陶瓷材料力学性能

TerminologyforMechanicalProperties

Stress-Forceorloadperunitareaofcross-sectionover whichtheforceorloadisacting.

Strain-Elongationchangeindimensionperunitlength.

Young’smodulus-Theslopeofthelinearpartofthe stress-straincurveintheelasticregion,sameas modulusofelasticity.

Shearmodulus(G)-Theslopeofthelinearpartofthe shearstress-shearstraincurve. •Tensilestress,s:•Shearstress,t:Stresshasunits:N/m2orlb/in2ENGINEERINGSTRESS•Elasticmodulus,E•E~curvatureatroEislargerifEoislarger.PROPERTIESFROMBONDING:E•ElasticShearmodulus,G:t=G

g•ElasticBulkmodulus,K:•Specialrelationsforisotropicmaterials:simpletorsiontestpressuretest:Init.vol=Vo.Volchg.=DVOTHERELASTICPROPERTIES•Tensilestrain:•Lateralstrain:•Shearstrain:qStrainisalwaysdimensionless.(L)(-LL)ENGINEERINGSTRAIN(c)2003Brooks/Cole,adivisionofThomsonLearning,Inc.ThomsonLearning™isatrademarkusedhereinunderlicense.Figure6.3(a)Tensile,compressive,shearandbendingstresses.(b)IllustrationshowinghowYoung’smodulusisdefinedforelasticmaterial.(c)Fornonlinearmaterials,weusetheslopeofatangentasavariablequantitythatreplacestheYoung’smodulusconstantTheTensileTest:UseoftheStress-StrainDiagramLoad-Theforceappliedtoamaterialduringtesting.StraingageorExtensometer-Adeviceusedformeasuringchangeinlengthandhencestrain.Glasstemperature(Tg)-Atemperaturebelowwhichanotherwiseductilematerialbehavesasifitisbrittle.Engineeringstress-Theappliedload,orforce,dividedbytheoriginalcross-sectionalareaofthematerial.Engineeringstrain-Theamountthatamaterialdeformsperunitlengthinatensiletest.(c)2003Brooks/Cole,adivisionofThomsonLearning,Inc.ThomsonLearning™isatrademarkusedhereinunderlicense.Figure6.7Aunidirectionalforceisappliedtoaspecimeninthetensiletestbymeansofthemoveablecrosshead.Thecross-headmovementcanbeperformedusingscrewsorahydraulicmechanism(c)2003Brooks/Cole,adivisionofThomsonLearning,Inc.ThomsonLearning™isatrademarkusedhereinunderlicense.Figure6.9Tensilestress-straincurvesfordifferentmaterials.Notethatthesearequalitative•Ductilefractureisdesirableforstructuralapplications!•Classification:Ductile:warningbeforefracture,i.e.changesgeometrybeforefailureBrittle:NowarningAdaptedfromFig.8.1,Callister6e.DUCTILEVSBRITTLEFAILURE(c)2003Brooks/Cole,adivisionofThomsonLearning,Inc.ThomsonLearning™isatrademarkusedhereinunderlicense.Figure6.10Thestress-straincurveforanaluminumalloy1.Initial2.Smallload3.UnloadElasticmeansreversible!ELASTICDEFORMATION31.Initial2.Smallload3.UnloadPlasticmeanspermanent!PLASTICDEFORMATION(METALS)(c)2003Brooks/Cole,adivisionofThomsonLearning,Inc.ThomsonLearning™isatrademarkusedhereinunderlicense.Figure6.11(a)Determiningthe0.2%offsetyieldstrengthingraycastion,and(b)upperandloweryieldpointbehaviorinalow-carbonsteelTrueStressandTrueStrainTruestressTheloaddividedbytheactualcross-sectionalareaofthespecimenatthatload.TruestrainThestraincalculatedusingactualandnotoriginaldimensions,givenbyεtln(l/l0).Figure6.17Therelationbetweenthetruestress-truestraindiagramandengineeringstress-engineeringstraindiagram.ThecurvesareidenticaltotheyieldpointTheBendTestforBrittleMaterialsBendtest-Applicationofaforcetothecenterofabarthatissupportedoneachendtodeterminetheresistanceofthematerialtoastaticorslowlyappliedload.Flexuralstrengthormodulusofrupture-Thestressrequiredtofractureaspecimeninabendtest.Flexuralmodulus-Themodulusofelasticitycalculatedfromtheresultsofabendtest,givingtheslopeofthestress-deflectioncurve.Figure6.18Thestress-strainbehaviorofbrittlematerialscomparedwiththatofmoreductilematerialsFigure6.19(a)Thebendtestoftenusedformeasuringthestrengthofbrittlematerials,and(b)thedeflectionδobtainedbybendingFigure6.21(a)Threepointand(b)four-pointbendtestsetupHardnessofMaterialsHardnesstest-Measurestheresistanceofamaterialtopenetrationbyasharpobject.Macrohardness-Overallbulkhardnessofmaterialsmeasuredusingloads>2N.MicrohardnessHardnessofmaterialstypicallymeasuredusingloadslessthan2NusingsuchtestasKnoop(HK).Nano-hardness-Hardnessofmaterialsmeasuredat1–10nmlengthscaleusingextremelysmall(~100µN)forces.Figure6.23IndentorsfortheBrinellandRockwellhardnesstestsVickersHardness,HvFRACTURETOUGHNESSFracturetoughness:Kc=Ysc(pa)0.5=Y(2Egs)0.5

KcisamaterialpropertyY~1,dependsongeometryincreasingBasedondatainTableB5,Callister6e.Compositereinforcementgeometryis:f=fibers;sf=shortfibers;w=whiskers;p=particles.Additiondataasnoted(vol.fractionofreinforcement):1.(55vol%)ASMHandbook,Vol.21,ASMInt.,MaterialsPark,OH(2001)p.606.2.(55vol%)CourtesyJ.Cornie,MMC,Inc.,Waltham,MA.3.(30vol%)P.F.Becheretal.,