Unit1MetalsTheuseofmetalshasalwaysbeenakeyfactorinthedevelopmentofthesocialsystemsofman.Oftheroughly100basicelementsofwhichallmatteriscomposed,abouthalfareclassifiedasmetals.Thedistinctionbetweenametalandanonmetalisnotalwaysclear-cut.Themostbasicdefinitioncentersaround[以…為中心]thetypeofbondingexistingbetweentheatomsoftheelement,andaroundthecharacteristicsofcertainoftheelectrons[某種電子]associatedwiththeseatoms.Inamorepracticalway,however,ametalcanbedefinedasanelementwhichhasaparticularpackageofproperties.在人類(lèi)社會(huì)的開(kāi)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(shí)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?chē)h(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(zhǎng)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(shuō)，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(dāng)大，盡管發(fā)生斷裂所需的力遠(yuǎn)沒(méi)有像所預(yù)期的撕開(kāi)金屬原子所需的力那么大。Oneofthemoresignificantofthesecharacteristicsfromourpointofviewisthatofcrystallinity[crystallinity[,krist?'lin?ti]].Acrystallinesolidisoneinwhichtheconstituentatomsarelocatedinaregularthree-dimensionalarrayasiftheywerelocatedatthecornersofthesquaresofathree-dimensionalchessboard[n.棋盤(pán)].Thespacingoftheatomsinthearrayisofthesameorderasthesizeoftheatoms,theactualspacingbeingacharacteristicoftheparticularmetal.Thedirectionsoftheaxesofthearraydefinetheorientationofthecrystalinspace.Themetalscommonlyusedinengineeringpracticearecomposedofalargenumberofsuchcrystals,calledgrains[晶粒].Inthemostgeneralcase[一般情況下],thecrystalsofthevariousgrainsarerandomlyorientedinspace.Thegrainsareeverywhereinintimatecontactwithoneanotherandjoinedtogetheronanatomicscale.Theregionatwhichtheyjoinisknownasagrainboundary.從我們的觀點(diǎn)來(lái)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(pán)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(shí)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(shí)質(zhì)的；內(nèi)容充實(shí)的substantialevidence:實(shí)〔質(zhì)〕體證據(jù)|實(shí)質(zhì)性證據(jù)|實(shí)質(zhì)證據(jù)substantialorder:大宗訂單|大訂單]amountsinengineeringmaterials.Theresultisknownasanalloy.絕對(duì)純潔的金屬?gòu)膩?lái)也沒(méi)有被生產(chǎn)出來(lái)過(guò)。即使絕對(duì)純潔的金屬可以生產(chǎn)出來(lái)，工程師們對(duì)它們也并不會(huì)特別感興趣，因?yàn)樗鼈兒苋彳?、脆弱。?shí)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(lái)金屬或非金屬元素，這些外來(lái)元素可能是有害的也可能是有益的或者它們對(duì)某種特定的屬性沒(méi)有影響。如果是有害的，這些外來(lái)元素被認(rèn)為是雜質(zhì)。如果是有益的，它們被認(rèn)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(wú)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(gè)詞可以包括工業(yè)用純金屬和它的合金。也許可以這樣說(shuō)，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(lái)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(dāng)想了解決定金屬和合金性質(zhì)的因素時(shí)，應(yīng)充分考慮它們的化學(xué)組成。Ofthe50orsometallicelements,onlyafewareproducedandusedinlargequantitiesinengineeringpractice.Themostimportantbyfarisiron[鐵],onwhicharebasedtheubiquitous[普遍的，無(wú)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(dāng)]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(shí)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(jiàn)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(lái)的金屬重量的98%。在結(jié)構(gòu)應(yīng)用〔也就是說(shuō)，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(duì)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(qiáng)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(qián)和高質(zhì)量的使用特性，事實(shí)上，它們高的本錢(qián)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(shuō)你愛(ài)我就夠了。Sufficeittosaythatthegunwashis.只需說(shuō)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?yuàn)W的特性。在合金材料被采用和應(yīng)用于工程實(shí)際之前，掌握其結(jié)構(gòu)強(qiáng)度和它的綜合性質(zhì)就夠了。舉例來(lái)說(shuō)，它可以強(qiáng)度很高，并且有好的耐磨性；它可以被例如拉伸加工，機(jī)械加工，或焊接等特殊工藝來(lái)加工出來(lái)；它可以被循環(huán)利用；它的本錢(qián)和實(shí)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(shí)能夠運(yùn)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(huì)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(méi)有太大的區(qū)別；所有的鋼在機(jī)械性能方面都是近似的。它們的選取標(biāo)準(zhǔn)是諸如脆硬性，價(jià)格，和可用性等。不僅僅是因?yàn)檫@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(méi)有的某些能力，或者是某種鋼具有神奇的名字。經(jīng)過(guò)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(jī)械加工性]),ratherthanpropertiesrequiredbyforging,governtheselectionofmaterial.Thepropertiesrequiredforforginghaveverylittlerelationtothefinalpropertiesofthematerial;therefore,notmuchcanbedone[無(wú)論做什么都是白費(fèi)力，都改變不了既定的現(xiàn)實(shí)]toimproveitsforgeability.Higher-carbonsteelisdifficulttoforge.Largegrainsizeisbestifsubsequentheattreatmentwillrefinethegrainsize.關(guān)于加工的考慮 最后零件的特性〔硬度、強(qiáng)度和可加工性〕而不是鍛造特性決定了材料的選擇。可鍛性與材料的最后特性聯(lián)系不大；因此，提高金屬的可鍛造性價(jià)值不大。高碳鋼很難鍛造。如果在隨后的熱處理過(guò)程進(jìn)行細(xì)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(duì)低碳鋼影響不大。鉻在鍛造溫度下時(shí)使鋼硬化，但釩沒(méi)有明顯的效果；兩種加工方法對(duì)高碳鋼沒(méi)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(dú)特的，顯著的〕inthelow-carbonsteels. 成形 鋼的冷成形是它的拉伸強(qiáng)度和延展性相結(jié)合的結(jié)果。拉伸強(qiáng)度和屈服點(diǎn)不能太高否那么在發(fā)生彎曲時(shí)需要做很多工作；與之相類(lèi)似，鋼應(yīng)該有高延展性，使其在沒(méi)有斷裂的情況下成形。加工力的大小取決于屈服點(diǎn)，因?yàn)殇撛谇c(diǎn)之上才開(kāi)始變形。與此同時(shí)，加工硬化也同時(shí)發(fā)生，金屬變得越來(lái)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(diǎn)，就此而論〕todiscoverthatdeepdrawscansometimesbemadeinonerapidoperationthatcouldnotpossiblybedoneleisurely〔緩慢地，沉著不迫地〕intwoorthree.Ifadrawishalfmadeandthenstopped,itmaybenecessarytoanneal〔退火〕beforeproceeding,thatis〔換句話說(shuō)〕,ifthepieceisgiventimetowork-harden.Thismaynotbeascientificstatement,butitisactuallywhatseemstohappen.在這方面，相當(dāng)有趣的是你將發(fā)現(xiàn)有時(shí)可通過(guò)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(shí)現(xiàn)。如果拉伸進(jìn)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(shuō)工件是否有時(shí)間進(jìn)行加工硬化。這不是一種科學(xué)的表達(dá)方法，但確實(shí)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(yán)格地，劇烈地〕duringheattreating.〔virtuen.德行,美德,貞操,優(yōu)點(diǎn),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(diǎn)的加工硬化區(qū)進(jìn)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(huì)發(fā)生回彈，在隨后的熱處理后，工件會(huì)發(fā)生翹曲。即使是一個(gè)簡(jiǎn)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(huì)在熱處理中呈現(xiàn)嚴(yán)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(dāng)是否內(nèi)應(yīng)力會(huì)引起翹曲的疑心存在時(shí)，可以通過(guò)將工件加工至1100然后進(jìn)行冷卻來(lái)驗(yàn)證。如果存在內(nèi)應(yīng)力，工件會(huì)發(fā)生變形。經(jīng)過(guò)熱處理的工件像我們看到的那樣會(huì)發(fā)生嚴(yán)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(guò)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(jìn)行熱處理就能平安焊接的最高碳含量為0.3％。高碳鋼通過(guò)適宜的預(yù)熱通常也可焊接。有兩點(diǎn)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(fēng)硬鋼〕steelsareweldableifpreheatedandweldedataslowrate. 低速焊接帶來(lái)了更多的熱量，這對(duì)金屬的大量體積進(jìn)行了加熱，所以冷卻速度降低。預(yù)熱可以取得與之相當(dāng)?shù)男Ч?。例如?dāng)被預(yù)熱至或時(shí)可以很好的焊接。由于周?chē)饘俚妮^高溫度，當(dāng)焊接弧移開(kāi)焊接點(diǎn)后，冷卻速度不會(huì)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(guò)預(yù)熱和慢速焊接到達(dá)良好的焊接效果。 MachinabilityMachinability〔機(jī)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(duì)于加工者來(lái)說(shuō)，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(zhǎng)的刀具壽命?？杉庸ば允堑毒吆土慵慕Y(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(shí)候，因?yàn)椴牧线^(guò)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(dòng)至刀具前端。柔軟的金屬往往會(huì)被參加合金從而犧牲它的延展性來(lái)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(fèi)力〕withwhichamaterialcanbemachinedbysharpcuttingtoolsinoperationssuchasturning〔車(chē)〕,drilling〔鉆〕,milling〔銑〕,broaching[['b?ut?i?]n.拉削；拉孔；推削；擴(kuò)孔v.鉆孔；開(kāi)口]〔拉削〕,andreaming〔鉸〕.機(jī)械加工性能是在指對(duì)工件材料使用刀具進(jìn)行諸如車(chē)、鉆、銑、拉削、鉸加工時(shí)的難易程度。Inthemachiningofmetal,themetalbeingcut,thecuttingtool,thecoolant,theprocessandtypeofmachinetool〔機(jī)床〕,andthecuttingconditionsallinfluencetheresults.Bychanginganyoneofthesefactors,differentresultswillbeobtained.Thecriterion[[krai'ti?ri?n]n.〔批評(píng)判斷的〕標(biāo)準(zhǔn)；準(zhǔn)那么；標(biāo)準(zhǔn)；準(zhǔn)據(jù)]〔標(biāo)準(zhǔn)〕uponwhichtheratings〔等級(jí)〕listedarebased(等級(jí)評(píng)定的標(biāo)準(zhǔn))istherelative[adj.相對(duì)的；有關(guān)系的；成比例的]volumeofvarious〔不同種〕materialsthatmayberemovedbyturningunderfixedconditionstoproduceanarbitrary〔任意的〕fixedamountoftoolwear.在對(duì)金屬進(jìn)行加工時(shí)，被切削的金屬，切削刀具，冷卻液，使用的機(jī)床的種類(lèi)，切削條件均影響著切削效果。改變?nèi)魏我环N均會(huì)產(chǎn)生不同的切削效果。切削效果評(píng)定的準(zhǔn)那么是：車(chē)削時(shí)在固定的切削條件下產(chǎn)生一定量的刀具磨損時(shí)，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(lèi)：(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(guò)多；胃酸過(guò)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?xì)w入到這個(gè)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(zhǎng)期使用時(shí)，抵抗腐蝕的能力。Mechanicalproperties Mechanicalpropertiesincludethestrengthpropertiesliketensile,compression,shear,torsion,impact,fatigueandcreep[n.爬行；毛骨悚然的感覺(jué)；諂媚者vi.爬行；蔓延；慢慢地移動(dòng)；起雞皮疙瘩creep:蠕變|潛變|漸變creepstrength:蠕變強(qiáng)度|潛變強(qiáng)度|蠕變?nèi)醵萩reepstrain:蠕變變形|蠕動(dòng)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(qiáng)度特性。一種材料的拉伸強(qiáng)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(biāo)；橫線])inatensiletest.Amaterialtendstochangeorchangesitsdimensionswhenitisloaded,dependinguponthemagnitude[大小]oftheload.Whentheloadisremoveditcanbeseenthatthedeformationdisappears.Formanymaterialsthisoccursupto[一直到；相當(dāng)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(yàn)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(shí)，隨著載荷大小的變化，尺寸會(huì)發(fā)生改變。當(dāng)卸載時(shí)，變形消失。對(duì)于許多材料來(lái)說(shuō)，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(gè)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(lái)的尺寸〕。在曲線的實(shí)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(shí)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(huì)vt.展覽；顯示；提出〔證據(jù)等〕vi.展出；開(kāi)展覽會(huì)]clearrangesofelasticity,copper,zinc〔鋅〕,tin〔錫〕,etc,arefoundtobeimperfectly[[im'p?:fiktli]adv.有缺點(diǎn)地；不完美地；未完成地]elasticevenatrelatively〔相當(dāng)?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(dāng)?shù)偷膽?yīng)力值下彈性也表現(xiàn)得不是很充分。實(shí)際上依靠測(cè)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(shí)〕thedeformationstartstooccurmorerapidlythantheincreasingload.ThispointiscalledtheyieldpointQ.themetalwhichwasresistingtheloadtillthen,startstodeformsomewhatrapidly,i.e.,yield.Theyieldstressiscalledyieldlimit.當(dāng)在彈性極限之上增大載荷時(shí)會(huì)產(chǎn)生塑性變形。同時(shí)，試件發(fā)生加工硬化。到達(dá)某點(diǎn)后變形的速度快于載荷增加的速度。這一點(diǎn)叫做屈服極限點(diǎn)。一開(kāi)始一直在抵抗載荷的金屬在這一點(diǎn)后開(kāi)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(zhǎng)。在這個(gè)塑性流動(dòng)期間的應(yīng)力-應(yīng)變關(guān)系表示為曲線上的QRST段。在T點(diǎn)試件斷裂，此時(shí)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(qiáng)度或簡(jiǎn)單地稱為拉伸強(qiáng)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(shì)]cross-sectionalareaofthespecimen,sufferedonaccountof[Onaccountoftheweather,wehadtocanceltheprojectedouting.]theplasticdeformation.邏輯上來(lái)說(shuō)，一旦超過(guò)彈性極限，金屬應(yīng)該就會(huì)屈服直至最后斷裂，在應(yīng)力值上應(yīng)該沒(méi)有增加。但是實(shí)際的曲線卻記錄了在超過(guò)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(qiáng)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(shí)會(huì)變得越來(lái)越硬。金屬拉伸越長(zhǎng)它的直徑越小。這種現(xiàn)象一直持續(xù)到曲線上的S點(diǎn)。AfterS,therateatwhichtheredutioninareatakesplace,exceedstherateatwhichthestressincreases.Strainbecomessohighthattheredutioninareabeginstoproducealocalizedeffectatsomepoint.Thisiscalledneching.超過(guò)S點(diǎn)后，面積減少的速度超過(guò)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(diǎn)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?？?；以至于實(shí)際上載荷降低。 伸長(zhǎng)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:①I(mǎi)nitialdesignconception;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