材料物理Material physics.docx

材料物理Material physics.docx

《材料物理Material physics.docx》由会员分享，可在线阅读，更多相关《材料物理Material physics.docx（8页珍藏版）》请在冰点文库上搜索。

材料物理Materialphysics

材料物理2（Materialphysics2）

Fillinthe.Nouninterpretation

1.phonon:

energyquantumofindependentharmonicoscillatorinlatticevibration.

Wavecharacteristics:

thepropagationmediumisnotconnectedwiththemedium.Itisthecrystallatticeoftheyard,ion,etc..Thelatticevibrationmode（waveisonthelatticethermalvibrationofatomscanbedescribedassimilartothemechanicalresultsofwavepropagation,thewaveiscalledlatticewave）

Griffithcracktheory:

Griffiththatmanytinycracksordefectsexistsinactualmaterial,undertheactionofexternalforce,andthesecracksaroundthedefectwillproducestressconcentrationphenomenon,whenthestressreachesacertainlevel,thecrackbegantorupturepropagation.ThisisthefamoustheoryofGriffithmicrocracks.

Themechanismofparticlereinforcedmaterialisthatparticlescanpreventdislocationmovementinthematrixorabsorbpartoftheenergythroughplasticdeformationofparticles,thusstrengtheningthepurpose.

Thereasonofthermalexpansionhysteresisincomplexisthattheexpansioncoefficientvariesgreatlyindifferentdirectionsbetweendifferentphasesorgrains,resultingingreatinternalstress,resultinginmicrocracks.

Thereareseveraltypesofcrackpropagation:

fracturetype（themaincauseoflowstressfracture）（ZhangKaihang,Itype）,staggertype（slidingtype,IItype）,tearingtype（IIItype）

Thenatureofthermalbreakdown:

amediuminanelectricfieldthatisheatedduetodielectriclossandmaybechargedfromaheatbalancestateofheatdissipationandheatingwhentheappliedvoltageishighenough.Iftheenergyemittedisgreaterthanthat,thetemperatureofthemediumwillbecomehigherandhigheruntilpermanentdamageoccurs.

Thecarriersinconductingmaterials:

anysubstance,aslongastheexistenceoffreeparticlecharge,whichcanbeproducedintheelectricfieldtostorethecurrent[carriermetalconductoristhefreeelectron,inorganicmaterials（electronicnegativeelectron,ion（hole）ionsorvoids）ascarrierionconductancesaidasacarrierforionicconductance,theelectronconductancecalledelectronicconductivity]

Theformofforceanddeformationofinorganicmaterials;elasticdeformation;plasticdeformation;viscousflow;hightemperaturecreep

Thefactorscausingphononscattering,phononfrequencyanddopingpointdefects

AttheCuriepointindielectricpolarizationmechanism;electronpolarization,iondisplacementpolarizationandionicrelaxationpolarization,spontaneouspolarization（somedielectricatacertaintemperature,whentheexternalelectricfieldafterthewithdrawalisstillacertainpolarization）

Themainstructureofferriteinstructure:

thespinelgarnettype3magnetoplumbitetype456perovskitetypeilmenitetypetungstenbronzetype

Theparticlediffusionmechanismincludes:

sublatticegapdiffusion;vacancydiffusion;interstitialdiffusionmechanism

Dielectricbreakdowntype:

thermalbreakdown,electricbreakdown,partialdischargebreakdown

Fractureenergy:

theactionofanexternalforceonanobjectperunitvolumeuntilanobjectisbrokenbyanexternalforce

Surfacedischarge;surfacedischargeofsolidmediumbelongstogasdischarge;solidmediumisofteninthesurroundinggasandcoal;sometimesthemediumitselfdoesnotbreakthrough,butsparksblowoveritssurface,whichissurfacedischarge.

Theintrinsicconductivityandimpurityconductivity;basicionsourceinthecrystallatticeofthemovementknownastheintrinsicconductance（intrinsicionconductance）causedbythemovementofthefixedionisweak,isthemainimpurityions,calledimpurityconductivity.

Spacechargepolarization:

undertheactionofelectricfield,thepositiveandnegativeinterstitialionsininhomogeneousmediamovetowardsnegativeandpositivepolesrespectively.Thechangeinthedensityoftheionsintheceramicbodyresultsinanelectricdipolemoment,whichiscalledspacechargepolarization.

Equilibriumcarriersandnonequilibriumcarriers:

atcertaintemperatures,carriersduetothermalexcitationinsemiconductorsarecalledequilibriumcarriers.Duetoexternalconditions（plusvoltage）.GuangZhao）acarrierwithalargenumberofcarriersiscalledanon-equilibriumcarrier

Pressuresensitiveeffectreferstotheeffectofnonlinearresistorsensitivetovoltagechanges,whichisinacriticalvoltagecondition,theresistancevalueisveryhigh,almostnocurrentthrough,exceedsthecriticalvoltage（voltagesensitiveresistor）valuedecreasedquickly,sothatthecurrentthroughthe.

Dielectricstrength:

whentheelectricfieldstrengthexceedsacriticalvalue.Thephenomenonthatadielectricchangesfromadielectricstateintoaconductivestateiscalledabreakdownindielectricstrength.Thecorrespondingcriticalfieldstrengthiscalleddielectricstrength.

Whatistheessenceofabsorptionoflightbyamedium?

Asanenergyflow,lightpassesthroughthemedium,causingthevalenceelectrontransitionofthemedium,ortheatomicvibration,toconsumeenergy.Inaddition,thevalenceelectronsinthemediumabsorbthephotonenergyandexciteit.Yetwhenaphotondeexcitation,collisionswithothermoleculesinmotion,i.e.thermalenergytransformationkineticenergyelectronsintomolecules,whichconstitutethelightattenuation,eveninthetransparentmediumisnotlightscatteringoflight,therewillbelossofenergy,lightabsorption.

4.,whydomostceramicmaterialsdonotproduceplasticdeformationatnormaltemperature,butbrittlefracture?

Ceramicmulticrystalplasticdeformationdependsnotonlyonthematerialconstitutingthecrystalitself,butalsotoagreatextentonthegrainboundarycontrolmaterial,sothepolycrystallineplasticdeformationincludingthefollowing,thedislocationscausedbyplasticdeformation,therelativeslidingbetweenthegrainandgrainboundary,vacancydiffusion,viscousflow,atroomtemperatureduetothestructurecharacteristicsofnonmetalliccrystalandgrainboundary,theplasticdeformationisdifficulttoachieve,becausethemicrocracksoftenexistinthematerial,whentheexternalstressisnotenoughtomaketheplasticdeformationvelocity,thecriticalstressofthestressmayhavebeenmorethanmicrocrackpropagationrequired,eventuallyleadtobrittlematerials.

5.whatistheruleoflatticesliding?

Theslipdistancemustbeintegertimesoflatticeconstant;crystalslipinthemiddlealwaysoccursinthemaincrystalsurfaceandmaincrystalorientation;slipoccurredintheshearstressundertheactionoftheslidingsurfaceonlywhentheshearstressexceedsthecriticalshearstress,canslipalongthecrystalsurface.

6.whatarethecausesofcrackinitiationandrapidpropagationinceramicmaterials?

Whatarethemeasurestopreventcrackpropagation?

Production:

thedevelopmentofmicrodefectsintothecrystalcrack;surfacemechanicalstrengthandchemicalcorrosiondamageformationofsurfacecrackscausedbythermalstress;crack;crackgasformation;crystalgrowthoramorphoustocrystaltransitionofcrackformation.Becausedynamic@@crackpropagation,whenCincreases,Gincreases,and##=4risaconstant,therefore,oncetheyreachacriticalsizeandinitialfractureinitiationandpropagationoffailureprocessisacriticalstage,becauseofbrittlematerialbasicallydidnotabsorblargeamountsofenergyofplasticdeformationmeasures:

theuseofstressdoesnotexceed#devicesettingsinenergyabsorption;materials;artificiallycausedalotofveryfineissmallerthanthecriticalsizecrackinthematerial

7.whatarethefactorsthataffectthermalconductivity?

Influenceoftemperature;theinfluenceofmicrostructure;theinfluenceofchemicalcomposition;theinfluenceofporosity;thethermalconductivityofmultiphaseceramics

8glassisadisordernetworkstructure,itisimpossibletohaveaslipsystemisbrittle,butathightemperaturescandeformation?

Why?

Answer:

itisbecauseofthenonlong-rangeorder,manyatomsarenotinthepotentialcurvetrough;somebondisweak,onlysmallstresscanmakethebondbreakingoftheseatoms;thegappositionneartheatomictransition,causedbyatomicmigrationandrearrangement,withouttheinitialyieldstresstodeformationofviscousflow.

9,thereasonofferromagneticdomainformationisexplainedfromtheviewpointofenergy

Answer:

accordingtothelawsofthermodynamics,thesteady-statemagneticstatemustbecorrespondingtothetotalfreeferromagneticmaterialwithintheenergyminimumstate,formationandstabilityofstructureofadomainiscorrespondingtothetotalfreeenergytomeettheminimumconditions.Forferromagneticmaterials,theenergyisreducedbeforesplittingintodomains.Therefore,whentheferromagneticmaterialismagnetizedspontaneously,itwillinevitablybedividedintomagneticdomainsinthesmallregion,whichmakesthetotalfreeenergythelowestandsatisfiestheminimumenergyprinciple.Itcanbeseenthatthedemagnetizingfieldisthereasonfortheformationofmagneticdomains.

Analysisquestions

Thecausesofcracksandtheirfracturemechanismsarebrieflydescribed.Howcancrackpropagationbeprevented?

Answer:

cause:

becauseofthedefectsinthecrystalmicrostructure,whensubjectedtoexternalforce,thesedefectscausedbystressconcentration,resultingincracknucleationofagrainswithdifferentorientationsBJournalofatomicstressconcentrationCthermaldefects

Mechanicaldamageandchemicalcorrosiononthesurfaceofthematerialformsurfacecracks

Cracksformedduetothermalstress

Themechanismofcrackordefect:

Griffithbelievedthatmanyofthesmalltotalactualmaterial,undertheactionof