材料成型及控制工程專業(yè)外文翻譯-材料的選擇

外文原文：PhysicalPropertiesofMaterialsIntheselectionofmaterialsforindustrialapplications,manyengineersnormallyrefertotheiraveragemacroscopicproperties,asdeterminedbyengineeringtests,andareseldomconcernedwithmicroscopicconsiderations.Others,becauseoftheirspecialtyorthenatureoftheirpositions,havetodealwithmicroscopicproperties.Theaveragepropertiesofmaterialarethoseinvolvingmatterinbulk?-g??????~t**?*!?*!withitsflaws,variationsincomposition,andvariationsindensitythatarecausedbymanufacturingfluctuations.Microscopicpropertiespertaintoatoms,molecules,andtheirinteractions.Theseaspectsofmaterialarestudiedfortheirdirectapplicabilitytoindustrialproblemsandalsosothatpossiblepropertiesinthedevelopmentofthenewmaterialscanbeestimated.Inordernottobecomeconfusedbyapparentlycontradictoryconceptswhendealingwiththerelationshipbetweenthemicroscopicaspectsofmatterandtheaveragepropertiesofmaterials,itiswisetoconsidertheprinciplesthataccountforthenatureofmatteratthedifferentlevelsofourawareness.Theselevelsarethecommonplace,theextremelysmall,andtheextremelylarge.Thecommonplaceleverdealswiththeaveragepropertiesalreadymentioned,andtheprinciplesinvolvedarethosesetforthbyclassicalphysics.Therealmoftheextremelysmallislargelyexplainedbymeansofquantummechanics,whereasthatoftheextremelylargeisdealtwithbyrelativity.Relativityisconcernedwithverylargemasses,suchasplanetsorstars,andlargevelocitiesthatmayapproachthevelocityoflight.Itisalsoapplicabletosmallermasses,rangingdowntosubatomicparticles,whentheymoveathighvelocities.Relativityhasadefiniteplaceinthetoolboxesofnuclearengineersandelectricalengineerswhodealwithparticleaccelerators.Forproductionengineers,relativityisofonlyacademicinterestandismentionedhereforthesakeofcompleteness.MechanicalPropertiesofMaterialsOncetheimportantphysicalpropertiesofamaterialhavebeenestablished,mechanicalpropertiessuchasyieldstrengthandhardnessmustbeconsidered.Mechanicalpropertiesarestructure-sensitiveinthesensethattheydependuponthetypeofcrystalstructureanditsbondingforces,andespeciallyuponthenatureandbehavioroftheimperfectionsthatexitswithinthecrystalitselforatthegrainboundaries.Animportantcharacteristicthatdistinguishesmetalsfromothermaterialistheirductilityandabilitytobedeformedplasticallywithoutlossinstrength.Indesign,5to15percentelongationprovidesthecapacitytowithstandsuddendynamicoverloads.Inordertoaccommodatesuchloadswithoutfailure,materialsneeddynamictoughness,highmoduliofelasticity,andtheabilitytodissipateenergybysubstantialplasticdeformationpriortofracture.Topredictthebehaviorofamaterialunderload,engineersrequirereliabledataonthemechanicalpropertiesofmaterials.Handbookdataisavailablefortheaveragepropertiesofcommonalloysat68°F.Indesign,themostfrequentlyneededdataaretensileyieldstrength,hardness,modulusofelasticity,andyieldstrengthsattemperaturesotherthan68F.Designerslessfrequentlyuseresistancetocreep,notchsensitivity,impactstrength,andfatiguestrength.Suppliers'catalogsfrequentlygivemorerecentorcompletedata.Production-engineeringdatathatisseldomfoundinhandbooksincludestrength-to-weightratios,costperunitvolume,andresistancetospecificserviceenvironments.Abriefreviewofthemajormechanicalpropertiesandtheirsignificancetodesignisincludedtoensurethatthereaderisfamiliarwiththeimportantaspectsofeachtest.SelectingMaterialsAnever-increasingvarietyofmaterialsisavailable,eachhavingitsowncharacteristics,applications,advantages,andlimitations.Thefollowingarethegeneraltypesofmaterialsusedinmanufacturingtoday:Ironsandsteels(carbon,alloy,stainless,andtoolanddiesteels)Nonferrousmetalsandalloys(aluminum,magnesium,copper,nickel,titanium,superalloys,refractorymetal,beryllium,zirconium,low-meltingalloys,andpreciousmetals)Plastics(thermoplastics,thermosets,andelastomers)Ceramics,glassceramics,glasses,graphiteanddiamond.Compositematerials(reinforcedplastics,metal-matrixandceramic-matrixcomposites,andhoneycombstructures).PropertiesofmaterialsWhenselectingmaterialsforproducts,wefirstconsidertheirmechnicalproperties:strength,toughness,ductility,hardness,elasticity,fatigue,andcreep.Thestrength-to-weightandstiffness-to-weightratiosofmaterialarealsoimportant,particularlyforaerospaceandautomotiveapplications.Aluminum,titanium,andreinforcedplastics,forexample,havehigherratiosthansteelsandcastirons.Themechanicalpropertiesspecifiedforaproductanditscomponentsshouldofcoursebefortheconditionsunderwhichtheproductisexpectedtofunction.Wethenconsiderthephysicalpropertiesofdensity,specificheat,thermalexpansionandconductivity,meltingpoint,andelectricalandmagneticproperties.Chemicalpropertiesalsoplayasignificantroleinhostileaswellasnormalenvironments.Oxidationcorrosion,generaldegradationofproperties,toxicity,andflammabilityofmaterialsareamongtheimportantfactorstobeconsidered.Insomecommercialairlinedisasters,forexample,manydeathshavebeencausedbytoxicfumesfromburningnonmetallicmaterialsintheaircraftcabin.Manufacturingpropertiesofmaterialsdeterminewhethertheycanbecastformed,machined,welded,andheattreatedwithrelativeease.Themethodusedtoprocessmaterialstothedesiredshapescanadverselyaffecttheproduct'sfinalpropertiesandservicelife.AvailabilityandcostAvailabilityandcostofrawandprocessedmaterialsandmanufacturedcomponentsaremajorconcernsinmanufacturing.Competitively,theeconomicaspectsofmaterialselectionareasimportantasthetechnologicalconsiderationsofpropertiesandcharacteristicsofmaterials.Ifraworprocessedmaterialormanufacturedcomponentsarenotavailableinthedesiredquantities,shapes,anddimensions,substitutesand/oradditionalprocessingwillberequired,whichcancontributesignificantlytoproductcost.Forexample,ifweneedaroundbarofacertaindiameteranditisnotavailableinstandardform,thenwehavetopurchasealargerrodandreduceitsdiameterbysomemeans,suchasmachining,drawingthroughadie,orgrinding.Reliabilityofsupply,aswellasdemand,affectscost.Mostcountriesimportnumerousrawmaterialsthatareessentialforproduction.NotetherelianceoftheUnitedStatesonimportedrawmaterials.Thebroadpoliticalimplicationofsuchrelianceonothercountriesisself-evident.Differentcostsareinvolvedinprocessingmaterialsbydifferentmethods.Somemethodsrequireexpensivemachinery,othersrequireextensivelabor,andstillothersrequirepersonnelwithspecialskillsorahighlevelofeducationorspecializedtraining.Appearance,servicelife,anddisposalTheappearanceofmaterialsaftertheyhavebeenmanufacturedintoproductsinfluences.theirappealtotheconsumer.Color,feel,andsurfacetexturearecharacteristicsthatweallconsiderwhenmakingadecisionaboutpurchasingaproduct.Timeandservice-dependentphenomenasuchaswear,fatigue,creep,anddimensionalstabilityareimportant.Thesephenomenacansignificantlyaffectaproduct'sperformanceand,ifnotcontrolled,canleadtototalfailureoftheproduct.Similarly,compatibilityofmaterialsusedinaproductisimportant.Frictionandwear,corrosion,andotherphenomenacanshortenaproduct'slifeorcauseittofail.Anexampleisgalvanicactionbetweenmatingpartsmadeofdissimilarmetals,whichcorrodestheparts.Recyclingorproperdisposalofmaterialsattheendoftheirusefulserviceliveshasbecomeincreasinglyimportantinanageconsciousofmaintainingacleanandhealthyenvironment.None,forexample,theuseofbiodegradablepackagingmaterialsorrecyclableglassbottlesandaluminumbeveragecans.Theproperdisposaloftoxicwastesandmaterialsisalsoacrucialconsideration.中文譯文：1.材料的物理性能在選擇工業(yè)用材料時，許多工程師通常都只考慮其平均的宏觀性能，因為這些特性是由工程實驗確定的，而很少考慮其微觀特性。但有些工程師由于其專業(yè)范圍或所從事工作的需要，也考慮其微觀性能。材料的平均性能包括制造過程的波動引起的缺陷、組織的變化以及密度變化。微觀性能則與原子、分子以及它們的相互作用有關(guān)。為了使材料可直接用于工業(yè)，也為了在開發(fā)新材料時對可有的性能進行評估，因而需對材料的這些問題進行研究。當研究物質(zhì)的微觀性能與材料的平均性能之間的關(guān)系時，為了不至于將明顯矛盾的概念混淆，就應了解造成材料具有各種性能的原因。這些性能有一般的，微觀的、宏觀的。一般性能則是以上提到的平均性能，這些性能屬經(jīng)典物理學的范疇，微觀特性主要是由量子力學理論來解釋，而宏觀特性則是要由相對論來說明。相對論涉及的是類似行星那樣大的物體或接近于光速的物體，同時也適合于較小的物質(zhì)，如高速運行的亞原子粒子。對于核工程師、研究粒子加速器的電氣工程師，相對論也有一定的地位。而對于生產(chǎn)工程師，相對論僅是學術(shù)上的興趣，或是只因?qū)W科上的完整性而被提及。2.材料的機械性能在確定了材料的重要物理性能之后，就必須考慮其機械性能（如屈服強度和硬度）。機械性能具有結(jié)構(gòu)敏感性，因為它們?nèi)Q于晶體結(jié)構(gòu)的類型及結(jié)合力，特別是取決于晶體內(nèi)容或晶粒邊界上缺陷的特性。區(qū)分金屬與其他材料的一個重要特性是其塑性及在強度沒有減少的條件下塑性變形的能力。設計時，延伸率為5—15%則可使其承受突然的動態(tài)過載。為了適應這類載荷而不破壞，材料應具有動態(tài)韌性、較大的彈性模量以及經(jīng)過斷裂之前產(chǎn)生足夠的塑性變形以消耗能量的能力。為了預測材料受載后的特性，工程師需要材料機械性能的可靠數(shù)據(jù)。手冊中的數(shù)據(jù)是普通合金在68°F時的平均特性。設計時最常用的數(shù)據(jù)是拉伸屈服強度、硬度、彈性模量，在其他溫度時（除68°F之外）的屈服強度。設計者很少用到抗蠕變特性、缺口敏感性、沖擊強度以及疲勞強度。材料廠商的樣本中通常也提供最新的或完整的數(shù)據(jù)。在手冊中很難找到生產(chǎn)工程中所需的象強重比、單位體積的成本以及對特定工作環(huán)境的承受能力等數(shù)據(jù)。材料的主要機械性能及其對設計的重要影響的簡單回顧可使讀者熟悉每一種試驗的重要性。3.材料的選擇各類實用的材料在不斷增長，而每種材料都具有各自的特點、應用范圍及優(yōu)缺點。當今制造業(yè)中常用的材料有：鐵和鋼（碳鋼、合金鋼、不銹鋼、工具鋼和模具鋼）。有色金屬及其合金（鋁、鎂、銅、鎳、鈦、超耐熱合金、高熔點金屬、鈹、鋯、低熔點合金以及貴金屬）。塑料（熱塑塑料、熱固塑料及合成橡膠）。陶瓷、玻璃陶瓷、玻璃、石墨、金剛石。復合材料（增強塑料、金屬基符合材料、陶瓷基復合材料、蜂窩結(jié)構(gòu)復合材料）。1）材料性能當選擇產(chǎn)品的材料時，首先要考慮的是材料的機械性能：強度、韌性、塑性、硬度、彈性、疲勞強度、抗蠕變性。材料的強重比以及剛度與重量比也是重要的特性，特別是用于航空及汽車工業(yè)的材料。鋁、鈦及增強塑料的上述二種比值比鋼和鑄鐵的高。當然，產(chǎn)品及其零件材料的機械性能應根據(jù)產(chǎn)品發(fā)