机械设计制造专业毕业设计中英翻译一残余应力针对不同的材料车削的建模方法.docx
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机械设计制造专业毕业设计中英翻译一残余应力针对不同的材料车削的建模方法.docx
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机械设计制造专业毕业设计中英翻译一残余应力针对不同的材料车削的建模方法
Amethodofmodelingresidualstressdistributioninturningfordifferentmaterials
M.H.El-Axir
DepartmentofProductionEngineeringandMechanicalDesign,MenoufiaUniversity,ShebinEl-Kom,Egypt
Received10July2001;receivedinrevisedform7March2002;accepted12March2002
Abstract
Thispaperintroducesamorecomprehensiveexperimentalmodelwhichhasthecapabilityofpredictingresidualstressprofile.Themainadvantageofthismodelovertheexistingmodelsthatitprovidestheeffectofmachiningparametersonmaximumresidualstressanddeterminesboththelocationanddepthofthismaximumresidualstress.Fivedifferentmaterialsnamely;stainlesssteel304,steel-37,7001and2024-aluminumalloysandbrassweremachinedbyturningutilizingoneofexperimentaldesigntechniquesbasedonresponsesurfacemethodology.Tensilestrengthofthesematerialsandbothcuttingspeedandfeedratesareconsideredasthreeinputparametersaffectingresidualstressdistribution.Theresidualstressdistributioninthemachinedsurfaceregionwasdeterminedusingadeflection-etchingtechnique.Itisproposedherethattheresidualstressprofileisadeterministicfunctionofthethreeinputparametersused.Also,itispostulatedthattheresidualstressprofilealongthedepthbeneathsurfaceisapolynomialfunctionofthedepthbeneathsurfaceandthecoefficientsofthispolynomialare,inturn,functionsoftheinputparameters.Themodelhasbeendevelopedandhasbeencheckedforaccuracy..2002ElsevierScienceLtd.Allrightsreserved.
1.Introduction
Fatiguelifeisanimportantdynamicpropertyanditisstronglyaffectedbythesurfaceconditionproducedduringmachining[1].Thefatiguecrack,ingeneral,nucleatesatthesurfaceofthepart,andthenpropagatesintothebulk.Asthecrackextendstheresistantsectionisreduced,andwhentheresidualsectioncannolongerwithstandtheappliedloadcomponentfatigueoccurs.Consequently,itisthestateofstressatthesurface,wherethecracknucleates,thatisofparamountimportance.Thisstateisthesumofthestressduetotheappliedloadandoftheresidualstresses(orselfstresses)generatedduringmachining.Residualstressistheresultofvariousmechanicalandthermalevents,whichoccurinthesurfaceregionduringmachining.Itisusuallyfoundthattheabsolutevalueoftheresidualstressclosetosurfaceithighanddecreasescontinuouslywithanincreaseindepthbeneaththemachinedsurfaceeventuallyvanishing.Residualstressmaybetensileorcompressiveandthestressedlayermaybeshallowordeep,dependinguponthecuttingconditions,workmaterial,andtoolgeometry.
Ithasbeenshown[2–4]thatresidualstressesmaybecompressiveatthesurfaceandtensilejustbelowthesurfaceorviceversa.Compressiveresidualstressesaregenerallyimprovecomponentperformanceandlifebecausetheyreduceservice(working)tensilestressesandinhibitcracknucleation.Ontheotherhand,tensileresidualstressescansignificantlyincreaseservice(working)stresseswhichcanleadtoprematurefailureofcomponents[5–10].SigwartandFessenmeyer[11],forexample,reportedthatfatiguetestsonturnedspecimensof42CrMo4steelpresentinghightensileresidualstresses(upto600:
800MPa)showedacloseto30%reductioninthefatiguelimit.Matsumotoetal.[12]reportedthatthefatiguestrengthofhardenedAISI4340steelspecimens(54HRC)afterflycuttingwas2–5%higherthataftergrindingprobablybecausethecompressiveresidualstressdistributionproducedbythesinglepointcuttingoperationpenetratedtoagraterwork-piecedepth.Similarly,PrataPinaetal.[13]foundthat,whenmillingannealedhotworkdiesteel(AISIH13),residualstressesclosetozerowereobtainedatthesurface,droppingsharplytoamaximumcompressivestressapproximately100μmbelowthesurface,thenrisingagaintothetensileside.
Accordingly,Itisveryclearthattheinformationconcerningresidualstressesprofile(magnitudeanddirectionalongthedepth)ofthemachinedsurfaceregionwillbevaluableinthedesignandmanufactureofparts.Therefore,itisimportantthattheeffectofthemachiningprocessparametersontheresidualstressprofileisdetermined,andsubsequently,suchmachiningparametersmaybechosenwhichwouldenhancefatiguelifebyinducingfavorableresidualstress(compressivestress).
Themajorityoftheresearchexistinginliteratureontheeffectofmachiningparametersontheresidualstressprofileareexperimentalinnature.Veryfewanalyticalmodelsareavailable.LiuandBarash[14,15]explainedtheformationofresidualstressbyconsideringthestressstrainhistorythatthesurfacelayerexperiencedduetothemovementofthecuttingtool.Linetal.[9]usedfiniteelementtechniquestodetermineresidualstressprofilesinorthogonalmachining.WuandMatusmoto[16]alsousedfiniteelementtodeterminefactors,whichaffectresidualstressformationinhardenedsteelmachining.Devarajanetal.[17]constructedanexperimentalmodelforpredictionofthesurfaceresidualstress.Althoughthesurfaceresidualstressisimportant,inmostmachiningprocesses,thesubsurfaceresidualstressesareatleastequallyimportant.
Thispaperintroducesamorecomprehensiveexperimentalmodeltopredictsurfaceandsubsurfaceresidualstressprofilesinturningoffivedifferentmaterials.Withthehelpofthisknowledgeitwillbecomepossibletooptimizemachiningparameterssuchthatthesurfaceintegrityofthemachinedcomponentforthesefivedifferentmaterialsismaximizedunderserviceconditions.
2.Experimentaldetails
2.1.Workpiecematerials
Workpiecesofstainlesssteel304,steel37,aluminumalloy7001,aluminumalloy2024,andbrasswereutilized.Thesematerialswereselectedbecausetheyhavedifferentmachiningcharacteristicsandareimportantinindustry.Moreover,bothofaluminumalloys7001and2024areparticularlywellsuitedforpartsandstructuresrequiringhighstrength-to-weightratios.ThechemicalcompositionsinweightpercentandtensilestrengtharegiveninTable1.Thetoolmaterialemployedwashigh-speedsteel.
2.2.Workpiecepreparation
ThefivedifferentmaterialsweremachinedintoringshapeswiththedimensionsshowninFig.1a.Fig.1bshowsthetestedringmountedonitsmandrel.Itisprobablethatresidualstressesareinducedinthesurfaceregionoftheworkpiecebecauseofthemachininginvolvedinpreparation,henceitwasnecessarytoremovethesestressesbyannealingtheworkpieces.
Stainlesssteel304,steel37,Al.7001,Al.2024andfreemachiningbrassworkpieceswereheatedto800,595,340,340,and260°Cfor3,6,2,2and1h,respectively,andthencooledinairorinfurnace.
Inthisinvestigation,thespecimensweremachinedusingoneoftheexperimentaldesigns.Accordingtoacentralcomposedsecond-orderrotatabledesignwiththreeindependentvariables,thetotalnumberofexperiments,N,wasdeterminedtobe20.ThecuttingconditionsandtheircodedaresummarizedinTable2.
Theresidualstressdistributioninthemachinedsurfacewasdeterminedutilizingadeflectionetchingtechniquewheretheresidualstressesintheremovallayerarerelivedandtheremainingresidualstressesareredistributeduntilanewequilibriumpositionisachieved.Thischangeinshapecanbemeasuredfromwhichresidualstressescanbecalculated.Alayerofapproximately15–25μmwasremovedwiththehelpofelectrochemicaletching.Layerswereremoveduntiltheresidualstressstatebecamenegligible.Theobtainedresidualstressprofilesfor20differentcombinationsaccordingtoTable3areshowninFig.2.
3.Proposedmodel
Theproposedmodelpostulatesthattheresidualstressprofileaswellasthedepthofresidualstressdistributionarefunctionsofthemachiningparameters.Themodelassumesthatprofileofresidualstressalongthedepthispolynomialfunctionofthedepth.Theprofilecanberepresentedas:
where:
siistheresidualstress,cniarethecoefficientsofthenthorderpolynomialtermandzisthedepthbeneaththemachinedsurface.
Further,itisproposedthatthecoefficientsofthepolynomialareindividualfunctionsofthemachiningparameters.Therelationofthecoefficienttothemachiningparametersis
whereCiisthecoefficientofpolynomialforresidualstressprofileandbxiistheeffectoffactor(orinteractionoffactor)x.
Thevaluesofthecodenumberofeachparameter,x,canbeobtainedfromthefollowingtransformationequations.
whereV,FandTarecuttingspeed,feedandtensilestrengthofthematerial,respectively.
Thevaluesofbxisaredeterminedexperimentally.Theprocedureisasfollows:
1.Twentyspecimensarecutusingdifferentcombinations(Table3)ofthefivelevelsofeachparameterusedinthiswork.。
2.Theresidualstressprofilesanddepthofdistributionforeachspecimenaredetermined.
3.Polynomialsofapre-decideddegreearefittedtotheresidualstressprofilesforeachspecimen.
4.Thecoefficient(rli)ofthesepolynomialsarethenusedtodeterminethevaluesofbxiswiththehelpofthefollowingexpressions:
4.Constructionoftheproposedmodel
Avisualinspectionoftheprofilesobtainedwarrantedthatatleastafourthdegreepolynomialwouldberegardedassufficienttofittheprofile.Preliminaryresultswithafourthdegreepolynomialwerenotencouraging.Therefore,itwasdecidedtousefifthdegreepolynomialtorepresenttheresidualstressprofile.Thecoefficients(rlis)correspondingtotheclosestfitwithfifthdegreepolynomialfordifferentcombinationsareshowninTable4.
Itshouldbepointedoutherethatmanyat
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- 机械设计 制造 专业 毕业设计 翻译 残余 应力 针对 不同 材料 车削 建模 方法
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