機械設(shè)計制造及其自動化專業(yè)英語

Unit1MetalsTheuseofmetalshasalwaysbeenakeyfactorinthedevelopmentofthesocialsystemsofman.Oftheroughly100basicelementsofwhichallmatteriscomposed,abouthalfareclassifiedasmetals.Thedistinctionbetweenametalandanonmetalisnotalwaysclear-cut.Themostbasicdefinitioncentersaround[以…為中心]thetypeofbondingexistingbetweentheatomsoftheelement,andaroundthecharacteristicsofcertainoftheelectrons[某種電子]associatedwiththeseatoms.Inamorepracticalway,however,ametalcanbedefinedasanelementwhichhasaparticularpackageofproperties.在人類社會的開展中，金屬的應(yīng)用起著關(guān)鍵性的作用。構(gòu)成物質(zhì)的大約100種根本元素中，大約有一半為金屬。金屬和非金屬之間的區(qū)別不是特別明顯。最根本的定義集中在元素原子間存在的連接形式和與這些原子相關(guān)聯(lián)的電子的某些特性。然而，在實際應(yīng)用中，可以將具有某些特性集合金屬定義為某種元素。Metalsarecrystalline[adj.晶體的]wheninthesolidstateand,withfewexceptions[極少例外](e.g.mercury),aresolidatambient[周圍環(huán)境的]temperatures.Theyaregoodconductorsofheatandelectricityandareopaque[不透明的]tolight.Theyusuallyhaveacomparativelyhighdensity.Manymetalsareductile[柔軟的；易延展的]-thatis,theirshapecanbechangedpermanently[永久地，長期不變地]bytheapplicationofaforcewithoutbreaking.Theforcesrequiredtocausethisdeformationandthoserequiredtobreakorfractureametalarecomparativelyhigh,although,thefractureforcesisnotnearly[=farfrom,muchlessthan]ashighaswouldbeexpectedfromsimpleconsiderationoftheforcesrequiredtotearaparttheatomsofthemetal.除了少數(shù)例外金屬在常溫下是固態(tài)的。它們是熱和電的良導(dǎo)體，不透光。它們往往具有較高的密度。許多金屬具有延展性，也就是說，在不被破壞的情況下它們的形狀在外力的作用下可以發(fā)生變化。引起永久變形所需的力和最終使金屬斷裂所需的力相當大，盡管發(fā)生斷裂所需的力遠沒有像所預(yù)期的撕開金屬原子所需的力那么大。Oneofthemoresignificantofthesecharacteristicsfromourpointofviewisthatofcrystallinity[crystallinity[,krist?'lin?ti]].Acrystallinesolidisoneinwhichtheconstituentatomsarelocatedinaregularthree-dimensionalarrayasiftheywerelocatedatthecornersofthesquaresofathree-dimensionalchessboard[n.棋盤].Thespacingoftheatomsinthearrayisofthesameorderasthesizeoftheatoms,theactualspacingbeingacharacteristicoftheparticularmetal.Thedirectionsoftheaxesofthearraydefinetheorientationofthecrystalinspace.Themetalscommonlyusedinengineeringpracticearecomposedofalargenumberofsuchcrystals,calledgrains[晶粒].Inthemostgeneralcase[一般情況下],thecrystalsofthevariousgrainsarerandomlyorientedinspace.Thegrainsareeverywhereinintimatecontactwithoneanotherandjoinedtogetheronanatomicscale.Theregionatwhichtheyjoinisknownasagrainboundary.從我們的觀點來看，在所有的特性中結(jié)晶性是最重要的。結(jié)晶體是這樣一種結(jié)構(gòu)，組成它的原子定位在規(guī)那么的三維排列中，仿佛位于三維棋盤的方格的角上。原子間距隨著原子大小呈規(guī)律性變化，原子間距是金屬的一種特性。三維排列的軸線決定了晶體在空間中的方向。在工程實踐中應(yīng)用的金屬由大量的晶體組成，這些晶體稱之為晶粒。在大多數(shù)情況下，晶粒在空間中是自由排列的。在原子范圍內(nèi)，晶粒之間相互接觸緊密結(jié)合。晶粒之間連接區(qū)域被稱為晶界。Anabsolutelypuremetal(i.e.[也就是]onecomposedofonlyonetypeofatom)hasneverbeenproduced.Engineerswouldnotbeparticularlyinterestedinsuchametalevenifitweretobeproduced,becauseitwouldbesoftandweak.Themetalsusedcommerciallyinevitably[不可防止地]containsmallamountsofoneormoreforeignelements,eithermetallic[metallic[mi't?lik,me-]adj.金屬的，含金屬的]ornonmetallic.Theseforeignelementsmaybedetrimental[有害的],theymaybebeneficial,ortheymayhavenoinfluenceatallonaparticularproperty.Ifdisadvantageous,theforeignelementstendtobeknownasimpurities[雜質(zhì)].Ifadvantageous,theytendtobeknownasalloyingelements[合金元素].Alloyingelementsarecommonlyaddeddeliberately[成心地，蓄意地]insubstantial[adj.大量的；實質(zhì)的；內(nèi)容充實的substantialevidence:實〔質(zhì)〕體證據(jù)|實質(zhì)性證據(jù)|實質(zhì)證據(jù)substantialorder:大宗訂單|大訂單]amountsinengineeringmaterials.Theresultisknownasanalloy.絕對純潔的金屬從來也沒有被生產(chǎn)出來過。即使絕對純潔的金屬可以生產(chǎn)出來，工程師們對它們也并不會特別感興趣，因為它們很柔軟、脆弱。實際應(yīng)用中的金屬往往都包含著一定數(shù)量的一種或多種外來金屬或非金屬元素，這些外來元素可能是有害的也可能是有益的或者它們對某種特定的屬性沒有影響。如果是有害的，這些外來元素被認為是雜質(zhì)。如果是有益的，它們被認為是合金元素。在工程材料中往往被特意地參加一定數(shù)量的合金元素。得到的物質(zhì)被叫做合金。Thedistinctionbetweenthedescriptors“metal”and“alloy”isnotclear-cut.Theterm“metal”maybeusedtoencompassbothacommerciallypuremetalanditsalloys.Perhapsitcanbesaidthatthemoredeliberatelyanalloyingadditionhasbeenmadeandthelargertheamountoftheaddition,themorelikelyitisthattheproductwillspecificallybecalledanalloy.Inanyevent[無論如何，不管怎樣],thechemicalcompositionofametaloranalloymustbeknownandcontrolledwithincertainlimitsifconsistent[一致的]performanceistobeachievedinservice.Thuschemicalcompositionhastobetakenintoaccountwhendevelopinganunderstandingofthefactorswhichdeterminethepropertiesofmetalsandtheiralloys.金屬和合金區(qū)別不大。金屬這個詞可以包括工業(yè)用純金屬和它的合金。也許可以這樣說，合金元素越成心的被添加，被添加的合金元素的量越大，那么生產(chǎn)出來的產(chǎn)品越傾向于被稱之為合金。不管怎樣，如果想使一種金屬或合金在使用中表現(xiàn)出穩(wěn)定一致的特性，在其中添加何種化學(xué)成分，它的量多大都應(yīng)該在控制范圍之內(nèi)。因此，當想了解決定金屬和合金性質(zhì)的因素時，應(yīng)充分考慮它們的化學(xué)組成。Ofthe50orsometallicelements,onlyafewareproducedandusedinlargequantitiesinengineeringpractice.Themostimportantbyfarisiron[鐵],onwhicharebasedtheubiquitous[普遍的，無處不在的]steelsandcastirons(basicallyalloysofironandcarbon).Theyaccountforabout98%byweightofallmetalsproduced.Nextinimportanceforstructuraluses(thatis,forstructuresthatareexpectedtocarryloads)arealuminum[鋁],copper,nickel,andtitanium[[tai'teini?m,ti-]n.[化]鈦〔金屬元素〕].Aluminumaccountsforabout0.8%byweightofallmetalsproduced,andcopperabout0.7%,leavingonly0.5%forallothermetals.Asmightbeexpected,theremaindersareallusedinrather[相當]specialapplications.Forexample,nickelalloysareusedprincipally[主要地]incorrosion-andheat-resistantapplications,whiletitaniumisusedextensively[廣泛地]intheaerospaceindustrybecauseitsalloyshavegoodcombinationsofhighstrengthandlowdensity.Bothnickelandtitaniumareusedinhigh-cost,high-qualityapplications,and,indeed,itistheirhighcostthattendstorestricttheirapplication.在50種左右的金屬元素里，工程實踐中只有少數(shù)金屬被大量生產(chǎn)和使用。到目前為止最重要的是鐵，以它為根底構(gòu)成了處處可見的鋼和鑄鐵?！仓饕设F和碳構(gòu)成的合金〕它們的重量占所有生產(chǎn)出來的金屬重量的98%。在結(jié)構(gòu)應(yīng)用〔也就是說，可以承受載荷的結(jié)構(gòu)〕中居于其次位置的是鋁、銅、鎳和鈦。在所有的金屬產(chǎn)量中，鋁占0.8％，銅占0.7％，剩下的占0.5％。剩下的金屬用于相對特殊的用途。例如，鎳合金主要用于抗磨損和耐高溫的用途，由于鈦合金具有高強度和低密度的綜合特性，鈦被廣泛應(yīng)用于航空工業(yè)中。鎳合鈦有高本錢和高質(zhì)量的使用特性，事實上，它們高的本錢限制了它們的應(yīng)用。Wecannotdiscussthesemoreesoteric[adj.秘傳的；限于圈內(nèi)人的；難懂的EsotericBuddhism:密宗|密宗，特別是指西藏的喇嘛教。]propertieshere.Sufficeittosay[Sufficeittosaythatyouloveme.只要說你愛我就夠了。Sufficeittosaythatthegunwashis.只需說這槍是他的就夠了。]thatawholecomplexofpropertiesinadditiontostructuralstrengthisrequiredofanalloybeforeitwillbeacceptedinto,andsurvivein,engineeringpractice.Itmay,forexample,havetobestrongandyethavereasonablecorrosionresistance;itmayhavetobeabletobefabricatedbyaparticularprocesssuchasdeepdrawing,machining,orwelding;itmayhavetobereadily[容易地]recyclable;anditscostandavailabilitymaybeofcriticalimportance.我們不能在這里討論這些深奧的特性。在合金材料被采用和應(yīng)用于工程實際之前，掌握其結(jié)構(gòu)強度和它的綜合性質(zhì)就夠了。舉例來說，它可以強度很高，并且有好的耐磨性；它可以被例如拉伸加工，機械加工，或焊接等特殊工藝來加工出來；它可以被循環(huán)利用；它的本錢和實用性是首要的。Unit2SelectionofConstructionMaterialsThereisnotagreatdifferencebetween“this”steeland“that”steel;allareverysimilarinmechanicalproperties.Selectionmustbemadeonfactorssuchashardenability[[,hɑ:d?n?'bil?ti]n.可硬化性；淬硬性],price,andavailability[[?,veil?'bil?ti]是產(chǎn)品在被調(diào)用時能夠運行〔即未處于失效或修復(fù)狀態(tài)〕的概率。此量度考慮了產(chǎn)品的可靠性〔多久會失效〕和可用性〔多久能被修復(fù)〕。],andnotwiththeideathat“this”steelcandosomethingnoothercandobecauseitcontains2percentinsteadof1percentofacertainalloyingelement,orbecauseithasamysterious[[mi'sti?ri?s]adj.神秘的；不可思議的；難解的](神秘的，不可思議的)name.Atremendous[adj.極大的，巨大的；驚人的]rangeofpropertiesisavailableinanysteelafterheattreatment;thisisparticularlytrueofalloysteels. 在鋼之間沒有太大的區(qū)別；所有的鋼在機械性能方面都是近似的。它們的選取標準是諸如脆硬性，價格，和可用性等。不僅僅是因為這種鋼含有2％的合金元素另一種鋼含有1％而使前者具有了后者沒有的某些能力，或者是某種鋼具有神奇的名字。經(jīng)過熱處理后，任何一種鋼都具有大范圍的特性；這種性質(zhì)同樣在合金鋼中存在。 Considerationsinfabrication(制造)Thepropertiesofthefinalpart(hardness,strength,andmachinability[[m?,?i:n?'bil?ti]n.切削性；機械加工性]),ratherthanpropertiesrequiredbyforging,governtheselectionofmaterial.Thepropertiesrequiredforforginghaveverylittlerelationtothefinalpropertiesofthematerial;therefore,notmuchcanbedone[無論做什么都是白費力，都改變不了既定的現(xiàn)實]toimproveitsforgeability.Higher-carbonsteelisdifficulttoforge.Largegrainsizeisbestifsubsequentheattreatmentwillrefinethegrainsize.關(guān)于加工的考慮 最后零件的特性〔硬度、強度和可加工性〕而不是鍛造特性決定了材料的選擇?？慑懶耘c材料的最后特性聯(lián)系不大；因此，提高金屬的可鍛造性價值不大。高碳鋼很難鍛造。如果在隨后的熱處理過程進行細化，大尺寸晶粒是最好的。Low-carbon,nickel-chromium(鉻)steelsarejustabout[幾乎，差不多j]asplasticathightemperatureunderasingle520-ft·lb(1ft·lb=1.35582J)blow[atasingleblow=atoneblowatasingleblow:一下子|一舉|一擊]asplainsteelsofsimilarcarboncontent.Nickeldecreasesforgeabilityofmedium-carbonsteels,buthaslittleeffectonlow-carbonsteels.Chromiumseemstohardensteelatforgingtemperatures,butvanadium[](釩)hasnodiscernible(可區(qū)分的)effect;neitherhasthemethodofmanufactureanyeffectonhigh-carbonsteel. 在高溫下低碳，鎳鉻合金鋼在受到520-ft·lb的沖擊下表現(xiàn)出與相同碳含量普通鋼幾乎同樣的塑性。鎳減少了中碳鋼的可鍛性，但對低碳鋼影響不大。鉻在鍛造溫度下時使鋼硬化，但釩沒有明顯的效果；兩種加工方法對高碳鋼沒有影響。FormabilityThecold-formabilityofsteelisafunction(功能)ofitstensilestrengthcombinedwithductility.Thetensilestrengthandyieldpointmustnotbehighortoomuchworkwillberequiredinbending〔彎曲〕;likewise〔同樣地〕,thesteelmusthavesufficient〔充足的〕ductilitytoflowtotherequiredshapewithoutcracking.Theforcerequireddependsontheyieldpoint,becausedeformationstartsintheplasticrangeabovetheyieldpointofsteel.Work-hardeningalsooccurshere,progressively〔日益增多地〕stiffening〔使變硬〕themetalandcausingdifficulty,particularly〔獨特的，顯著的〕inthelow-carbonsteels. 成形 鋼的冷成形是它的拉伸強度和延展性相結(jié)合的結(jié)果。拉伸強度和屈服點不能太高否那么在發(fā)生彎曲時需要做很多工作；與之相類似，鋼應(yīng)該有高延展性，使其在沒有斷裂的情況下成形。加工力的大小取決于屈服點，因為鋼在屈服點之上才開始變形。與此同時，加工硬化也同時發(fā)生，金屬變得越來越硬，增加加工難度，尤其在低碳鋼中容易發(fā)生。Itisquiteinterestinginthisconnection〔關(guān)于這一點，就此而論〕todiscoverthatdeepdrawscansometimesbemadeinonerapidoperationthatcouldnotpossiblybedoneleisurely〔緩慢地，沉著不迫地〕intwoorthree.Ifadrawishalfmadeandthenstopped,itmaybenecessarytoanneal〔退火〕beforeproceeding,thatis〔換句話說〕,ifthepieceisgiventimetowork-harden.Thismaynotbeascientificstatement,butitisactuallywhatseemstohappen.在這方面，相當有趣的是你將發(fā)現(xiàn)有時可通過一次快速加載完成大拉伸，但以緩慢的方式兩三次加載卻不能實現(xiàn)。如果拉伸進行了一半就停止了，那么在再加工之前應(yīng)先退火，也就是說工件是否有時間進行加工硬化。這不是一種科學(xué)的表達方法，但確實是發(fā)生了。 InternalstressesColdformingisdoneabovetheyieldpointinthework-hardeningrange,sointernalstressescanbebuiltupeasily.Evidenceofthisisthespringback〔回彈〕astheworkleavestheformingoperationandthewarpage〔翹曲，扭曲〕inany〔任何一種〕subsequentheattreatment.Evenasimplewashermight,byvirtueof[由于，憑借](依靠)theinternalstressesresultingfrompunching〔沖壓〕andthenflattening〔整平〕,warp〔彎曲〕severely〔嚴格地，劇烈地〕duringheattreating.〔virtuen.德行,美德,貞操,優(yōu)點,成效,效力,英勇believedinthevirtueofprayer.相信祈禱的力量 內(nèi)應(yīng)力在高于屈服點的加工硬化區(qū)進行冷加工很容易產(chǎn)生內(nèi)應(yīng)力。例如工件停止成型加工后會發(fā)生回彈，在隨后的熱處理后，工件會發(fā)生翹曲。即使是一個簡單的墊圈，由于打孔和隨后的平整加工中產(chǎn)生內(nèi)應(yīng)力，也會在熱處理中呈現(xiàn)嚴重的翹曲。Whendoubtexistsasto〔關(guān)于〕whetherinternalstresseswillcausewarpage,apiececanbecheckedbyheatingittoabout1100andthenlettingitcool.Ifthereareinternalstresses,thepieceislikelyto〔可能〕deform.Piecesthatwillwarpseverelywhilebeingheatedhavebeenseen,yet〔然而〕theheat-treater[熱處理爐]wasexpectedto[有望做某事；被期待做某事]putthemthrough[putthrough完成]andbringthemoutbetterthantheywereinthefirstplace.當是否內(nèi)應(yīng)力會引起翹曲的疑心存在時，可以通過將工件加工至1100然后進行冷卻來驗證。如果存在內(nèi)應(yīng)力，工件會發(fā)生變形。經(jīng)過熱處理的工件像我們看到的那樣會發(fā)生嚴重的翹曲，但是我們?nèi)匀幌Ｍぜ蝗拥綗崽幚頎t中被處理，這樣好過它存在內(nèi)應(yīng)力的狀態(tài)。 WeldingThemaximumcarboncontentofplaincarbonsteelsafeforweldingwithoutpreheatingorsubsequentheattreatmentis0.3%.higher-carbonsteelisweldedeveryday,butonlywithproperpreheating.Therearetwoimportantfactors:theamountofheatsthatisputin;therateatwhichitisremoved. 焊接不需要預(yù)熱或之后進行熱處理就能平安焊接的最高碳含量為0.3％。高碳鋼通過適宜的預(yù)熱通常也可焊接。有兩點值得注意：吸收熱量的多少；移除速度。Weldingataslowerrateputsinmoreheatandheatsalargevolumeofmetal,sothecoolingrateduetolossofheattothebasemetalisdecreased(減少).Apreheatwilldothesamething.Forexample,sae4150steel,preheatedto600or800,canbeweldedreadily〔容易地〕.Whentheflameorarcistakenawayfromtheweld,thecoolingrateisnotsogreat,owingtothehighertemperatureofthesurroundingmetalandslowercoolingresults.Eventhemostrapidair-hardening〔風硬鋼〕steelsareweldableifpreheatedandweldedataslowrate. 低速焊接帶來了更多的熱量，這對金屬的大量體積進行了加熱，所以冷卻速度降低。預(yù)熱可以取得與之相當?shù)男Ч?。例如當被預(yù)熱至或時可以很好的焊接。由于周圍金屬的較高溫度，當焊接弧移開焊接點后，冷卻速度不會太快，產(chǎn)生了低速冷卻的結(jié)果。即使是冷作硬化速度最快的金屬也可以通過預(yù)熱和慢速焊接到達良好的焊接效果。 MachinabilityMachinability〔機械加工性能〕meansseveralthings.Toproductionmenitgenerallymeansbeingabletoremovemetalatthefastestrate,leavethebestpossiblefinish,andobtainthelongestpossibletoollife.Machinabilityappliesto〔應(yīng)用于〕thetool-work〔工具，零件〕combination.可加工性可加工性意味著幾件事情。對于加工者來說，它意味著可以快速的移除金屬，取得最好的加工效果，得到最長的刀具壽命。可加工性是刀具和零件的結(jié)合。Itisnotdeterminedbyhardness〔硬度〕alone,butbythetoughness〔韌性〕,microstructure,chemicalcomposition〔成分〕,andtendency〔傾向〕ofametaltohardenundercoldwork.Inthemisleadingexpression“toohardtomachine”,theword“hard”isusuallymeanttobesynonymous〔同義的〕with“difficult”.Manytimesamaterialisactuallytoosofttomachinereadily.Softnessandtoughnessmaycausethemetaltotear〔撕裂〕andflowaheadofthecuttingtoolratherthancutcleanly.Metalthatareinherently〔天性地，固有地〕softandtougharesometimesalloyedtoimprovetheirmachinabilityatsomesacrifice[['s?krifais]n.犧牲；祭品；供奉A(yù)llgainsaremadeatsomesacrifice.Mostpeoplemightchoosetodivertthecourseofthetrain,andsacrificeonlyonechild.]〔犧牲〕inductility.Examplesareuseoflead〔鉛〕inbrass〔黃銅〕andofsulfur[['s?lf?]]〔硫磺〕insteel.加工性不僅僅只由硬度決定，它還由韌性，微觀結(jié)構(gòu)，化學(xué)成分和在冷加工下金屬所呈現(xiàn)的硬化特性所決定。在容易混淆的表示“難加工”中，“hard”與“difficult”同義。許多時候，因為材料過軟而難于穩(wěn)定加工。材料柔軟性和韌性能夠產(chǎn)生金屬撕裂，使金屬在完成切削前流動至刀具前端。柔軟的金屬往往會被參加合金從而犧牲它的延展性來提高加工性能。如黃銅中參加鉛鋼中參加硫磺。Machinabilityisatermusedtoindicatetherelative〔比擬的〕ease〔不費力〕withwhichamaterialcanbemachinedbysharpcuttingtoolsinoperationssuchasturning〔車〕,drilling〔鉆〕,milling〔銑〕,broaching[['b?ut?i?]n.拉削；拉孔；推削；擴孔v.鉆孔；開口]〔拉削〕,andreaming〔鉸〕.機械加工性能是在指對工件材料使用刀具進行諸如車、鉆、銑、拉削、鉸加工時的難易程度。Inthemachiningofmetal,themetalbeingcut,thecuttingtool,thecoolant,theprocessandtypeofmachinetool〔機床〕,andthecuttingconditionsallinfluencetheresults.Bychanginganyoneofthesefactors,differentresultswillbeobtained.Thecriterion[[krai'ti?ri?n]n.〔批評判斷的〕標準；準那么；標準；準據(jù)]〔標準〕uponwhichtheratings〔等級〕listedarebased(等級評定的標準)istherelative[adj.相對的；有關(guān)系的；成比例的]volumeofvarious〔不同種〕materialsthatmayberemovedbyturningunderfixedconditionstoproduceanarbitrary〔任意的〕fixedamountoftoolwear.在對金屬進行加工時，被切削的金屬，切削刀具，冷卻液，使用的機床的種類，切削條件均影響著切削效果。改變?nèi)魏我环N均會產(chǎn)生不同的切削效果。切削效果評定的準那么是：車削時在固定的切削條件下產(chǎn)生一定量的刀具磨損時，被加工試件相應(yīng)的材料去除量。Unit3MechanicalPropertiesofMaterialsThematerialpropertiescanbeclassifiedintothreemajorheadings:(i)Physical,(ii)Chemical,(iii)Mechanical.Physicalproperties Densityorspecificgravity,moisture[['m?ist??]n.水分；濕度；潮濕；降雨量]content,etc.,canbeclassifiedunderthiscategory.材料特性主要分為三類：(i)物理特性，(ii)化學(xué)特性，(iii)力學(xué)性能。物理特性 密度或特定的重力，濕度等都屬于此范疇。Chemicalproperties Manychemicalpropertiescomeunder[歸入]thiscategory.Theseincludeacidity[[?'sid?ti]n.酸度；酸性；酸過多；胃酸過多]oralkalinity[[,?lk?'lin?ti]n.堿度；堿性],reactivity[化學(xué)反響的活性]andcorrosion.Themostimportantoftheseiscorrosionwhichcanbeexplainedinlayman’stermsastheresistanceofthematerialtodecay[腐朽，腐爛]whileincontinuoususeinaparticularatmosphere.化學(xué)特性 許多化學(xué)特性都歸入到這個范疇。其中包括酸性或堿性，活性和耐腐蝕性。而在這其中最重要的是耐腐蝕性，通俗的解釋是材料在特定大氣中長期使用時，抵抗腐蝕的能力。Mechanicalproperties Mechanicalpropertiesincludethestrengthpropertiesliketensile,compression,shear,torsion,impact,fatigueandcreep[n.爬行；毛骨悚然的感覺；諂媚者vi.爬行；蔓延；慢慢地移動；起雞皮疙瘩creep:蠕變|潛變|漸變creepstrength:蠕變強度|潛變強度|蠕變?nèi)醵萩reepstrain:蠕變變形|蠕動應(yīng)變|蠕變應(yīng)變].Thetensilestrengthofamaterialisobtainedbydividingthemaximumload,whichthespecimenbearsbytheareaofcross-sectionofthespecimen.力學(xué)特性 力學(xué)特性包括諸如拉伸，壓縮，剪切，扭轉(zhuǎn)，沖擊，疲勞和蠕變等強度特性。一種材料的拉伸強度由試件承載的最大載荷除以試件的橫截面積得到。 ThisisacurveplottedbetweenthestressalongtheY-axis(ordinate)andthestrainalongtheX-axis(abscissa[[?b'sis?]n.[數(shù)]橫坐標；橫線])inatensiletest.Amaterialtendstochangeorchangesitsdimensionswhenitisloaded,dependinguponthemagnitude[大小]oftheload.Whentheloadisremoveditcanbeseenthatthedeformationdisappears.Formanymaterialsthisoccursupto[一直到；相當于；忙于，在做；由決定的]acertainvalueofthestresscalledtheelasticlimit.Thisisdepictedbythestraightlinerelationshipandasmalldeviation[[,di:vi'ei??n]n.偏差；誤差；背離averagedeviation:平均偏差|平均差|平均偏差，均差]thereafter,inthestress-straincurve.如下圖為在拉伸試驗中沿著X軸〔橫軸〕的應(yīng)變和沿著Y軸〔縱軸〕的應(yīng)力之間的關(guān)系曲線。材料在加載時，隨著載荷大小的變化，尺寸會發(fā)生改變。當卸載時，變形消失。對于許多材料來說，上述情況發(fā)生的應(yīng)力極限值稱為彈性極限。在應(yīng)力-應(yīng)變曲線中，直線關(guān)系和隨后的小小的彎曲描述了上述的加載和卸載。Withintheelasticrange,thelimitingvalueofthestressuptowhichthestressandstrainareproportional,iscalledthelimitofproportionality.Inthisregion,themetalobeysHooke’slaw,whichstatesthatthestressisproportionaltostrainintheelasticrangeofloading(thematerialcompletelyregainsitsoriginaldimensionsaftertheloadisremoved). Intheactualplottingofthecurve,theproportionalitylimitisobtainedataslightlylowervalueoftheloadthantheelasticlimit.Thismaybeattributedtothetime-lagintheregainingoftheoriginaldimensionsofthematerial.Thiseffectisveryfrequentlynoticedinsomeno-ferrous[有色金屬][鐵的，含鐵的]metals.在彈性范圍內(nèi)，應(yīng)力應(yīng)變成比例的應(yīng)力極限值稱為比例極限。在這個區(qū)域中，金屬服從胡克定律—闡述了在加載的彈性范圍內(nèi)，應(yīng)力和應(yīng)變成比例關(guān)系〔材料在卸載后，能夠完全回復(fù)它原來的尺寸〕。在曲線的實際繪制中，比例極限值要稍微比彈性極限值低。這可能是由于材料回復(fù)原尺寸需要的時間延遲。這種現(xiàn)象在一些有色金屬中常常出現(xiàn)。 Whileironandnickelexhibit[[iɡ'zibit]n.展覽品；證據(jù)；展示會vt.展覽；顯示；提出〔證據(jù)等〕vi.展出；開展覽會]clearrangesofelasticity,copper,zinc〔鋅〕,tin〔錫〕,etc,arefoundtobeimperfectly[[im'p?:fiktli]adv.有缺點地；不完美地；未完成地]elasticevenatrelatively〔相當?shù)亍砽owvaluesofstresses.Actuallytheelasticlimitisdistinguishable〔可區(qū)分的〕fromtheproportionality〔比例性〕limitmoreclearlydependinguponthesensitivity〔靈敏性〕ofthemeasuringinstrument.鐵和鎳存在明顯的彈性范圍，銅，鋅，錫等即使在相當?shù)偷膽?yīng)力值下彈性也表現(xiàn)得不是很充分。實際上依靠測試儀器的精確性可以使比例極限和彈性極限區(qū)分得更清晰。 Whentheloadisincreasedbeyondtheelasticlimit,plasticdeformationstarts.Simultaneouslythespecimengetswork-hardened.Apointisreachedwhen〔這時〕thedeformationstartstooccurmorerapidlythantheincreasingload.ThispointiscalledtheyieldpointQ.themetalwhichwasresistingtheloadtillthen,startstodeformsomewhatrapidly,i.e.,yield.Theyieldstressiscalledyieldlimit.當在彈性極限之上增大載荷時會產(chǎn)生塑性變形。同時，試件發(fā)生加工硬化。到達某點后變形的速度快于載荷增加的速度。這一點叫做屈服極限點。一開始一直在抵抗載荷的金屬在這一點后開始迅速地發(fā)生形變，也就是，屈服。屈服應(yīng)力叫做屈服極限。 TheelongationofthespecimencontinuesformQtoSandthentoT.thestess-strainrelationinthisplasticflowperiodisindicatedbytheportionQRSTofthecurve.AtTthespecimenbreaks,andthisloadiscalledthebreakingload.ThevalueofthemaximumloadSdividedbytheoriginalcross-sectionalareaofthespecimenisreferredtoastheultimatetensilestrengthofthemetalorsimplythetensilestrength.試件從Q到S在到T不斷地延長。在這個塑性流動期間的應(yīng)力-應(yīng)變關(guān)系表示為曲線上的QRST段。在T點試件斷裂，此時的載荷稱為斷裂載荷。最大荷載值S除以試件的橫截面積為金屬的最大拉伸強度或簡單地稱為拉伸強度。Logicallyspeaking,oncetheelasticlimitisexceeded,themetalshouldstartstoyield,andfinallybreak,withoutanyincreaseinthevalueofstress.Butthecurverecordsanincreasedstressevenaftertheelasticlimitisexceeded.Tworeasonscanbegivenforthisbehavior:thestrainhardeningofthematerial;thediminishing[[di'mini?i?]adj.逐漸縮小的；衰減的v.減少；遞減；衰減；削弱的權(quán)勢]cross-sectionalareaofthespecimen,sufferedonaccountof[Onaccountoftheweather,wehadtocanceltheprojectedouting.]theplasticdeformation.邏輯上來說，一旦超過彈性極限，金屬應(yīng)該就會屈服直至最后斷裂，在應(yīng)力值上應(yīng)該沒有增加。但是實際的曲線卻記錄了在超過彈性極限后的增加了的應(yīng)力。這種現(xiàn)象的發(fā)生可能有兩種原因：1材料的應(yīng)變強化；2由于塑性變形引起的試件橫截面積的縮小。 Themoreplasticdeformationthemetalundergoes,theharderitbecomes,duetowork-hardening.Themorethemetalgetselongatedthemoreitsdiameter(andhence,cross-sectionalarea)isdecreased.ThiscontinuesuntilthepointSisreached.由于加工硬化，金屬在發(fā)生塑性變形時會變得越來越硬。金屬拉伸越長它的直徑越小。這種現(xiàn)象一直持續(xù)到曲線上的S點。AfterS,therateatwhichtheredutioninareatakesplace,exceedstherateatwhichthestressincreases.Strainbecomessohighthattheredutioninareabeginstoproducealocalizedeffectatsomepoint.Thisiscalledneching.超過S點后，面積減少的速度超過了應(yīng)力增加的速度。應(yīng)變變得很大，面積的減少在某些點產(chǎn)生了局部效應(yīng)。叫做頸縮。 Reductionincross-sectionalareatakesplaceveryrapidly;sorapidlythattheloadvalueactullydrops.ThisisindicatedbyST.FailureoccursatthispointT. Thenpercentageelongationandreductioninareaindicatetheductilityorplasticityofthematerial:Whereandaretheoriginalandthefinallengthofthespecimen;andaretheoriginalandthefinalcross-sectionalarea.橫截面積減小的速度非?？欤灰灾劣趯嶋H上載荷降低。 伸長率和面積減少率表示了材料的延展性。Uint5DesignofmachineandmachineelementsMachinedesignMachinedesignistheartofplanningordevisingneworimprovedmachinestoaccomplishspecificpurposes.Ingeneral,amachinewillconsistofacombinationofseveraldifferentmechanicalelementsproperlydesignedandarrangedtoworktogether,asawhole.Duringtheinitialplanningofamachine,fundamentaldecisionsmustbemadeconcerningloading,typeofkinematicelementstobeused,andcorrectutilizationofthepropertiesofengineeringmaterials.Economicconsiderationsareusuallyofprimeimportancewhenthedesignofnewmachineryisundertaken.Ingeneral,thelowestover-allcostsaredesigned.Considerationshouldbegivennotonlytothecostofdesign,manufacturethenecessarysafetyfeaturesandbeofpleasingexternalappearance.Theobjectiveistoproduceamachinewhichisnotonlysufficientlyruggedtofunctionproperlyforareasonablelife,butisatthesametimecheapenoughtobeeconomicallyfeasible.Theengineerinchargeofthedesignofamachineshouldnotonlyhaveadequatetechnicaltraining,butmustbeamanofsoundjudgmentandwideexperience,qualitieswhichareusuallyacquiredonlyafterconsiderabletimehasbeenspentinactualprofessionalwork.DesignofmachineelementsTheprinciplesofdesignare,ofcourse,universal.Thesametheoryorequationsmaybeappliedtoaverysmallpart,asinaninstrument,or,toalargerbutsimilarpartusedinapieceofheavyequipment.Innoease,however,shouldmathematicalcalculationsbelookeduponasabsoluteandfinal.Theyareallsubjecttotheaccuracyofthevariousassumptions,whichmustnecessarilybemadeinengineeringwork.Sometimesonlyaportionofthetotalnumberofpartsinamachinearedesignedonthebasisofanalyticcalculations.Theformandsizeoftheremainingpartsaredesignedonthebasisofanalyticcalculations.Ontheotherhand,ifthemachineisveryexpensive,orifweightisafactor,asinairplanes,designcomputationsmaythenbemadeforalmostalltheparts.Thepurposeofthedesigncalculationsis,ofcourse,toattempttopredictthestressordeformationinthepartinorderthatitmaysagelycarrytheloads,whichwillbeimposedonit,andthatitmaylastfortheexpectedlifeofthemachine.Allcalculationsare,ofcourse,dependentonthephysicalpropertiesoftheconstructionmaterialsasdeterminedbylaboratorytests.Arationalmethodofdesignattemptstotaketheresultsofrelativelysimpleandfundamentaltestssuchastension,compression,torsion,andfatigueandapplythemtoallthecomplicatedandinvolvedsituationsencounteredinpresent-daymachinery.Inaddition,ithasbeenamplyprovedthatsuchdetailsassurfacecondition,fillets,notches,manufacturingtolerances,andheattreatmenthaveamarketeffectonthestrengthandusefullifeofamachinepart.Thedesignanddraftingdepartmentsmustspecifycompletelyallsuchparticulars,mustspecifycompletelyallsuchparticulars,andthusexercisethenecessaryclosecontroloverthefinishedproduct.Asmentionedabove,machinedesignisavastfieldofengineeringtechnology.Assuch,itbeginswiththeconceptionofanideaandfollowsthroughthevariousphasesofdesignanalysis,manufacturing,marketingandconsumerism.Thefollowingisalistofthemajorareasofconsiderationinthegeneralfieldofmachinedesign:①Initialdesignconception;②Strengthanalysis;③Materialsselection;④Appearance;⑤Manufacturing;⑥Safety;⑦Environmenteffects;⑨Reliabilityandlife;Strengthisameasureoftheabilitytoresist,withoutfails,forceswhichcausestressesandstrains.Theforcesmaybe;①Graduallyapplied;②Suddenlyapplied;③Appliedunderimpact;④Appliedwithcontinuousdirectionreversals;⑤Appliedatloworelevatedtemperatures.Ifacriticalpartofamachinefails,thewholemachinemustbeshutdownuntilarepairismade.Thus,whendesigninganewmachine,itisextremelyimportantthatcriticalpartsbemadestrongenoughtopreventfailure.Thedesignershoulddetermineaspreciselyaspossiblethenature,magnitude,directionandpointofapplicationofallforces.Machinedesignismot,however,anexactscienceanditis,therefore,rarelypossibletodetermineexactlyalltheappliedforces.Inaddition,differentsamplesofaspecifiedmaterialwillexhibitsomewhatdifferentabilitiestoresistloads,temperaturesandotherenvironmentconditions.Inspiteofthis,designcalculationsbasedonappropriateassumptionsareinvaluableintheproperdesignofmachine.Moreover,itisabsolutelyessentialthatadesignengineerknowshowandwhypartsfailsothatreliablemachineswhichrequireminimummaintenancecanbedesigned.Sometimes,afailurecanbeserious,suchaswhenatireblowsoutonanautomobiletravelingathighspeeds.Ontheotherhand,afailuremaybenomorethananuisance.Anexampleisthelooseningoftheradiatorhoseintheautomobilecoolingsystem.Theconsequenceofthislatterfailureisusuallythelossofsomeradiatorcoolant,aconditionwhichisreadilydetectedandcorrected.Thetypeofloadapartabsorbsisjustassignificantasthemagnitude.Generallyspeaking,dynamicloadswithdirectionreversalscausegreaterdifficultiesthanstaticloadsand,therefore,fatiguestrengthmustbeconsidered.Anotherconcerniswhetherthematerialisductileorbrittle.Forexample,brittlematerialsareconsideredtobeunacceptablewherefatigueisinvolved.Ingeneral,thedesignengineermustconsiderallpossiblemodesoffailure,whichincludethefollowing:①Stress;②Deformation;③Wear;④Corrosion;⑤Vibration;⑥Environmentaldamage;⑦Looseningoffasteningdevices.Thepartsizesandshapesselectedmustalsotakeinto