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)》请在冰豆网上搜索。
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