A-study-on-the-strength-improvement-of-the-multi-b

Astudyonthestrengthimprovementofthemulti-boltedjointJong-HwaYun,Jin-HoChoi⇑,Jin-HweKweonResearchCenterforAircraftPartsTechnology,SchoolofMechanicalandAerospaceEngineering,GyeongsangNationalUniversity,Jinju,Gyeongnam660-701,SouthKoreaarticleinfoArticlehistory:Availableonline29September2013Keywords:CompositejointMechanicalboltedjointHoleclearanceFailuremodeabstractThejoiningofcompositematerialshastraditionallybeenachievedbyadhesivebondingormechanicalfastening.Mechanicallyfastenedcompositejointsarefreefromsurfacetreatments,andtheyareunaf-fectedbytheservicetemperature,humidityandotherenvironmentalconditions.Mostaircraftboltjointsconsistofmultiplebolts,andtheymaysharetheloadunequallyduetotherelativelybrittlenatureofthecomposites.Inthispaper,anewmethodforimprovingthestrengthofthemulti-boltedcompositejointwasevaluated.Multi-boltedcompositejointswithfiveboltsweremanufacturedandtested.Thediffer-encesofdisplacementbetweentheboltswerecalculatedbyfiniteelementanalysisbyapplyingauni-formloadtoeachboltofthemulti-boltedjoint.Whenthesevalueswereusedforthepositiveclearancesofthemulti-boltedjoints,itwasexperimentallydemonstratedthattheloadacteduponalloftheboltsuniformlycomparedtothemulti-boltedjointwithouttheclearance.Additionally,thefailurestrengthofthejointspecimenwasimprovedbymorethan13.1–21.8%.2013ElsevierLtd.Allrightsreserved.1.IntroductionCompositematerialshaveahigherspecificstiffnessandspecificstrengththanexistingisotropicmaterials,andtheyhavesuperiordampingandimpactcharacteristics.Therefore,theuseofcompos-itematerialshasincreased,andtheirapplicationsarecontinuouslychanging[1].Ingeneral,compositejointsareclassifiedbasedonthejoiningmethodaseithermechanicallyfastenedoradhesivelybonded.Formechanicallyfastenedjoints,thejoiningisperformedbyprocessingopenholesonthebasematerialandthenusingaboltandrivetorapintojointhestructure.Asaresultofthisjoin-ingmethod,thestrengthofthecompositematerialsisreduced,andthismaycauseastructuralfailurebecauseofthehighstressconcentrationinthejointarea.However,thistypeofjointiseasytodisassembleorassemble.Furthermore,itiseasytocheckforfailuresandmakearepair,andthereisalmostnoneedforsurfacetreatment[2,3].Thejointsinaircraftstructuresaremostlymechanicallyfastenedjoints.Atsitesthataresubjectedtoacom-parativelyhighload,amulti-boltedjointstructureconsistingofmanyboltsisused.Thefailurestrengthofamulti-boltedjointisaffectedbythegeometricalformofthejointandbytheopen-holeclearance,althoughthestudiesontheseeffectsarelimited.Choi[4]studiedthestrengthofboltjointsandpinjointswithopen-holeclearances.Sen[5]investigatedthefailuremodeandbearingstrengthofmechanicallyfastenedboltedjointswithopen-holeclearancesunderapre-load.Kiral[6]examinedtheeffectoftheclearanceandtheinterference-fitonthefailuremode,thefailureloadandthebearingstrengthofpin-loadedjoints.Khashaba[7]investigatedtheeffectofwashersizeandtighteningtorqueontheperformanceofboltedjoints.Eriksson[8]studiedthecontactstressanalysisofboltedjointsusingthefiniteelementmethod.Lawlor[9]studiedtheeffectofamulti-boltedjointfas-tenedwiththreeboltsonthearbitraryclearance.McCarthy[10]analyzedthefailureoftheareaaroundtheopenholesofamulti-boltedjointwithadoublelapjointthroughfiniteelementanalysis.Inthisstudy,weevaluatedthestrengthofmulti-boltedjointswithadoublelapjointwithcompositematerials.Toconsiderthecharacteristicsofthemulti-boltedjoint,weperformedafailuretestforasingle-boltedjoint.Weselectedasingle-boltedjointwithtwodifferentfailuretypes,andfromthisstandard,wedesignedamulti-boltedjointandperformedthetensiletest.Additionally,weperformedthetestforamulti-boltedjointthathadbeenman-ufacturedforthreetypesofjoints:negativeclearancebetweentheboltandthehole,zeroclearance,andpositiveclearance.Weap-pliedtheoreticallycalculatedvaluesforthepositiveopen-holeclearancethroughfiniteelementanalysis.2.Single-boltedjointWemanufacturedtwotypesofcompositematerialsthathaddifferentstackingsequencesandfabricatedasingle-boltedjointforwhichthecompositematerialswerejoinedwithametalspec-imen.Then,weevaluatedthefailurestrengthandthefailuremodeofthesingle-boltedjoint.Fromthisevaluation,wedesignedamul-ti-boltedjointandexaminedthecharacteristicsofthejointfailure.0263-8223/$-seefrontmatter2013ElsevierLtd.Allrightsreserved.⇑Correspondingauthor.Tel./fax:[phone].E-mailaddress:[e-mail](J.-H.Choi).CompositeStructures108(2014)409–416ContentslistsavailableatScienceDirectCompositeStructuresjournalhomepage:[0/45/0/-45/90/0/90/0]Sand[0/45/0/-45/90/0/-45/0/45/0/90/0]S,andthethicknessesofthecompositematerialswere2mmand3mm,respectively.Thecompositematerialswerecuredusingtheautoclavevacuumbagprocess.ThematerialusedformanufacturingthespecimenwasSKChemical’sCarbon/EpoxyunidirectionalprepregUSN-125B,andthematerialpropertiesareshowninTable1.Astraightshankdrillwasusedforthedrillingpro