材料的机械行为

CHAPTER2MechanicalBehavior,Testing,andManufacturingPropertiesofMaterials材料的機械行為、測試及製造特性WorkingMediumofManufacturingProcessForceHeatLightAcoustics(聲音、音響)ElectricityChemistryBiology室溫時材料之相對機械性質(RelativeMechanicalPropertiesofMaterialsatRoomTemperature)TABLE2.1StrengthHardnessToughnessStiffnessStrength/DensityGlassfibersGraphitefibersKevlarfibersCarbidesMolybdenumSteelsTantalumTitaniumCopperReinforcedReinforcedThermoplasticsLeadDiamondCubicboronnitrideCarbidesHardenedsteelsTitaniumCastironsCopperThermosetsMagnesiumthermosetsthermoplasticsLeadRubbersDuctilemetalsReinforcedplasticsThermoplasticsWoodThermosetsCeramicsGlassCeramicsReinforcedThermoplasticsTinThermoplasticsDiamondCarbidesTungstenSteelCopperTitaniumAluminumTantalumplasticsWoodThermosetsReinforcedplasticsTitaniumSteelAluminumMagnesiumBerylliumCopperTensile-TestSpecimenandMachine(b)Figure2.1(a)Astandardtensile-testspecimenbeforeandafterpulling,showingoriginalandfinalgagelengths.(b)Atypicaltensile-testingmachine.應力應變曲線（Stress-StrainCurve）Figure2.2Atypicalstress-straincurveobtainedfromatensiontest,showingvariousfeatures.•P-δ；σ-ε•彈性區經過放大•斜率=E•比例限、彈性限、降伏強度•Offset=0.2%•反覆循環負荷之曲線形狀•曲線下面積＝材料韌性•neckingE0lnll0ApApEng.stressTrue.stressEng.strainTruestrainTensionTestll0AA000lllP•Necking(Fig.2.2)•Springback(Fig.2.3)Engineeringstrain=Truestrain=Engineeringstress=Truestress=LoadingandUnloadingofTensile-TestSpecimenFigure2.3Schematicillustrationoftheloadingandtheunloadingofatensile-testspecimen.Notethat,duringunloading,thecurvefollowsapathparalleltotheoriginalelasticslope.MechanicalPropertiesofVariousMaterialsatRoomTemperatureTABLE2.2MechanicalPropertiesofVariousMaterialsatRoomTemperatureMetals(Wrought)E(GPa)Y(MPa)UTS(MPa)Elongationin50mm(%)AluminumanditsalloysCopperanditsalloysLeadanditsalloysMagnesiumanditsalloysMolybdenumanditsalloysNickelanditsalloysSteelsTitaniumanditsalloysTungstenanditsalloys69–79105–1501441–45330–360180–214190–20080–130350–40035–55076–110014130–30580–2070105–1200205–1725344–1380550–69090–600140–131020–55240–38090–2340345–1450415–1750415–1450620–76045–465–350–921–540–3060–565–225–70NonmetallicmaterialsCeramicsDiamondGlassandporcelainRubbersThermoplasticsThermoplastics,reinforcedThermosetsBoronfibersCarbonfibersGlassfibersKevlarfibers70–1000820–105070-800.01–0.11.4–3.42–503.5–17380275–41573–8562–117———————————140–2600—140—7–8020–12035–17035002000–30003500–460028000———1000–510–100000Note:IntheuppertablethelowestvaluesforE,Y,andUTSandthehighestvaluesforelongationareforpuremetals.Multiplygigapascals(GPa)by145,000toobtainpoundspersquarein.(psi),megapascals(MPa)by145toobtainpsi.ExmpleATruestressTruestrainB利於進行製造的材料:BB材質塑性區大，降伏強度低，較易進入加工區域。(然而A較易滿足設計需求，強度大)Ch2.2.2Ductility延性Elongation=（伸長量）Reductionofarea=（面積縮率、斷面縮率）100)(00lllf100)(00AAAfElongationversus%AreaReductionFigure2.4Approximaterelationshipbetweenelongationandtensilereductionofareaforvariousgroupsofmetals.Ch2.2.4應力-應變曲線之建立Stress-straincurvesTruestrainTruestressnKn:strain-hardeningexponent(n=0，表示沒有加工硬化現象)TypicalValuesforKandnatRoomTemperatureTABLE2.3K(MPa)nAluminum1100–O2024–T46061–O6061–T67075–OBrass70–30,annealed85–15,cold-rolledCobalt-basealloy,heat-treatedCopper,annealedSteelLow-Cannealed4135annealed4135cold-rolled4340annealed304stainless,annealed410stainless,annealed18069020541040090058020703155301015110064012759600.200.160.200.050.170.490.340.500.540.260.170.140.150.450.10各種不同金屬在常溫下的TrueStress-TrueStrainCurvesFigure2.6Truestress-truestraincurvesintensionatroomtemperatureforvariousmetals.Thecurvesstartatafinitelevelofstress:Theelasticregionshavetoosteepaslopetobeshowninthisfigure,andsoeachcurvestartsattheyieldstress,Y,ofthematerial.Proveε=natnecking010()00nnnndPdddeKAeddneenAtnecking:000[,.63]nnPAKAKnAUTSExampleP0PANeckingUTSCh2.2.5?2.2.6溫度效應TemperatureEffectsonStress-StrainCurvesFigure2.7Typicaleffectsoftemperatureonstress-straincurves.Notethattemperatureaffectsthemodulusofelasticity,theyieldstress,theultimatetensilestrength,andthetoughness(areaunderthecurve)ofmaterials.T↑，則ductility↑，yieldstress和modulusofelasticity↓(因為T↑，原子動能↑，容易克服差排障礙，延展性佳)表2.32.2.7變形速率的影響EffectofStrainRateonUltimateTensileStrength2.2.7變形速率的影響EffectofStrainRateonUltimateTensileStrengthFigure2.8Theeffectofstrainrateontheultimatetensilestrengthforaluminum.Notethat,asthetemperatureincreases,theslopesofthecurvesincrease;thus,strengthbecomesmoreandmoresensitivetostrainrateastemperatureincreases.Source:J.H.Hollomon.strainrate↑tensilestrength↑（應變硬化）直線斜率m：應變硬化敏感度指數，Temp↑m↑,m大可以延緩necking發生，應用在金屬薄板的成形。2.2.7變形速率的影響EffectofStrainRateonUltimateTensileStrength超塑性（superplasticity）:某些材料在拉伸試驗時，頸縮及破壞前，發生大量的均質伸長變形量，這種變形量從幾百個百分比到兩千個百分比之間。例如：口香糖、玻璃、熱塑性塑膠、Zn-Al合金及鈦合金。壓力：幾個ATM到3.5GPa(500KST)，液壓增加時，材料破壞時的應變量會大量增加（不容易破壞）。脆性材料之金屬成形：液壓擠製、粉末冶金壓製。當加工製造stress超過材料破裂點，可使用下列方法避免：加溫加液靜壓(HydrostaticPressureEffect):脆性材料加工2.2.8靜液壓的影響（Hydrostaticpressureeffects)暴露在高能量輻射下：鋼料及其他種類金屬會發生降伏應力、抗拉強度及硬度會增加；延展性及韌性會減少。塑膠材料對其機械性質也有不好的影響。2.2.9輻射的影響（Raditioneffects)桶形失真（barreling）:摩擦力2.3壓縮(Compressio