本科畢業(yè)論文-1600鎂合金帶材精整機(jī)組-分條圓盤(pán)剪設(shè)計(jì)

1600鎂合金帶材精整機(jī)組-分條圓盤(pán)剪機(jī)架設(shè)計(jì))式中——聯(lián)軸器的許用轉(zhuǎn)矩/；T——聯(lián)軸器長(zhǎng)期承受的理論轉(zhuǎn)矩/；——聯(lián)軸器工作條件系數(shù)。所以：7.4齒輪機(jī)座的作用及類(lèi)型為了將電動(dòng)機(jī)或減速器的扭矩分配給每個(gè)刀盤(pán)軸，除電動(dòng)機(jī)單獨(dú)傳動(dòng)每個(gè)刀盤(pán)軸的情況外，大多數(shù)分條圓盤(pán)剪的主傳動(dòng)系統(tǒng)中都設(shè)有齒輪機(jī)座。因?yàn)辇X輪機(jī)座傳遞的扭矩較大，而中心距又受到刀盤(pán)軸中心距的限制，為了滿足強(qiáng)度要求，齒輪的模數(shù)較大（8~45），齒寬較寬（齒寬系數(shù)為1.6~2.4），而齒數(shù)較少，通常為22~44。齒輪機(jī)座的箱體有高立柱式、矮立柱式和水平剖分式三種形式。齒輪機(jī)座通常直接安裝在基礎(chǔ)上，安裝方式有兩種，一種是將整個(gè)底座都安放在基礎(chǔ)上，另一種是由地腳安裝在基礎(chǔ)上。7.5齒輪機(jī)座的結(jié)構(gòu)齒輪機(jī)座由齒輪軸、軸承及軸承座和機(jī)蓋等主要部件組成。由于傳遞的扭矩大，因此傳動(dòng)軸的直徑很大，相比之下，齒輪的直徑很小，所以一般與傳動(dòng)軸作成一體，即齒輪軸。齒輪多做成具有漸開(kāi)線齒形的人字齒，這樣，只能將一根軸的一端在軸向予以固定，而另外一根齒輪必須設(shè)計(jì)成軸向游動(dòng)的，在運(yùn)轉(zhuǎn)過(guò)程中依靠人字齒的嚙合自動(dòng)定位，從而避免載荷在兩側(cè)斜齒上的不均勻分布。另外，在溫度發(fā)生變化時(shí)，相嚙合的齒輪軸均可自由伸縮，保證正常嚙合。在齒輪機(jī)座中采用雙圓弧齒輪軸，可提高齒輪軸的使用壽命和承載能力，使齒輪軸的外形尺寸減小。齒輪軸的材料為45、40Cr、32Cr2MnMo、35SiMn2MoV、40CrMn2MoV等。由于分條圓盤(pán)剪齒輪箱齒輪軸的齒面接觸應(yīng)力很高,應(yīng)采用硬齒面,齒面淬火硬度為HB480~570。齒輪機(jī)座的軸承主要采用滾動(dòng)軸承，齒輪機(jī)座箱體應(yīng)保證齒輪傳動(dòng)具有良好的密封性，并具有足夠的剛性，以使軸承具有堅(jiān)固的支撐，為此，應(yīng)盡可能加強(qiáng)箱體軸承處的強(qiáng)度和剛度。由于齒輪箱大多是單件或少量生產(chǎn)，為了降低成本，機(jī)座的箱體采用鍛焊結(jié)構(gòu)或鑄焊結(jié)構(gòu)。

8系統(tǒng)的潤(rùn)滑8.1潤(rùn)滑劑的作用機(jī)械零件的表面在接觸的時(shí)候產(chǎn)生相對(duì)運(yùn)動(dòng)，在此過(guò)程中，避免不了會(huì)產(chǎn)生摩擦。假如潤(rùn)滑不當(dāng)，效率會(huì)下降，并且引起發(fā)熱、振動(dòng)、噪聲等。由于零件磨損，機(jī)械精度下降，壽命降低，影響了正常工作而發(fā)生早期報(bào)廢。因此，在機(jī)械設(shè)計(jì)中，潤(rùn)滑是一個(gè)很重要的問(wèn)題。在機(jī)械的摩擦副中加潤(rùn)滑劑的主要作用是：減小摩擦因數(shù)，提高機(jī)械效率。減輕磨損，延長(zhǎng)機(jī)械使用壽命。液體潤(rùn)滑劑能帶走摩擦所產(chǎn)生的熱量，使零件的表面工作溫度下降。循環(huán)潤(rùn)滑能起排污作用。點(diǎn)、線接觸的摩擦表面，油膜能起到緩沖吸振的作用，能夠?qū)⑤d荷分布到較大的面積上，使最大應(yīng)力下降。緩蝕、密封。8.2潤(rùn)滑方式的選擇8.2.1軸承的潤(rùn)滑滾動(dòng)軸承潤(rùn)滑的作用是降低摩擦阻力、減少磨損、防止銹蝕，同時(shí)還可以起到散熱、減小接觸應(yīng)力、吸收振動(dòng)等作用?？紤]軸承潤(rùn)滑時(shí)，選用脂潤(rùn)滑方式，潤(rùn)滑膜強(qiáng)度高，能承受較大的載荷，不易流失，容易密封，能防止灰塵等雜物侵入軸承內(nèi)部，對(duì)密封要求不高，一次加脂可以維持相當(dāng)長(zhǎng)的一段時(shí)間。其缺點(diǎn)是：摩擦損失大，散熱效果差。對(duì)于那些不便經(jīng)常添加潤(rùn)滑劑的部位，或不允許潤(rùn)滑油流失而導(dǎo)致污染產(chǎn)品的工業(yè)機(jī)械來(lái)說(shuō)，這種潤(rùn)滑方式十分適宜。潤(rùn)滑脂的填充量要適中，一般為軸承內(nèi)部空間容積的。8.2.2齒輪傳動(dòng)的潤(rùn)滑齒輪在傳動(dòng)時(shí)，相嚙合的齒面間有相對(duì)滑動(dòng)，因此就要發(fā)生沖突和磨損，添加動(dòng)力消耗，降低傳動(dòng)效率。特別是高速傳動(dòng)，就更要做好齒輪的潤(rùn)滑。齒輪嚙合面之間需要加入潤(rùn)滑劑，能夠防止金屬直接碰觸，減小摩擦損耗，還能夠散熱及防銹蝕。因而，對(duì)齒輪傳動(dòng)系統(tǒng)進(jìn)行必要的潤(rùn)滑，能夠大大改善輪齒的工況，確保運(yùn)轉(zhuǎn)正常及預(yù)期的壽命。通用閉式齒輪傳動(dòng)，其潤(rùn)滑方法依據(jù)齒輪圓周速度大小決定。當(dāng)齒輪的圓周速度時(shí)，通常是將大齒輪輪齒浸入油池中進(jìn)行浸油潤(rùn)滑。這樣，齒輪傳動(dòng)時(shí)，就把潤(rùn)滑油帶到嚙合的齒面上，也能將油甩到箱壁上，借以散熱。齒輪浸入油中的深度可視齒輪圓周速度大小決定，對(duì)圓柱齒輪一般不宜超過(guò)一個(gè)齒高，但一般不該小于10mm。8.2.3滑塊式萬(wàn)向接軸的潤(rùn)滑由于滑塊式萬(wàn)向接軸的摩擦表面不能很好地密封，潤(rùn)滑油不能很好地保存在摩擦面上。同時(shí)分條圓盤(pán)剪的運(yùn)行特點(diǎn)和萬(wàn)向接軸所處的位置，使其潤(rùn)滑較為困難，造成滑塊的磨損加快，壽命降低，嚴(yán)重影響分條圓盤(pán)剪的作業(yè)率。目前潤(rùn)滑方式主要是人工定期加注潤(rùn)滑油和采用自動(dòng)潤(rùn)滑油裝置兩種。另外，采用密封油包包覆和內(nèi)存潤(rùn)滑劑的方式也可以較好地解決潤(rùn)滑問(wèn)題。潤(rùn)滑劑可用潤(rùn)滑脂或潤(rùn)滑油。8.2.4齒輪機(jī)座的潤(rùn)滑分條圓盤(pán)剪的齒輪機(jī)座連續(xù)運(yùn)轉(zhuǎn)時(shí)間很長(zhǎng)，因此機(jī)座的冷卻與潤(rùn)滑是很重要的。對(duì)于齒輪，采用兩種方式，一種是用側(cè)向噴嘴直接向齒輪嚙合區(qū)噴射潤(rùn)滑油；另一種是用一排位于上齒輪軸上部的噴油嘴，通過(guò)側(cè)擋板向齒輪嚙合區(qū)注油。齒輪箱的軸承通常與齒輪使用同一潤(rùn)滑系統(tǒng)，在齒輪箱體上應(yīng)有潤(rùn)滑軸承的油溝。

結(jié)論經(jīng)過(guò)一個(gè)學(xué)期的學(xué)習(xí)、分析、設(shè)計(jì)，在老師的耐心指導(dǎo)和同學(xué)們的熱情幫助下，我最終完成了1600鎂合金帶材精整機(jī)組-分條圓盤(pán)剪機(jī)架設(shè)計(jì)。分條圓盤(pán)式剪切機(jī)主要功能是對(duì)已經(jīng)軋制過(guò)的AZ31鎂合金板進(jìn)行分條。我設(shè)計(jì)的這臺(tái)分條圓盤(pán)式剪切機(jī)主要是對(duì)于刀盤(pán)軸的設(shè)計(jì)校核、軸承的選擇校核、電動(dòng)機(jī)的核算選擇校核、傳動(dòng)裝置中主要的萬(wàn)向連接軸和齒輪的計(jì)算校核，部分鍵的計(jì)算，以及對(duì)潤(rùn)滑系統(tǒng)進(jìn)行了分析。在設(shè)計(jì)和核算過(guò)程中涉及、運(yùn)用了許多基礎(chǔ)及專(zhuān)業(yè)知識(shí)，如：軋鋼機(jī)械設(shè)計(jì)、機(jī)械制造、機(jī)械原理、材料力學(xué)，理論力學(xué)、金屬工藝學(xué)等。對(duì)這些知識(shí)的應(yīng)用使我大大加強(qiáng)了本專(zhuān)業(yè)知識(shí)功底。由于我的水平有限，設(shè)計(jì)中不可避免存在一些不足，在核算、設(shè)計(jì)及繪圖過(guò)程中不可避免地出現(xiàn)錯(cuò)誤，請(qǐng)各位老師給予批評(píng)指正。

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外文翻譯Chapter5Edgecracking5.1OverviewofcrackingstudiesEdgecrackingoftenresultsinedgetrimmingtoremovethedamagedmaterialorcancausetheworkpiecetobreakupintherollgap.Insomecasesthequantityofscraphasbeenquotedas6%ormoreforcertainaluminummagnesiumalloys(45).Creatingthesecracksrequiresbothinadequateductilityandsecondarytensilestressontheedge(15).Obviouslyjustliketheneedtopredicttheresultofrolling,edgecrackinghassolicitedresearchtobetterunderstandtheconceptsandcausesassociatedwiththisdefect.Becauserollingisanindustrialprocess,theconcernofexperimentsisinmakingsurethatresultstranslatefromthelabbacktothefactoryfloor.Thisisacomplicatedprocess,especiallyforhotrolling,becauseindustrialmillsaremuchlargerthanthosetypicallyusedforlaboratoryexperiments.Whilegrossgeometryiseasilyscalable,themetallurgicalparametersincludingmicro-structuralandthermalvariablesarenot.Forexample,laboratoryrollingmillsareusuallymuchsmallerthantheonesusedinindustry,thereforetheworkpiecesaresmaller,thiscausesissuesbecausethethermalmassesofthetwodiffer.Thereforetheheatdistributiondiffersbetweenthetwocaseswhichgreatlyeffectsflowstress.ThisproblemhasbeenaddressedbyBurmanbyreheatingthespecimensafteratemperaturedropofmorethan40°Cbelowthatofthefirstrollingpass(46).Accuratelymodelingrollinginthelabhascreatedsomeuniquetestingmethods;forexample,inordertoaccuratelymodelforwardslipconditionsusedincoldrollinganupsettingrollingtestisused.Thishasbeenusedtostudytheeffectofchangingtheforwardslipconditionandcontactconditionseasily.Inthistest,thematerialisdrawnthroughthedeviceusingatensiletestmachine.Thisdeviceonlyreproducescontactconditionsononlyonesideofthestrip(47).Indifferentexperiments,toestimatethecreationoftensilestressesinrolling(whichisrelatedtocrackpropagation),oftentimesagridwouldbeetchedontoamaterialsampleeitheronthesideorbetweentwopiecesofmaterialwhichthenarerivetedtogether.Thesetestpiecesarethenrolled.Afterrolling,thestreamlinedataiscollectedbymeasuringgridchanges.Modelingisthenemployedtoback-trackoutthestresses(46).Instudyingmaterialfactors,oftentimesdifferentmethodsareusedtorevealthemicrostructureofthematerialincluding:opticalmicroscopy,TEM,andx-raydiffraction(48).Thesenotonlyattempttolookatlocationsandmaterialinclusionsthattendtocausecrackingbutattempttotracktheevolutionofthemicrostructureinthesematerials.Tostudyedgecrackingcreatingaccuratefiniteelementmodelshavebecomenecessaryasexperimentsareexpensiveanddifficulttorelatebacktoindustrialconditions.ThemaindebateinusingthismethodisthedamagemodelasdiscussedinChapter4.Perhapsthesimplestmethodattemptedtomodelcrackingisusingstressintensityfactors(49).Thestressintensityfactor(SIF)helpscharacterizesthecracktipandisusedcommonlyinfracturestudies.Thedeterminationofthisfactorisdependentonthesizeofthecrack,geometryofthecrackandpart,theappliedload,andboundaryconditions.Thefactoriscalculatedthencomparedtofracturetoughnessinformation.WhileXieet.al.study,asdescribedhere,providessomeinsightsintoedgecracking,caremustbetaken.TheSIFismainlyvalidforlinearelasticmaterialsandprocesses;inthecaseofrollingdeformationplasticityisinherenttotheprocess(41).Inaddition,SIFanalysisdoesnottakeintoaccountcrackcreationbutonlydealswithcrackpropagation.WhileXie’sstudycouldbeusedtodescribeacoldrollingsituationwithalightpasses,whichmaylimitthezoneofplasticity,thevalidityofthismethodwithhotrollingwouldnotbeappropriate(49).Morerelevanttothedamagemethodusedhere,manyauthorscreateafracturecriterionandsimplydeleteelementswhenthiscriterionismet.Manyfracturecriteriahavebeenproposed;somearebasedoncriticalstrain,criticalstress,orplasticwork(50).OneexampleofthisistheworkofOhandKobayashi(51)wheretheyusetheprincipaltensilestrainsandprincipalcompressivestrain.Theconstantsintheseformulationsaredeterminedbyexperiment.Anexampleisgivenbelow: （5.1）Thiscriteriavalidityislimitedtomaterialinquestion,AA7075-T6andonlyforrollingcases.Themostcomplicateddamagemodel,usedinfiniteelementanalysis,utilizestheideaofvoidvolumefraction.Sinceductilecrackingisbasedontheinitiation,growth,andthenlinkingofvoids,thisisamorephysicalbasedanalysis.Inthistypeofstudythevoidvolumefractionisallowedtoincreaseanddecreaseuntilitreachesacriticalvalueinwhichthematerialfractures.InastudybyRiedeletal.(50)theyattemptedtomodeledgecrackingthiswayusingtheGologanumodel,whichisbasedonthemorecommonlyusedGursonmodel.Theusesofeitherofthesemodelsareproblematicduetomodelcomplexityandadifficulttodeterminesetofmaterialproperties.But,sincethemodelisbelievedtobeclosertothephysicsofthesituationitismorelikelytobevalidoverdifferentstressstates.Thesetypesofmodelsalsoshowtheevolutionofdamagethroughoutthemodel.Therearetwointerestingthingstonoteaboutthisstudy:sincetheyweretryingtorecreatethe45°fracturepatternthatisinherenttoedgecracking1)theyhadpreviouslyusedafracturecriteriontorecreatethepatternand2)theGursonmodelwasunabletocreatethispattern.OnlywhentheyusedtheGologanumodelwhichassumesellipticalvoidshapes(insteadofsphericalones)weretheyabletorecreatethecrackingcondition.5.2Causesofcracking5.2.1MaterialPropertiesAsmentionedatthebeginningofthischapter,oneoftherequiredconditionsforedgecrackingisinsufficientductility.Therefore,studiesofedgecrackinginrollingoftenmeasuredifferentmaterialpropertiesandmicrostructuresandhowthoseparametersaffectductility.Ductilityisinfluencedbytemperature,grainsize,preferredorientationofthematerial,andcompositionofthematerial(1).Thisisespeciallytruewithsecondphaseinclusionswhichshape,size,andstrengthcanbeinitiationpointsforedgecracking(15).Additionallyinhotductility:temperature,strainrate,composition,andpreviousthermalandmechanicaltreatmentsarealsomajorfactorsaffectingductility(48).Themechanismsofcrackgrowthandthereforeductilityinalloysdifferintensiletesttothatofrolling.Sowhenlookingatmaterialsandtheirtensileresponse,somereviewmustbedoneonhowitvaryingcompositionandmicrostructureactuallyeffectspecificaspectsoftheductilecrackprocess.Forexample,inreviewingAl-4.5Cu-3.4Femetalmatrixcomposites,amaterialwhichcontainsrandomlyoriented“needles”ofanintermetalliccompound,thetensiletestindicatesthatthecrackingofparticlescontrolstheductility,butforrolledsamplesvoidnucleation,growthandlinkagecontroltheductility(52).Atomiccrystallinestructurecanplayapartofcrackinglikelihood.Forexample,inlookingatamagnesiumalloyswhichhasahexagonalclosepackedstructuretheratiooflatticeparameters(c/a)effectsprobabilityofcracking;asthisratiocontrolsthelikelihoodofdifferentslipsystemsbeingactivated.Inthesematerials,itwasfoundthatgrainsizehadaweakercorrelationtocrackingthanthelatticeparameterratio.Thiswascausedbytheinterplayofthesetwolatticeparametersandtheirabilitytolimitandorinduceslippingandtwinning.Inaddition,whenthesematerialstwinnedthecrackingresistancevariedonthetypeoftwinform,makingthiscrackingcasemorecomplicated(53).Theexistenceofinclusionsisnotenoughtodetermineductility,butthecompositionsoftheinclusionsmatters.Forexample,inmachiningsteelsthatcontainingnon-metallicinclusionstoimprovemachinabilitysuchasMnSormetallicinclusionssuchasPb,Bi,andSn,theneedtobalancetheeffectsofinclusioninterfaces,whichbothdecreasestheforcerequiredformachiningandincreasesthelikelihoodofcrackingbyinitiatingvoids,isdifficult.ThisstudywasconductedbycomparinginclusionsformedbyPdandBi,inordertoreducePd-S(lead)use,becauseofthehumanandenvironmentalharmthatitcauses.ItwasfoundthatBi-Ssteelsweremoredifficulttorollcomparedtotheleadbasedones.Apparently,thelowmeltingtemperatureandthepoordeformationofBiwiththematrixacceleratestheformationofcracks;soMnisthoughttobeabettersolutiontotheproblem(54).Otherexamplesofmaterialstudiesincludestudyingcompositionsofausteniticstainlesssteelsafterhotrolling.Thesestudiescontainededgecracksofdifferentsizeandfrequency.Thesecracksweresensitivetothecontentandamountofthedeltaferrite.Itisbelievedthatdeltaferriteslowsthemigrationofaustenitegrainboundaryduringsolidificationwhichleadstocorrugatedboundariesresistanttocrackpropagation,becausetheseboundariesactasnucleationsitestoincreaserecrystallizationrates.Thedistributionofthematerialisinhomogeneous,asthehighestferritecontentislocatedinthevicinityoftheplateedge.Thedeltaferritecontentalsoaffectsthedegreeofedgecracksbothinnumberandinsize(48).Contaminationalsocomesintoplayinthecracking.Forexampleinelectricalsheet,oxidationseemstocreatemorecracksofgreaterseverity(55).Oxidationisalsoaffectedbydifferentaddonmaterials.Forexample,theadditionofsulfurcanleadtothedetrimentalformationofoxidesinsteelbillets.OftentimesreducingtheimpactofoxidationrequiresacertainanamountofMntobeaddedtofree-machiningsteels.Theoxideincreasestheprobabilityofcrackformationbycreatingstressconcentrationpoints(54).Hydrogenembrittlementcanalsocausecrackingissuesindifferentmaterials.InAl-Mgalloystheadditionsofsodiummaketheedgespronetocrackingastheadditionofsodiumisknowntoincreasetheamountofhydrogendissolvedinthematerial.Whilethemechanismofhydrogenembrittlementisunknownforaluminum,crackingnucleationisincreasedbyanincreaseinporosityduetohydrogenandotherdissolvedgasses(46).Notallmaterialcontaminationincreasestheprobabilityofedgecrackinginrolling.Inastudyofhotrollingofalloy5182,sodiumandcalciumcontaminationwerereviewed.Whiletheadditionofsodiumiswellknowntoinducecrackingasdiscussedabove;theeffectofcalciumisunderdebate.Ascalciumislikelytobepickedupduringcasting,astudymonitoringcalcium’seffectoncrackingwasperformed.Todosospecificamountsofbothcalciumwereaddedtoaperfectlycastmaterial.Thealloywiththeelevatedcalciumleveldidnotcrack.Whenbothcalciumandsodiumareaddedtothealloy,attypicalconcentrations,theresultingmaterialhadfewerandlessseverecracksafterrolling(45).Ultimately,thematerialmicrostructureandcompositionprovidesnosimpleinsightintothelikelihoodofcrackingandeachcomponentmustbereviewedseparatelyforitseffectoncrackformation.Tensiletestsareoftenaplacetostart,butdifferentmethodsoftestinghavebeendevelopedtobetterreplicaterollingconditionsthatexist.Manyofthesemethodstrytoviewfractureconditionsatdifferenttriaxialities(especiallynegativeones).Methodsincludetheconicalsplaytest(56)andtensileandcompressiontestingofuniquegeometriesexploredbyKweon(33)andBoaetal.(43).Rollingofmaterialisaprocessandduringthatprocessmicrostructureandstrengthevolveovertime.Whilematerialcompositionisthefirststeptodeterminewhatthematerialwillbecome,itisnecessarytolookattheentireprocessandreviewtheductilityofthematerialthrougheachstageinmetalsheetandbarcreation.Thefirststepinmostrollingprocessesistheinitialcast;whetherthematerialisinitiallycastintoaningotorasheetusingacontinuouscastingmethod.Thisisthefirstplacetocombateedgecracking;ascontrollingmeltingandcastingtechniquescanproduceaworkpiecefreeofsurfaceandcenterplaneweakeningfeaturesandprovideinitialductilityofthesample(57).Foranexampleofweakeningfeatures,Graset.al.(58)studiedtheevolutionofbleedsincontinuouscaststeels.Bleedsaresmallsectionsofregionspackedwithintermetallicparticles.Theseareformedassmallbucklesinthematrixareformed,whichfillwithahighlyenrichedmetalmixture,andthensolidifiedrapidly.Thiscreatesmaterialpocketsinthematrixthataremuchharderthanthesurroundingmatrix.EvenwiththesehardparticlescrackingisnotcertainasfoundinGrasstudy,astheparticlesmustbehardenoughtocausevoidnucleationinthematrix.Inthecasesofingotforming(asquotedforAl-Mgalloysbutaccurateforothers)controllingingotreheating,passschedule,ingotsideprofile,edgescalping,castingtechnology,andingotdefectsdirectlyaffectrollingastheseeffectthecreationofweakeningfeaturesandductility(45).Solidificationcannotbeignoredinrolling.Oftensegregationbandsareformedontheoutsideofingotswhichgetpropagatedtotheedgesofsheetmetalwhentheyarerolled.InonestudybyThomsonandBurman(59),whichlookedatsolidificationbandsonindustrialingotsinAl-Mgalloys,theysawthreetypesofcracks:smallcracksthatwerecontainedwithinthesegregationband,largecracksthatstartedinthesegregationbandbutmovedintomaterialbulk,andlargecracksthatstartedoutsidetheband.Inthisstudythemajorityofcrackswerethesmallkindthatwherecontainedinthesegregationbandandwhilethesesmallercrackswerenotsufficientfortheformationoflargercracksitwaswherethemajorityofcracksinitiated.Aftercastingandhomogenization,theheatflow,intermediateannealing,scaling,lubrication,andconditionsoftherollingmillalleffectmicrostructureandcrackingdevelopmentasthematerialmovesthroughtheprocessofedgecracking(57).Forexamplewhenlookingatcontinuouscastmaterials,whichoftenhasmoremicro-defectsandpoortextureevolutionwithheavydeformation,Grasetal.noticedthatafter50%reductionthematerialmicrostructurebecameuniformasdeformationcausedthegrainstorotateinthematerial(58).Rollingstepsarenotabadthingwhenproperlychosen;ascracksarealsoknowntohealincontinuousdeformationaswell.Temperaturecontrolcannotbeignoredasitcaneffectandcreatevariationsinthemicrostructureofthematerial.Inonestudyofnon-orientedelectricalsteelsheet,Hanetal.showedgrainsizesdifferedalongthesheetbecauseofthetemperatureeffectsduringprocessing.Theshortercoolingtimecausedelongatedgrainsintheedgeregion;whilethelongercoolingtimeallowedformoredynamicrecrystallizationtooccurandcausedequiaxedgrainsinthecenteroftheplate.Thelargergrains(andlessenedductility)ontheedgescausedcrackingmorereadilyherethaninthecenteroftheplate(55).AnotherexampleisinanAlcompositematerialwhererollingoftenbreaksupparticlesandrefinesthemtoasmallermicrostructurethatbecomesmoreorderedandorientatedalongtherollingdirection,improvingthestrengthandothermechanicalpropertiesofthematerial(52).5.2.2CreationofTensileEdgeStressesEventhoughrollingisoftenmodeledasaplanestrainprocess,anedgeregionexistswithstressesvaryingacrossthewidthoftherolledmaterial.Withoutmodelingthissection,theunevenlateraldeformationwhichleadstoedgecrackingcannotbestudied(30).Inthisregion,lateralflowcreatesagradualdropoftheinterfacepressureclosetotheedges.Herethematerialdoesdeformlongitudinallybutonlybecauseitisattachedtothebulkofthestrip.Inthisareayieldingoccurswithacombinedeffortofbothcompressiveandsecondarytensilestresses(57).Thesestressesoccuronthefreeedgeaftertherollbitewithamaximumatthecentralsymmetryplane.Notonlydothesetensilestressescauseinhomogeneousdeformationthatresultinconcaveandconvexedgeprofileswhichcaninducestrongertensileforces,butthesetensilestressesaretheonlywayforvoidgrowthtooccur(30).Becausetherestofthestripisincompression,damageisusuallyconfinedtotheedgeregion.Thecreationandtheeffectoftheseedgeswillbediscussedingreaterdetailinthenextchapter.OnewaytocombatthesetensileforcesisfromSaxl(60)whorecommendedtheuseofedgerestraintbarswhichhelpsmaintainsquareedgesandcontainslateralflowwhichoccur--whichaccordingtohisexperimentsworkedwell.5.2.3FinalcommentsItisimportanttorememberthatedgecrackingrequiresbothconditions:lackofductilityandsecondarytensilestresses.Bothoftheseconditionsplayapartintheedgecrackingandoftentimesthespecificlimitingfactormaybedifficulttodetermine.Forexample,inthecaseofedgeshearingwhichcreatesaburrontheedgeoftheworkpiecethatmayinduceanincreaseintensilestresses.Itwasfoundthatcomparinganannealedshearedsampletoanascutmaterialinasecondpassofrolling,theannealedsteeldidnotcrackliketheascutversiondid.Therefore,inthiscase,theworkhardeningofthematerialcreatedbytheshearingprocessplayedamuchlargerpartinthecrackingthantheshapechange(61).Thetworequirementsforedgecrackingdiscussedinlengthinthischapterarenotalwaysthereasonsquotedinliterature.Someauthorshavechosen(57)tocitethreereasons.Thethirdislistedastherollingofanon-squareedgeshape.Thisisnotspecificallyincludedinthiswork,mainlybecausetheeffectofthetensilestressesisbothcreatedandincreasedbytheoverhangingmaterialanditisdifficulttodecouplethesetwoeffects.Whenreviewingliteratureonthepreventionofedgecrackingitisimportanttokeepthesetworequirementsinmind,assomerollingparameterssparkmuchdebateastowhethertheyaffectedgecrackingornot.Forinstance,passsequencehasbeendebated.WhileDoddsandBoddington(15)saysitdoesnotaffectcracking;ThomsonandBurmanhassomeevidencethatitdoes(59).Whilethisdebatewillnotbesettledinthispaper,perhapsitisbettertoreviewtheseissueswiththetworequirementsofcrackinginmind.Inthenextchapter,someofthedifferentrollingparametersandconditionswillbereviewedwiththehopeofprovidingsomeexplanationastotheireffectsonrolling.

Chapter6ProcessParametersandtheireffectonrollingWhilesecondarytensilestressesandgeometricaleffectsarequotedasbeinglessertoductilityforcausingedgecracking,thispaperwillfocusonthesesecondaryissueswhicharefairlyeasytotestusingamodelingmethod.Forthemostpart,thesefactorsaremuchlessstudiedthanthematerialductilityfactors.Themajorfactorsstudiedherearetemperatureandspeedeffects(whicharerelatedtoductility),widthtothicknessratios,edgeshape,friction,andasymmetricrolling(whichareallgeometricaleffects).Whilethereareotherparametersthateffectcracking,theywillnotbediscussedormodeledhere,asthislistisagoodstartofmanyfactorsbelievedtocontributetoedgecrackingotherthanstraightductility.Othergeometricalfeaturesnotconsideredherebutbelievedtocontributetoedgecrackingisthedeviationfromaparallelrollgap,whichcanleadtoawidevarietyofrollingdefectsincludingedgecracking(15).Inaddition,changesinforwardslipcanalsoaffectthelikelihoodofcracking(47).Figure12-Typicaltriaxialityanddamagelegendforthefollowingsection.Intheremainingsectionsofthechapter,predictionsofedgecrackingaremadethroughthemodelandthedamageparametersetupinChapter1andChapter4,respectively.Generallyspeakingthreedifferentsetsofdatawillbeprovidedforeachcase:vonMisesstress,triaxiality,anddamage.Inallcases,theparametersaresetupwiththesamerangeofvaluesforeachsetofcontourplots.Forthedamageandtriaxialityvalues,thecontourplotisalwayssettomodelfromzerotoone(seeFigure12)unlessotherwisenoted.Inthecaseoftriaxiality,thelowerlimitiszerobecausethedamageisbelievedtoonlyaccumulatewhentriaxialityisapositivevalue;theupperlimitwaschosenbecause,whileitdidnotcoverallthepeaks,itgaveagooddistributionofthevalues.Whilenotaddressedhere,sometimewastakentolookattriaxialitiesfrom-1/3toone,aswell,becauseofthelikelihoodthatvaluesgiveninthisrangecouldcausecrackingasdiscussedinChapter4.InFigure13oneofthesegraphsispresented.Astruewithmostofthesecasesofrollingintherollbite,triaxialityvariesmostlyfrom-1/3tooneinthisregion.So,thereforeaneffortshouldbetakeninthefuturetoincludeorevaluatetheeffectsofthe1/3tozerotriaxialityrangeinthedamagemodel.Figure13-Triaxialitygraphedfrom-1/3toone.Inaddition,itshouldbenotedthatthetriaxialityconditionontheedgeisquitedifferentwhencomparedtothecenter(seeFigure14).Thefocusontheedgeregionismainlybecausethisregionproducespositivetriaxialityandthereforedamage.Whilethedamageparameterisdiscrete,theinterpolationofvalueswhenplottedusingtheABAQUScodeleadstographedvaluesthatcanbeoutsideandinthemiddleoftherange.Typicallyiftheregionislightblueorgreen,thiscorrespondswithonenodeyieldingineachelement.CentersectionEdgesectionFigure14-Triaxialityfordifferentsectionsoftherollbite.Generally(unlessotherwisenoted),thevonMisesstressscalecorrespondstoFigure15.Typicallythevaluesarenotcriticaltothediscussionasmuchasthechangesbetweenthevalues.Figure15-TypicalvonMisesstressscaleusedinthefollowingsection.

第五章邊緣裂紋5.1開(kāi)裂研究的概述邊緣開(kāi)裂通常以去除材料導(dǎo)致邊緣修整或?qū)е鹿ぜ怏w在輥縫中。在某些情況下，大量廢金屬被引述為6%或更肯定了鋁鎂合金。這些邊緣裂紋的產(chǎn)生需要足夠的延展性和二次拉伸應(yīng)力。顯然，軋制的結(jié)果就需要預(yù)測(cè)。邊緣裂紋的研究，更好的理解這個(gè)缺點(diǎn)的概念和相關(guān)原因。因?yàn)檐堉剖枪I(yè)生產(chǎn)方法，實(shí)驗(yàn)關(guān)注的是確保結(jié)果應(yīng)用到生產(chǎn)車(chē)間。這是一個(gè)復(fù)雜的過(guò)程，特別是對(duì)于熱軋，因?yàn)閺氖鹿I(yè)的工廠通常比做實(shí)驗(yàn)的實(shí)驗(yàn)室更大。雖然，總的幾何形狀易于擴(kuò)展，該冶金參數(shù)包括微觀機(jī)構(gòu)和熱變量都沒(méi)有。例如，實(shí)驗(yàn)室軋機(jī)通常比在工業(yè)中使用的那些小得多，因此工件較小，因?yàn)閮烧叩臒豳|(zhì)不同這會(huì)引起問(wèn)題。因此，熱分配不同的情況下大大影響了流動(dòng)應(yīng)力。在實(shí)驗(yàn)室中準(zhǔn)確地模擬軋制，創(chuàng)造了一些獨(dú)特的測(cè)試方法。例如：為了準(zhǔn)確地模擬前滑條件，使用冷軋?jiān)囼?yàn)。這已被用來(lái)容易地研究影響改變前滑條件和接觸條件。在該實(shí)驗(yàn)中，材料通過(guò)使用拉伸試驗(yàn)機(jī)設(shè)備拉出。此裝置僅再現(xiàn)了帶材一側(cè)的接觸條件。在不同試驗(yàn)中，在軋制過(guò)程中對(duì)拉伸應(yīng)力的估計(jì)（與其裂紋擴(kuò)展有關(guān)）。通常一個(gè)網(wǎng)格將蝕刻到材料樣品的一側(cè)或兩塊材料然后鉚接在一起。然后，將這些試驗(yàn)片進(jìn)行軋制，軋制后通過(guò)測(cè)量網(wǎng)格變化來(lái)收集數(shù)據(jù)流。建模后采用回歸應(yīng)力。在研究物質(zhì)因素中，通常使用不同的方法來(lái)揭示材料的微觀結(jié)構(gòu)包括：光學(xué)顯微鏡、透射電子顯微鏡、X射線衍射。這些不僅試圖尋找位置和材料的夾