Materials characterization and testing

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1、MITMediaLabMaterialscharacterizationandtestingHTMSTM(A)Aclass2007GeorgePopescuProf.NeilGershenfeldSummaryMaterialsIntroductionStatesofmatterandphasesEutecticsHeattreatmentSolidmechanicsTunablematerials(Polymers,Metamaterials,DigitalMaterials)Activematerials(WavesandPatte

2、rns)GranularmaterialsCharacterizationMechaniccharacterizationThermocharacterization(meltingpoint)Opticalcharacterization(diffractionangle)NMR(andotherresonances)SpectroscopyElectricalcharacterizationMaterialscienceSomevocabulary•σ:stresssensor(think:pressure)•ε:strainsen

3、sor(think:displacement)•E:Youngmodulus(scalar?no!)•v:Poissonration(scalar?No!)•ΔT:temperaturechange.•k*=bulkmodulus(pressureincreaseneededtoeffectagivenrelativedecreaseinvolume)F=-kxσ=EεStatesofmattervsphasesDifferentstatesofmattermustbedifferentphasesHowever,thereversei

4、snottrue.ThemostcommonstateofmatterintheuniverseisplasmaLessfamiliarphasesinclude•Quark-gluonplasma•BoseEinstaincondensates•Fermioniccondensates•Strangematter•Superfluids•Supersolids.Plasma…PhasetransitionsEhrenfestclassification:First-orderphasetransitionsexhibitadiscon

5、tinuityinthefirstderivativeofthefreeenergy.Second-orderphasetransitionshaveadiscontinuityinasecondderivativeofthefreeenergyWhatifderivativeoffreeenergydiverges?first-orderphasetransitions:involvelatentheatsecond-orderphasetransitions:noassociatedlatentheat(example:superf

6、luidtransition)PhasesSupercriticalCO2Youthoughtyouknewice?Si/Aualloylooklikethis:EutecticsLead/tinDefectsinCrystalsStrengthvsdefectdensityHeatTreatmentTradeoffbetweenductilityandbrittleness•Annealing,•Casehardening•Precipitationstrengthening,•Tempering•QuenchingTempering

7、Theaverageunitcellofausteniteis,onaverage,aperfectlittlecube,thetransformationtomartensiteseesthiscubedistortedbyinterstitialcarbonatomsthatdonothavetimetodiffuseoutduringdisplacivetransformation,sothatitisatinybitlongerthanbeforeinonedimensionandalittlebitshorterintheot

8、hertwo.Forthisclass:solidsHooke'slaw:F=-kxPoisson'sratio:ElasticityViscoelasticityPlasticityTherm