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1、材料英语证书考试(PEC)-材料特性术语DensityUnits:SI:Mg/m3;cgs:g/cm3;Imperial:lb/ft3Thedensityistheweightperunitvolume.WemeasureittodayasArchimedesdid:byweighingthematerialinairandinafluidofknowndensity.AtomicVolumeUnits:SI:m3/kmol;cgs:106cm3/kmol;Imperial:in3/kmolTheatomic(orm
2、olecular)volumeVmistheaveragevolumeper103N0 ofatomsinthestructure,whereN0 isAvogadro'snumber(6.022x1023/mol).Forapureelement,itissimply:whereAistheatomicweightinkg/kmoland r isthedensityinkg/m3.ForcompoundstheaverageatomicvolumeiswhereMisthemolecularweightandni
3、sthenumberofatomsinthemolecule.ThusforacompoundwiththeformulaAxBy itiswhereAA istheatomicweightofelementA,andAB istheatomicweightofelementB.Forapolymer(CxHyOz)nitisthereforewhereAC istheatomicweightofcarbon,andsoon.Theatomicvolumeisinvolvedinmanypropertycorrela
4、tions(andthusiscrucialfor checkingandestimating properties)and,togetherwiththedensity,itgivestheatomicweight.EnergyContentUnits:SI:MJ/kg;cgs:kcal/g;Imperial:kcal/lbTheenergycontentofamaterialisanapproximateestimateoftheenergyusedtomakeitfromitsnaturally-occurri
5、ngores,feedstocksorsources,plustheenergycontentofthesourcematerialitself.(Usuallytheenergycontentofthesourcematerialissmall,except,forexample,whenthesourceisoil.)ThustheenergycontentofAluminiumisdominatedbytheelectricpowerabsorbedinitsextractionfromBauxite;that
6、forpolymers,forwhichthefeedstockiscrudeoilistheenergycontainedintheoilitselfplusthatofthesubsequentprocessing;andthatforwoodistheenergycontentofwoodplustheenergyrequiredtoharvestit.Young'sModulusUnits:SI:GPa;cgs:1010dyne/cm2;Imperial:106psiYoung'smodulus,E,isth
7、eslopeoftheinitial,linear-elasticpartofthestress-straincurveintensionorcompression.Forisotropicmaterialsitisrelatedtothe bulkmodulus Kandtothe shearmodulus Gbywhere n is Poisson'sratio.Commonly n =1/3,andhenceE=K,andE=(8/3)G.BulkModulusUnits:SI:GPa;cgs:1010dyne
8、/cm2;Imperial:106psiThebulkmodulus,K,measurestheelasticresponsetohydrostaticpressure,p:wherevisthevolume.Forisotropicsolidsitisrelatedto Young'smodulus Eandtothe shearmodulu
