Statistical Tensile Strength for High Strain Rate of Aramid and UHMWPE Fibers46材料工程/2006年5期StatisticalTensileStrengthforHighStrainRateofAramidandUHMWPEFibersYANGBin.XIoNGTao,XIONGJie(KeyLaboratoryofAdvancedTextileMaterialsandManufacturingTechnology,MinistryofEducation,ZhejiangSciTechUniversity,Hangzhou310018,China)Abstract:Dynamictensileimpactpropertiesofaramid(Technora)andUHMWPE(DC851)fiberbundleswerestudiedattwohighstrainratesbymeansofreflectingtypeSplitHopkinsonBar,andstressstraincurvesoffiberyarnsatdifferentstrainrateswereobtained.Experimentalresultsshowthattheinitialelasticmodulus,failurestrengthandunstablestrainofaramidfiberyarnsarestrainrateinsensitive,whereastheinitialelasticmodulusandunstablestrainofUHMWPEfibervamsarestrainratesensitive.Afiber-bundlestatisticalconstitutiveequationwasusedtodescribethetensilebehaviorofaramidandUHMWPEfiberbundlesathighstrainrates.ThegoodconsistencybetweenthesimulatedresultsandexDerimenta1dataindicatesthatthemodifieddoubleWeibullfunctioncanrepresentthetensilestrengthdistributionofaramidandUHMWPEfibersandthemethodofextractingWeibullparametersfromfiberbundlesstressstraindataisvalid.KeywOrds:aramidfiber;UHMWPEfiber;impactbehaviour;statisticalproperties;statisticalconstitutiVeequationCLCnumber:TB33Documentcode:AArticleID:1001-4381(2006)05004605Technora,madefromaramidfibersandsomewhatsim订artothecommonlyknowKevlar,andUltrahighlyorientedhighmolecularweightpolyethvlene_UHMWPEfibersarealloftenusedinflexiblearmourapplicationsandhencesubjectedtohighratesofloading.Theutilizationoftheirreinforcedcompositesarmourincertainballisticapplicationsisincreasinglypreferredoverconventionalrigidmetalarmoursystemsbecauseofitssuperiorstrength.toweightratioandflexibility.Todate,thedesignanddevelopmentofsuchfabricarmoursystemshavelargelybeenapproachedempirically卜.Theballisticresistanceoffiberreinforcedcompositeisessentiallydependentonthemechanicalbehaviorofthereinforcingcomponentandthematrix.Fibersandfiberbundlescarrythebulkoftheappliedloadinafiber-reinforcedcomposite.Thustheunderstandingofthestrainratesensitivityofthefibersisveryimportantfortheuseanddesignofthefiberreinforcedcomposites.Nevertheless,forTechnoraandUHMWPEfibersandfiberbundles,fewexperimentalresultsonthehighstrainratehavebeenreported.ItiswellknownthatengineeringfibersoftenexhibitabrittlefracturebehaviorandtheirtensilestrengthobeyWeibullstatisticaldistribution.Twoexperimentalmethodscanbeusedtodeterminethestrengthstatisticaldistributionparametersoffibersunderquasistaticloading.Oneisthesinglefibertestandtheotheristhefiberbundletest一.Thefiberbundletestingmethodisincreasinglyusedtoday.Ontheotherhand,duetothetechniquedifficulty,nosuitableexperimentaltechniqueisavailabletoperformthedynamicsinglefibertensiontests.Therefore,thefiberbundletestingmethodistheonlychoicefordeterminingthedynamictensilestrengthdistributionoffibersunderimpactloadingconditions.一.Inthispaper.tensileimpacttestsofaramid(Technora)andUHMWPE(DC851)fiberbundlesarecarriedoutundertwohighstrainratesbyusingaSplitHopkinsonTensileBar(SHTB),andtheexperimentaldataareusedtoderivestatisticalconstitutiveequationofaramidandIIHMPEfiberbundles.Foundationitems:supportedbytheNationalNaturalScienceFoundationofChina(10372092).E-mail:yangbin5959yahoo.com.cnStatisticalTensileStrengthforHighStrainRateofAramidandUHMWPEFibers471ExperimentalApparatusandTensileImpactTestTensileimpacttestswereconductedonthereflectedindirecttensileimpactapparatusfrommodifiedSHPB(SplitHopkinsonPressureBar).Aschematicofthesetupandstresswavepropagation.z-tschemearepresentedinFig.1.Throughtheimpactofthestrikerbarontheoutputbar,producingastresswavevialiningblocktransmitsthroughtheinputbar.Suchstressimpulsetravelsdowntheinputbarandispartiallyreflectedattheinputbar/specimeninterfaceandpartiallytransmittedtothespecimenandtheoutputbar.Measurementsofthereflectedandtransmittedwavesweremadeusingstraingagesarrangedontherespectivebarsofthesystem.Theincidentstraini(t),reflectedstrain(t)andtransmittedstraint(t)arerecordedatstraingagesmountedontheinputbarandoutputbars,respectively.Accordingtotheone-dimensionalsimple-wavetheory,thedynamictensilestress口.(t),dynamictensilestrain.()andstrainrate()inthespecimencanbeobtainedfromthefollowing:伪,l</L2l,:.,一一一一一!A.A1-strikerbar;2-outputbar;3一inputbar;4一absorbingbar;5-superdynamicamplifier;6-transientconverter;7-computer;8-speedometer;9-liningblock;10一specimenFig.1Tensileapparatussketchandstresswavepropagationx-tscheme)(1)(r)(r)dr)一2LC.oi()一()(2)(3)whereEandA0aretheYoungsmodulusandthecrosssectionalareaoftheinput/outputbar,Coisthelongitudinalwavevelocityofthebar,A.andL0arethecrosssectionalareaandgagelengthofthespeci-men,respectively.Thematerialinvestigatedinthispaper