机械工程英语翻译.docx

机械工程英语翻译.docx

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机械工程英语翻译

第一单元：

TypesofMaterials材料的类型

Materialsmaybegroupedinseveralways.Scientistsoftenclassifymaterialsbytheirstate:

solid,liquid,orgas.Theyalsoseparatethemintoorganic（onceliving）andinorganic（neverliving）materials.

Forindustrialpurposes,materialsaredividedintoengineeringmaterialsornonengineeringmaterials.Engineeringmaterialsarethoseusedinmanufactureandbecomepartsofproducts.

Nonengineeringmaterialsarethechemicals,fuels,lubricants,andothermaterialsusedinthemanufacturingprocess,whichdonotbecomepartoftheproduct.

Engineeringmaterialsmaybefurthersubdividedinto:

①Metal②Ceramics③Composite④Polymers,etc.

•MetalsandMetalAlloys金属和金属合金

Metalsareelementsthatgenerallyhavegoodelectricalandthermalconductivity.Manymetalshavehighstrength,highstiffness,andhavegoodductility.

Somemetals,suchasiron,cobaltandnickel,aremagnetic.Atlowtemperatures,somemetalsandintermetalliccompoundsbecomesuperconductors.

Whatisthedifferencebetweenanalloyandapuremetal?

Puremetalsareelementswhichcomefromaparticularareaoftheperiodictable.Examplesofpuremetalsincludecopperinelectricalwiresandaluminumincookingfoilandbeveragecans.

Alloyscontainmorethanonemetallicelement.Theirpropertiescanbechangedbychangingtheelementspresentinthealloy.Examplesofmetalalloysincludestainlesssteelwhichisanalloyofiron,nickel,andchromium;andgoldjewelrywhichusuallycontainsanalloyofgoldandnickel.

Whyaremetalsandalloysused?

Manymetalsandalloyshavehighdensitiesandareusedinapplicationswhichrequireahighmass-to-volumeratio.

Somemetalalloys,suchasthosebasedonaluminum,havelowdensitiesandareusedinaerospaceapplicationsforfueleconomy.Manyalloysalsohavehighfracturetoughness,whichmeanstheycanwithstandimpactandaredurable.

Whataresomeimportantpropertiesofmetals?

金属有哪些重要特性？

Densityisdefinedasamaterial’smassdividedbyitsvolume.Mostmetalshaverelativelyhighdensities,especiallycomparedtopolymers.

Materialswithhighdensitiesoftencontainatomswithhighatomicnumbers,suchasgoldorlead.However,somemetalssuchasaluminumormagnesiumhavelowdensities,andareusedinapplicationsthatrequireothermetallicpropertiesbutalsorequirelowweight.

Fracturetoughnesscanbedescribedasamaterial’sabilitytoavoidfracture,especiallywhenaflawisintroduced.Metalscangenerallycontainnicksanddentswithoutweakeningverymuch,andareimpactresistant.Afootballplayercountsonthiswhenhetruststhathisfacemaskwon’tshatter.

Plasticdeformationistheabilityofbendordeformbeforebreaking.Asengineers,weusuallydesignmaterialssothattheydon’tdeformundernormalconditions.Youdon’twantyourcartoleantotheeastafterastrongwestwind.

However,sometimeswecantakeadvantageofplasticdeformation.Thecrumplezonesinacarabsorbenergybyundergoingplasticdeformationbeforetheybreak.

Theatomicbondingofmetalsalsoaffectstheirproperties.Inmetals,theoutervalenceelectronsaresharedamongallatoms,andarefreetotraveleverywhere.Sinceelectronsconductheatandelectricity,metalsmakegoodcookingpansandelectricalwires.

Itisimpossibletoseethroughmetals,sincethesevalenceelectronsabsorbanyphotonsoflightwhichreachthemetal.Nophotonspassthrough.

Alloysarecompoundsconsistingofmorethanonemetal.Addingothermetalscanaffectthedensity,strength,fracturetoughness,plasticdeformation,electricalconductivityandenvironmentaldegradation.

Forexample,addingasmallamountofirontoaluminumwillmakeitstronger.Also,addingsomechromiumtosteelwillslowtherustingprocess,butwillmakeitmorebrittle.

•CeramicsandGlasses陶瓷和玻璃

Aceramicisoftenbroadlydefinedasanyinorganicnonmetallicmaterial．Bythisdefinition,ceramicmaterialswouldalsoincludeglasses;however,manymaterialsscientistsaddthestipulationthat“ceramic”mustalsobecrystalline.

Aglassisaninorganicnonmetallicmaterialthatdoesnothaveacrystallinestructure.Suchmaterialsaresaidtobeamorphous.

PropertiesofCeramicsandGlasses

Someoftheusefulpropertiesofceramicsandglassesincludehighmeltingtemperature,lowdensity,highstrength,stiffness,hardness,wearresistance,andcorrosionresistance.

Manyceramicsaregoodelectricalandthermalinsulators.Someceramicshavespecialproperties:

someceramicsaremagneticmaterials;somearepiezoelectricmaterials;andafewspecialceramicsaresuperconductorsatverylowtemperatures.Ceramicsandglasseshaveonemajordrawback:

theyarebrittle.

Ceramicsarenottypicallyformedfromthemelt.Thisisbecausemostceramicswillcrackextensively（i.e.formapowder）uponcoolingfromtheliquidstate.

Hence,allthesimpleandefficientmanufacturingtechniquesusedforglassproductionsuchascastingandblowing,whichinvolvethemoltenstate,cannotbeusedfortheproductionofcrystallineceramics.Instead,“sintering”or“firing”istheprocesstypicallyused.

Insintering,ceramicpowdersareprocessedintocompactedshapesandthenheatedtotemperaturesjustbelowthemeltingpoint.Atsuchtemperatures,thepowdersreactinternallytoremoveporosityandfullydensearticlescanbeobtained.

Anopticalfibercontainsthreelayers:

acoremadeofhighlypureglasswithahighrefractiveindexforthelighttotravel,amiddlelayerofglasswithalowerrefractiveindexknownasthecladdingwhichprotectsthecoreglassfromscratchesandothersurfaceimperfections,andanoutpolymerjackettoprotectthefiberfromdamage.

Inorderforthecoreglasstohaveahigherrefractiveindexthanthecladding,thecoreglassisdopedwithasmall,controlledamountofanimpurity,ordopant,whichcauseslighttotravelslower,butdoesnotabsorbthelight.

Becausetherefractiveindexofthecoreglassisgreaterthanthatofthecladding,lighttravelinginthecoreglasswillremaininthecoreglassduetototalinternalreflectionaslongasthelightstrikesthecore/claddinginterfaceatananglegreaterthanthecriticalangle.

Thetotalinternalreflectionphenomenon,aswellasthehighpurityofthecoreglass,enableslighttotravellongdistanceswithlittlelossofintensity.

•Composites复合材料

Compositesareformedfromtwoormoretypesofmaterials.Examplesincludepolymer/ceramicandmetal/ceramiccomposites.Compositesareusedbecauseoverallpropertiesofthecompositesaresuperiortothoseoftheindividualcomponents.

Forexample:

polymer/ceramiccompositeshaveagreatermodulusthanthepolymercomponent,butaren’tasbrittleasceramics.

Twotypesofcompositesare:

fiber-reinforcedcompositesandparticle-reinforcedcomposites.

Fiber-reinforcedComposites纤维加强型复合材料

Reinforcingfiberscanbemadeofmetals,ceramics,glasses,orpolymersthathavebeenturnedintographiteandknownascarbonfibers.Fibersincreasethemodulusofthematrixmaterial.

Thestrongcovalentbondsalongthefiber’slengthgivethemaveryhighmodulusinthisdirectionbecausetobreakorextendthefiberthebondsmustalsobebrokenormoved.

Fibersaredifficulttoprocessintocomposites,makingfiber-reinforcedcompositesrelativelyexpensive.

Fiber-reinforcedcompositesareusedinsomeofthemostadvanced,andthereforemostexpensivesportsequipment,suchasatime-trialracingbicycleframewhichconsistsofcarbonfibersinathermosetpolymermatrix.

Bodypartsofracecarsandsomeautomobilesarecompositesmadeofglassfibers（orfiberglass）inathermosetmatrix.

Fibershaveaveryhighmodulusalongtheiraxis,buthavealowmodulusperpendiculartotheiraxis.Fibercompositemanufacturersoftenrotatelayersoffiberstoavoiddirectionalvariationsinthemodulus.

Particle-reinforcedcomposites微粒加强型复合材料

Particlesusedforreinforcingincludeceramicsandglassessuchassmallmineralparticles,metalparticlessuchasaluminum,andamorphousmaterials,includingpolymersandcarbonblack.

Particlesareusedtoincreasethemodulusofthematrix,todecreasethepermeabilityofthematrix,todecreasetheductilityofthematrix.Anexampleofparticle-reinforcedcompositesisanautomobiletirewhichhascarbonblackparticlesinamatrixofpolyisobutyleneelastomericpolymer.

•Polymers聚合材料

Apolymerhasarepeatingstructure,usuallybasedonacarbonbackbone.Therepeatingstructureresultsinlargechainlikemolecules.Polymersareusefulbecausetheyarelightweight,corrosionresistant,easytoprocessatlowtemperaturesandgenerallyinexpensive.

Someimportantcharacteristicsofpolymersincludetheirsize（ormolecularweight）,softeningandmeltingpoints,crystallinity,andstructure.Themechanicalpropertiesofpolymersgenerallyincludelowstrengthandhightoughness.Theirstrengthisoftenimprovedusingreinforcedcompositestructures.

ImportantCharacteristicsofPolymers

Size.Singlepolymermoleculestypicallyhavemolecularweightsbetween10,000and1,000,000g/mol—thatcanbemorethan2,000repeatingunitsdependingonthepolymerstructure!

Themechanicalpropertiesofapolymeraresignificantlyaffectedbythemolecularweight,withbetterengineeringpropertiesathighermolecularweights.

Thermaltransitions.Thesofteningpoint（glasstransitiontemperature）andthemeltingpointofapolymerwilldeterminewhichitwillbesuitableforapplications.Thesetemperaturesusuallydeterminetheupperlimitforwhichapolymercanbeused.

Forexample,manyindustriallyimportantpolymershaveglasstransitiontemperaturesneartheboilingpointofwater（100℃,212℉）,andtheya