Polymer Materials in Additive Manufacturing: Modelling and Simulation

213 Pages·2023·17.071 MB·English

by  Mohammadali Shirinbayan, Nader Zirak, Khaled Benfriha, Sedigheh Farzaneh, Joseph Fitoussi

Polymer Materials
in Additive
Manufacturing
Modelling and Simulation
Edited by
Mohammadali Shirinbayan, Nader Zirak, Khaled Benfriha,
Sedigheh Farzaneh and Joseph Fitoussi
Printed Edition of the Special Issue Published in Polymers
www.mdpi.com/journal/polymers
Polymer Materials in Additive
Manufacturing: Modelling and
Simulation
Polymer Materials in Additive
Manufacturing: Modelling and
Simulation
Editors
Mohammadali Shirinbayan
Nader Zirak
Khaled Benfriha
Sedigheh Farzaneh
Joseph Fitoussi
MDPI‚Basel‚Beijing‚Wuhan‚Barcelona‚Belgrade‚Manchester‚Tokyo‚Cluj‚Tianjin
Editors
MohammadaliShirinbayan NaderZirak KhaledBenfriha
PIMM PIMM LCPI
ArtsetMetiersInstitute ArtsetMetiersInstitute ArtsetMetiersInstitute
ofTechnology ofTechnology ofTechnology
HESAMUniversity HESAMUniversity HESAMUniversity
Paris Paris Paris
France France France
SedighehFarzaneh JosephFitoussi
PIMM PIMM
ArtsetMetiersInstitute ArtsetMetiersInstitute
ofTechnology ofTechnology
HESAMUniversity HESAMUniversity
Paris Paris
France France
EditorialOffice
MDPI
St. Alban-Anlage66
4052Basel,Switzerland
This is a reprint of articles from the Special Issue published online in the open access
journalPolymers(ISSN2073-4360) (availableat: www.mdpi.com/journal/polymers/special issues/
Additive Manufacturing Polymers Polymer Composites).
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ISBN978-3-0365-6863-8(Hbk)
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Contents
MohammadAhmadifar,KhaledBenfrihaandMohammadaliShirinbayan
Thermal, Tensile and Fatigue Behaviors of the PA6, ShortCarbonFiber-Reinforced PA6, and
ContinuousGlassFiber-ReinforcedPA6MaterialsinFusedFilamentFabrication(FFF)
Reprintedfrom: Polymers2023,15,507,doi:10.3390/polym15030507 . . . . . . . . . . . . . . . . . 1
MuhammadAbas,TufailHabib,SaharNoor,BashirSalahandDominikZimon
Parametric Investigation and Optimization to Study the Effect of Process Parameters on the
DimensionalDeviationofFusedDepositionModelingof3DPrintedParts
Reprintedfrom: Polymers2022,14,3667,doi:10.3390/polym14173667 . . . . . . . . . . . . . . . . 21
FatehEnouarMamache,AmarMesbah,HanbingBianandFahmiZa¨ıri
Micromechanical Modeling of the Biaxial Deformation-Induced Phase Transformation in
PolyethyleneTerephthalate
Reprintedfrom: Polymers2022,14,3028,doi:10.3390/polym14153028 . . . . . . . . . . . . . . . . 43
LaszloRaczandMirceaCristianDudescu
NumericalInvestigationoftheInfillRateuponMechanicalProprietiesof3D-PrintedMaterials
Reprintedfrom: Polymers2022,14,2022,doi:10.3390/polym14102022 . . . . . . . . . . . . . . . . 57
SyedHammadMian,KhajaMoiduddin,SherifMohammedElseufyandHishamAlkhalefah
AdaptiveMechanismforDesigningaPersonalizedCranialImplantandIts3DPrintingUsing
PEEK
Reprintedfrom: Polymers2022,14,1266,doi:10.3390/polym14061266 . . . . . . . . . . . . . . . . 75
SedighehFarzanehandMohammadaliShirinbayan
ProcessingandQualityControlofMasks: AReview
Reprintedfrom: Polymers2022,14,291,doi:10.3390/polym14020291 . . . . . . . . . . . . . . . . . 93
NaderZirak,MohammadaliShirinbayan,MichaelDeligantandAbbasTcharkhtchi
TowardPolymericandPolymerCompositesImpellerFabrication
Reprintedfrom: Polymers2021,14,97,doi:10.3390/polym14010097 . . . . . . . . . . . . . . . . . 115
Toma´sˇ Tichy´,OndrˇejSˇefl,PetrVesely´,KarelDusˇekandDavidBusˇek
MathematicalModellingofTemperatureDistributioninSelectedPartsofFFFPrinterduring3D
PrintingProcess
Reprintedfrom: Polymers2021,13,4213,doi:10.3390/polym13234213 . . . . . . . . . . . . . . . . 141
Chil-ChyuanKuo,Ding-YangLi,Zhe-ChiLinandZhong-FuKang
Characterizations of Polymer Gears Fabricated by Differential Pressure Vacuum Casting and
FusedDepositionModeling
Reprintedfrom: Polymers2021,13,4126,doi:10.3390/polym13234126 . . . . . . . . . . . . . . . . 151
ZohrehShakeri,KhaledBenfriha,MohammadaliShirinbayan,MohammadAhmadifarand
AbbasTcharkhtchi
Mathematical Modeling and Optimization of Fused Filament Fabrication (FFF) Process
ParametersforShapeDeviationControlofPolyamide6UsingTaguchiMethod
Reprintedfrom: Polymers2021,13,3697,doi:10.3390/polym13213697 . . . . . . . . . . . . . . . . 173
ZhongqiuDing,BenWang,HongXiaoandYugangDuan
HybridBio-InspiredStructureBasedonNacreandWoodpeckerBeakforEnhancedMechanical
Performance
Reprintedfrom: Polymers2021,13,3681,doi:10.3390/polym13213681 . . . . . . . . . . . . . . . . 191
v
polymers
Article
Thermal, Tensile and Fatigue Behaviors of the PA6,
Short Carbon Fiber-Reinforced PA6, and Continuous
Glass Fiber-Reinforced PA6 Materials in Fused Filament
Fabrication (FFF)
MohammadAhmadifar1,2,*,KhaledBenfriha1 andMohammadaliShirinbayan2,*
1 ArtsetMetiersInstituteofTechnology,CNAM,LCPI,HESAMUniversity,F-75013Paris,France
2 ArtsetMetiersInstituteofTechnology,CNAM,PIMM,HESAMUniversity,F-75013Paris,France
* Correspondence:[email protected](M.A.);[email protected](M.S.)
Abstract:Utilizationofadditivemanufacturing(AM)iswidespreadinmanyindustriesduetoits
uniquecapabilities.Thesematerialextrusionmethodshavebeendevelopedextensivelyformanufac-
turingpolymerandpolymercompositematerials.Therawmaterialinfilamentformareliquefied
intheliquefiersectionandareconsequentlyextrudedanddepositedontothebedplatform. The
designedpartsaremanufacturedlayerbylayer.Therefore,thereisagradientoftemperaturedue
totheexistenceofthecyclicreheatingrelatedtoeachdepositedlayerbythenewerdepositedones.
Thus,thestatedtemperatureevolutionwillhaveasignificantroleontherheologicalbehaviorofthe
materialsduringthismanufacturingprocess.Furthermore,eachprocessingparametercanaffectthis
cyclictemperatureprofile.Inthisstudy,differentprocessingparametersconcerningthemanufactur-
ingprocessofpolymerandpolymercompositesampleshavebeenevaluatedaccordingtotheircyclic
temperatureprofiles. Inaddition,themanufacturedpartsbytheadditivemanufacturingprocess
(theextrusionmethod)canbehavedifferencescomparedtothemanufacturedpartsbyconventional
methods.Accordingly,weattemptedtoexperimentallyinvestigatetherheologicalbehaviorofthe
manufacturedpartsafterthemanufacturingprocess.Thusthethree-pointbendingfatigueandthe
Citation:Ahmadifar,M.;Benfriha,K.;
tensilebehaviorofthemanufacturedsampleswerestudied.Accordingly,theeffectofthereinforce-
Shirinbayan,M.Thermal,Tensileand
mentexistenceanditsdirectionanddensityonthetensilebehaviorofthemanufacturedsampleswere
FatigueBehaviorsofthePA6,Short
studied.Therefore,thisstudyishelpfulformanufacturersanddesignerstounderstandthebehaviors
CarbonFiber-ReinforcedPA6,and
ofthematerialsduringtheFFFprocessandsubsequentlythebehaviorsofthemanufacturedpartsas
ContinuousGlassFiber-Reinforced
PA6MaterialsinFusedFilament afunctionofthedifferentprocessingparameters.
Fabrication(FFF).Polymers2023,15,
507. https://doi.org/10.3390/ Keywords:materialextrusion;rheologicalbehavior;mechanicalproperties;temperatureprofile
polym15030507
AcademicEditor:CarolaEsposito
Corcione
1. Introduction
Received:4October2022 Additive manufacturing (AM) is growing due to the low amount of wasted mate-
Revised:2January2023 rial in the manufacturing process and the ability to manufacture complex shapes [1–3].
Accepted:5January2023 Therearedifferenttechniquesconcerningtheadditivemanufacturingprocess,whilefused
Published:18January2023 filamentfabrication(FFF)isthemostcommonlyutilizedtechnique[4]. Mechanicalprop-
erties and dimensional accuracy of the FFF-processed parts are affected by the utilized
processing parameters during the manufacturing process [5]. The importance and the
influenceoftheassortmentofprocessingparametershavebeenstudied,suchastheeffect
Copyright: © 2023 by the authors.
ofprintspeed[6,7],bedplatformtemperature[8–10],liquefiertemperature[11],andlayer
Licensee MDPI, Basel, Switzerland.
height[12,13]. Theevolutionofthetemperatureofthedepositedlayersisconsiderably
This article is an open access article
affected by the aforementioned processing parameters during the FFF process [5]. The
distributed under the terms and
temperatureevolutioncausedagradientofthetemperatureinthestructure,whichsignifi-
conditionsoftheCreativeCommons
cantlyaffectedtheadhesionandthebondingofthedepositedlayersandconsequentlythe
Attribution(CCBY)license(https://
strengthofthemanufacturedparts. Severalstudiesrelatedtothetemperatureevolution
creativecommons.org/licenses/by/
duringtheFFFprocesshavebeenconducted[5,14,15].
4.0/).
1
Polymers2023,15,507
Christiyan et al. [16] investigated the flexural and tensile strength of the printed
ABScompositematerialsunderthedifferentprintspeedvaluesof50,40,and30mm/s
andthelayerheightvaluesof0.3,0.25,and0.2mm. Asfortheresults,itwasobserved
thatthelowerlayerheightandprintspeedvalues(0.2mmand30mm/s)increasedthe
flexuralandtensilestrengths. Moreover,severalstudieshavebeencarriedoutregarding
theFFFprocessofpolymercompositematerials[17–19]. Durgaetal.[20]evaluatedthe
influenceoftheliquefiertemperatureandlayerheightofthedepositedlayersonthetensile
strengthoftheprintedCF-PLAspecimens. ThemanufacturedCF-PLAspecimensunder
thelowestselectedlayerheightvalueandthehighestselectedliquefiertemperaturehad
thehighertensilestrength. AninvestigationwasconductedbyDingetal.[21]todetermine
theinfluenceofliquefiertemperatureonthemechanicalpropertiesoftheFFF-processed
PEEKandPEI.Theydiscoveredthattheflexuralstrengthwasgraduallyimprovedasthe
temperature increased. Berretta et al. [22] manufactured the reinforced PEEK with 1%
and5%carbonnanotubes(CNTs). TheyreportedthattheCNTsdidnothaveasignificant
effectonthemechanicalbehaviorsofthePEEK-processedspecimens. Theyintroduced
the nozzle temperature as one of the most crucial parameters in the FFF process, due
to its direct contact with the polymer. Yang et al. [23] studied the effect of the thermal
PoPlyomlyemrse r2s0 22032, 135, 1, 5x, FxO FRO PRE PEERE RRE RVEIVEWIEW 3 o3 f o2f4 2 4
processingconditiononmechanicalbehaviorsandcrystallinityofthePEEKmaterial.Based
ontherelatedresults,crystallinityincreasedfrom17%to31%inresponsetotheincreasein
ambienttemperaturefrom25to200 C.
◦
2.21..1 M. Mataerteiarilas ls Fewstudieshavebeenperformedtoinvestigatetheeffectoftheutilizedfiberrein-
forcementsontherheologicalbehaviorofthematerialsduringandafterthemanufacturing
process. Thisstudytriedtoinvestigatetherheologicalbehaviorofthematerialsduringand
ThTeh see sleecletecdte dm matearteiarlisa lfso fro trh tihs isst ustduyd yw ewreer pe oploylaymamidied 6e 6(P (AP6A)6 a)n adn dsh sohrot rcta crabrobno nfi bfiebre-rre-rineifnofrocrecde dp oploylaymamidied 6e 6(O (nOynxy x
aftertheFFFprocessbyconsideringtheroleofthefiberreinforcements. Theselectedmate-
oro Cr FC-FP-AP6A)6 p) rpordoudcuecde db yb yM MarakrFkoFrogregde®d.® T. hTeh ceh cohpoppepde dca crabrobno nfi bfiebres rhs ahda da ma masass cso cnotnentetn ot fo 6f .65.%5% in i nth teh Ce FC-FP-AP6A 6
rialsforthisstudywerePA6,shortcarbonfiber-reinforcedPA6(CF-PA6),andcontinuous
filfaimlamenetn bt absaegsdlea dos nso finth bteeh rpe- yrperyoinrloyfolsyriscs eipsd rpoCrcoFec-sPesAs. sT6. hTceoh mceh pcahoraasirctateecrmteisratitisectrsici aosl fso .tfh teh ue tuiltiizleizde dfi lfaimlamenetns tass a tsh teh rea rwa wm matearteiarlias lasr aer e
prperseesnetnedte din i nT aTbalbe l1e .1 .
2. MaterialsandMethods
2.1. Materials
Theselectedmaterialsforthisstudywerepolyamide6(PA6)andshortcarbonfiber-
TaTbalbe l1e .1 T. hTeh ceh cahraarcatecrteizraiztiaotinosn os fo tfh teh ue tuiltiizleizde dra rwa wm mataetreiarlisa.l s.
reinforcedpolyamide6(OnyxorCF-PA6)producedbyMarkForged®. Thechoppedcarbon
RfiaRbwear wsM hMaatdaetreiaarmlias lass scontentof6.5%intheCF-PA6filamentbasedonthepyrolysisprocess.
ThecharacteristicsoftheutilizedfilamentsastherawmaterialsarepresentedinTable1.
PhPyhsyicsaicl aaln adn dC hCehmemicaicl al PAP6A 6 CFC-FP-AP6A 6
TablPerP1o.rpoTephreetircethsiea sra cterizationsoftheutilizedrawmaterials.
DeDnesnitsyit y 1.11. 1g /gcm/cm3 3 1.12. 2g /gcm/cm3 3
RawMaterials
GlGaslass tsr atrnasnitsiiotino nte mtempepreartuatruer e PA6 CF-PA6
PhysicalandChemicalProperties
454 5°C ° C 474 7°C ° C
Density(T(gT) g) 1.1g/cm3 1.2g/cm3
CrCyrsytasltlailzlaiztiaotino nte mtempepreartuatruer e
Glasstransitiontemperature(Tg) 17137 3°C ° C 45◦C 16126 2°C ° C 47◦C
(T(T) )
Crystallizationtcemcperature
(TMc)Melteilntign gte mtempepreartuatruer e 173◦C 162◦C
20250 5°C ° C 19189 8°C ° C
Meltingtemperature
(T(mT()mT)m ) 205◦C 198◦C
SpoolSIpmSopaogoleo Ilm Imagaeg e

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bebheahvaivoiro or fo tfh teh me matearteiarlias lds udruinrign gth teh Fe FFFF Fp rporcoecsess, sa, sai nsignlge lwe awlla llla ylaeyre srp sepceicmimene n(F (iFgiugruer 1e )1 w) awsa ds edseigsingende.d T. hTihs is
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dedpeopsoitseidte dla ylaeyres.r sI.n I nad addidtiiotino,n t,h teh leo lcoactiaotino no fo tfh teh ree rqeuqiureirde dsp sepceimcimenesn fso fro trh teh seu sbusbesqeuqeunetn cth cahraarcatecrteizraiztiaotinosn asr aer e
dedteertemrminiende din i nF iFgiugruer 1e .1 T. wTow od idffieffreernetn pt rpinritnertes rws ewreer ue tuiltiizleizde dd udruinrign go uoru srt ustduidesie. sT. oT ost ustduyd yth teh eef efeffcetsc tos fo tfh teh e
prporcoecsessinsign gp apraarmameteetres,r sF, lFaslahsfhofrogreg Ae DAVDEVNETNUTRUERRE-R3- 3(f r(ofrmom C hCihnian)a w) awsa us tuiltiizleizde.d M. Moroeroevoevre, ra,s a fso fro srt ustduydiynign gth teh e
inifnilfli lpl eprecrecnetnagtaeg, ei,n ifnilfli lpl apttaetrtenr nef efeffcetsc,t sa,n adn dfa ftiagtiugeu be ebheahvaivoiros,r sa, Ma Marakrfkofrogregde-dM-Marakr kT wTow o(f r(ofrmom th teh Ue SUAS)A p) rpinritnerte wr awsa s
utuiltiizleizde.d T. hTihs iiss ibs ebceacuasues Me Marakrfkofrogregde-dM-Marakr kT wTow op rpinritnertes rcsa cna np rporvoivdied teh teh pe opsossibsiibliitlyit yo fo mf manaunfuafcatuctruinrign gco cmompopsoitsei te
obojbecjetsc tws iwthit hco cnotnintiunouuosu rse rineifnofrocrecmemenetn. t.
Polymers 2023, 15, x FOR PEER REVIEW 3 of 21

Spool Image

Polymers2023,15,507
As for the investigation of the fiber-reinforcement impact and the processing param-
eter effects on the rheological behavior of the materials during the FFF process, a single
Asfortheinvestigationofthefiber-reinforcementimpactandtheprocessingparameter
wall layer specimen (Figure 1) was designed. This specimen let us study the effect of the
effectsontherheologicalbehaviorofthematerialsduringtheFFFprocess,asinglewall
selected processlainyger psapreacmimeetenrs(F oignu trhee1 a)dwhaessidoens iagnnded t.heT hbiosnsdpiencgim oefn thleet duespsotusidteydt hlaeyeefrfesc. t of the
In addition, thes eloleccatetidonp roofc etshsein rgepqauriarmede tseprseocinmtheensa dfoher stihone asnudbstehqeubeonntd icnhgaorafcthteerdizeaptoiosintesd layers.
are determinedI nina dFdigituiorne, 1th. eTlwocoa tdioinffoefrethnet rpeqriunitreedrss pweecrime euntsilfiozretdh edsuurbinsegq uoeunrt cshtuadraicetse.r iTzaot ionsare
study the effectsd eotfe trhmei nperdocinesFsiignugr ep1a.rTawmoetdeirffse,r Fenlatsphrfionrtegres AwDerVeEutNiliTzUedRdEuRr-in3g (foruorms tCudhiiensa.)T ostudy
theeffectsoftheprocessingparameters,FlashforgeADVENTURER-3(fromChina)was
was utilized. Moreover, as for studying the infill percentage, infill pattern effects, and fa-
utilized. Moreover,asforstudyingtheinfillpercentage,infillpatterneffects,andfatigue
tigue behaviors, a Markforged-Mark Two (from the USA) printer was utilized. This is be-
behaviors,aMarkforged-MarkTwo(fromtheUSA)printerwasutilized. Thisisbecause
cause Markforged-Mark Two printers can provide the possibility of manufacturing com-
Markforged-MarkTwoprinterscanprovidethepossibilityofmanufacturingcomposite
posite objects with continuous reinforcement.
objectswithcontinuousreinforcement.

Figure 1. The prinFtiegdu rsein1.gTleh-ewparliln stepdecsiinmgelen-sw aanllds pperceimpaernastiaonnd opfr etphaer taetinosniloef ttehset tsepnesciliemteesntss p[5e]c.i mens[5].
2.2. Methods
2.2. Methods
2.2.1. InSituMonitoringofTemperatureEvolution
2.2.1. In Situ Monitoring of Temperature Evolution
AnOptrisPI450infraredcamerawasappliedintheconductedstudyoftheprocessing
An Optris pPaIr4a5m0e tienrfirmarpeadc tscaomntehrea thwearms aalpapnldiemde icnh atnhieca clopnrodpuecrttieeds osftuthdeyp oolfy mtheer apnrdo-polymer-
cessing paramebtears eimdcpoamctpso osnit etshues tihnegrtmheaFl FaFndp rmoceecshs.aTnhiceaslt aptreodpienrftriaerse dofc athmee praowlyamsepro saintido nedata
polymer-based scpoemcipficospirteeds eutesrimngin tehde dFisFtFa npcreofcreosms. thTeheex sttrautseiodn inlofcraatrieodn ocfamtheerpar iwntaesr. pTohsiis-attempt
tioned at a speciafiimc epdretdoemteornmitoinreadnd doisbtsaenrvcee afrcoomns tishtee netxptrlauisniofinel dloocfavtiioenw o(Ff OthVe) parcirnostesra.l Tlchoins secutive
layers. Thetemperatureriseduringtheperformedfatiguetestwasmonitoredandmea-
attempt aimed to monitor and observe a consistent plain field of view (FOV) across all
suredbythestatedinfraredcameraaswell. Regardingsometechnicalspecificationsofthe
consecutive layers. The temperature rise during the performed fatigue test was monitored
infraredcamerausedinthisexperiment,frequency,accuracyvalues,wavelengthrange,
and measured by the stated infrared camera as well. Regarding some technical specifica-
opticalresolution,andtherateoftheframeswere32Hz,2%,8–14µm,382 288pixels,
×
and80Hz,respectively.
2.2.2. MicrostructuralObservations
Usingascanningelectronicmicroscope(HITACHI4800SEM,manufacturedinJapan),
observationsandimageanalyseswereperformedtoqualitativelyanalyzethecomposite
microstructure, especially in relation to damage assessment. In this study, an optical
microscope(OLYMPUSBH2,manufacturedinJapan)wasusedtoassessthequalityofthe
3
Polymers2023,15,507
manufacturedsamplesatthevariousselectedprocessingparameterswithmagnifications
from100to500mm.
2.2.3. DifferentialScanningCalorimetric(DSC)
Bymeansofdifferentialscanningcalorimetry(Q1000),bothrawfilamentmaterialsand
printedspecimenscouldbeassessedfortheirrespectiveglasstransition(T ),crystallization
g
temperatures(T ),andtheirheatcapacitiesbasedontheselectedprocessingparameters.
c
DSCcharacterizationwasperformedontherawfilamentmaterials(CF-PA6andPA6)over
threetemperatureramps: rangeof20to220 Cunderarateof10 C/min. Thisattempt
◦ ◦
causedaneliminationofthethermalhistoryofthefilamentsconcerningtheirproduction
process. Furthermore,theprintedandfabricatedspecimenswereanalyzedbyDSCintwo
ramps(heatingandcooling).
2.2.4. Thermo-MechanicalBehaviorAnalysis(DMTA)
Underthemulti-frequencycondition, DMTAflexuraltestswereperformedonthe
printed samples using the DMA Q800 instrument from the TA Company, in order to
determinethemajortransitiontemperaturesandviscoelasticcharacteristics. Thischaracter-
izationwasutilizedtostudytheviscoelasticbehaviorofthematerialduringthefatigue
testandthesubsequenttemperaturerise. DMTAcharacterizationwasperformedinthe
temperaturerangeof30to80 C,frequenciesof1,2,5,10,and30Hz,andtemperaturerate
◦
of2 C/min.
◦
2.2.5. Quasi-StaticTensileTest
Aswasstated,twodifferentconditionsforstudyingthetensilebehaviorwerecon-
ducted. Thefirstconditionwasconsideredtostudytheeffectoftheprocessingparameters
on the manufacturing of the polymer and composite specimens (Figure 1). Therefore,
basedonISO527-2,tensiletestspecimensweresliced/cutfromtheprintedsingle-wall
layersample(Figure1),inordertoconducttherelatedstudyofthefirstcondition. The
requiredtensilespecimenswerecutfromtheprintedsingle-wallsamplesutilizingatensile
sample-cuttingdieandapplyingthehomogenousforce. Inaddition,thehomogeneityof
theprintedsingle-walllayerswasensuredbyusingthecaliperforthicknessmeasurement.
Followingthecuttingofthetensiletestspecimensfromthesingle-walllayers,acaliperwas
usedtoensurethatgaugelengthdimensionswereuniform. Inaddition,theobservationof
thesamplesundertheopticalmicroscope(OM)tocontrolthequalityofthespecimensafter
themanufacturingandcuttingprocesswastakenintoaccount. Thesecondconditionwas
appliedtostudytheimpactoffillpercentageofthepolymerandthedifferentdetermined
densitiesanddirectionsoftheutilizedcontinuousreinforcements. Moreover,inorderto
investigatetherheologicalbehavioroftheadditivemanufacturedspecimensafterthepro-
ductionprocess,therelatedtensiletestspecimenswereprintedbasedonthestandardISO
527-1. Thequasi-statictensileexperimentwasconductedbymeansoftheINSTRON5966
machinewithadisplacementrateof5mm/minandaloadingcellof10kN.Aminimum
ofthreespecimenswerepreparedforeachconditioninordertoconductthequasi-static
tensiletests.
2.2.6. ThreePointsBendingFatigueTests
Asforthefatiguetestofthefabricatedspecimensconcerningthestudyoftherheolog-
icalbehavioroftheFFF-processedcompositematerials(afterthemanufacturingprocess),a
three-pointsbendingfatiguetestwasconductedatvariousappliedmaximumstrains(ε ).
max
Theconsideredstrainratiowas0.1(Rσ=0.1);moreover,therelatedmeanstrainlevelwas
0.55ε . Thistestwasconductedontheshortcarbonfiber-reinforcedpolyamide6(Onyx
max
orCF-PA6)andthecontinuousglassfiber-reinforcedpolyamide6(Onyx+GF)composite
specimenstobeabletostudytheeffectofthecontinuousglassfiberreinforcementandits
subsequentimpactontherheologicalbehavioroftheFFF-processedspecimens. During
thethree-pointbendingfatiguetest,thetemperatureofthespecimenswasraised,which
4
Polymers2023,15,507
wasmeasuredbytheinfraredcameratodeterminetheimportanceandinfluenceofthe
utilizedcontinuousglassfiberreinforcementinthisphenomenon. Thedimensionsofthe
preparedrectangularcompositespecimenswere120 10 4mm3. Inordertoperforma
× ×
fatiguetest,atleastthreespecimenswerepreparedforeachcondition.
3. ResultsandDiscussions
3.1. StudyoftheRheologicalBehaviorofthePolymerandPolymerCompositeMaterialsduringthe
FFFProcess
Therheologicalbehavior ofthepolymer andpolymer compositematerialsduring
theFFFprocessareinvestigatedinthissection. Inaddition,themodificationsintherhe-
ologicalbehaviorofthematerialsastheconsequenceoftheshortcarbonfiberexistence
are discussed. As part ofthis effort, fourmain processing parameters were considered
to investigate their impacts on the tensile behavior of the manufactured specimens. In
addition,theinsitutemperatureevolutionduringthemanufacturingprocesswasmoni-
tored. Theselectedprocessingparameterswereprintspeed(13,15,and17mm/s),liquefier
temperature(220,230,and240 C),layerheight(0.1,0.2,and0.3mm),andbedplatform
◦
temperature(25,50,60,and80 C).Theaforementionedprocessingparameterswerestud-
◦
ied individually by considering the rest of the processing parameters as constant. The
referencevaluesconcerningeachoftheselectedparameterswere15mm/sasprintspeed,
240 Casliquefiertemperature,0.1mmaslayerheight,and25 Casbedtemperature. The
◦ ◦
selectedmaterialsforthissectionwerePA6andCF-PA6[5].
3.1.1. EffectofthePrintSpeed
Inlightoftheimportanceoftheprintspeedparameterinproductiontime,itwasstud-
iedtohowitimpactstherheologicalbehaviors. Tostudytheimpactofthismanufacturing
processingparameter,13,15,and17mm/sasthedifferentprintspeedvaluesweretaken
intoconsideration. AccordingtoFigure2,thetensilestrengthandthecrystallinitypercent-
agepertainingtothemanufacturedspecimenswiththeabove-selectedprintspeedvalues
wereevaluated. Thetensilestrengthvaluesof57.78 0.84,68.92 0.9,and69 0.05MPa
± ± ±
Polymers 2023, 15, x FOR PEER REVIEcWon cerningthemanufacturedPA6specimensand65 0.5, 55 0.6, and63 1.3MPa6 of 21
± ± ±
concerningthemanufacturedCF-PA6specimenspertainingto theselectedprintspeed
valuesof13,15,and17mm/swereobtained,respectively.

Figure2.Obtainedtensilestrengthandcrystallinitypercentagevaluesconcerningtheprintspeed
Figure 2. Obtained tensile strength and crystallinity percentage values concerning the print speed
eeffffeecctt iinnvveesstitgigaatitoionn. .
Figure3depictsthetemperatureprofile,obtainedfromtheinsitumonitoringofthe
Figure 3 depicts the temperature profile, obtained from the in situ monitoring of the
temperatureevolutionconcerningthePA6andCF-PA6specimensproducedbytheabove-
temperature evolution concerning the PA6 and CF-PA6 specimens produced by the
above-stated print speed values. As printing speed was increased, the measured temper-
ature of the first printed layer stayed above the related crystallization temperature values
5
in all examined PA6 and CF-PA6 specimens. The print speed affected the cooling time
and polymer arrangement and the resultant crystallinity degree. All selected print speeds
yielded higher crystallinity degree values for CF-PA6 specimens than PA6 specimens.

Figure 3. The obtained temperature evolution from the in situ temperature monitoring (a) PA6 and
(b) CF-PA6 [5] under different print speeds.
3.1.2. Effect of the Liquefier Temperature
The impact of the liquefier temperature on the rheological behavior of the PA6 and
CF-PA6 specimens were investigated. The decided liquefier temperature values for this
study were 240, 230, and 220 °C. Figure 4 depicts the crystallinity percentage and tensile
strength concerning the manufactured specimens with the above-selected liquefier tem-
perature values. The tensile strength values of 55.48 ± 0.78 and 68.92 ± 0.9 MPa concerning
the manufactured PA6 specimens by the liquefier temperature values of 230 and 240 °C
were achieved, respectively. One can note that the lowest strength was observed in the
printed specimens by the liquefier temperature values of 220 °C. This liquefier tempera-
ture value could not provide a suitable fluidity of the material during the FFF process,
which caused low and inappropriate adhesion between the deposited layers. This low