材料的机械行为

CHAPTER2MechanicalBehavior,Testing,andManufacturingPropertiesofMaterials材料的機械行為、測試及製造特性WorkingMediumofManufacturingProcessForceHeatLightAcoustics(聲音、音響)ElectricityChemistryBiology室溫時材料之相對機械性質(RelativeMechanicalPropertiesofMaterialsatRoomTemperature)Tensile-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neckingEEng.stressTrue.stressEng.strainTruestrainTensionTestll0AA0PNecking(Fig.2.2)Springback(Fig.2.3)Engineeringstrain=Truestrain=Engineeringstress=Truestress=LoadingandUnloadingofTensile-TestSpecimenFigure2.3Schematicillustrationoftheloadingandtheunloadingofatensile-testspecimen.Notethat,duringunloading,thecurvefollowsapathparalleltotheoriginalelasticslope.MechanicalPropertiesofVariousMaterialsatRoomTemperatureExmpleATruestressTruestrainB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）Elongationversus%AreaReductionFigure2.4Approximaterelationshipbetweenelongationandtensilereductionofareaforvariousgroupsofmetals.Ch2.2.4應力-應變曲曲線之之建立立Stress-straincurvesTruestrainTruestressn:strain-hardeningexponent(n=0，表示沒沒有加加工硬硬化現現象)TypicalValuesforKandnatRoomTemperature各種不不同金金屬在在常溫溫下的的TrueStress-TrueStrainCurvesFigure2.6Truestress-truestraincurvesintensionatroomtemperatureforvariousmetals.Thecurvesstartatafinitelevelofstress:Theelasticregionshavetoosteepaslopetobeshowninthisfigure,andsoeachcurvestartsattheyieldstress,Y,ofthematerial.Proveε=natneckingAtnecking:NeckingUTSCh2.2.5?e=2.2.6溫度效效應TemperatureEffectsonStress-StrainCurvesFigure2.7Typicaleffectsoftemperatureonstress-straincurves.Notethattemperatureaffectsthemodulusofelasticity,theyieldstress,theultimatetensilestrength,andthetoughness(areaunderthecurve)ofmaterials.T↑，則ductility↑，yieldstress和modulusofelasticity↓(因為T↑，原子動動能↑，容易克克服差差排障障礙，延展性性佳)表變形速速率的的影響響EffectofStrainRateonUltimateTensileStrength2.2.7變形速速率的的影響響EffectofStrainRateonUltimateTensileStrengthFigure2.8Theeffectofstrainrateontheultimatetensilestrengthforaluminum.Notethat,asthetemperatureincreases,theslopesofthecurvesincrease;thus,strengthbecomesmoreandmoresensitivetostrainrateastemperatureincreases.Source:J.H.Hollomon.strainrate↑↑tensilestrength↑↑（應變變硬化化）直線斜斜率m：應變硬硬化敏敏感度度指數數，Temp↑m↑↑,m大可以以延緩緩necking發生，，應用用在金金屬薄薄板的的成形形。2.2.7變形速速率的的影響響EffectofStrainRateonUltimateTensileStrength超塑性性（superplasticity）:某些材材料在在拉伸伸試驗驗時，，頸縮縮及破破壞前前，發發生大大量的的均質質伸長長變形形量，，這種種變形形量從從幾百百個百百分比比到兩兩千個個百分分比之之間。。例如如：口口香糖糖、玻玻璃、、熱塑塑性塑塑膠、、Zn-Al合金及及鈦合合金。。壓力：：幾個ATM到3.5GPa(500KST)，液壓壓增加加時，，材料料破壞壞時的的應變變量會會大量量增加加（不不容易易破壞壞）。。脆性材材料之之金屬屬成形形：液液壓擠擠製、、粉末末冶金金壓製製。當加工工製造造stress超過過材料料破裂裂點，可使使用下下列方方法避避免：：加溫加液靜靜壓(HydrostaticPressureEffect):脆性材材料加加工2.2.8靜液壓壓的影影響（（Hydrostaticpressureeffects)暴露在在高能能量輻輻射下下：鋼料及及其他他種類類金屬屬會發發生降伏應應力、、抗拉拉強度度及硬硬度會會增加加；延展性性及韌韌性會會減少少。塑膠膠材料料對其其機械械性質質也有有不好好的影影響。。2.2.9輻射的的影響響（Raditioneffects)桶形失失真（（barreling）:摩擦力力2.3壓縮(Compression)2.3壓縮(Compression)Figure2.9Disktestonabrittlematerial(陶瓷、、玻璃璃),showingthedirectionofloadingandthefracturepath.2.3壓縮(Compression)蒲辛格格效應應（Bauschingereffect1881）:金屬受受拉力力進入入到塑塑性狀狀態，，將負負荷釋釋放再再施以以壓縮縮應力力，此此時，，壓縮縮的降降伏應應力值值比拉拉伸時時低許許多。。應變軟軟化（（strainsoftening）、作作工軟軟化（（worksoftening）:因負荷荷的方方向轉轉換，，使降降伏應應力值值下降降。2.4扭轉轉(Torsion)DiskandTorsion-TestSpecimensFigure2.10Typicaltorsion-testspecimen;itismountedbetweenthetwoheadsofatestingmachineandtwisted.Notethesheardeformationofanelementinthereducedsectionofthespecimen.2.5彎曲（（撓曲曲）Bending（Flexure）Figure2.11Twobend-testmethodsforbrittlematerials:(a)three-pointbending;(b)four-pointbending.Theareasonthebeamsrepresentthebending-momentdiagrams,describedintextsonmechanicsofsolids.Notetheregionofconstantmaximumbendingmomentin(b);bycontrast,themaximumbendingmomentoccursonlyatthecenterofthespecimenin(a).硬脆材料通通常都使用用bending實實驗量測材材料性質(因為tension實驗不不易進行)設備便宜且且方便，所所以產業界界常用Brinell(布氏硬度1900):HBP對表面積的的比值Rockwell(洛氏硬硬度1922):HR深度Vickers(維氏硬度度1922)：HV深度Knoop(克氏氏硬度)：：HKLoad極極小(5-25kg)，做微硬度測測試，可用用於薄脆試件。Scleroscope(蕭氏硬度)：：反跳高度、、大面積Mohs(莫氏硬度1822)：互相摩擦，，值1（滑石））-10（鑽石）。。Durometer硬度測試計計Hothardness熱硬度Ch2.6硬度（Hardness）HardnessTestsFigure2.12Generalcharacteristicsofhardness-testingmethodsandformulasforcalculatinghardness.ThequantityPistheloadapplied.Source:H.W.Hayden,etal.,TheStructureandPropertiesofMaterials,Vol.III(JohnWiley&Sons,1965).BrinellTesting(c)Figure2.13IndentationgeometryinBrinelltesting;(a)annealedmetal;(b)work-hardenedmetal;(c)deformationofmildsteelunderasphericalindenter.Notethatthedepthofthepermanentlydeformedzoneisaboutoneorderofmagnitudelargerthanthedepthofindentation.Forahardnesstesttobevalid,thiszoneshouldbefullydevelopedinthematerial.Source:M.C.ShawandC.T.Yang.HardnessConversionChartFigure2.14Chartforconvertingvarioushardnessscales.Notethelimitedrangeofmostscales.Becauseofthemanyfactorsinvolved,theseconversionsareapproximate.硬度測試對對照表HRC機械械工業常用用(範圍對對應鋼材)HRC55以上是很很硬的鋼材材HardnessislinearlyproportionaltoStrength(UTS)UTS[MPa]=3.5(HB)Eq.(2.13)UTS[psi]=500(HB)Eq.(2.14)Ch2.6.2硬度和強度度（Hardnessandstrength）疲勞破壞：：工件在未達達到靜態負負荷時的降降伏應力下下，發生破破裂。金屬的疲勞限與其極限抗抗拉強度（（UTS）有關，鋼鋼料約為1/2，鋁則無（（以107）。如下圖圖2.152.7疲勞（Fatigue）2.7疲勞（Fatigue）S-NCurves2.7疲勞（Fatigue）S-NCurvesFigure2.15TypicalS-Ncurvesfortwometals.Notethat,unlikesteel,aluminumdoesnothaveanendurancelimit.EnduranceLimit/TensileStrengthversusTensileStrengthFigure2.16Ratioofendurancelimittotensilestrengthforvariousmetals,asafunctionoftensilestrength.Becausealuminumdoesnothaveanendurancelimit,thecorrelationforaluminumarebasedonaspecificnumberofcycles,asisseeninFig.2.15.潛變：機械零件在在長時間承承受一靜態態負荷時所所進行的永永久變形，，原因為晶界滑移（（grain-boundarysliding）。例如：熱熱塑性塑膠膠及橡膠會會在任何溫溫度下進行行潛變。鉛鉛會在室溫溫定力下潛潛變、老房房子的玻璃璃。鋁合金（200度C）、高熔點點金屬（1500度C）應力釋放（（stressrelaxation）：螺栓、卯釘釘、guywires2.8潛變（Creep）2.8潛變（Creep）潛變曲線：：分三階段段2.9衝擊（Impact）ImpactTestSpecimensFigure2.18Impacttestspecimens:(a)Charpy;簡支樑(b)Izod.懸臂樑Ch2.10材料在製造造過程及使使用中的破破壞與斷裂裂破裂破裂面走向破裂Figure2.19、2.20Ch2.10材料在製造造過程及使使用中的破破壞與斷裂裂Ch2.10材料在製造造過程及使使用中的破破壞與斷裂裂圖0.1延性破壞（（Ductilefracture)2.10.1延性破壞（（Ductilefracture)杯錐狀斷裂裂（Cup-and-conefracture）：：空孔累積積、生長合合併。2.10.1延性破壞（（Ductilefracture)雜質的影響響轉換溫度（（TransitionTemperature