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第一单元应力与应变Thatbranchofscientificanalysiswhichmotionstimesandforcesiscalledmechanicsandismadeupoftwopartsstaticsanddynamics.研究位移、时间和力运动乘力是科学分析法的一个分歧,被称作力学,力学由两大部分组成,静力学和动力学Forexampleiftheforceoperatingonasleevebearingbecomestoohighitwillsqueezeouttheoilfilmandcausemetal-to-metalcontactoverheatingandrapidfailureofthebearing.例如如果止推轴承上的作用力过大的话,会挤出油膜,引起金属和金属之间的相互接触,轴承将过热而迅速失效Ourintuitiveconceptofforceincludessuchideasasplaceofapplicationdirectionandmagnitudeandthesearecalledthecharacteristicsofaforce.力的直观概念包括力的作用点、大小、方向,这些被称为力的三要素Allbodiesareeitherelasticorplasticandwillbedeformedifacteduponbyforces.Whenthedeformationofsuchbodiesissmalltheyarefrequentlyassumedtoberigidi.e.incapableofdeformationinordertosimplifytheanalysis.所有的物体既可以是弹性的也可以是塑性的,如果受到力的作用就产生变形当变形很小的时候它们被假设成刚体,也就是不产生变形以此来简化分析Therigid-bodyassumptioncannotbeusedininternalstressesandstrainsduetotheappliedforcestobeanalyzed.Thusweconsiderthebodytobecapableofdeforming.刚体假设不能应用于内应力和内应变的分析,所以在实际力的分析时,要考虑物体的形变Ifalltheforcesactingonaparticlearebalancedtheparticlewilleitherremainatrestorwillcontinuetomoveinastraightlineatauniformvelocity.如果作用在质点上所有的力是平衡的,质点将会保持静止或做做匀速直线运动第二单元材料的强度与塑性Atensiletestconsistsofslowlypullingasampleofmaterialwithatensileloaduntilitbreaks.Theendsoftensilespecimensareusuallyenlargedtoprovideextraareaforgrip-pingandtoavoidhavingthesamplebreakwhereitisbeinggripped.拉伸试验包括慢慢加载拉伸载荷直到断裂拉伸试件两端加粗为了提供装夹区域和避免试件断裂Theusualmannerofconductingthetestistodeformthespecimenataconstantspeed.Forexampleintheuniversaltestingmachinesthemotionbetweenthefixedandmovingcrossheadscanbecontrolledataconstantspeed.通常进行试验的方法就是使试件以恒定速度发生变形例如,在万能拉伸试验机上,固定端和移动的十字滑块之间的变形是以恒定速度进行的Theloadthatmustbeappliedtoenforcethisdisplacementratevariesasthetestproceeds.ThisloadFmaybedividedbythecross-sectionalareaAtoobtainthestressinthespecimenatanytimeduringthetest.随着实验的进行,用来产生位移的载荷是随位移的变化而变化在实验中,载荷F除以横截面积A可以得到任意时刻点的应力HoweveractualmeasurementofΔLispreferablewherethisisfeasible.StressandstrainbasedontheinitialundeformeddimensionsAiandLiarecalledengineeringstressandstrain.然而,在可行的位置上ΔL的实际测量是更可取的,基于原始尺寸Ai和Li的应力和应变称为工程应力和工程应变Ductileandbrittlematerialsbehavedifferentlyincompressiontestaswell.Thecompressiontestisconductedonshortcylindricalspecimensplacedbetweenparallelplates.塑性和脆性材料在压缩试验中表现的特性是不相同的压缩试验是把短圆柱形试件放在两平行平板之间进行的Thecompressiontestdiagramforthesematerialsretainsthequalitativefeaturesofthetensiontestdiagram.Theultimatecompressivestrengthofabrittlematerialisdeterminedinthesamewayasintension.材料压缩试验图保持了拉伸试验图性能上的特征脆性材料的最大压缩强度与最大拉伸强度得到的方法相同第三单元轴设计Virtuallyallmachinescontainshafts.Themostcommonshapeforshaftsiscircularandthecrosssectioncanbeeithersolidorhollowhollowshaftscanresultinweightsavings.几乎所有的机器都有轴,最常用的外形是圆形的,横截面是空心的或实心的圆形截面(空心轴可以减少重量)Ashaftmusthaveadequatetorsionalstrengthtotransmittorqueandnotbeoverstressed.Itmustalsobetorsionallystillenoughsothatonemountedcomponentdoesnotdeviateexcessivelyfromitsoriginalangularpositionrelativetoasecondcomponentmountedonthesameshaft.一个轴必须有足够的扭转强度来传递扭矩而不会破坏,同样也必须有足够的扭转刚度,这样安装轴就不能过度偏离相对于安装在同一轴上第二个零件的原始位置Shaftsaremountedonbearingsandtransmitpowerthroughsuchdevicesasgearspulleyscamsandclutches.Thesedevicesintroduceforceswhichattempttobendtheshaft;hencetheshaftmustberigidenoughtopreventoverloadingofthesupportingbearings.轴安装在轴承上通过齿轮,滑轮,凸轮和离合器这些装置传递力这些装置可以产生使轴弯曲的力,所以轴必修有足够的刚性防止支撑轴承的过载Inadditiontheshaftmustbeabletosustainacombinationofbendingandtorsionandbending.另外,轴必须能承载弯扭组合的载荷,因此,这样就必须考虑弯扭组合的等效载荷Componentssuchasgearsandpulleysaremountedonshaftsbymeansofkey.Thedesignofthekeyandthecorrespondingkeywayintheshaftmustbeproperlyevaluated.齿轮和滑轮构件是用键的方式连接在轴上的,键和对应的键槽的设计必须进行估算Anotherimportantaspectofshaftdesignisthemethodofdirectlyconnectingoneshafttoanother.Thisisaccomplishedbydevicessuchasrigidandflexiblecouplings.轴设计的另一个重要方面是直接连接两轴,通过刚性和柔性的联轴器装置来实现第四单元SpurGears齿轮Pressureanglesforspurgearsareusually
14.5or20degreesalthoughothervaluescanbeused.Meshinggearsmusthavethesamepressureangles.直齿轮的压力角通常为
14.5°或20°,另外也使用其它的角度,啮合齿轮必须具有相同的压力角Theshapeofthespacebetweengearteethonthegearaswellastoothmodulesomostgearmanufacturingmethodsgeneratethetoothflankinsteadofforming.齿轮轮齿之间齿槽的形状是复杂的,并且随着齿的数目和模数变化而变化,因此大多数齿轮的加工方法是展成齿腹齿廓而不是齿形成形加工Wormgearsareusedwherehighratiosaredesiredandwheretheshaftsarenonintersectingandatrightangles.蜗杆蜗轮应用于传动比大而且两轴不相交但相互垂直的情况下Ithasthegreatadvantagethatthecuttingtoolisasimplerackwithnearlystraightsidedteethwhichcaneasilybegroundaccurately.这种方法有很大的优势,切削工具是一个简单的带有直齿边的齿条Modernshaperscuttingcargearscanrunat2000cuttingperminute.Theshapeofthecutterisroughlythesameasaninvolutegearbutthetipsoftheteetharerounded.现代切削汽车的成型器齿轮转速可达每分钟2000转,齿刀形状与渐开线大致相同,但齿顶是圆形的Bevelgearsareoftenusedwhentwoshaftsareatrightanglestoeachotherandtheircenterlineextensionsintersect;howeversomebevelgearsareatanglesotherthan90degrees.圆锥齿轮一般应用于相互垂直的两轴或两个中心线延长线的相交轴中,也可用于不垂直的两轴中第五单元cams凸轮Thepurposeofanycamistoproduceadisplacementofitsfollower;asecondaryfollowerisoftenusedtoproduceadditionaldisplacementinanotherlocation.使用凸轮的目的是使从动件产生位移,次级从动件在另一位置产生附加运动TherelativeverticalpositionofpointAwithrespecttoBneedstoberaisedifthereactionvalueatBisexcessive.如果B点的作用力过大,A点相对B点的相对垂直位置必须被提高Ingeneralthefollowerisconsideredtobethepartthatcomesincontactwiththecamprofile.Howeverwhenasecondaryfollowerisusedthemotionofthesecondaryfollowerisdictatedbythatoftheprimaryfollower.总的来说,从动件是与凸轮轮廓相接触的零件,然而,当用次级从动件时,次级从动件的运动就需通过主要从动件来实现Thesimplesttypeoffolloweristhereciprocatingtypethatmerelymovesupanddownorinandoutwiththerotationofthecam;thecenterlinecanbeeithercollinearwiththecamcenterlineoroffsetformit.最简单的从动件就是随着凸轮的转动而仅做上下(或进出)运动的从动件,其中心线可与凸轮中心共线,也可与之偏离Fastenersaredeviceswhichpermitoneparttobejoinedtoasecondpartandhencetheyareinvolvedinalmostalldesigns.紧固件是一种连接一个部分和另一个部分的装置,因此,它涉及到几乎所有的设计Springsaremechanicalmemberswhicharedesignedtogivearelativelylargeamountofelasticdeflectionundertheactionofanexternallyappliedload.弹簧是一种被设计于在外力作用下产生相对弹性变形较大的机械构件第七章砂型铸造
1.Thefirststageintheproductionofsandcastingmustbethedesignandmanufactureofasuitablepattern.Castingpatternhastobemadelargerthanthefinishedcastingsizetoallowfortheshrinkagethattakesplaceduringsolidificationandcooling.在型砂铸造生产中,第一阶段是必须设计和制造合适的模型,考虑到铸件在凝固和冷却期间产生的收缩铸件模型的尺寸要比铸件的尺寸大
2.Ifahollowcastingistobemadethepatternwillincludeextensionpiecessothatspacestoacceptthesandcorearemoldedintothesand.Theseadditionalspacesinthemoldaretermedcoreprints.如果铸造空心铸件时模型上包含伸长杆便于在砂中放置砂芯的空间称为型芯座
3.Sandmoldsfortheproductionofsmallandmedium-sizedcastingsaremadeinamoldingbox.Themoldismadeintwoormorepartsinorderthatthepatternmayberemoved.中小型尺寸的铸件砂型是在一个砂箱中制造,砂型由两部分或更多部分组成,以利于模型的顺利取出
4.Thisprocessoffillingandrammingmaybedonebyhandbutmoldproductionisautomatedinalargefoundrywiththemoldboxesmovingalongaconveyorfirstlytobefilledwithsandfromhoppersandthentopassundermechanicalhammersforramming.填充和夯实的过程可以手工完成,但在大型铸造中砂型的制造是自动完成的,砂箱随着传送带移动,首先被料斗中的砂子填满,然后通过机械锤时被打实
5.Therisersshouldcoincidewiththehighestpointsofthemoldcavitysothatthedisplacedaircanreadilyescapefromthemold.Thesizesofrisersshouldbesuchthatthemetalinthemdoesnotfreezetoorapidly.冒口应该与型腔的最高点相连接,使得进入的空气可以容易的从模型中溢出,冒口的尺寸应该足够大使模型中金属不会太快凝固
6.Whenthemetalthathasbeenpouredintoasandmoldhasfullysolidifiedthemoldisbrokenandthecastingisremoved.Thecastingstillhastherunnerandrisersattachedtoitandtherewillbesandadheringtoportionsofthesurface.当熔的金属被倾倒到砂型内并充分凝固以后,砂型将被打破取出铸件,铸件上依然带有横浇口和冒口并且依然有砂子粘在表面造是自动完成的,砂箱随着传送带移动,首先被料斗中的砂子填满,然后通过机械锤时被打实第8课锻造
1.Forgingmeanstheshapingofmetalbyaseriesofhammerblowsorbyslowapplicationofpressure.Thesimplestexampleisablacksmith’sforgingofahotpieceofmetalbyhammeringthework-pieceonananvil.铸造是通过一系列的锤打或是在缓慢的加载压力的场合使金属成型的一种方法,最简单的实例就是热的金属的自由锻,即通过铁砧上锤打锻件
2.Heavysmith’sforgingisfundamentallysimilardifferingonlyinthescaleoftheoperation.Thework-piecemaybeaningotof100tonsandthedeformingforceprovidedbyamassiveforginghammerbutthewholeprocessiscontrolledbythemastersmithwhodecideseachtimewhereandwithwhatforcetheblowshouldtakeplace.重型自由锻和自由锻基本相似,仅在操作的规模上有所不同,锻件可以是一个100吨的铁块,锻压力由一个巨大的锻锤提供,但是整个锻造过程由操作者控制他来决定什么时候用多大力打到什么地方
3.Forgingoperationsmaybecarriedoutusingeitherforginghammersorforgingpresses.Withapressasopposedtoahammerpressureisslowlyappliedandplasticdeformationtendstooccurfairlyuniformlythroughoutthematerial.锻造操作者既可以用锻锤也可以用锻压力来实现操作,用锻压力和锻锤相反,在压力缓慢作用使整个均匀杆产生塑性变形的趋势
4.Forginghammersareoftwobasictypeswiththelargehammereitherdroppingontothework-pieceacceleratedbygravityaloneorasinthesteamhammeracceleratedbybothgravityandsteampressure.锻锤有两种基本类型,既可以用很大的锤子通过作用在工件上也可以用蒸汽压力作用在工件上或者是两者结合
5.Smith’soropen-dieforgingisusedformakingverylargeforgingsorwhenthenumberofforgingsofaparticulardesignissmall.Open-dieforgingisalsousedtopreformmetalpriortofinalshapingbymeansofclosed-dieforging.自由锻或开模锻用于制造大型的锻件或者特殊设计的小锻件,开模锻用于预成型金属,在最终金属成型之前通常使用闭模锻
6.Closed-dieforginginvolvestheuseofaccuratelymachineddieblocks.Thecapitalcostofapairofdieblocksishighbutthisisallowablewhenitisrequiredtomakeforgingstoclosedimensionaltolerancesandinlargequantityaswouldbethecaseforsayconnectingrodsfortheengineofapopularcar.闭模锻包括精确的机械加工的模具,一对模具的成本很高,但是只适用于大批量生产和小的公差要求的锻件,例如,汽车发动机的连杆就是一个典型的例子第九章电弧焊
1.Arcweldinginoneformoranotheristhemostwidelyusedformofwelding.theelectricalsupplyislowvoltagebuthighamperageandmaybeeitheralternatingordirect.电弧焊在一种或另一种形式是应用最广泛的焊接形式电力供应是低电压,但是大电流,并且可以是交流或直流
2.theearliestformsofarcweldingusedcarbonelectrodes.butnowadaysthearcisstruckbetweenametalelectrodeandworkpiece.theelectrodemayeitherbeoftungstenorbeaconsumablemetalelectrodethatmeltsactingasasourceoffillermetal.电弧焊接的最早的形式使用碳电极,但现在的电弧触发一个金属电极与工件之间,电极可以是钨或可熔化,作为填充金属供源的消耗性金属电极
3.analternating-currentarcisbrokenandre-establishedateachhalfcycleandthisleadstoarcinstabilityalthoughtheuseofarc-establishedagentsinthefluxcoatingofelectrodewirescanovercomethisproblem.交流电弧被打破并且重新建立在每个半周期,这导致电弧不稳定虽然在电极布线焊剂涂层使用电弧建立剂可以克服这个问题
4.uncoatedweldingrodscanbeusedforarcwilding.butitismoreusualtouseflux-coatedelectrodes.whensteelsareweldedusinguncoatedelectrodesoxidesandnitridescanformandremainintheweldwithaconsequentlossoftoughness.未涂覆的焊条可以用于电弧焊但更通常使用的焊剂涂覆的电极当钢在使用未涂覆的电极焊接,氧化物和氮化物能够形成并保持在焊缝韧性因此而丧失
5.flux-coatedelectrodesarewidelyused.thecompositionofthecoatingsiscomplexandavarietyofdifferentcoatingsareusedtocaterfordifferenttypesofweldingapplication.焊剂涂覆的电极被广泛使用涂层的组成是复杂和各种不同的涂料是用于配合不同类型的焊接应用
6.inthiscasetheelectronflowisfromelectrodetowork-piece.Aconcentratedarcissuesfromtheelectrodetipandheatingofthework-pieceislargelyconfinedtotheverysmallaresbeneaththeelectrode.在这种情况下电子流动是从电极到工件,从电极头和工件的加热浓缩的弧的问题在很大程度上仅限于电极下方的非常小顷第十章钢
1.Insimpletermsaplaincarbonsteelmaybesaidtobeanalloyofironandcarboncontaininglessthan
1.7%carbon.Inpracticehoweverthesesteelsrarelycontainmorethan
1.4%carbonandotherelementsarealsopresenteitherasdeliberateadditionse.g.manganeseorasimpuritiese.g.sulphurandphosphorus.简单来说,普通碳素钢也被称为含碳量少于
1.7%的合金钢然而事实上,这些钢材中很少有含碳量多于
1.4%,同时也含有其它元素,例如一些额外添加物(如锰)或者杂质(如硫和磷)
2.Inthemanufactureofthismaterialcompletedeoxidationisnotcarriedoutanditismadeasrimmingsteel.Itisproducedashotandcoldwordedsheetstriprodwireandtubeandisavailableinthehot-workedorprocessannealedcondition.在材料的生产加工中,不能实现脱氧还原反应的钢被称为沸腾钢它被用来生产热处理或冷处理的薄片、带、棒、电线、和管,并且它适用热轧和退火的情况下
3.Thestrengthandhardnessofthesesteelislowbutahardsurfacecanbeobtainedbycarbursinginordertocombineawear-resistantsurfacewithtoughcoreproperties.钢的强度和硬度低,可以通过渗碳的方法获得表面硬化以达到表面耐寒内部韧性较好的特性
4.Asthecarboncontentisraisedabove
0.2%thestrengthincreasesintotherangerequiredforconstructionalpurposesbuttheductilitydecreases.Thefabricationqualitiesworkingandweldingcharacteristicsofthismaterialareverygood.一旦钢中含碳量上升超过
0.2%,结构上的强度会发生巨大变化,但是其延展性会下降材料的制造质量(承载和焊接特性)非常好
5.Mediumcarbonsteelsareoftenquenched-hardenedandfullytemperedtogivegoodstrengthwithmaximumtoughnesswhicharethepropertiesrequiredofcomponentssuchasshaftsgearsandconnectingrods.中碳钢常被淬火硬化和高温回火处理以便给予良好的温度和最大的韧性,这些是轴、齿轮和连杆所要求的能力特性
6.Highcarbonsteelsarequenchhardenedandlightlytemperedtogivehighhardnesswithonlylimitedtoughness.Materialinthisclassificationismainlyusedformakingfairlysmallrelativelyinexpensivecuttingtoolssothatthegroupasawholeisknownascarbontoolsteel.高碳钢常被淬火硬化和低温回火处理以便给予高硬度和一定韧性此类材料主要被用于生产相当小、可靠地、廉价的切削工具,者这就是碳素工具钢第十一章金属热加工
1.Theprincipalkindsofheat-treatmentusedinpractice.whichdifferentlyaffectthestructureandpropertiesandwhichareassignedtomeettherequirementsmadetothesemifabricatedmaterialscastingsforgingsrolledstocketc.andfinishedarticles:are1annealing2normalizing3hardeningand4tempering.所用的主要种类热处理的做法,以不同方式影响结构和性能,并分配给满足于半加工材料制成的要求(铸件锻件,轧材等)和必要的类型是
(1)退火
(2)正火,
(3)淬火和
(4)回火
2.Normalizingraisesthestrengthandhardnessofmediumandhigh-carbonsteelsby10to15percentascomparedtoannealedsteel.正火引起较退火的钢的强度和中等和高碳钢硬度由10至15%
3.Martensiteisveryhardandbrittlehavingamuchhighertensilestrengththanthesteelwithapearlitemicrostructure.马氏体是非常硬且脆的,具有高得多的抗张强度比钢具有珠光体组织
4.Temperingordrawingisaprocessofreheatingasteelpartthathasbeenpreviouslyhardenedtotransformhardmartensiteintosofterstructure.thehigherthetemperingtemperatureusedthesofterandtougherthepiecebecomes.回火,是再加热先前已硬化改造硬马氏体成较软的结构的钢部件的工艺回火温度中使用的较高,较软及更韧的片而成
5.Forlowcarbonsteelsnormalizingenablesabettersurfacefinishtobeobtainedinmachiningandraisetheproductioncapacity.对于低碳钢,正火使得能够在加工得到更好的表面光洁度,并提高生产能力
6.Incommercialtemperingthetemperaturerangeof250-425℃isusuallyavoidedbecauseofanunexplainedembrittlementorlossofductilitythatoftenoccurswithsteelstemperedinthisrange.在商业回火250-425℃的温度范围通常是可以避免的,因为一种原因不明的脆化,或塑性的损失,经常发生回火钢在此范围内15课Themaincomponentsofalathearetheheadstockandtailstockatoppositeendsofabedandatool-postbetweenthemwhichholdsthecuttingtool.车床的一个主要组成部分是车头和在床对面末的尾架,和在它们之间的刀架Thesizeofalatheisdesignatedbytwodimensions.Thefirstisknownastheswing.Thisisthemaximumdistancebetweencenters.Smallerenginelathes——withswingsusuallynotover330mm13inches——alsoareavailableintypedesignedforthebedtobemountedonabenchorcabinet.该车床的大小被指定两个维度第一个被称为摆动这是工作的最大直径可旋转车床第二个层面是大小中心之间的最大距离Althoughenginelatheareversatileandusefulbecauseofthetimerequiredforchangingandsettingtoolsandformakingmeasurementsontheworkspacetheyarenotsuitableforquantityproduction.虽然车床是多功能和有用的,因为改变和设置工具和工件上进行测量所需的时间,他们不合适的大量生产Howevermuchoftheoperator’stimeisconsumedbysimplerepetitiousadjustmentsandinwatchingchipsbeingmade.不过,运营商的大部分时间是消耗在简单,重复的调整和看芯片正在取得进展Consequentlytoreduceoreliminatetheamountofskilledlaborthatisrequiredturretlathesscrewmachinesandothertypesofsemiautomaticandautomaticlatheshavebeenhighlydevelopedandarewidelyusedinmanufacturing.因此,要减少或消除所需要的劳动技能,转塔车床,螺丝机量,半自动及自动车床等类型已经高度发达,被广泛用于生产中。