中北大学材料科学与工程基础考试重点

MaterialsScience：involvesinvestigatingtherelationshipsthatexistbetweenthestructuresandpropertiesofmaterials(研究结构与MaterialsEngineering:designingthestructureofamaterialtoproduceapredeterminedsetofproperties,basedonthesestructure-propertycorrelations.(根据性能要求来,设计材料结构)2.材料的四部分重要组成元素1).Structure(结构)：relatestothearrangementofitsinternal2).Property(性质)：amaterialtraitintermsofthekindandmagnitudeofresponsetoaspecificimposedstimulus.(对于外界施特别外力，材料所表现出的特征反应)cessingperformance四元素的关系：Thestructureofamaterialwilldependonhowitisprocessed.Amaterial’sperformancewillbeafunctionofitsproperties.3.材料的分类(按结构分)(1)Metals(金属)：Metallicmaterialarenormallyextremelygoodconductorsofelectricityandheatandarenottransparenttovisiblelight。csCeramicsarecompoundsbetween (3)Polymers(聚合物)：polymerareorganiccompoundsthatarechemicallybasedoncarbon,hydrogen,andothernonmetallicle (4)Composites(复合材料)：AnumberofcompositematerialsnsistofmorethanonematerialtypemechanicalProperties(机械性能)：relatedeformationtoanappliedloadorforce;examplesincludeelasticmodulusandstrength.electrical(电性能)：thestimulusisanelectricfield;electricalconductivity(电导率)anddielectricthermal(热性能)：Thethermalbehaviorofsolidscanberepresentedintermsofheatcapacity(热容)andermalconductivityofamaterialtotheapplicationofamagneticfield.optical(光学性)Thestimulusiselectromagneticorlightradiation;indexofrefraction(折射)andreflectivityures(1)晶体(crystal)：Itissolidandthearrangementofatomsinthecrystalisperiodic(周期性).(2)Threecrystalstructuresare:(FCC)Face-centeredcubic例如Cu,Al,Au,Ag(面心立方);ForFCCstructure,assignedtoagivenunitinationnumberatotaloffouratomsareAPF=volumeofatomsinaunitAPF=totalunitcellvolume33===0.74162R332UnitcelllengthaandatomicradiusRarerelatedas:EachBCCunithasatomsThecoordinationnumberis8.Atomicpackingfactoris0.68.EachHCPunithasatoms;Atomicedgelengthc=1.633aThecoordinationnumberis12.AtomicpackingfactorisSodiumChloridestructure(Rocksaltstructure)(氯化钠结构，食盐结构)：coordinationnumber=6CesiumChlorideStructure(氯化铯结构)：Coordinationnumber=8ZincBlendeStructure(ZnS)(硫化锌结构)：coordinationnumber=4n(xAc+xAA)p=pAGeneraldensityEquation：VNAdfacepositionsofthecubiccellarealloccupiedbyCarbonatoms.butthegraphitestructure石墨结构isposedoflayersofhexagonallyarrangedcarbonatomsPolymerStructure(1)聚合物的定义：Polymerwasacompoundconsistingoflong-chainmolecules,eachmoleculemadeupofrepeatingunitsconnectedtogether.(2)聚合物的种类(按主链上的原子种类分)：碳链聚合物，机聚合物 (3)平均相对分子量umberaveragedegreeofpolymerizationgedegreeofpolymerizationMn=xxiMiMw=xwiMiMnn=nwmtDistribution Condensationpolymerizationproduct(缩聚产物d＝nRadicalproduct(自由基产物d＝3~5Side-branchd＝25~30(PE)d.03~1.05能上的特点softenhardensasitcools.Sowhentheparticlesstrongmaterialinsoftstatebymoldingorextrusionmolding.这种聚合物当加热时变软冷却时变硬。所以当这heatingwillnotbesoftenedormeltedEngineeringstrain应变):l0:originallengthbeforeanyloadappliedlitheinstantaneouslengthandl=li-l0.Engineeringstress(工程应力)：F:theinstantaneousloadappliedperpendiculartothespecimencrosssection(N);A0:theginalcrossectionalareabeforeanyloadisappliedTruestrain表达式：trueandengineeringstressandstrainarerelatedaccordingto(真实应力-应变与4.ElasticDeformation(弹性变形)的概念：Whenthestressisremoved,thematerialreturnstothedimensionithadbeforetheloadwasappliedremoved,thematerialdoesnotreturntoitspreviousdimensionbutthereisapermanent,irreversibledeformation(不可回复的变形)6.Tensilestrength(拉伸强度)基本概念：1)thestressatthe2)correspondstothemaximumstressthatcanbesustainedbyastructureintension;ifthisstressisappliedandmaintained,fracturewillresult.tisuniformthroughoutthenarrowregionofthetensilespecimen.Yieldstrength(屈服强度)基本概念:thestresscorrespondingtotheintersectionoftheline,whichparallelstotheelasticportionofthestress-straincurveatsomespecifiedstrainoffset,andthestressstraincurveasitbendsoverintheplasticregion.8.Ductility(延展性)：Itisameasureofthedegreeofplasticdeformationthathasbeensustainedatfracture.Amaterialthatexperiencesverylittleornoplasticdeformationuponfractureistermedbrittle延展性可用percentelongation(延伸率)和percentreduction表示。1.金属的(formingtechniques)成型方法：Castingandwelding铸(1)Theductilitypropertiesofthemetal例如plasticdeformation--formingtechniquessolowinductility--cast(2)thesizeandshapeofthefinishedpiece例如solargeorcomplicatedCastingtwoormoremetalpartswelding(3)cost——Casting--mosteconomicaltiallythesurfacecoolsmorerapidlyandoncehavingdroppedtoatemperaturebelowthestrainpoint，rapidlyisatahighertemperatureabovethestrainpointandgreaterdegreethanthenowrigidexteriorwillallow.Thus，theinsidetendstodrawintheoutside，ortoimposeinwardradialstresses.Aftertheglasspiecehascooledtoroomtemperature，itsustainscompressivestressesonthesurface，withtensilestressesatregionsAcompositeisamultiphase(多相)materialthatisartificially 然地).Inaddition,theconstituent(连续)phasesmustbechemicallydissimilar(不同的)andseparatedbyadistinct(明显)interface.1.CuhasaFCCcrystalstructure,anatomicradiusof0.128nm,andanatomicweightof63.5g/mol.Compute(1)thevolumeofaunitSolution：1Thelengthofafacediagonal4R,ThecelledgelengthForFCCitisacube.So,therehasarighttriangleontheface:(2)l(2)2.Aspecimen(E=90GPa)havingarectangularcrosssection15mmnwithNforcesproducingonlyelasticdeformation.CalculatetheresultingstrainandSoeasy3.Forabronzealloy,thestressatwhichplasticdeformationbeginsis300MPa,tensilestrengthis355MPaandthemodulusofelasticityis165GPa.(a)Whatisthemaximumloadthatmaybeappliedtoaspecimenwithacross-sectionalareaof125mm2withoutplasticdeformation?(b)Iftheoriginalspecimenlengthis215mm,whatisthemaximumlengthtowhichitmaybestretchedwithoutcausingplastic Mg Mg==0.501.Apieceofcopperoriginally305mm(12in.)longispulledintensionwithastressof276MPa(40,000psi).Ifthedeformationisentirelyelasticwhatwillbetheresultantelongation?SOLUTION：Sincethedeformationiselastic,strainisdependentsaccordingto2.AssumethatthemolecularweightdistributionsshowninfigureareforPVC.Forthismaterial,compute(a)thenumber-averagemolecularweight;(b)thenumber-averagedegreeofpolymerization;and(c)theweightaveragemolecularweight.(P86)2.Onthebasisofcrystalstructure,computethetheoreticaldensitydiumchlorideP3.ItShowsthatMgOhasthesodiumchloridecrystalstructureandcalculatethedensityofMgO.olsince0.414<0.50<0.732,thecoordinationnumberforeachis,andedgeofthecu0.396nm=3.96×thesodiumchloridestr2uctureisposedgeofthecu0.396nm=3.96×5.acylindricalbrassrodthathasadiameterof10mm(0.4in.)ispulledintensionwith5600Nforce,producingonlyelasticdeformation.Calculatetheresultingstrain.SOLUTION