Carbon_fiber_reinforced_composite4.pdf

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1、CHAPTER4PropertiesofCarbonFibersIntroductionThepropertiesofcarbonfibersvarywidelydependingonthestructure(Chapter3)ofthefibers.Ingeneral,attractivepropertiesofcarbonfibersincludethefollowing:0lowdensity0hightensilemodulusandstrength0lowthermalexpansioncoefficientthermalstabilityintheabse

2、nceofoxygentoover30oO"C0excellentcreepresistance0chemicalstability,particularlyinstrongacids0biocompatibility0highthermalconductivity0lowelectricalresistivity0availabilityinacontinuousform0decreasingcost(versustime)Disadvantagesofcarbonfibersincludethefollowing:anisotropy(intheaxialvers

3、ustransversedirections)lowstraintofailurecompressivestrengthislowcomparedtotensilestrengthtendencytobeoxidizedandbecomeagas(e.g.,CO)uponheatinginairaboveabout400°CoxidationofcarbonfibersiscatalyzedbyanalkalineenvironmentAseachpropertyisdeterminedbythestructure,thedifferentpropertiesarei

4、nterrelated.Thefollowingtrendsusuallygotogether:0increaseinthetensilemodulusdecreaseinthestraintofailure0decreaseinthecompressivestrength6566CARBONFIBERCOMPOSITESincreaseintheshearmodulusincreaseinthedegreeofanisotropydecreaseintheelectricalresistivityincreaseinthethermalconductivitydec

5、reaseinthecoefficientofthermalexpansionincreaseindensityincreaseinthermalstability(oxidationresistance)increaseinchemicalstabilityincreaseincostMechanicalPropertiesTable4.1[l]showsthetensilepropertiesofcarbonfibersalongthefiberaxiscomparedtothoseofagraphitesinglecrystalalongthea-axis,i.

6、e.,paralleltothecarbonlayers.Althoughthecarbonlayersinacarbonfiberexhibitastrongpreferredorientationparalleltothefiberaxis,thealignmentofthelayersisfarfrombeingperfectandthecrystallitesizeisfinite.Therefore,thetensilemodulusandstrengthofcarbonfibersareconsiderablybelowthoseofagraphitesi

7、nglecrystal.ThemodulusofHM-typefibersapproachesthatofagraphitesinglecrystal,butthatofHT-typefibersismuchbelowthatofagraphitesinglecrystal.ThetensilestrengthsofbothHMandHTfibersareverymuchbelowthatofagraphitesinglecrystal,althoughthestrengthofHTishigherthanthatofHM.Thereisthusmu