Development of a fast shape memory alloy based actuator for morphing airfoils

215 Pages·2016·18.51 MB·English

by  Adrián Lara Quintanilla

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Adrián Lara Quintanilla
DEVELOPMENT OF A FAST SHAPE MEMORY ALLOY
BASED ACTUATOR FOR MORPHING AIRFOILS

DEVELOPMENT OF A FAST SHAPE MEMORY ALLOY
BASED ACTUATOR FOR MORPHING AIRFOILS
Proefschrift
terverkrijgingvandegraadvandoctor
aandeTechnischeUniversiteitDelft,
opgezagvandeRectorMagnificusprof.ir.K.C.A.M.Luyben,
voorzittervanhetCollegevoorPromoties,
inhetopenbaarteverdedigenop
donderdag24maart2016om10:00uur
door
Adrián LARA QUINTANILLA
IngenieroIndustrial,
UniversidadCarlosIIIdeMadrid,Spain,
geborenteBurgos,Spain.
Ditproefschriftisgoedgekeurddoorde
promotor:Prof.dr.ir.R.Benedictus
copromotor:dr.ir.H.E.N.Bersee
Samenstellingpromotiecommissie:
RectorMagnificus, voorzitter
Prof.dr.ir.R.Benedictus Promotor
Dr.ir.H.E.N.Bersee Copromotor
Onafhankelijkeleden:
Prof.Dr.Ir.G.A.M.vanKuik, DelftUniversityofTechnology
Prof.Dr.Ir.A.deBoer, UniversityofTwente
Prof.Dr.D.Polyzos, UniversityofPatras
Prof.Dr.J.A.PuértolasRafales, UniversidaddeZaragoza
Prof.Dr.G.vanBussel, DelftUniversityofTechnology(reservelid)
Overigeleden:
Dr.Ir.J.W.vanWindergen, DelftUniversityofTechnology
Thisresearchwascarriedoutaspartofthe"SmartFixedWingAircraft"Europeanproject
undertheCleanSkyJointTechnologyInitiativeprogram.
Keywords: Shapememoryalloy,actuator,actuationfrequency,control,morphing
airfoils
Printedby: BOXPress
Coverdesign: AdriánLara-Quintanilla
Cartoon: StephanTimmers
Copyright©2016byAdriánLara-Quintanilla
Allrightsreserved.Nopartofthematerialprotectedbythiscopyrightnoticemaybe
reproducedorutilisedinanyformorbyanymeans,electronicormechanical,including
photocopying,recordingorbyanyinformationstorageretrievalsystem,withoutprior
permissionoftheauthor.
ISBN978-94-6186-612-7
Anelectronicversionofthisdissertationisavailableat
http://repository.tudelft.nl/.
Amispadresymihermana,aquienesselodebotodo

S
UMMARY
Thedesignofaerodynamicairfoilsareoptimizedforcertainconditions. Forinstance,
theshapeofthewingsoffixed-wingaircraftsaredesignedandoptimizedforacertain
flightcondition(intermsofaltitude,speed,aircraftweight,etc.). However,theseflight
conditionsvarysignificantlyduringtheflight.Currently,aircraftareprovidedwithcon-
trolsurfacessuchasflaps,slatandailerons,normallygovernedbypowerfulbutheavy
hydraulicmechanisms. Thesemovingpartsallowtheaircrafttoflyundermanydiffer-
entflightconditions,althoughusuallywithnon-optimalperformance. Moreover,these
mechanisms introduce hinges and surface discontinuities between parts which cause
undesirableeffectssuchasturbulencesandnoiseoradecreaseofthelift-to-dragratio.
Thisissuemotivatestheresearchanddevelopmentoftheso-called‘morphingaircraft’
or‘morphingwings’. Ideally,amorphingaircraftisabletomodifyquicklytheshapeof
itswingsin-flight,thusreachingoptimumaerodynamicperformanceunderanyflight
condition.Thisideaisapplicabletoanyotheraerospaceapplicationssuchasrotorcraft
orwindturbines.
Morphingappliedtoaerodynamicairfoilsbringsalonginterestingbenefits: reduc-
tionofmechanicalfatiguewhichhasaspecialimportanceinwindturbinesandrotor-
crafts(byminimizingvibrationsonthestructure), reductionofthewingrootbending
moment,reductionoffuelconsumptionofflyingmachinesandincreaseoftheperfor-
manceofwindturbinesbyincreasingthelift-to-dragratioofthewingsorblades,and
thereductionofgeneratednoise.
Thisdissertationgivesanintroductionontheconceptofmorphingappliedtoaero-
dynamicairfoilsanddescribesthebenefitsandchallengesbroughtbymorphingstruc-
tures.Subsequently,thepotentialofsmartmaterialstodevelopnovelactuationsystems
isintroduced. Thedescriptionofthemotivationforthisworkleadstothepurposeof
thisresearch,whichaimsatdevelopingaprototypeofageneral-purposemorphing
flat surface based on embedded shape memory alloy wires with increased working
frequencyformorphingairfoils. Inordertoachievethispurpose, theresearchisdi-
videdintotworesearchobjectives.Thefirstresearchobjectiveistodevelopaprofound
understandingofthebehaviourofshapememoryalloys(SMAs)and,subsequently,to
deviseamethodtoincreasetheiractuationfrequency.Thesecondresearchobjective
istodevelopnovelcontrolalgorithmsandactuatortechnologyaswellasanintegra-
tiontechnologyfortheSMAwireswithincreasedactuationfrequency.
Followingtheintroduction,thisthesisdescribesthepotentialofsmartmaterialsin
general,andSMAsinparticular,todevelopnovelsmartactuatorsformorphingwings.
Themaindifferencesbetweenconventionalandsmartactuatorsareexplainedtogether
withtheiradvantagesandintroducedchallengesintermsofdesignandcontrol.These-
lectionofSMAsisjustifiedasthebestcandidatestoachievetheresearchobjectives. A
detaileddescription,workingprinciples,features,capabilities,limitationsandapplica-
tionsofSMAbasedactuatorsisgivenaswell.
vii
viii SUMMARY
Inordertofulfillthefirstresearchobjective,aseriesoflogicalstepswerefollowed.
OncetherequirementsoftheSMAbasedactuatorwerestated,acommercialSMAwire
waschosenandcharacterized(i.e., thephasediagramoftheSMAwirewasobtained)
whichshowsthephasecompositionoftheSMAwhenitissubjectedtodifferentlevels
ofstressandtemperature. Thephasediagramwasobtainedfromdatacollectedfrom
isothermal, isobaricanddifferentialscanningcalorimetertests. Duringanisothermal
test,thetemperatureiskeptconstantandtheSMAwireissubjectedtoincreasingand
decreasinglevelsofstressinordertofindthosestressesatwhichtheSMA’sphasetrans-
forms.Similarly,anisobarictestkeepsthestressontheSMAconstantovertimeandthe
temperatureisincreasedanddecreasedtofindthoseatwhichtheSMA’sphasetrans-
forms. Subsequently,thefunctionalfatigueoftheSMAwirewasstudiedbytrainingthe
SMAwire. Thistrainingprocessconsistinapplyingrepetitiveheatingandcoolingcy-
clesinanisobaricconfiguration. Highrepeatabilitywasfoundontheresults. Afteran
averageof7289trainingcycles,thewirewasabletorecoveronly77%ofitsoriginalre-
coverablelengthforthetestedconditionsofappliedcurrent,heatingtime,coolingtime
andappliedstress.
Subsequently,anSMAmodelforSMAwiresisimplementedinafiniteelementanal-
ysis software. The equations that describe the model and their physical meaning are
explained. Oneoftheadvantagesofthechosenmodelistheeaseofobtainingthepa-
rametersrequiredbythemodel,whichcanbeobtainedfromafewexperiments. Inad-
dition,andalsoasapartofthemodel’srequiredparameters,thecharacteristicsofthe
forcedcoolingsystemarestudiedhere,andtheheattransfercoefficientofsuchairflow
fordifferentairflowratesismeasured.Finally,themodelissatisfactorilyvalidated.
OneofthelimitationsofSMAbasedactuatorsistheirpooractuationfrequency(usu-
allylowerthan0.1Hz).Thisisduetothefactthattheyarethermallyactivated,normally
byJouleheating,whichisaquickprocess.However,theymustbecooledbeforethenext
actuationcycle, whichnormallyhappensbynaturalconvection. Thiscoolingprocess
canbeacceleratedbymeansofactivecoolingsystems. Inthisresearch,anactivecool-
ingairflowatroomtemperatureisused. Theeffectsofapplyingdifferentheatingand
coolingratesonthetimethatittakesforthewiretocontractandelongate(respectively)
wereexperimentallymeasuredusinganisobaricconfiguration. Inaddition, thesame
experimentsweresimulatedbythemodelforSMAwiresimplementedpreviously.There
isanoverallquantitativedisagreementbetweentheresultsyieldedbythesimulations
andbytheexperiments. However, theresultsareusefulqualitatively. Itisfoundthat
thecontractingandthecoolingtimesaresignificantlydecreasedastheappliedpower
andairflowisincreased. Moreimportantly,itisfoundthatwhenthewireworksatlow
workingfrequencies, theheatingrateisthelimitingfactorwhereasthecoolingrateis
thelimitingfactorwhenitworksathighworkingfrequencies. Inaddition,theseexper-
imentsshowthatincreasingthelevelofappliedstressresultsinslightlyhigherworking
frequenciesoftheSMAwire.
Theknowledgeacquiredinthepreviousexperimentsandsimulationsleadstothe
development of a method to improve the attainable actuation frequency of the SMA
wires.Thismethodisbasedontheideathat,inmanySMAbasedapplications,theSMA
wiresdonotworkthroughouttheirfullrecoverablestrainbuttheyworkonlywithina
portionofit.Takingadvantageofthenonlinearityofthestrain-temperaturerelationship
SUMMARY ix
forSMAs,themethodproposedhereisabletoincreasetheSMA’sactuationfrequencyby
threeandahalftimesjustbymakingtheSMAwireworkwithinthemostsuitablerange
ofstrains,withoutvaryingtheheating,coolingandstressconditions. Thedevelopment
ofthismethodfulfillsthefirstresearchobjective.
Lateroninthisthesis,thedesign,manufacturingandassemblingprocessesofthe
SMAbasedactuatoraswellastheirchallengesaredetailed.First,abeam-likemoduleof
theSMAbasedactuatorwasconceived,designedandmanufactured.Subsequently,the
designwasexpandedinthespanwisedirection, thusobtainingamodularSMAbased
actuator that forms a morphing plate. The morphing plate was tested by heating the
SMA wires embedded in the actuator. This test revealed an unexpected behaviour of
theplate. Theexpectedbehaviourwasthatitwouldbendupwardswhenthewireson
thetopside wereheated. However, insteadofbendinguniformly alongthespanwise
direction,thecenteroftheplatebendedupwardsandthesidesdownwards. Asimilar
responsewasobservedwhenthewiresonthebottomsidewereheated.Thiswasfound
tobecausedbyinhomogeneousthermalexpansion(inthespanwisedirection)through
thethicknessoftheplate.
Due to the unexpected response observed on the morphing plate, a single beam-
likemoduleSMAbasedactuatorwascontrolledundertwodifferentcontrolstrategies,
fuzzylogiccontrol(FLC)andproportional-integrative-derivative(PID)control. Inboth
cases, theSMAbasedactuatorwasmadetotracksinusoidalandstepsignalsinorder
tomeasureitsperformance. TheoverallperformanceofthesystemunderFLCisbet-
terthanthatunderPID.UnderFLC,itreachesactuationfrequenciesabove0.6Hz for
workingatamplitudesofupto6mm,andfrequenciesabove1Hzforamplitudesofup
to3mmwhiletrackingthereferencesignalaccurately(maintainingrelativeerrorbelow
10%). UnderPIDcontrol,itreachesactuationfrequenciesabove0.5Hz whenworking
atamplitudesupto3mm,andfrequenciesabove0.7Hzforamplitudesupto2mm.The
actuatorisabletotrackstepsignals(thatis,toreachandmaintainaconstantdeflection
over time) under both types of controller, although under FLC it is significantly more
stable. Thesedevelopeddesign,manufacture,assemblyandcontrolmethodsfulfillthe
secondresearchobjective.
Thisthesispresentsnovelmethodsaimingtoincreasetheaccuracyandactuation
frequencyofSMAbasedactuators. Inparticular, thisworkisfocusedonthedevelop-
mentofamorphingsurfaceintendedtobeintegratedinmorphingairfoils. However,
the methods and ideas developed in this research are applicable to other SMA based
applications,especiallythosewhichrequirefast,cyclicandaccurateactuation.