UnitlMetals

Theuseofmetalshasalwaysbeenakeyfactorinthedevelopmentofthesocialsystemsofman.Oftheroughly

100basicelementsofwhichallmatteriscomposed,abouthalfareclassifiedasmetals.Thedistinctionbetween

ametalandanonmetalisnotalwaysclear-cut.Themostbasicdefinitioncentersaround［以，??為中心］thetype

ofbondingexistingbetweentheatomsoftheelement,andaroundthecharacteristicsofcertainofthe

electrons［某種電子］associatedwiththeseatoms.Inamorepracticalway,however,ametalcanbedefinedas

anelementwhichhasaparticularpackageofproperties.

在人類社會(huì)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?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。

Metalsarecrystallii同adj.晶體的］wheninthesolidstateand,withfewexceptions［極少例外］(e.g.mercury),

arcsolidatambient1周圍環(huán)境的］temperatures.Theyarcgoodconductorsofheatandelectricityandarc

opaque［不透明的］lolight.Theyusuallyhaveacomparativelyhighdensity.Manymetalsareductile［柔軟的；

易延展的］-thatis,theirshapecanbechangedpeimanently［永久地，長期不變地］bytheapplicationofaforce

withoutbreaking.Theforcesrequiredtocausethisdeformationand(hoserequiredtobreakorfractureametal

arecomparativelyhigh,although,thefractureforcesisnotnearly［=farfrom.muchlessthan］ashighaswould

beexpectedfromsimpleconsideraiionoftheforcesrequirediotearaparttheatomsofihemeial.

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(dāng)大，盡管發(fā)生斷裂所需的力遠(yuǎn)沒有像所預(yù)期的撕開金屬

原子所需的力那么大。

Oneofthemoresignificantofthesecharacteristicsfromourpoin:ofviewisthatofcrystallinity［cryslallinily

［,krist?'lin?ti］］.Acrystallinesolidisoneinwhichtheconstituentatomsarelocatedinaregular

three-dimensionalarrayasiftheywerelocatedat(hecornersofChesquaresofathree-dimensional

chessboard［n,棋盤］.Thespacingoftheatomsinthearrayisofthesameorderasthesizeoftheatoms,the

actualspacingbeingacharacteristicoftheparticularmetal.Thedirectionsoftheaxesofthearraydefinethe

orientationofthecrystalinspace.Themetalscommonlyusedinengineeringpracticearecomposedofalarge

numberofsuchcrystals,calledgrains［晶粒］.InthemostgeneralcaseL般情況F］,thecrystalsofthevarious

grainsarerandomlyorientedinspace.Thegrainsareeverywhereinintimatecontactwithoneanotherand

joinedtogetheronanatomicscale.Theregionatwhichtheyjoinisknownasagrainboundary.

從我們的觀點(diǎn)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)則的三維排列中，仿佛位于三維棋盤的方格的先上。原子訶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,becauseitwould

besoftandweak.Themetalsusedcommerciallyinevitably［不可防止地］containsmallamountsofoneor

moreforeignelements,eithermetiillic［nietallic［mi't?lik,me-］adj.金屬的,含金屬的］ornomnetallic.These

foreignelementsmaybedetrimenlal［有害的］,theymaybebeneficial,ortheymayhavenoinfluenceatallona

particularproperty.Ifdisadvantageous,theforeignelementstendtobeknownasimpurities［雜質(zhì)］.If

advantageous,theytendtobeknownasalloyingelements［合金元索］.Alloyingelementsarccommonlyadded

deliberately［成心地，蓄意地］insubstanlial|adj.大量的；實(shí)質(zhì)的；內(nèi)容充實(shí)的substanlialevidence:實(shí)(質(zhì))

體證據(jù)I實(shí)質(zhì)性證據(jù)I實(shí)質(zhì)證據(jù)substantialorder:大宗訂單|大訂亙］amountsinengineeringmaterials.The

resultisknownasanalloy.

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(huì)特別感興趣，因?yàn)樗鼈兒苋彳洝⒋嗳?。?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(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”isnotclcar-cut.Theterm“metal”maybeusedto

encompassbothacommerciallypuremetalanditsalloys.Perhapsitcanbesaidthatthemoredeliberatelyan

alloyingadditionhasbeenmadeandthelargertheamountoftheaddition,themorelikelyitisthattheproduct

willspecificallybecalledanalloy.Inanyevent［無論如何,不管怎樣］,thechemicalcompositionofametalor

analloymustbeknownandcontrolledwithincertainlimitsifconsistent［一致的］performanceistobe

achievedinservice.Thuschemicalcompositionhastobetakenintoaccountwhendevelopingan

understandingofthefactorswhichdeterminethepropertiesofmeUlsandtheiralloys.

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，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?種金屬或合金在使用中表現(xiàn)出穩(wěn)定?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.

Themostimponambyfarisiron［次］,onwhicharebasedtheubiquhous［普遍的，無處不在的］sieelsandcast

irons（basicallyalloysofironandcarbon）.Theyaccountforabout98%byweightofallmetalsproduced.Next

inimportanceforstructuraluses（thatis,forstructuresthatareexpectedtocarryloads）arcaluminum［鋁，

copper,nickel,andtitaniumf［tai'teini?m,［化］鈦（金屬元素）］.Aluminumaccountsforabout0.8%by

weightofallmetalsproduced,andcopperabout0.7%,leavingonly0.5%forallothermetals.Asmightbe

expected,theremaindersareallusedinraiher［相當(dāng)］specialapplications.Forexample,nickelalloysareused

principally［主要地］incorrosion-andheat-resistantapplications,whiletitaniumisusedextensively［廣泛地］in

theaerospaceindustrybecauseitsalloyshavegoodcombinationsofhighstrengthandlowdensity.Bothnickel

andtitaniumareusedinhigh-cost,high-qualityapplications,and,indeed,itistheirhighcostthattendsto

restricttheirapplication.

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)成了處處可見的鋼和鑄鐵。（主要由鐵和碳構(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、銀和鈦。

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，銀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。銀合鈦有高本錢和高質(zhì)量的使用特性，事實(shí)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［Sufficeittosay

thatyouloveme.

只要說你愛我就夠了。

Sufficeittosaythatthegunwashis.

只需說這槍是他的就夠了。］thatawholecomplexofpropertiesinadditiontostructuralstrengthisrequiredof

analloybeforeitwillbeacceptedinto,andsurvivein,engineeringpractice.Itmay,forexample,havetobe

strongandyethavereasonablecorrosionresistance;itmayhavetobeabletobefabricatedbyaparticular

processsuchasdeepdrawing,machining,orwelding;itmayhavetobereadily［容易地］recyclable;andits

costandavailabilitymaybeofcriticalimportance.

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。舉例來說，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加工出來：它可以被循環(huán)利用：它的本錢和實(shí)用性是首要的。

Unit2SelectionofConstructionMaterials

Thereisnotagreatdifferencebetween“this"steeland“thal”steel;allareverysimilarinmechanical

properties.Selectionmustbemadeonfactorssuchashardenability[[,ha: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)

aw

失效）和可用性（多久能被修復(fù)[。]Tandnotwiththeideathatthissteelcandosomethingnoothercan

dobecauseitcontains2percentinsteadof1percentofacertainalloyingelement,orbecauseithasa

mystcrious[[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;thisisparticularly（rueofalloysteels.

在鋼之間沒有太大的區(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

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。

Considerationsinfabricaiion（制造）

Thepropertiesofthefinalpart（hardness,strength,andmachinability][m?,?i:n?'bil?ti]

n.切削性；機(jī)械加工性]）,raiherihanpropertiesrequiredbyforging,governtheselectionofmaterial.The

propertiesrequiredforforginghaveverylittlerelationtothefinalpropertiesofthematerial;therefore,not

muchcanbedone[無論做什么都是白費(fèi)力,都改變不了既定的現(xiàn)實(shí)]toimproveitsforgeability.

Higher-carbonsteelisdifficulttoforge.Largegrainsizeisbeslifsubsequenthealireatmentwillrefinethe

grainsize.

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?？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(jià)值不大。高碳鋼很難鍛造。如果在隨后的熱處理過程進(jìn)

行細(xì)化，大尺寸晶粒是最好的。

Low-carbon,nickel-chromium（^）steelsarejustabout[幾乎，差小多

j]asplastica（hightemperatureunderasingle52O-ft-lb（lftlb=l.35582J）blowfatasingleblow

=atoneblow

a（asingleblow:一下子|一舉|一擊]asplainsteelsofsimilarcarboncontent.Nickeldecreasesforgeabilityof

medium-carbonsteels,buthaslittleeffectonlow-carbonsteels.Chromiumseemstohardensteelatforging

temperatures,butvanadium1]（銳）hasnodiscernible（可【區(qū)分的）effect;neitherhasthemethodofmanufacture

anyeffectonhigh-carbonsteel.

在高溫下低碳，銀銘合金鋼在受到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。

銀減少了中碳鋼的可鍛性，但對低碳鋼影響不大。倍在鍛造溫度下時(shí)使鋼硬化，但鈕沒有明顯的效果；

兩種加工方法對高碳鋼沒有影響。

Formability

Thecold-formabilityofsteelisafunction（功能）ofitstensilestrengthcombinedwithductility.Thetensile

strengthandyieldpointmustnotbehighortoomuchworkwillberequiredinbending（彎Hh〕;likewise（同

樣地）,thesteelmusthavesufficient（充足的）ductilitytoflowtotherequiredshapewithoutcracking.The

forcerequireddependsontheyieldpoint,becausedefonnationstartsintheplasticrangeabovetheyieldpoint

ofsteel.Work-hardeningalsooccurshere,progressively（日益增多地）stiffening（使變硬）ihemetaland

causingdifficulty,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

Machinability

Machinability（機(jī)械力口工性能）meansseveralthings.Toproductionmenitgenerallymeansbeingableto

removemetalatthefastestrate,leavethebestpossiblefinish,andobtain（helongestpossibletoollife.

Machinability叩plieslo（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?？杉庸ば允堑毒吆土慵慕Y(jié)合。

Itisnotdeterminedbyhardness（硬度）alone,butbythetoughness（韌性）,microstructure,chemical

composition（成分）,andtendency（傾向）ofametaltohardenundercoldwork.Inthemisleadingexpression

41toohardtomachinev,theword“hard"isusuallymcanltobesynonymous（同義的）withdifficult".

Manytimesamaterialisactuallytoosofttomachinereadily.Sofrnessandtoughnessmaycausethemetalto

tear（撕裂）andflowaheadofthecuttingtoolratherthancutcleanly.Metalthatareinherently（天性地，固

有地）softandtougharesometimesalloyedtoimprovetheirmachinabilityatsomesacrificeff'sVkrifais]n.犧

牲；祭品；供奉

AHgainsaremadeatsomesacrifice.

Mostpeoplemightchoosetodivertthecourseofthetrain,andsacrificeonlyonechild.]（犧牲）inductility.

Examplesareuseoflead（鉛）inbrass1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)的使化特性所

決定。在容易混淆的表示“難加工”中，“hard”與“difficuh”同義。許多時(shí)候，因?yàn)椴牧线^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）withwhichamaterialcanbe

machinedbysharpcuttingtoolsinoperationssuchasturning（車），drilling[鉆）,milling（銃）,

broaching[['b?ul?i?]n.拉削；拉孔；推削;擴(kuò)孔v.鉆孔；開口]（拉削）,andreaming（較）.

機(jī)械加工性能是在指對工件材料使用刀具進(jìn)行諸如車、鉆、銃、拉削、錢加工時(shí)的難易程度，

Inthemachiningofmetal,themetalbeingcut,thecuttingtool,thecoolant,theprocessandtypeofmachine

tool（機(jī)床），andthecuttingconditionsallinfluencetheresults.Bychanginganyoneofthesefactois,different

resultswillbeobtained.Thecriterion![krai'ti?ri?n]n.（批評判斷的J標(biāo)準(zhǔn);準(zhǔn)那么;標(biāo)準(zhǔn);準(zhǔn)拈]（標(biāo)準(zhǔn)J

uponwhichtheratings（等級(jí)）listedarebased（等級(jí)評定的標(biāo)準(zhǔn)）isIherelative[adj.相對的;有關(guān)系的；

成比例的]volumeofvarious（不同種）materialsthatmayberemovedbyturningunderfixedconditionsto

produceanarbitral（任意的）fixedamountoftoolwear.

在對金屬進(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，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。切削效果評定的準(zhǔn)那么是：車削時(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。

Unit3MechanicalPropertiesofMaterials

Thematerialpropertiescanbeclassifiedintothreemajorheadings:（i）Physical,（ii）Chemical,（iii）Mechanical.

Physicalproperties

Densityorspecificgravity,nioisturc[[*m?ist??]n.水分;濕度：潮濕；降雨量]content,etc.,canbe

classifiedunderthiscategory.

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?tiln酸度;酸

性;酸過多;胃酸過多]oralkalinity[L?lk?'lin?ti]n.堿度：堿性工reactivity[化學(xué)反響的活性]andcorrosion.

Themostimportantoftheseiscorrosionwhichcanbeexplainedinlayman'stermsastheresistanceofthe

materialtodecay［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；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?/p>

creepstrain:蠕變變形|蠕動(dòng)應(yīng)變|蠕變應(yīng)變］.Thetensilestrengthofamaterialisobtainedbydividingthe

maximumload,whichthespecimenbearsby（heareaofcross-seclionofthespecimen.

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（ordinatc）andthestrainalongthe

X-axis（abscissa［［?bsis?］n.［數(shù)］橫坐標(biāo)；橫線］）inatensiletest.Amaterialtendstochangeorchangesits

dimensionswhenitisloaded,dependinguponthemagnitude［大d、］oftheload.Whentheloadisremovedit

canbeseenthatihedeformationdisappears.Formanymaterials（hisoccursup相當(dāng)于；忙于，在

做；由決定的］acertainvalueofthestresscalledtheelasticlimit.Thisisdepictedbythestraightline

relationshipandasmalldeviation［［,di:vi'ei??n］n.18^；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,thelimitingvalueofthestressuptowhichthestressandstrainarcproportional,is

calledthelimitofproportionality.Inthisregion,themetalobeysHooke'slaw,whichstatesthatihestressis

proportionaltostrainintheelasticrangeofloading（thematerialcompletelyregainsitsoriginaldimensions

aftertheloadisremoved）.Intheactualplottingofthecurve,theproportionalitylimitisobtainedata

slightlylowervalueoftheloadthantheelasticlimit.Thismaybeattributedtothetime-lagintheregainingof

theoriginaldimensionsofthematerial.Thiseffectisveryfrequentlynoticedinsonicno-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，金屬服從胡克定律一闡述

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(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［［ig'zibit］n.展覽品；證據(jù);展示會(huì)vl.展覽；顯示；提出（證據(jù)等）vi.展

出;開展覽會(huì)］clearrangesofelasticity,copper,zinc（鋅）,tin（錫）,etc,arefeundtobe

imperfectly［［im'p?:fiktli］adv.有缺點(diǎn)地；不完美地；未完成地］elasticevenatrelatively（相當(dāng)?shù)兀﹍owvalues

ofstresses.Actuallytheelasticlimitisdistinguishable（可區(qū)分的）fromtheproportionality（比例性）limit

moreclearlydependinguponthesensitivity（靈敏性）ofthemeasuringinstrument.

鐵和銀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.Simultaneouslythe

specimengetswork-hardened.Apointisreachedwhen（這時(shí)）thedeformationstartstooccurmorerapidly

thantheincreasingload.ThispointiscalledtheyieldpointQ.themetalwhichwasresistingtheloadtillthen,

startstodeformsomewhatrapidly,i.c.,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)。一開始一直在抵抗載荷的金屬在這?點(diǎn)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-strainrelationinthisplastic

flowperiodisindicatedbytheportionQRSTofthecurve.AtTthespecimenbreaks,andthisloadiscalledthe

breakingload.ThevalueofthemaximumloadSdividedbytheoriginalcross-sectionalareaofthespecimenis

referredtoastheultimatetensilestrengthofthemetalorsimplythetensilestrength.

試件從Q到S在到T不斷地延長。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除以式件的橫截面枳為金屬的最大拉伸強(qiáng)度或

簡單地稱為拉伸強(qiáng)度。Logicallyspeaking,oncetheelasticlimitisexceeded,themetalshouldstartstoyield,

andfinallybreak,withoutanyincreaseinthevalueofstress.Butthecurverecordsanincreasedstresseven

aftertheelasticlimitisexceeded.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,we

hadtocancel(heprojectedouting.

]thcplasticdeformation.

邏輯上來說，一旦超過彈性極限，金屬應(yīng)該就會(huì)屈服直至最后斷裂，在應(yīng)力值上應(yīng)該沒有增加。但是實(shí)

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：

I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.The

morethemetalgetselongatedthemoreitsdiameter(andhence,cross-sectionalarea)isdecreased.This

continuesuntilthepointSisreached.

由于加工硬化，金屬在發(fā)生塑性變形時(shí)會(huì)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(diǎn)。

AfterS,therateatwhichtheredutioninareatakesplace,exceedstherateatwhichthestressincreases.Strain

becomessohighthattheredutioninareabeginstoproducealocalizedeffectatsomepoint.Thisiscalled

ncching.

超過S點(diǎn)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(diǎn)產(chǎn)生了局部

效應(yīng)。叫做頸縮。

Reductionincross-sectionalareatakesplaceveryrapidly;sorapidlythattheloadvalueaclullydrops.

ThisisindicatedbyST.FailureoccursatthispointT.

Thenpercentageelongationandreductioninareaindicatetheductilityorplasticityofthematerial:

Whereandaretheoriginalandthefinallengthofthespecimen;andaretheoriginalandthefinal

cross-scctionalarea.

橫截面積減小的速度非?？欤灰灾劣趯?shí)際上載荷降低。

伸長率和面積減少率表示了材料的延展性。

Uint5Designofmachineandmachineelements

Machinedesign

Machinedesignistheartofplanningordevisingneworimprovedmachinestoaccomplishspecificpurposes.Ingeneral,a

machinewillconsistofacombinationofseveraldifferentmechanicalelementsproperlydesignedandarrangedtoworktogether,

asawhole.Duiingiliciniiialplanningofamacliiiic,fuiidaincnialdecisionsmusibemadecuncciiiiiigloading,typeufkiiicmaiic

elementstobeused,andcorrectutilizationofthepropertiesofengineeringmaterials.Economicconsiderationsareusuallyof

primeimportancewhenthedesignofnewmachineryisundertaken.Ingeneral,thelowestover-allcostsaredesigned.

Considerationshouldbegivennotonlytothecostofdesign,manufactun;thenecessarysafelyfeaturesandbeofpleasing

externalappearance.Theobjectiveistoproduceamachinewhichisnotonlysufficientlyruggedtofunctionproperlyfora

reasonablelife,butisatthesametimecheapenoughtobeeconomicallyfeasible.

Theengineerinchargeofthedesignofamachineshouldnotonlyhaveadequatetechnicaltraining,butmusibeamanof

（；oundjudgmentandwideexperience,qualitieswhichareusuallyacquiredcnlyafterconsiderabletimehasbeenspentinactual

professionalwork.

Designofmachineelements

Theprinciplesofdesignare,ofcourse,universal.Thesametheoryorequationsmaybeappliedtoaverysmallpart,asinan

instilment,or.toalargerbutsimilarpartusedinapieceofheavyequipment.Innoease,however,shouldmathematical

calculationsbelookeduponasabsoluteandfinal.Theyareallsubjecttotheaccuracyofthevariousassumptions,whichmust

necessarilybemadeinengineeringW3ik.Sometimesonlyaportionofthetotalnumberofpartsinamachinearedesignedon

[hebasisofanalyticcalculations.Theformandsizeoftheremainingpartsaredesignedonthebasisofanalyticcalculations.On

iheotherhand,ifthemachineisveryexpensive,orifweightisafactor,asinairplanes,designcomputationsmaythenbetnadc

foralmostalltheparts.

Thepurposeofthedesigncalculationsis,ofcourse,toattempttopredictthestressordeibrmationinthepartinorderthatit

maysagelycarrytheloads,whichwillbeimposedonit,andthatitmaylastfortheexpectedlifeofthemachine.All

calculationsare.ofcourse,dependentonthephysicalpropertiesoftheconstructionmaterialsasdeterminedbylaboratorytests.

Arationalmethodofdesignattemptstotaketheresultsofrelativelysimpleandfundamentaltestssuchastension,compression,

torsion,andfatigueandapplythemtoallthecomplicatedandinvolvedsitua.ionsencounteredinpresent-daymachinery.

Inaddition,ithasbeenamplyprovedthatsuchdetailsassurfacecondilion,fillets,notches,manufacturingtolerances,and

healtreatmenthaveamarketeflectoniheslrcnglhandusefullifeofamachinepari.Thedesignanddraftingdepartnientsmust

specifycompletelyallsuchparticulars,mustspecifycompletelyallsuchparticulars,andthusexercisethenecessaryclose

controloverthefinishedproduct.

Asmentionedabove,machinedesignisavastfieldofengineeringtechnology.Assuch,itbeginswiththeconceptionofan

ideaandfollowsthroughthevariousphasesofdesignanalysis,manufacturing,marketingandconsumerism.Thefollowingisa

listofthemajorareasofconsiderationinthegeneralfieldofmachinedesign:

①Initialdesignconception;

②Strengthanalysis;

⑤Maicrialsscicciion;

④Appearance;

⑤Manufacturing;

⑥Safety;

⑦Environmenteffects;

⑨Reliabilityandlife;

Strengthisameasureoftheabilityioresist,withoutfails,forceswhichcausestressesandstrains.Theforcesmaybe:

①Graduallyapplied;

②Suddenlyapplied;

③Appliedunderimpact;

④Appliedwithcontinuousdirectionreversals;

⑤Appliedatloworelevatedtemperatures.

Ifacriticalpartofamachinefails,thewholemachinemustbeshutdownuntilarepairismade.Tims,whendesigninganew

machine,itisextremelyimportantthatcriticalpartsbemadestrongenoughtopreventfailure.Thedesignershoulddetermineas

preciselyaspossiblethenature,magnitude,directionandpointofapplicationofallforces.Machinedesignismot,however,an

exactscienceanditis,therefore,rarelypossibletodetermineexactlyalltheappliedforces.Inaddition,differentsamplesofa

specifiedmaterialwillexhibitsomewhatdifferentabilitiestoresistloads,temperaturesandotherenvironmentconditions.In

spiteofthis,designcalculationsbasedonappropriateassumptionsareinvaluableintheproperdesignofmachine.

Moreover,itisabsolutelyessentialthatadesignengineerknowshowandwhypartsfiiilsothatreliablemachineswhich

requireminimummaintenancecanbedesigned.Sometimes,afailurecanbeserious,suchaswhenatireblowsoutonan

automobiletravelingathighspeeds.Ontheotherhand,afailuremaybenomorethananuisance.Anexampleistheloosening

oftheradiatorhoseintheautomobilecoolingsystem.Theconsequenceofthislatterfailureisusuallythelossofsomeradiator

eoolant,aconditionwhichisreadilydetectedandcorrected.

Thetypeofloadapartabsorbsisjustassignificantasthemagnitude.Generallyspeaking,dynamicloadswithdirection

reversalscausegreaterdifficultiesthanstaticloadsand,therefore,fatiguestrengthmustbeconsidered.Anotherconcemis

whetherthematerialisductileorbrittle.Forexample,brittlematerialsareconsideredtobeunacceptablewherefatigueis

involved.

Ingeneral,thedesignengineermustconsiderallpossiblemodesoffailure,whichincludethefollowing:

①Stress;

②Deformation;

③Wear;

④Corrosion;

⑤Vibration;

⑥Environmentaldamage;

⑦Looseningoffasteningdevices.

Thepartsizesandshapesselectedmustalsotakeintoaccountmanydimensionalfactorswhichproduceexternalloadeffects

suchasgeometricdiscontinuities,residualstressesduetoformingofdesiredcontours,andtheapplicationofinterferencefit

joint.

Selectedfrom'*designofmachineelements"，6lhedition,m.f.sports,prentice-hall,inc.,1985and“machinedesign5',

AnthonyEsposito,Charlese..Merril)publishingcompany,1975.

機(jī)器和機(jī)器零件的設(shè)計(jì)

機(jī)器設(shè)計(jì)

機(jī)器設(shè)計(jì)為了特定的目的而創(chuàng)造或改良機(jī)器的一種藝術(shù)。一般來講，機(jī)器時(shí)有多種不同的合理設(shè)計(jì)并有序裝配在一

起的部件構(gòu)成的，在最初的機(jī)器設(shè)計(jì)階段，必須根本明確負(fù)載、元件的運(yùn)動(dòng)情況、工程材料的合理使用性能。負(fù)責(zé)新機(jī)

器的設(shè)計(jì)最初的最重要的是經(jīng)濟(jì)性考慮。?般來說，選擇總本錢最低的i殳計(jì)方案，不僅要考慮設(shè)計(jì)、制造、銷售、安裝

的本錢。還要考慮效勞的費(fèi)用，機(jī)械要保證必要的平安性能和美觀的外形。制造機(jī)器的目標(biāo)不僅要追求保記只用功能的

合理壽命，還要保證足夠廉價(jià)以同時(shí)保證其經(jīng)濟(jì)的可行性。負(fù)責(zé)設(shè)計(jì)機(jī)器的工程師，不僅要經(jīng)過專業(yè)的培VI,而且必須

是一個(gè)準(zhǔn)確判斷而又有豐富經(jīng)驗(yàn)的人，具有一種有足夠時(shí)間從事專門的買際工作的素質(zhì)。

機(jī)器零件的設(shè)計(jì)

相同的理論或方程可應(yīng)用在一個(gè)一起的非常小的零件上，也可用在一個(gè)復(fù)雜的設(shè)備的大型相似件上，既然如此，

書無疑問，數(shù)學(xué)計(jì)算是絕對的和最終的。他們都符合不同的設(shè)想，這必須由工程量決定。有時(shí)，一臺(tái)機(jī)器的零件全部計(jì)

算僅僅是設(shè)計(jì)的一局部。零件的結(jié)構(gòu)和尺寸通常根據(jù)實(shí)際考慮。另一方面，如果機(jī)器和昂貴，或者質(zhì)量很重要，例如飛

機(jī)，那麼每一個(gè)零件都要設(shè)計(jì)計(jì)算。

當(dāng)然，設(shè)計(jì)計(jì)算的目的是試圖預(yù)測零件的應(yīng)力和變形，以保證其平安的帶動(dòng)負(fù)載，這是必要的，并且其也許影響

到機(jī)器的最終壽命。當(dāng)然，所有的計(jì)算依賴于這些結(jié)構(gòu)材料通過試驗(yàn)測定的物理性能。國際上的設(shè)計(jì)方法試圖通過從一

些相對簡單的而根本的實(shí)驗(yàn)中得到一些結(jié)果，這些試驗(yàn)，例如結(jié)構(gòu)復(fù)雜的及現(xiàn)代機(jī)械設(shè)計(jì)到的電壓、轉(zhuǎn)矩和疲勞強(qiáng)度。

另外，可以充分證明，一些細(xì)節(jié)，如外表粗糙度、圓角、開槽、制造公差和熱處理都對機(jī)械零件的強(qiáng)度及使用壽

命有影響。設(shè)計(jì)和構(gòu)建布局要完全詳細(xì)地說明每?個(gè)細(xì)節(jié)，并且對最終產(chǎn)品進(jìn)行必要的測試。

綜上所述，機(jī)械設(shè)計(jì)走一個(gè)非常寬的工程技術(shù)領(lǐng)域。例如，從設(shè)計(jì)理念到設(shè)計(jì)分析的每一個(gè)階段，制造，市場，

鏡售。以下是機(jī)械設(shè)計(jì)的一般領(lǐng)域應(yīng)考慮的主要方面的清單：

①最初的設(shè)計(jì)理念②受力分析③材料的選擇④外形

⑤制造⑥平安性⑦環(huán)境影響⑧可耗性及壽命

在沒有破壞的情況下，強(qiáng)度是抵抗引起