机械全APS.docx

机械全APS.docx

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机械全APS

一、EngineeringMaterialsandHeatTreatment

Thislesson,istudyengineeringmaterialsandheattreatment.Engineeringmaterials,istudysteelandcastiron,includeiron-carbonphasediagram.

Heattreatment,istudynormalizingquenchingtemperingandannealing.

Iron-carbonphasediagram,showingthetemperatureandcarbonrangesforcertaintypesofheattreatments.

Withthecarbonrise/increase,materialsbecomemoreandmorebrittle,strengthincrease,hardnessincrease,butplasticitydecrease.

ABCD---liquidline,upisliquidzone

AHJECF---solidline,downissolidzone

HJB---peritecticline,whenthecarbonrangefrom0.09percentto0.53percent,materialscooldownthisline,itwillperitectictransformation

ECF---eutecticline,whenthecarbonrangefrom2.11percentto6.69percent,materialscooldownthisline,itwilleutectictransformation

produceledeburite.

PSK---eutectoidline,whenthecarbonrangefrom0.0218percentto2.11percent,materialscooldownthisline,itwilleutectoidtransformation

producepearlite.

Ferrite:

aninterstitialsolidsolutionofcarboninFeα,atroomtemperatureferriteisductilebutnotverystrong.

Austenite:

aninterstitialsolidsolutionofcarboninFeγ

Cementite:

acompoundofcarbonandFe

Steelisanalloyofcarbonandironandotheralloyingelements（e.g.Mn,Si）withcontentupto2.11%intendedforwroughtproductsorsemi-products.

Castironisanalloyofcarbonandironandotheralloyingelements（e.g.Mn,Si）withcarboncontentover2.11%intendedforcasting.

Perliteisastructure（i.e.Consistsoftwophases）consistsofalternatelayersofferriteandcementite[intheproportion87:

13byweight]

Perliteisformedfromausteniteateutectoidtemperature（A1）727℃uponslowcooling.

Therearethreegroupsofsteelsaccordingtocarboncontent:

Hypoeutectoidsteelscontaininglessthan0.77%C

Eutectoidsteelswithcarboncontentabout0.77%

Hypereutectoidsteelscontainmorethan0.77%C（upto2.11%C）

Ledeburiteisastructure（i.e.Consistsoftwophase）consistsofalternatelayersofausteniteandcementite.

Ledeburiteisformedfromliquidateutectictemperature1148℃uponslowcooling.

Fromeutectictemperature1148℃toeutectoidtemperature727℃,ledeburiteiscalledbyhightemperatureledeburite.

Beloweutectoidtemperature727℃，ledeburiteiscalledbylowtemperatureledeburite.

Therearethreegroupsofcastironaccordingtocaarboncontent:

Hypoeutecticcastironcontaininglessthan4.3%C（upto2.11%C）

Eutecticcastironwithcarboncontentabout4.3%

Hypereutecticcastironcontainmorethan4.3%C（upyo6.69%C）

Normalizing

Heatthesteeltoacertaintemperature,keepthetemperatureforaperiodoftime,thenputitintheair,slowlycoolittotheroomtemperature.

CertaintemperatureisaboveAC3orACm,from30℃to50℃。

Carbonsteelheatedtoapproximately55℃aboveAC3orACmfor1hour,thisassuresthesteelcompletelytransformstoaustenite.Thesteelisthenair-cooled,whichisacoolingrateofapproximately38℃perminute.Thisresultsinafinepearliticstructure,andamore-uniformstructure.

Normalizingsteelhasahigherstrengththanannealedsteel,ithasarelativelyhighstrengthandductility.

Quenching

Heatthesteeltoacertaintemperature,keepthetemperatureforaperiodoftime,thenputitintowateroroil,makeittobecooledquicklytotheroomtemperature.

CertaintemperatureisaboveAC3orAC1,from30℃to50℃。

Carbonsteelwithatleast0.4%Cisheatedtonormalizingtemperatureandthenrapidlycooled（quenched）inwater,brineoroiltothecriticaltemperature.

Quenchedsteelisextremelyhardbutbrittle,usuallytoobrittleforpracticalpurposes.Theseinternalstressescausestresscranksonthesurface.Quenchedsteelisapproximatelythreetofourfoldharderthannormalizedsteel.

Tempering

Heatthequenchedtobemartensitesteeltoacertaintemperature,keepthetemperatureforaperiodoftime,thencoolittotheroomtemperatureintheair.

CertaintemperatureisbelowAC1

150℃~260℃370℃~650℃

Temperinginvolvesreheatingquenchedsteeltoatemperaturebelowtheeutectoidtemperaturethencooling.

Function:

1.Improvesductilityandtoughness

2.Reducecranking

3.Improvesmachinability

4.Increaseimpactresistance

5.Improvesmalleability

Temperingintherangeof260℃~370℃issometimesavoidedtoreducetemperingbrittling.

Lowtempering150℃~260℃1mold

Averagetempering370℃~500℃5spring

Hightempering500℃~650℃3gear

Annealing

Heatthesteeltoacertaintemperature,keepthetemperatureforaperiodoftime,putitinthefurnaceslowlycoolittoroomtemperature.

Annealingisusedtoinduceductility,softenmaterial,relieveinternalstresses,refinethestructurebymakingithomogeneous,andimprovecoldworkingproperties.

Processannealing500℃~650℃restoressomeoftheductilitytoaworkpieceallowingitbeworkedfurtherwithoutbreaking.

Fullannealing.Carbonsteelisheatedtoapproximately40℃aboveAc3orAc1for1hour,thisassuresalltheferritetransformsintoaustenite.Thesteelmustthenbecooledslowlyintherealmof38℃perhour.Usuallyitisjustfurnacecooled,wherethefurnaceisturnedoffwiththesteelstillinside.Thisresultsinacoarsepearliticstructure,whichmeansthe"bands"ofpearlitearethick.Fully-annealedsteelissoftandductile,withnointernalstresses,whichisoftennecessaryforcost-effectiveforming.Onlyspheroidizedsteelissoferandmoreductile.

Spheroidizing.Spheroidizeformswhencarbonsteelisheatedtoapproximately700℃forover30hours.Theresultsisastructureofrodsorspheresofcementitewithinferriteorpearlite.Thepurposeistosoftenhighercarbonsteelsandallowmoreformability.

2、Mechanicsofmaterials（问过此课程）

Inmaterialsscience,thestrengthofamaterialreferstomaterial`sabilitytoresistanappliedforce.

Compressstress:

（orcompression）isthestressstatewhenthematerial（compressionmember）tendstocompact.

Tensilestress:

isaloadingthattendstoproducestretchingofamaterialbytheapplicationofaxiallydirectedpullingforce.

Shearstress:

iscausedwhenaforceisappliedtoproduceaslidingfailureofamaterialalongaplanethatisparalleltothedirectionoftheappliedforce.

Yieldstrength:

istheloweststressthatgivespermanentdeformationinamaterial.Insomematerials,likealuminumalloys,thepointofyieldingishardtodefine,thusitisusuallygivenasthestressrequiredtocause0.2%plasticstrain.

Compressivestrength:

isalimitstateofcompressivestressthatleadstocompressivefailureinthemannerofductilefailureorinthemannerofbrittlefailure.

Tensilestrength:

orultimatetensilefailureisalimitstateoftensilestressthatleadstotensilefailureinthemannerofductilefailureorinthemannerofbrittlefailure.

Fatiguestrength:

isameasureofthestrengthofamaterialoracomponentundercyclicloading,andisusuallymoredifficulttoassessthanthestaticstrengthmeasures.

Impactstrength:

itisthecapabilityofthematerialinwithstandingbythesuddenlyappliedloadsintermsofenergy.

Deformationofthematerialisthechangeingeometrywhenstressisapplied.

Strainorreduceddeformationisamathematicaltermtoexpressthetrendofthedeformationchangeamongthematerialfield.

Deflectionisatermtodescribethemagnitudetwhichastructuralelementbendsunderaload.

Elasticityistheabilityofamaterialtoreturntoitspreviousshapeafterstressisreleased.Inmanymaterials,therelationbetweenappliedstressandtheresultingstrainisdirectlyproportional（uptoacertainlimit）,andagraphrepresentingthosetwoquantitiesisastraightline.

TheslopeofthislineknownasYoung`sModulus,orthe"ModulusofElasticity".Themodulusofelasticitycanbeusedtodeterminestress-strainrelationshipsinthelinear-elasticportionofthestress-straincurve.Thelinear-elasticregionistakentobebetween0and0.2%strain,andisdefinedastheregionofstraininwhichnoyielding（permanentdeformation）occurs.

Plasticityorplasticdeformationistheoppositeofelasticdeformationandisacceptedasunrecoverablestrain.Plasticdeformationisretainedevenaftertherelaxationoftheappliedstress.Mostmaterialsinthelinear-elasticcategoryareusuallycapableofplasticdeformation.Brittlematerials,likeceramics,donotexperienceanyplasticdeformationandwillfractureunderrelativelylowstress.Materialssuchasmetalsusuallyexperienceasmallamountofplasticdeformationbeforefailurewhilesoftofductilepolymerswillplasticitydeformmuchmore.

Plasticmaterial:

tensilestrengthiswell,compressivestrengthisbad.

ab:

elasticphase:

giveaforce/tensileforworkpiece,thisparthavenottheobviousdeformation,whenwecanceltheforce,thestressandstrainwilldisappear,thesteelwillreturntotheoriginalshape.

bc:

yieldphase:

giveaforceforworkpiece,thestrainwillincrease,thestresshasalittlechanging,ifwecanceltheforce,theworkpiecehasplasticdeformation.

cd:

strengthphase:

giveaforceforworkpiece,thestrainandstresswillincrease,workpiecehasaobviousdeformation,theinnerstructurehasbedestroy,itwillbecomeslender,point"d"meansthematerialcanbearthebiggeststress.

de:

localdeformationphase:

giveaforceforworkpiece,thestresswillreduce,thestainwillincrease,theplasticdeformationwillgoonincreasing,atthistime,thematerialwillhaveaphenomenon,wecalled"necking"deformationfocusonnecking,atlast,thematerialwillbreakout.

Brittlematerial:

tensilestrengthisbad,compressiveiswell.

3、Fundamentalsofmechanic