suchascrankshafts.Thismachineachievedtheobjectivewithverysimplemechanisms(vectorsumoftwocrankthrowsofeccentricdisksyieldbendingmoments;vectordifferences,twistingmoments),butwithmorecomputationinsettingthedesiredparameters.Bendingdataandtorsiondataproducedbythemachinewereingoodagreementwiththedatabyaconventionalfatiguetestingmachine.Multiaxialdataproducedbythemachinewerealsoingoodagreementwiththepredictionbyawellprovedmultiaxialfatiguetheory.Applicationsofthemultiaxialfatiguetestingmachinearedescribed.
KeyWords:
MultiaxialFatigue,Bending,Torsion,Out-of-Phase,DeflectionControlled,TestingMachine,DiscriminatingSpecimen
1.INTRODUCTION
Mostengineeringcomponentssuffermultiaxialcyclicloadings.Fatiguecrackinitiationandpropagationundermultiaxialloadingsshowdifferentbehaviorfromthoseofuniaxialloading.Fatiguelifepredictionofstructuresormachinepartsundermultiaxialloadingsisessentialtotheirreliabledesignandfailureprevention.Suchpredictionwasoftenbasedonsimplelaboratorydatageneratedundercyclicuniaxialloading.
ResearchbyBrownandMiller(l973),Krempl(1974),Lee(1980)andGarud(1981)indicatedthatuniaxialdataalonecannotbeapplieddirectlytothepracticalsituationsofcomplexmultiaxialfatigue,i.e.,movingprincipalaxesandnonproportionalloading.Manyfatiguetheoriesorcriteriahavebeenproposedbutnonewasgenerallyaccepted(Garud,1981;Lee,1985).Verylittleexperimentalworkhasbeendoneinthisfieldowingtothelackofpropermultiaxialfatiguetestingmachines.Thereforereliablefatiguetestingfacilitiesarerequiredformultiaxialfatigueresearch.Varioustypesofmultiaxialfatiguetestingmachinesarepossiblesuchasservo-hydraulicaxial-torsionsystem,orservo-hydraulicaxial-torsionandinternal/externalpressuretypesystem,servo-hydrauliccruciformspecimenloadingmachine.Howevertheseservo-hydraulicsystemsareveryexpensiveandmoreovertheirloadtypesmaynotbeversatile.Thereforewedesignedadeflectioncontrolledeccentrictypemultiaxialfatiguetestingmachinetoproducearatherversatileloadingssuchasstaticandcyclicbending,staticandcyclictorsion,andthecombinationofbendingandtorsionwithanyphaseanglebetweenthem.Amongthevariousloadingsproducedbythemultiaxialfatiguetestingmachine,thecyclicbendingandout-of-phasetorsionload,whichiscommonlyencounteredinengineeringpractice,suchascrankshaftsinautomobileindustry,isanexampleofcomplexmultiaxialloadings.
Theconstructionofthemultiaxialtestingmachine,somedetaileddescriptionsoftheframeandthedrivingmechanism,kinematicanalysisofthemachine,measurementofmoments,andcontroldeviceswillbedescribed.Toevaluatethemultiaxialfatiguetestingmachine,thetestdataperformedwiththemultiaxialfatiguetestingmachinewerecomparedwiththetestdatawithacommonlyusedfatiguetestingmachinewhichcanapplybendingandtorsionseparately.MultiaxialfatiguedataperformedwiththemultiaxialfatiguetestingmachinewerecomparedwiththepredictionofthewellprovedtheorysuggestedbyLee(1985)forcombinedbendingandout-of-phasetorsion.
Toshowtheapplicabilityofthemultiaxialfatiguetestingmachineindiscriminatingmultiaxialfatiguecriteria,adiscriminatingspecimenwasdesignedtobesuitableforthemultiaxialfatiguetestingmachine.ThreemultiaxialfatiguecriteriasuggestedbyLee(1989)werechosentobecomparedinthediscriminatingspecimen.Atypicalapplicationofthemultiaxialfatiguetestingmachinetoastructuralmemberwasalsodiscussed.
2.DEVELOPMENTOFTHEMACHINE
2.1Construction
Thepurposeofthemachineistoapplybendingmomentsandtwistingmomentsatthesamefrequencybutwithadjustablephaseangles,amplitudes,andmeanvalues.ThemultiaxialfatiguetestingmachinewasconstructedasshowninFig.1.Themachineachievedtheobjectiveswithsimplemechanisms,butwithmorecomputationinsettingthedesiredparameters.TheschematicdiagramofthemultiaxialfatiguetestingmachineisshowninFig.2.Therearetwoeccentriccrankswhichmovethetwoendsofasymmetriccrossbeamattachedtothemovingendofacantileverspecimen.Theeccentriccranksareadjustableinthrowandphaserelation.ThevectorsumofthetwocrankthrowsproducesthebendingmomentandmodeIcrack,andvectordifferenceproducesthetwistingmomentandmode
crackpropagationonroundorflatspecimen.Theconstantswhichconvertthevectorstoactualbendingandtwistingdeflectionsandstressesdependonthesizeofthespecimenandonthelengthofthecrossbeam.
2.2FrameandDrivingMechanism
Thefatiguemachineconsistsofaframe,amotor,twoeccentricdisks,aphaseplateassembly,twoconnectingrods,amainshaft,gripsandloadcells.Fig.3showsthelayoutdrawingofthefatiguemachinedesigned.Theeccentriccrankproducesalternatingbendingdeflectionsupto140mmonthespecimen.Theeccentriccrankwasdesignedtobeadjustablecontinuouslytoformthefluctuatingcomponentofstress.Theconnectingrodsweredesignedtoproducestaticstressonthespecimenbyadjustingtheirlength.Theconnectingrodassemblycanbeextendedorcontractedbytwistingtherodbecausetheendsoftheconnectingrodhaveoppositethreads.Thephaseplateassemblyconnectsthetwosectionsofthemainshaftwhichwassplittoallowrelativemotionbetweentheeccentricsforphaseadjustment.Thedriveplateanddrivenplateweredesignedforcontinuousadjustment.Thespecimenispartoftheframe,andthemomentsonthespecimenaretransmittedtothefixedgripandtothethreeloadcells.Thefixedgrips,connectingrods,themainshaft,andthetestframeweredesignedsothathighstressesandfatiguestressesoccuratthespecimenandnotanyofthemachinecomponents.
Variablespeed(150-1500rpm)ACmotorwasdeterminedforpowersourceofthefatiguemachine.Motorcapacityof3Hpwasdeterminedtoproduce500MPabendingstressand300MPatorsionalstressontheroundspecimenof10mmindiameterand300mminlength.Atimingbelttransmittedpowersmoothlytothemainshafts.
2.3KinematicAnalysisoftheMachine
Themachineproducesvariouscombinationsofbendingmomentsandtwistingmomentswithverysimplemechanisms.ThekinematicanalysisofthemachineincludestheinstantaneousvectorcomponentsofthemachinemechanismasshowningFig.4andtheirtrigonometriccalculation.Thevectorsumofcrankthrowsofrighteccentricdisk,Randlefteccentricdisk,LyieldsbendingdeflectionB,whilethevectordifference,producestorsionaldeflectionT.TheangleФisthephasedifferencebetweenbendingandtorsionalmoments.TheangleAisthephaseplateadjustmentsbetweentwoeccentricdisks.
OnemustsetthemachinewithparametersofR,L,andAtoproducethedesireddeflectionsofbending(B)andtorsion(T)withphaseargleФ.
Themechanismissimple,butthekinematicanalysisinvolveslengthycalculations.HoweversuchtrigonometriccalculationwasperformedeasilytomakeamachinesettingtableforvariousvaluesofB,T,andФ,withasimpleFORTRANprogram.
2.4MeasurementofMoments
Three500kgtension-compressionloadcells,U2Ml500K,werearrangedunderfixedgriptomonitorloadsonthespecimen.Threeloadcellsworkasthesensorofcracks.Thesignalofloadcellsareamplifiedandconnectedtothecontroldevicesdescribedinthelatersection.Fig.5showsthearrangementofthreeloadcellsunderfixedgrip.Theconstantswhichconvertthemomentstoactualstressesatapointinthespecimendependonthegeometryofthespecimen.
2.5ControlDevices
Duringafatiguetesting,itisnecessarytodetectthespecimenfailure.Whenitfailsthetestshouldbediscontinuedsothatthespecimenwillnotbedestroyedandtheaccuratecyclestofailurecanbecounted.Forthispurpose,anautomaticpowercut-offdevicewasmade.Itconsistsofthreemainstages;sensing,signalprocessing,andactivatingrelay.
Thiscontrolsystemmonitorstheloadlevelandactivatesarelaytoturnoffthemotorwhenthemaximumloadislessthanaspecifiedlevel(normally90%oftheoriginalone).Fig.6showstheschematicdiagramofthecontrolcircuit.
Severalothercontroldevicessuchasopticalmethodscyclecounter,timer,loadindicator,andtestingspeedcontrollerwereusedforaccuratetesting.
3.Evaluationandapplicationofthemaching
Themultiaxialfatiguetestingmachinewasevaluatedbycomparingitstestdataagainstthedatabyacommonlyusedfatiguetestingmachine,andagainstthepredictionofthewellprovedtheorysuggestedbyLee(1985)forcombinedbendingandout-of-phasetorsion.Theapplicabilityofthemultiaxialfatiguetestingmachinewasshowninadiscriminatingspecimentestandfatiguetestofagolfshaft.
3.1Evaluation1:
ComparingwithaConventionalMachine
Constantamplitudefatiguetestswereperformedundercyclicbending,andundercyclictorsionseparatelywiththemultiaxialfatiguetestingmachine,andalsowithaSchenck
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