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1、材料英语证书考试(PEC)•材料特性术语DensityUnits:SI:Mg/m";cgs:g/cm3;Imperial:lb/ft3Thedensityistheweightperunitvolume.WemeasureittodayasArchimedesdid:byweighingthematerialinairandinafluidofknowndensity.AtomicVolumeUnits:SI:ln/kmol;cgs:l(fcm3/kmol;Imperial:in/kmolTheatomic(ormolecular)volumeVmistheaverag
2、evolumeper103N0ofatomsinthestructure,whereNOisAvogadro^number(6.022x1023/mol).Forapureelement,itissimply:whereAistheatomicweightinkg/kmolandristhedensityinkg/mForcompoundstheaverageatomicvolumeisMnpwhereMisthemolecularweightandnisthenumberofatomsinthemolecule・Thusforacompoundwiththeform
3、ulaAxByitis(x+y)pwhereAAistheatomicweightofelementA,andABistheatomicweightofelementB.Forapolymer(CxHyOz)nitisthereforeXAC+YAh+ZAO(X+Y+Z)pwhereACistheatomicweightofcarbon,andsoon.Theatomicvolumeisinvolvedinmanypropertycorrelations(andthusiscrucialforcheckingandestimatingproperties)and,tog
4、etherwiththedensity,itgivestheatomicweight.EnergyContentUnits:SI:MJ/kg;cgs:kcal/g;Imperial:kcal/lbTheenergycontentofamaterialisanapproximateestimateoftheenergyusedtomakeitfromitsnaturally-occurringores,feedstocksorsources,plustheenergycontentofthesourcematerialitself.(Usuallytheenergycon
5、tentofthesourcematerialissmall,except,forexample,whenthesourceisoil.)ThustheenergycontentofAluminiumisdominatedbytheelectricpowerabsorbedinitsextnictionfromBauxite;thatforpolymers,forwhichthefeedstockiscrudeoilistheenergycontainedintheoilitselfplusthatofthesubsequentprocessing;andthatfor
6、woodistheenergycontentofwoodplustheenergyrequiredtoharvestit.Young'sModulusUnits:SI:GPa;cgs:1010dyne/cm2;Imperial:106psiYoung'smodulus,E,istheslopeoftheinitial,linear-elasticpartofthestress-straincurveintensionorcompression.ForisotropicmaterialsitisrelatedtothebulkmodulusKandtotheshearmo
7、dulusGbyE=3(1-2v)KE=2(1+v)GwherenisPoisson'sratio.Commonlyn=1/3,andhenceE=K,andE=(8/3)G.BulkModulusUnits:SI:GPa;cgs:10l()dyne/crn2;Imperial:IO6psiThebulkmodulus,K,measurestheelasticresponsetohydrostaticpressure,p:“dpK=dvwherevisthevolume.ForisotropicsolidsitisrelatedtoYou
