FabricstructureandmoldcurvatureeffectsonpreformpermeabilityandmoldfillingintheRTMprocess.PartI.ExperimentsS.Bickerton,E.M.Sozer,P.J.Graham,S.G.Advani*DepartmentofMechanicalEngineering,UniversityofDelaware,Newark,DE19716,USAReceived15October1998；receivedinrevisedform31August1999；accepted23September1999AbstractLiquidcompositemolding(LCM)processesrequiretheimpregnationofapolymericresinthroughaporouspreform,beingcomposedofglass,carbon,orkevlarfibers.Thesuccessfulmanufactureofcompositepartsthroughthesemethodsisdependentonthesuccessfulfillingofthemoldcavity,expellingallairfromwithin.Numericalsimulationsarebeingdevelopedtomodelthisprocess,andarepowerfulmolddesigntools.Theaccuracyofsuchsimulationsisstronglydependentonthespecificationofthepreformpermeabilitytensorthroughoutthemoldcavity,beinganumericaldescriptionoftheresistancetoresinflow.Changesinpreformarchitecturecaneasilymodifylocalpermeability,andhencethemoldfilling.Cornersinmoldcavitiesareapotentialsitesforpreformdeformation,andarethefocusofthisstudy.Afamilyoffivemoldshavebeenstudied,containingcornerradiifrom0.06to8.0in.Adetailedflowvisualizationstudyhasbeencompletedtoinvestigatetheinfluenceofmoldcornerradiionflowfrontprogressionandinjectionpressure.Whileflowfrontprogressionwasnotsignificantlyaffectedbydifferentcornerradii,injectionpressureswerefoundtobegreaterforthemoldswithsmallercornerradii.Actualcompositepartsmanufacturedinthesamemoldshaverevealedthatthemoldsarenotofconstantcavitythickness,aswastheoriginalgoal.Todeterminetheimportanceofcornerradiionmoldfilling,itwillbenecessarytoseparatetheeffectsofin-planepreformcompressionfromanyeffectduetocorners.Toaccomplishthisgoal,theexperimentaldatapresentedhereisbeingcomparedwithdetailednumericalstudies,whichwillbepresentedinpartIIofthiswork.Keywords:Liquidcompositemolding；E.Resintransfermolding1.IntroductionLiquidcompositemolding(LCM)processesarepopularcompositematerialmanufacturingtechniquesgainingfavorinthecivil,aerospace,automotiveanddefenseindustries.Theseprocessespossessseveraladvantages,includingnetshapeproduction,relativelylowinjectionpressures,moder-atelylowcycletimes,andsimpletoolingrequirements.LCMprocesseshavethepotentialtoproducelowcost,highquality,geometricallycomplexcompositeparts.Resintransfermolding(RTM),structuralreactioninjectionmolding(SRIM),Seemancompositeresininfusionmoldingprocess(SCRIMP),andinjectioncompressionmoldingareexamplesofthemanyLCMprocessvariations.Generally,LCMprocessescanbedescribedasfollows.First,thefiberpreformismanufactured,beingthereinforce-mentoftheintendedpart.OneofthemajoradvantagesofLCMprocessesistheabilitytotailorthepreformexactlytotheneedsofthepart,placingreinforcementasrequired.Fiberpreformsareconstructedfromawidevarietyofarchitectures,constructedfromglass,carbonorkevlarfibers.Thefiberpreformwillprovidethefinishedpiecewiththemajorityofitsstructuralproperties.Thepreformisplacedwithinthemoldcavity,andthemoldissealed.Next,thepolymericresinisinjectedintothemoldcavity,saturatingthepreformandexpellinganyairpresent.Acuringreactionisinitiated,eitheraftercompletelyfillingthemoldcavity,orpossiblyatsomestageduringimpreg-nation.Afterthepieceissufficientlycured,thefinishedcompositeproductcanberemovedfromthemold1.ThesuccessfulmanufactureofLCMpartsissensitivetothepreforming,impregnation,andcuringstages.Thispaperwillfocusonthedeformationofpreformsaroundcornerswithinmolds,studyingitsinfluenceonthesubsequentimpregnationstage.Defectsincurredthroughunsuccessfulmoldfillingincludebothmicroscopicandmacroscopicvoids2,3.Microscopicvoidsrefertotinyairbubblestrappedwithin,andaroundfiberbundlesofthepreform.Suchvoidsareoftenverydifficulttoeradicatecompletely,butattemptsshouldbemadetominimizethem4.Macro-scopicvoidsrefertolargeairpocketsthathavebeentrappedwithinthemoldcavityduetoafaultyinjectionschemeComposites:PartA31(2000)423438*Correspondingauthor.(e.g.incorrectlyplacedinjectionportsandvents).Usuallysuchvoidswillresultinapartthatisunusable,asportionsofthepartwillbeformedbydrypreformhavingnostructuralrigidity.Theaimofthisworkwastoinvestigatewhethercornersofdifferentradiiwouldhaveanysignificanteffectontheprogressoftheresinflowfrontwithinamoldcavity,andpossiblycausetheformationofmacroscopicvoids.LCMfillingprocessesaretypicallymodelednumericallyusingDarcyslaw,whichrelatespressuregradientswithinamoldtoanumericalmeasureoftheresistancetoflowthroughthepreform,beingthepermeability.Inrecenttimes,muchefforthasbeenplacedintothedevelopmentofDarcyslawbasednumericalprocesssimulationsofLCMfillingprocesses511.Suchsimulationscanpredicttheflowpatternsandpressuredistributionaslongaswehavepriorknowledgeofthematerialparameters,beingprimarilythecomponentsofthepermeabilitytensor.ManypapershavebeenpublishedconcerningpermeabilityS.Bickertonetal./Composites:PartA31(2000)423438424(a)(b)Fig.1.MoldA:(a)aluminumbase；(b)aluminumbaseandacrylictop.measurements,andanalyticalpermeabilitypredictions1215.Thoughmuchprogresshasbeenmadeinbothfields,thewidevarietyofpreformstyles,andtheirvariationinarchitecturewithcompaction,haveinhibitedtheformationofacomprehensivepermeabilitydatabase.Preformpermea-bilitiescanalsobefurtheralteredbyseveralsecondaryeffects,includingracetracking16,17,multi-layeredpreforms18,preformcompaction19,andpreformshearing17,20,amongothers.ThisworkhasaimedtodeterminethemagnitudeofeffectonLCMmoldfillingprocessesduetomoldcornersofvariousradii.Ifanyeffectsduetomoldcornersaresignifi-cant,modelsneedtobedevelopedtoaccountforanyvariationinpermeabilityintheseregions.Iftheeffectsareshowntobenegligible,permeabilitytensorsdeterminedforflatportionsofamold(withthesamefibervolumefraction)canbeappliedtothesecornerregions.PreliminarystudiesintotheflowaroundcornershasbeenpresentedbyFriedmanetal.21.Verydetailedexperimentsandcalcu-lationshavebeenpreformed,however,theevidencepresenteddoesnotclearlydemonstratethemagnitudeofanyeffectsduetomoldcorners.Theexperimentalportionofthisstudyhasbeencompletedintwoparts.Detailedflowvisualizationexperi-mentshavebeencompletedtodeterminethenatureandmagnitudeofeffectcornersofvariousradiihaveonthemoldfillingprocess.Fivemoldswereused,havingmoldradiivaryingfrom0.06to8.0in.Thefemalehalvesofthemoldsweremachinedfromacrylic,allowingforthemoldfillingtobevisualized.Threedifferentpreformstyleswereinvestigated,atavarietyoffibervolumefractions.Injectionpressurehistoriesandflowfrontprogressionhavebeenrecorded.Thesecondportionoftheexperimentalprogramhasfocusedonthemanufactureofactualcompositepiecesinthesamemolds.Somesmallmodificationsweremadetothemolds,inordertoprotecttheacrylicmoldhalvesfromtheresinused.Partsweremanufacturedusingthesamepreformsusedintheflowvisualizationstudy.Thesepartshaveservedtwopurposes,verifyingthegeometryofthemoldcavities,andprovidingsomeinsightintothestateofpreformdeformationnearcorners.ThefindingsofourexperimentalstudiesarepresentedinS.Bickertonetal./Composites:PartA31(2000)423438425VentsPortInjectionStiffeningBarsFig.2.Overheadviewofassembledmold,withstiffeningbars.Fig.3.Schematicdefiningmoldgeometricaldata:(a)moldsAD；(b)moldE.Table1MoldgeometricaldataR1(m/in.)R2(m/in.)T1(m/in.)T2(m/in.)MoldA1:5241023(0.060)4:6991023(0.185)3:0481023(0.120)2:2351023(0.088)MoldB2:5401023(0.100)5:7151023(0.225)2:9971023(0.118)2:1591023(0.085)MoldC6:3501023(0.250)9:5251023(0.375)3:0231023(0.119)2:1591023(0.085)MoldD12:701023(0.500)15:881023(0.625)2:9971023(0.118)3:0231023(0.119)MoldE203:21023(8.000)206:41023(8.125)3:0731023(0.121)thispaper.Duetotheactualmoldcavitygeometries,twotypesofpreformdeformationhavebeenintroduced.Astwoofthemoldcavitieshaveportionswithsignificantlydifferentthicknesses,effectsduetopreformcompressionhavebeenidentified,andarecoupledwiththosethatmaybepresentduetocornerradii.Afollowuppaperwillpresentadetailednumericalstudythatwillservetoidentifytheinfluenceofbothdeformationstyles.ThisisneededtoassesstheimportanceofmoldcornerradiionLCMfillingprocesses.2.ExperimentalprogramDetailedflowvisualizationexperimentshavebeenperformed,providingextensivevalidificationdataforthenumericalsimulationswhicharepresentedinoursecondpaper.Experimentallymeasuredinjectionpressurehistorieswillbepresentedforthreepreformstyles,andatvariousvolumefractions.Videosnapshotsareprovidedfromselectedexperiments.Themolds,beingdesignedforflowvisualization,havebeenmodifiedtoallowthemanufactureofactualcompositeparts,usingthesamepreforms,andavinylesterresin.Thesepartshavebeenanalyzedtop