会员注册 | 登录 | 微信快捷登录 支付宝快捷登录 QQ登录 微博登录 | 帮助中心 人人文库renrendoc.com美如初恋!
站内搜索 百度文库

热门搜索: 直缝焊接机 矿井提升机 循环球式转向器图纸 机器人手爪发展史 管道机器人dwg 动平衡试验台设计

   首页 人人文库网 > 资源分类 > DOC文档下载

外文翻译--残余应力.doc

  • 资源星级:
  • 资源大小:42.50KB   全文页数:9页
  • 资源格式: DOC        下载权限:注册会员/VIP会员
您还没有登陆,请先登录。登陆后即可下载此文档。
  合作网站登录: 微信快捷登录 支付宝快捷登录   QQ登录   微博登录
友情提示
2:本站资源不支持迅雷下载,请使用浏览器直接下载(不支持QQ浏览器)
3:本站资源下载后的文档和图纸-无水印,预览文档经过压缩,下载后原文更清晰   

外文翻译--残余应力.doc

附录ResidualStressesAresidualstressisonethatexistswithoutexternalloadingorinternaltemperaturedifferencesonastructureormachine.Itisusuallyaresultofmanufacturingorassemblingoperations.Sometimesitiscalledinitialstress,andtheoperations,prestressing.Whenthestructureormachineisputintoservice,theserviceloadssuperimposestresses.Iftheresidualstressesaddtotheserviceloadstresses,theyaredetrimentaliftheysubtractfromtheserviceloadstressestheyarebeneficial.Intheplasticdeformationtheexternalforcedoesthemeritturnsintooutsidetheheatexceptthemajorityofextensions,butalsosomesmallpartbythedistortioncantheformstoresupinthedeformationmaterial.Thispartofenergynamedstorageenergy.ThestoragecantheconcretemanifestationwayisMacroscopicresidualstress,microscopicresidualstressandlatticedistortion.Accordingtotheresidualstressbalancescopedifference,usuallymaydivideintoitthreekinds1Firstkindofinternalstress,alsocalledthemacroscopicresidualstress,itiscausesbytheworkpiecedifferentpartmacroscopicdistortionnonuniformity,thereforeitsstressbalancescopeincludingentireworkpiece.Forexample,serveswithJinShubangthecurvingload,thenaboveispulledelongates,underreceivesthecompressionThedistortionsurpasseswhenthelimitofelasticityhashadtheplasticdeformation,afterthentheexternalforceeliminationbyelongatedonesideontheexistencecompressedstress,thelegofrighttriangleisthetensilestress.Thiskindofresidualstresscorrespondsthedistortioncannotbebig,onlyaccountsforalwaysstoresupcanabout0.1.2Secondkindofinternalstress,alsocalledthemicroscopicresidualstress,itisproducesbybetweenthecrystalgrainorthesubgraindistortionnonuniformity.Itssphereofactionandthecrystalgrainsizequite,namelymaintainthebalancebetweenthecrystalgrainorthesubgrain.Sometimesthiskindofinternalstressmayachievetheverygreatvalue,evenpossiblycreatesthemicrocrackandcausestheworkpiecedestruction.3Thirdkindofinternalstress,alsocallsthelatticedistortion.Itssphereofactionisseveraldozenstoseveralhundrednanometers,itisbecausetheworkpieceformsintheplasticdeformationthemassivelatticeflawforexamplevacancy,interstitialatom,dislocationandsooncause.Inthedistortionmetalthestoragecanthemajorpart8090usesinformingthelatticedistortion.Thispartofenergyenhancedthedistortioncrystalenergy,causesittobeatthethermodynamicsnonsteadystate,thereforeithasonekindtomakethedistortionmetaltorestoretothefreeenthalpyloweststablestructureconditionspontaneoustendency,andcausestheplasticdeformationmetalinheatingtimereplyandtherecrystallizationprocess.Onlyafewexamplesofdetrimentalresidualstresseswillbegivenhere.One,intheassemblyofmachinery,occurswhentwoshaftsarenotinlineorareafewthousandthsofaninchoutofparallel,andtheyareforcedintoconnectionbyrigidcouplings.Theresultingstressesintheshaftsbecomereversingstresseswhentheshaftsarerotated.Thecorrection,whenperfectalignmentcannotbeeconomicallyattained,asisfrequentlythecase,istouseflexiblecouplingsofatypenecessaryforthedegreeofmisalignment.Theprecedingcaseoccurswithelasticstressesonly,andtheresidualstressesaremaintainedbybearingconstraints.Inapplicationswheremechanicalworkcausesplasticyielding.stressesremainwhentheconstraintsareremoved.Forexample,theforgingofshaftsandcrankshaftsandthecoolingafterforgingmayinduceresidualstresses,theequilibriumofwhichidchangedinmachining,causingsomewarpingoftheshafts.Itisthencommonpracticetostraightentheshaftsinapressbeforethefinalmachiningoperation.Straighteningrequiresabendingmomentlargeenoughtocausepermanentsetoryielding.Detrimentalresidualstressescommonlyresultfromdifferentialheatingorcooling.Aweldisacommonexample,Theweldmetalandtheareasimmediatelyadjacentare,aftersolidification,atamuchhighertemperaturethanthemainbodyofmetal.Thenaturalcontractionofthemetalalongthelengthoftheweldispartiallypreventedbythelargeadjacentbodyofcoldmetal.Henceresidualtensilestressesaresetupalongtheweld.Ingeneral,localorshallowheatingwhichwouldexpandtheregionorsurface,ifitwerefree,adistancewellbeyondthatwhichtheadjacentlargervolumewillallowcausesyieldingandupsettingoftheheatedmaterial,Thisreadilyoccursbecauseofthereducedyieldstrengthatelevatedtemperatures.Thesamecoolervolumepreventstheupset,heatedregionfromfullycontractingduringitscooling,andtensilegeneralruleisthatthelasttocoolisintension,althoughthereisanexceptionifcertaintransformationsofmicrostructureoccur.Methodsforminimizingorreversingthesestressesincludeannealingforstressreliefandhammerorshotpeeningoftheweakenedsurface.Annealingrequiresheatingmildsteelto11001200F,followedbyslowcooling,Somepreheatingofthepartstobejoinedmayminimizethetensilestressesinwelds.Athinbuthighlyeffectivesurfacelayerofcompressivestressmaybeinducedbycoldrolling,coining,andpeeningprocesses.Itisseenthattheseprocessesworkhardenanouterlayer,thuscausingcompressivestressestoremain,togetherwithminortensilestressesinadjacentinteriorlayers.Sincethecompressivelayerisreadilyobtainedallaround,theseprocessesaresuitableforreversingloadsandrotatingcomponentswherethestressvariesbetweentensionandcompression.Theprocessesmustbecarefullycontrolledinrespecttorollerpressuresandfeeds,shotsizeandspeed,etc.,forwhichextensiveinformationisavailableinengineeringbooksandperiodicals.Coldrollingisappliedprimarilytocylindricalandothershapesthatcanberotated,suchasthreadsandshaftfillets.Theshape,size,andpressureoftherollerandtheyieldstrengthoftheshaftdeterminethedepthofpenetration,whichcanbecalculated.Aspecialfixturemaybeattachedtothecarriagesofalatheandmadetoslowlytraversethedesiredrollingofboltsandscrewshaslongbeenpartofaformingprocessthatnotonlyformsbutstrengthensthethreadsbydeformationandgrainflowaroundtherootsandbyinducingcompressiveresidualstresses.Coiningofholes,alsocalledballdrifting,isamanufacturingprocessofforcingahard,tungstencarbideorAIDI52100steel,slightlyoversizeballthroughaholeinaplate,bushing,ortubingtogivetheholesfinalsizeandafinefinish.Thelengthoftheholemaybefrom1/20to10timesitsdiameter.Themachineisoftensetupforahighproductionofsmallpartswithunskilledlabor.Anincidentalresultisthattheprocessincreaseshardness,hencewearresistance,andinducesaroundtheholeacompressiveresidualstressthatisusuallyadvantageous,asinrollerchainlinks.Thelinksatehighlystressedinpulsatingtensionwithaconcentrationofthestressatandneartheholesurfaces.Withthecompressivestressfromballdrifting,thenettensilestressinserviceisdecreased,andfailureisminimized.Peeningisthemostwidelyusedmethodforprestressingbymechanicallyinducedyielding.Bytheimpactofroundedstrikingobjects,thesurfaceisdeformedinamultitudeofshallowdimples,whichintryingtoexpandputthesurfaceundercompression.Hammerpeening,usuallybyairdriventoolwitharoundedend,isusefulonlimitedareas,suchasaweldinshaftoronareasfoundweakenedbycorrosion,decarburization,orminorfatiguedamage.Withahardsphericalendtothetool,thedepthofthecompressedlayer,whichoccursbelowthesurface,isabouthalfthestrainhardenedregion.Shotpeeningisdoneonsteelsbythehighvelocityimpingementofsmall,round,steelorchilledcastironshotwithdiametersfrom0.007to

注意事项

本文(外文翻译--残余应力.doc)为本站会员(英文资料库)主动上传,人人文库网仅提供信息存储空间,仅对用户上传内容的表现方式做保护处理,对上载内容本身不做任何修改或编辑。 若此文所含内容侵犯了您的版权或隐私,请立即通知人人文库网([email protected]),我们立即给予删除!

温馨提示:如果因为网速或其他原因下载失败请重新下载,重复下载不扣分。

copyright@ 2015-2017 人人文库网网站版权所有
苏ICP备12009002号-5