Mechanical behaviour evaluation of adhesively bonded joints of aircraft structures Aerospace ...

124 Pages·2016·33.15 MB·English

by  Andre C. Marta

Mechanical behaviour evaluation of adhesively bonded
joints of aircraft structures
Sérgio Nunes Correia
Thesis to obtain the Master of Science Degree in
Aerospace Engineering
Supervisor(s): Prof. Luís Filipe Galrão dos Reis
Prof. Vítor Manuel Rodrigues Anes
Examination Committee
Chairperson: Prof. Filipe Szolnoky Ramos Pinto Cunha
Supervisor: Prof. Luís Filipe Galrão dos Reis
Member of the Committee: Prof. Rosa Marat-Mendes
October 2016
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Acknowledgments
Iwouldliketothankmysupervisors,Prof. Lu´ısReisandProf. V´ıtorAnes,fortheirguidancethroughout
therealizationofthiswork.
Also,Iwouldliketoexpressmygratitudetomyparents,Joa˜oandFernanda,andmybrother,Alexan-
dre,fortheirencouragementandforalwaysbeingpresent,alongallthoseyearsatIST.
Moreover, I cannot pass this opportunity to thank my girlfriend, Mafalda, for all the support and
patience during this journey. She stand for me even in the most difficult periods and helped me in
everythingIhaveachieveduptonow. Thankyouforalwaysbeingthereforme!
Besides,Iexpressmygratitudetoallmyfamily,withaspecialthankstomyaunt,Patricia,forallthe
helpandalltheacademicmaterialprovided.
Continuing, I cannot leave out my dear friend Nicolau. With him, this years at IST were much more
easyandfun.
Ofcourse,Icouldnotleaveallmyotherfriendsout. Allofthemareabigpartofmylife.
Finally,butnolessimportant,IneedtothanktoEngineerDavidMartinsLopesandEngineerRoge´rio
Sa˜oPedro,fromTAPMaintenanceandEngineering,fortheirgreathelpduringthiswork.
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Resumo
Aintegridadeestruturaldecertasestruturase´ muitasvezesdeterminadapelaresisteˆnciadassuasjun-
tas. Aolongodosanos,juntasadesivasteˆmsidofrequentementeutilizadasemvezdeoutrasbaseadas
em sistemas mecaˆnicos, como a soldadura ou a aplicac¸a˜o de rebites. Entre outras, a reduc¸a˜o de
concentrac¸a˜o de tenso˜es, a capacidade de produzir superf´ıcies lisas, sem descontinuidades, e o seu
reduzido peso sa˜o algumas das vantagens que tornam este tipo de juntas ta˜o atrativas. Contudo,
quando comparadas com outras te´cnicas de unia˜o, pode-se verificar que na˜o existem praticamente
diretrizes aceites para prever a resisteˆncia de uma junta adesiva, sendo o seu desenho muitas vezes
baseado na experieˆncia pessoal e em regras emp´ıricas. Recentemente, alguns me´todos nume´ricos
teˆmsidopropostoscomointuitodeestimaracargadefalhadeumajuntaadesiva. Oseugrandeprob-
lema esta´ relacionado com o facto de, para a maior parte destes me´todos ser aplica´vel, alguns testes
experimentaisteremdeserrealizados,oquenemsempree´ conveniente.
Dito isto, um estudo experimental foi realizado, baseado na junta adesiva simples da norma de en-
saio ASTM D 1002, com o objetivo de determinar qual o melhor tratamento de superf´ıcie, para juntas
alum´ınio-alum´ınio, utilizando dois tipos de adesivos. Ainda, foi implementado um modelo computa-
cional, utilizando o Me´todo dos Elementos Finitos, com o intuito de prever o comportamento dos ade-
sivos,utilizandoapenascomoinputasuacurvatensa˜o-extensa˜o.
Palavras-chave:
Adesivo,JuntaAdesiva,JuntaAdesivaSimples,TratamentodeSuperf´ıcie,
ASTMD1002,FEM
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Abstract
Thestructuralintegrityofsomestructurescanberelatedtothestrengthoftheirunions. Overtheyears,
adhesively bonded joints have been often chosen over several mechanical systems based joints, as
weldingorriveting. Amongothers,thereductioninstressconcentrations,theabilityofproducingsmooth
surfaces,withnodiscontinuitiesandthereducedweightpenaltiesaresomeofthefactorsthatmakethis
type of joints so attractive. However, when compared with these other joining techniques, it can be
verifiedthattherearepracticallynoacceptedguidelinesforpredictingthestrengthofanadhesivejoint,
being the design of some joints still based in personal experience and in the so-called rules of thumb.
Recently,somenumericalmodelshavebeenproposedtoestimatethefailureloadofbondedjoints. The
main problem is related with the fact that, for most of these methods to be applied, some experimental
testsmustbeperformedtoidentifysomematerialmodels,whichisnotalwaysconvenient.
Withthisinmind,anexperimentalstudywasperformed,basedintheSingleLapJointfromtheASTM
D1002standardmethod,withtheobjectiveofdeterminingthebestsurfacetreatment,foraluminum-to-
aluminum joints, using two types of adhesives. Furthermore, a computational model, using the Finite
Element Method, has been implement in order to predict the adhesive behavior, taking only the stress-
straincurveoftheadhesiveasaninput.
Keywords:
Adhesive,AdhesivelyBondedJoint,SingleLapJoint,SurfaceTreatment,ASTMD
1002,FEM
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