j - METU | Aerospace Engineering

1 CareandRepairofAdvancedComposites~~ resinmatrix,butit canalsoincludemetal-skinnedhoneycombpane ls, a g~odexampleofa ,becausetheyworktogether,thesteelcarries the~nsionloadsandtheconcn; , ~>nsistoftwoormorephysicallydist,jPctaq4 mechanicallyseparableD1i!teriab.'.., J,~~,;'"Theyaremadebymixingtheseparatema terialsinsucha wayastoachievecontrolledandlIniformdispe rsionoftbecon~titu~!1ts! (modulus) "specific"strengthand"specific" clearlyseenwithglass-reinforcedplastics( GRP).I~thecaseofGRP,theepoxyre~iriis 11relativelyweak,flexible,andbrittlemate rial,andalthoughtheglassfibersarestronga ndstiff,theycanbeloadedintensiononlyasa ~encombined,theresinandfil:>e~givea strong, is )(luctioncostis widerangeofprocesses.;~ '1/)v6.\ Compositesofferexcellentresistancetocorr osion,chemicalattack,andoutdoorweath-,er ing;however,somechemicalsaredamagingto composites( ,paintstripper), ~ ~ ,bydefinition,somethingmadefrOJDtWQormor ecomponents-inourcasehere,a fiberanda ~itesareno,tf1newic:lIW' o~e~floateddownt~eNileinabasketmadefrom' papyrusreedscoatedwithp~~S~'PaJlYI11~is ~ formofpaperwitha vis-iblefibrousreinforcement;therefore,i t wouldnothav~been4jfftculttomakea ,it "mud"butswerereinforcedwitJtgras~ , mixtureofcowdungand",ud,Wereusedtobuildh ousew;1llsinEnglandin1500'B.

2 <::.It wouldbeinterestingtolCnowhowthecorrectmixratioforthecowdungcpldthemudwasdetermined!ThelathandplasterwallsinoldEnglishhouseswerea formofcomposit~.Althoughtheconceptisold, ,aramid,andglassfibersareveryexpensivecom-paredtostraw,andepoxyresinsarecostlycomparedtoa mixtureofcowdungandmud!Fortunately,theperformancefora givenweightis treeconsistsoflong,strongcellulosefibersbondedtogetherbya ~ , necessaryinmanycases, rivetshavebeenusedandmustberemoved, ~~ ' (interiorsandfueltanksandengineparts). " <~setreliincompositesoverthennoplasticresincompositesincludethefollowing:' ,thermosetscanbemanufacturedat lowertemperaturesthanthermoplast\ (PEEK)250to300 C(482to572 F). \vo-partsystemscanbecuredat roomtemperature,andtheircurecanbespeededbyheatingtoapproximately80 C(176 F).\ ,particularlywithepoxysystems,allowsrepairat ,somehigh-strengthinteriorparts, (RTM)aroundreinforcingfiberoruseinconventionalapplicationmode( ,pre-pregstacking).

3 Generallygood, ,someepoxiesaremoreresistanttochemicalst hanothers." '(coldstore/thaw/cure). ,especiallyif ( ). ,environmentalperformance, ~. ,Yachts,Cars,and1i' :Earlyaircraftwerecomposite-basedstructu resbecausetheywere'builtfromwood,whichis a compositematerialcomprisinga ,woodis subjectto ,woodenaircraftstructuresbegantobereplac edbystressed-skin,monocoquealuminumalloy structur~ ~.cessingtimesandgoodenvironmentalperfor mance, ,checkeachmaterialanditsresponsetoeachso lventlikelytobeencountered.,45