機(jī)械工程材料雙語課件1

Chapter1PropertiesofMaterialsApplicationProperties：Propertiesperformedwhenthematerialswereapplied,includingmechanicalproperties,physicalpropertiesandchemicalproperties.Processesproperties：Propertiesperformedwhenthematerialsweremachined,includingcasting,forging,jointing,heattreatmentandcuttingproperties.第一章材料的性能使用性能：材料在使用過程中所表現(xiàn)的性能。包括力學(xué)性能、物理性能和化學(xué)性能。工藝性能：材料在加工過程中所表現(xiàn)的性能。包括鑄造、鍛壓、焊接、熱處理和切削性能等。神舟一號(hào)飛船Deformationisthealternationofshapeandsizeofmaterialsunderexternalforce.Elasticdeformationcouldrecoveraftertheexternalforceismovedaway.Plasticdeformationcouldnotrecoveraftertheexternalforceismovedaway.材料在外力的作用下將發(fā)生形狀和尺寸變化，稱為變形。外力去處后能夠恢復(fù)的變形稱為彈性變形。外力去處后不能恢復(fù)的變形稱為塑性變形。五萬噸水壓機(jī)低碳鋼的應(yīng)力-應(yīng)變曲線拉伸試樣拉伸試驗(yàn)機(jī)應(yīng)力(R)=P/F0應(yīng)變

=(l-l0)/l01.ElasticityandRigidityElasticity:Elasticlimit

Re(e)，thestresswhenmaterialisbearingthemaximumdeformation.Rigidity：Young’smodulusE,thematerial’sabilitytoresistplasticdeformation.eYoung’smodulusismainlydeterminedbythenatureofthematerial,theparts’rigiditycouldbeimprovedbyincreasingthecross-sectionareaoralteringtheshapeofthecross-sectionareas.

一、彈性和剛度彈性：指標(biāo)為彈性極限e(Re)，即材料承受最大彈性變形時(shí)的應(yīng)力。剛度：材料受力時(shí)抵抗彈性變形的能力。指標(biāo)為彈性模量E。e彈性模量的大小主要取決于材料的本性，除隨溫度升高而逐漸降低外，其他強(qiáng)化材料的手段如熱處理、冷熱加工、合金化等對(duì)彈性模量的影響很小?？梢酝ㄟ^增加橫截面積或改變截面形狀來提高零件的剛度。

2.StrengthandPlasticityStrength：theabilitytoresistdeformationandruptureunderexternalforces。

Yieldstrengths：thestresswhenplasticdeformationoccurs.

Offsetyieldstrength0.2：thestresswhenresidualdeformationis0.2%.

Tensilestrengthb：themaximumstressbeforethematerialcollapse.s0.2二、強(qiáng)度與塑性強(qiáng)度：材料在外力作用下抵抗變形和破壞的能力。

屈服強(qiáng)度ss：材料發(fā)生微量塑性變形時(shí)的應(yīng)力值。

條件屈服強(qiáng)度0.2：殘余變形量為0.2%時(shí)的應(yīng)力值。

抗拉強(qiáng)度b：材料斷裂前所承受的最大應(yīng)力值。s0.2Plasticity：theabilitytobearthemaximumplasticdeformationbeforethematerialcollapseunderexternalforces.

Extensibility：Contractionrateofcrosssectionalarea：斷裂后塑性：材料受力破壞前可承受最大塑性變形的能力。

指標(biāo)為：

伸長率：斷面收縮率：斷裂后拉伸試樣的頸縮現(xiàn)象Instructions:①

Contractionrateofcrosssectionalareais

closertoactualdeformationthanextensibility.②Whend0isthesame,l0,.Onlywhenl0/d0isaconstant,plasticsindexiscomparable.Whenl0=10d0,

isusedforextensibility.Andwhenl0=5d0,5isusedforextensibility,obviously,5>③

When

>,nonecking,brittlematerial

When

<時(shí),necking,plasticmaterial說明：①

用面縮率表示塑性比伸長率更接近真實(shí)變形。②直徑d0相同時(shí)，l0，。只有當(dāng)l0/d0為常數(shù)時(shí)，塑性值才有可比性。當(dāng)l0=10d0時(shí)，伸長率用

表示；當(dāng)l0=5d0時(shí)，伸長率用5表示。顯然5>③

>時(shí)，無頸縮，為脆性材料表征

<時(shí)，有頸縮，為塑性材料表征3.Impactflexibility

Theabilitytoresistimpactloadwithoutruptures.Impactflexibilityak(obtainedbyexperiments)。三、沖擊韌性是指材料抵抗沖擊載荷作用而不破壞的能力。指標(biāo)為沖擊韌性值ak(通過沖擊實(shí)驗(yàn)測(cè)得)。Ductile-brittletransitiontemperatureImpactductilityofthematerialsdecreasesastemperature.Therapiddecreaseofimpactductilityundercertaintemperaturescopeiscalledductile-brittletransition.Thetemperaturescopeofductile-brittletransitioniscalledductile-brittletransitiontemperature.Applicationtemperatureofmaterialsshouldbeabovetheductile-brittletransitiontemperature.韌Thereisaductile-brittletransitiontemperature

formetalsofbodycenteredcubicstructurehave,butnotformostfacecenteredmetals.韌脆轉(zhuǎn)變溫度材料的沖擊韌性隨溫度下降而下降。在某一溫度范圍內(nèi)沖擊韌性值急劇下降的現(xiàn)象稱韌脆轉(zhuǎn)變。發(fā)生韌脆轉(zhuǎn)變的溫度范圍稱韌脆轉(zhuǎn)變溫度。材料的使用溫度應(yīng)高于韌脆轉(zhuǎn)變溫度。韌體心立方金屬具有韌脆轉(zhuǎn)變溫度，而大多數(shù)面心立方金屬?zèng)]有。TITANIC建造中的Titanic號(hào)TITANIC的沉沒與船體材料的質(zhì)量直接有關(guān)Titanic號(hào)鋼板（左圖）和近代船用鋼板（右圖）的沖擊試驗(yàn)結(jié)果Titanic近代船用鋼板4.FatigueMaterialruptureoccursunderrepeatingalternatestressbelows.Fatiguelimitisthemaximumstressunderwhichthematerialdoesnotruptureaftergiventimesofstresscycles,namedas-1.Thegiventimesis107forsteelandiron,108fornonferrousmetals.疲勞應(yīng)力示意圖疲勞曲線示意圖四、疲勞材料在低于s的重復(fù)交變應(yīng)力作用下發(fā)生斷裂的現(xiàn)象。材料在規(guī)定次數(shù)應(yīng)力循環(huán)后仍不發(fā)生斷裂時(shí)的最大應(yīng)力稱為疲勞極限。用-1表示。鋼鐵材料規(guī)定次數(shù)為107，有色金屬合金為108。疲勞應(yīng)力示意圖疲勞曲線示意圖FatiguefractureFatigueresistancecouldbeimprovedbyimprovetheshapeandstructures,lessensurfacefaults,improvesurfacesmoothness,andsurfacepeening.ThefatiguefractureofshaftFatiguestriation（bySEM）疲勞斷口通過改善材料的形狀結(jié)構(gòu)，減少表面缺陷，提高表面光潔度，進(jìn)行表面強(qiáng)化等方法可提高材料疲勞抗力。軸的疲勞斷口疲勞輝紋（掃描電鏡照片）5.HardnessTheabilitytoresistlocalplasticdeformationonthesurfaceBrinellhardness:HB布氏硬度計(jì)五、硬度材料抵抗表面局部塑性變形的能力。布氏硬度HB布氏硬度計(jì)

HBSisusedwhenthepressure

headissteelball,whichissuitableformaterialsbelow450.HBWisusedwhenthepressure

headishardalloyball,whichissuitableformaterialsbelow650.ThenumberbeforeHBSorHBWmeanshardness,andnumbersafteritmeandiameteroftheball,loadandholdingtimeoftheload.Forexample,120HBS10/1000/30meanshardnessis120whenthediameterofsteelballis10mm,andaloadof1000kgf(9.807kN)iskeptfor30s.布氏硬度壓痕

壓頭為鋼球時(shí)，布氏硬度用符號(hào)HBS表示，適用于布氏硬度值在450以下的材料。壓頭為硬質(zhì)合金球時(shí)，用符號(hào)HBW表示，適用于布氏硬度在650以下的材料。符號(hào)HBS或HBW之前的數(shù)字表示硬度值,符號(hào)后面的數(shù)字按順序分別表示球體直徑、載荷及載荷保持時(shí)間。如120HBS10/1000/30表

示直徑為10mm的鋼球在1000kgf（9.807kN）載荷作用下保持30s測(cè)得的布氏硬度值為120。布氏硬度壓痕Merits:smallmeasuringerror,stabledataDemerits:largeindentation，unsuitableforthinparts,finishproductsandmaterialsharderthanthepresshead.Applicabletomeasurethehardnessofannealed,normalized,hardenedandtemperedsteel,castiron,aswellasnonferrousmetals.TherelationshipbetweenbandHB:forlowcarbonsteel:

b(MPa)≈3.6HB

forhighcarbonsteel:b(MPa)≈3.4HB

forcastiron:

b(MPa)≈1HBorb(MPa)≈

0.6(HB-40)HBb(MPa)鋼黃銅球墨鑄鐵布氏硬度的優(yōu)點(diǎn)：測(cè)量誤差小，數(shù)據(jù)穩(wěn)定。缺點(diǎn)：壓痕大，不能用于太薄件、成品件及比壓頭還硬的材料。適于測(cè)量退火、正火、調(diào)質(zhì)鋼,

鑄鐵及有色金屬的硬度。材料的b與HB之間的經(jīng)驗(yàn)關(guān)系：對(duì)于低碳鋼:

b(MPa)≈3.6HB

對(duì)于高碳鋼：b(MPa)≈3.4HB

對(duì)于鑄鐵：

b(MPa)≈1HB或b(MPa)≈

0.6(HB-40)HBb(MPa)鋼黃銅球墨鑄鐵RockwellhardnessRockwellhardness:HR,HR=k-(h1-h0)/0.002Classifiedinto9scalesaccordingtothedifferent

pressureheadtypeandmainload,amongwhichA,BandCaremostusuallyused.h1-h0洛氏硬度測(cè)試示意圖洛氏硬度計(jì)洛氏硬度洛氏硬度用符號(hào)HR表示，HR=k-(h1-h0)/0.002根據(jù)壓頭類型和主載荷不同，分為九個(gè)標(biāo)尺，常用的標(biāo)尺為A、B、C。

h1-h0洛氏硬度測(cè)試示意圖洛氏硬度計(jì)ThenumberbeforeHRishardness,scaleisafterHRHRAisusedtomeasurehighhardnessmaterials,suchashardalloys,surfacequenchedlayersandcarburizedlayers.HRBisusedtomeasurelowhardnessmaterials,suchasnonferrousmetals,annealedsteelsandnormalizedsteels.HRCisusedtomeasuremediumhardnessmaterials,suchashardenedandtemperedsteels,quenchedsteels.

Merits:easytooperate,smallindentation,widescopeofapplications.Demerits:largedispersiondegreeofmeasuringresults.鋼球壓頭與金剛石壓頭洛氏硬度壓痕符號(hào)HR前面的數(shù)字為硬度值，后面為使用的標(biāo)尺。HRA用于測(cè)量高硬度材料,如硬質(zhì)合金、表淬層和滲碳層。HRB用于測(cè)量低硬度材料,如有色金屬和退火、正火鋼等。HRC用于測(cè)量中等硬度材料，如調(diào)質(zhì)鋼、淬火鋼等。洛氏硬度的優(yōu)點(diǎn)：操作簡便，壓痕小，適用范圍廣。缺點(diǎn)：測(cè)量結(jié)果分散度大。鋼球壓頭與金剛石壓頭洛氏硬度壓痕VickersHardnessVickershardmeterTestprinciplesIndentation維氏硬度維氏硬度計(jì)維氏硬度試驗(yàn)原理維氏硬度壓痕Vickershardness:HV,thenumberbeforeHVishardness,andnumbersafteritmeanloadandloadholdingtime.Threetestingmethodaredefinedaccordingtothedifferentloadscope:vickershardnesstest,smallloadvickershardnesstestandmicroscopevickershardnesstest.Vickershardnesskeepsthemeritsof

brinellhardnessandrockwellhardness小負(fù)荷維氏硬度計(jì)顯微維氏硬度計(jì)維氏硬度用符號(hào)HV表示，符號(hào)前的數(shù)字為硬度值，后面的數(shù)字按順序分別表示載荷值及載荷保持時(shí)間。根據(jù)載荷范圍不同，規(guī)定了三種測(cè)定方法—維氏硬度試驗(yàn)、小負(fù)荷維氏硬度試驗(yàn)、顯微維氏硬度試驗(yàn)。維氏硬度保留了布氏硬度和洛氏硬度的優(yōu)點(diǎn)。小負(fù)荷維氏硬度計(jì)顯微維氏硬度計(jì)6FracturetoughnessRuptureofoiltankandengineshellexplosionofPolarismissilearerelevantwithfaultsinthematerials.1943年美國T-2油輪發(fā)生斷裂北極星導(dǎo)彈裂紋擴(kuò)展的基本形式六、斷裂韌性油輪斷裂和北極星導(dǎo)彈發(fā)動(dòng)機(jī)殼體爆炸與材料中存在缺陷有關(guān)

1943年美國T-2油輪發(fā)生斷裂北極星導(dǎo)彈裂紋擴(kuò)展的基本形式Stressintensityfactor:

theindextodescribethestressintensityaroundthecracktip.Fracturetoughness:

theabilitytoresisttheinternalunstablecrackgrowthCisrupturestress,aCishalflengthofcriticalcrack,itsunitisMN/m3/2應(yīng)力強(qiáng)度因子：描述裂紋尖端附近應(yīng)力場強(qiáng)度的指標(biāo)。斷裂韌性：材料抵抗內(nèi)部裂紋失穩(wěn)擴(kuò)展的能力。C為斷裂應(yīng)力，aC為臨界裂紋半長，單位為1.1.7ThermalfatigueSomepartsworkingundertheconditionsthattemperaturealternativesdramaticallyandrepeatedly,bearingthermalstressorthermalstraincausedbythermalcycle,willbedestroyedbyfatiguedamage,whichiscalledthermalfatigue.七、熱疲勞