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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
