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APFIS2017-6thAsia-PacificConferenceonFRPinStructuresSingapore,19-21stJuly20171HaiFang,HuiyuanShi,WeiqingLiu,YujunQi,andRuiliHuoENHANCEMENTEFFECTANALYSISOFLATTICE-WEBSTOGFRP-WOODSANDWICHBEAMSINFLATWISEANDSIDEWISEBENDINGHaiFang1*,HuiyuanShi2,WeiqingLiu3,YujunQi4,RuiliHuo51Correspondingauthor,CollegeofCivilEngineering,NanjingTechUniversity,Nanjing,ChinaEmail:fanghainjut@njtech.
edu.
cn,WebPage:http://cce.
njtech.
edu.
cn/view.
aspid=527&class=2212SchoolofCivilEngineering,SoutheastUniversity,Nanjing,ChinaEmail:hyshiseu@yeah.
net3AdvancedEngineeringCompositesResearchCenter,NanjingTechUniversity,Nanjing,ChinaEmail:wqliu@njtech.
edu.
cn,WebPage:http://cce.
njtech.
edu.
cn/view.
aspid=485&class=2404CollegeofCivilEngineering,NanjingTechUniversity,Nanjing,ChinaEmail:qiyujun11@163.
com,WebPage:http://cce.
njtech.
edu.
cn/view.
aspid=1385&class=2215CollegeofCivilEngineering,NanjingTechUniversity,Nanjing,ChinaEmail:ruilihuo@njtech.
edu.
cnKeywords:GFRP-woodsandwichbeams,lattice-webreinforced,flexural,flatwise,sidewiseAbstractThispaperinvestigatestheflexuralbehaviorinflatwiseandsidewisepositionsofnovelgenerationcompositesandwichbeamswithPaulowniaandsouthernpinewoodcoreandglass-fiberreinforcedpolymer(GFRP)facesheetandlattice-webs.
Avacuumassistedresininfusionprocess(VARI)wasemployedtoformsandwichbeamswithdifferentnumbersofwebs.
Twocontrolwoodenbeamsandeighteenlattice-webreinforcedsandwichbeamsweresubjectedtofour-pointbendingteststodeterminetheirstiffness,capacity,andfailuremechanismsintheflatwiseandsidewisepositions.
Theexperimentalresultsrevealedthatthecompositesandwichbeamsfailedinflatwisebendingtestsunderlowerloadbutproducedagreaterdeflectioncomparedtothebeamsinsidewisebendingtests.
Withtheincreaseinthenumberoflattice-webs,ductilitywasfoundtoincreaseinflatwisepositionswhiledecreasinginsidewisepositions.
Analyticalformulasforcalculatingthebendingstiffness,capacity,andductilityoftheGFRP-woodsandwichbeamswereprovided,andtheanalysisresultsformechanicalperformanceshowedgoodagreementwiththeexperimentalresults.
1.
IntroductionComparedtotraditionalconstructionmaterials,themainbenefitsofGFRPcompositematerialinstructuralcomponentsareitshighstrength,excellentcorrosionresistance,easeofhandingandapplication,andflexibilityofdesign[1].
Inthispaperwepresentanewgenerationofcompositesandwichbeamsintendedforuseasloading-bearingcomponents.
Thecompositesandwichisintegrallyformedinthemoldbyavacuum-assistedresininfusionprocessinvolvingcompositeface-skins,webs,andcorematerials,asshowninFigure1.
Onenovelfeatureisthebundlingofthecorematerials,mainlycharacterizedbyhighstrength,intoinbothwebs.
Thesandwichbeams,thatclearlyenhancetheantistrippingandcooperativeperformancebetweensurfacelayerandcore,areconstructedbycloselywrappingwoodcorematerialstogetherusinglattice-websandface-skinsthatcangivefullplaytothepropertiesofthebendingandshearcapacityofthesandwichbeams.
Whenthesurfacelayerofthecompositesandwichbeamisundernormalload,themainfunctionofthewoodcoreistoimproveshapingandbearingandtoprovideelasticsupportsforthesandwichbeams.
Thecompositesandwichbeamavoidstheoccurrenceoflocalbucklinganddebonding,becausethecorematerialimprovesthedistributionofsectionstress,APFIS2017-6thAsia-PacificConferenceonFRPinStructuresSingapore,19-21stJuly20172HaiFang,HuiyuanShi,WeiqingLiu,YujunQi,andRuiliHuoeffectivelyreducingthestressconcentrationattheintersectionofthesurfacelayerandlattice-webs,significantlydelayingsplittingfailure.
Meanwhile,theGFRPlattice-webscaneffectivelyincreasethecapacityofshear,compression,andstripping,bothintheflatwise(horizontal)orinthesidewise(vertical)position.
Inthispaper,theultimatefailuremechanisms,initialbendingstiffness,load-deflectionbehaviorandstress-strainbehaviorofGFRP-woodsandwichbeamsunderfour-pointstaticbendingintheflatwiseandsidewisepositionsarereportedanddiscussed.
Thetheoreticaloutcomesforthestiffnessandstrengthofthecompositesandwichbeamsarealsopredictedandcomparedwiththeexperimentalresults.
(a)(b)(c)Figure1.
Lattice-webreinforcedcompositesandwichbeams(a)flatwise,(b)sidewise,and(c)cross-sectionalviewofrealobject.
2.
ExperimentalProgram2.
1.
TestSpecimensandMaterialsThestructuralsandwichbeamstestedinthisstudywereemployedusingGFRPskinsandlattice-webscomposedofbi-axial[0/90]glassfiberlaminates(800g/m2)andHS-2101-G100unsaturatedpolyesterresintowrapthecorematerialstogether.
High-classPaulowniaorsouthernpinewood,weighing280kg/m3and500kg/m3respectively,werefilledascorematerialsinthesespecimens.
Theoveralldensityofthecompositesandwichbeamswasmuchlessthanthatofconcreteandsteel,withdensitiesof2400kg/m3and7850kg/m3respectively.
Table1summariestheultimatestrengthandYoung'smodulusoftheGFRPface-skins,lattice-webs,andcorematerials.
Table1.
Effectivemechanicalpropertiesoftheglassfiberskinsandcorematerials.
PropertiesSkinsandwebsPaulowniawoodSouthernpinewoodCompressionUltimatestrength(MPa)223.
7426.
5332.
76Young'smodulus(GPa)16.
011.
863.
57TensionUltimatestrength(MPa)305.
00——Young'smodulus(GPa)20.
95——ShearUltimatestrength(MPa)16.
273.
346.
55Young'smodulus(GPa)7.
680.
420.
68Twentysandwichbeamswithidenticaldimensions(1400mm*120mm*120mm),including2woodenbeams,2compositesandwichbeamswithoutlattice-webs,and16sandwichbeamswithlattice-webs,werefabricatedandmanufacturedintheAdvancedCompositeStructuresResearchInstituteatNanjingTechUniversity.
DetailsofeachspecimenaresummarizedinTable2.
Horizontallattice-websVerticallattice-websAPFIS2017-6thAsia-PacificConferenceonFRPinStructuresSingapore,19-21stJuly20173HaiFang,HuiyuanShi,WeiqingLiu,YujunQi,andRuiliHuoTable2.
Descriptionofspecimens.
SpecimensSizeofspecimenSizeofcoreOrientationoftestingl(mm)B(mm)H(mm)b(mm)h(mm)PA/SP-CON-F/S1400120120120120FlatwiseandsidewisePA/SP-0-F/S1400120120110110FlatwiseandsidewisePA/SP-1-F140012012011053.
0FlatwisePA/SP-2-F140012012011034.
0FlatwisePA/SP-3-F140012012011024.
5FlatwisePA/SP-4-F140012012011018.
8FlatwisePA/SP-1-S140012012053.
0110SidewisePA/SP-2-S140012012034.
0110SidewisePA/SP-3-S140012012024.
5110SidewisePA/SP-4-S140012012018.
8110Sidewise2.
2.
TestSet-upandInstrumentationThespecimenswereloadedunderstaticfour-pointbendinginaccordancewiththeASTMC393standard[2]byauniversaltestingmachine.
Theloadingexperimentalsetupemployedinthetestswassimplysupportedandthenetspanwas1200mmbetweenthetworollersupports.
Averticalmonotonicloadingwassetbya300kNcapacityhydraulicjack,whichwasequallysplituptotwocentralpointsonthespecimensbyasteeltransferbeamandmovedataloadingrateof2mm/min,asshowninFigure2.
Duringtesting,straincollectionwasperformedbyaDH3816staticstraintestsystem.
TheverticaldisplacementwasmeasuredbyaLVDT(linearvariabledeflectiontransducer)arrangedatthebottomofmid-spanandthetopofsupport.
Twolongitudinalstraingaugestoobservetherelationoftheloadandthestrainoftheface-skinwereattachedtothetopandbottomface-skinsofthemid-span.
Figure2.
Experimentalsetupofflexuralbehaviorofthebeam:(a)pictureofflexuraltestsetup,(b)schematicplot,and(c)straingaugearrangement.
3.
ExperimentalResultsandDiscussionControlspecimensPA-CON-F/SandSP-CON-F/Sfailedinabrittlemanner,asshowninFigure3a.
Theappearanceofsheartensilecrackswasfirstobserved.
Owingtothemaximumshearstrainofthewoodexceedsitscrushingstrain,thesecracks,thatsuddenlyproducedaloudnoise,rapidlyextendedupwardandcausedimmediatefailurewiththeincreaseofslowloadandquickdeflection.
InthecompositesandwichspecimensPA-0-F/SandSP-0-F/S,withoutlatticewebs,brittlefailuredidnotoccurbecausethefibercompositeexternalskinsonthetensilefaceofthespecimensbridgedthecrackedcorecomponentstogethertopreventfailure.
Whenthemaximumcompressivestrainoftheexternalsurfaceexceededitscompressivestrain,toplocalindentationoccurredaswellascompressivecracksonthelateralface-skin,asshowninFigure3b.
Specimenswith1,2,3,and4websintheAPFIS2017-6thAsia-PacificConferenceonFRPinStructuresSingapore,19-21stJuly20174HaiFang,HuiyuanShi,WeiqingLiu,YujunQi,andRuiliHuoflatwisepositionsmainlyfailedbycrushingofthefibercompositeskinsattheloadingpointfollowedbytheoccurrenceofsplittingofthebottomglassfibercausedbyalargedeformationatthebottomofthebeam,asshowninFigure3c.
Compressivewrinklingwasobservedinthesidewisepositions,asshowninFigure3d,andcontinuousapplicationofloadcausedcrackspreadingextendingfromtheuppermosttotheundersection,followedbycompressivefailure.
(a)(b)(c)(d)Figure3.
FailuremodesofGFRP-woodsandwichbeams.
Fromtheexperimentaldataitcanbeseenthattheload-deflectionbehaviorofthespecimenschangesfromlineartononlinearwiththeincreaseinappliedload.
AsshowninFigure4aand4b,whenthecoreisPaulownia,theultimatebendingstrengthofspecimensPA-(1~4)-SisbasicallygreaterthanthatofspecimensPA-(1~4)-F,amongwhichPA-3isthemostobvious.
ThesetrendsinFigure4cand4dcanalsobefoundwithsouthernpinecore.
Meanwhile,theultimatebearingcapacityofthebeamswithsouthernpinewoodisslighterhigherthanthatofbeamswithPaulownia.
Itcanbeconcludedthattheuseofverticalwebsandtheapplicationofhigh-strengthcorematerialwillobtaingreaterbendingstiffnessofthebeam.
(a)(b)(c)(d)Figure4.
Load-deflectioncurvesforsandwichbeam.
4.
ConclusionsInvestigationoftheflexuralbehaviorofinnovativecompositesandwichbeamsreinforcedbylattice-websunderfour-pointstaticbendingtestintheflatwiseandsidewisepositionswasundertakenexperimentallyinthispaper.
WiththisstudyoftheseGFRPsandwichbeams,onegoalistomaximallyincreasethevalueofthesespecimens;theothergoalistoseekastructuretosubstitutefortraditionalbeamsthatwereeasilysubjecttobrittlefailureanddelamination.
Itwasfoundthat,toimprovethecapacityofstiffness,strength,andmonolithicstability,settingupappropriatelaminationandorientationofthelatticewebsforthesandwichbeamsisnecessary.
TheapplicationoffiberinsertionswasfoundtobeviableinthereinforcementandrecoveryofGFRP-woodbeams.
Thistechniqueisnotonlyeasybutalsoconfersgreaterstrengthandstiffnessofreinforcedstructuralelements.
Italsorendersthesystemmorereliable,reducingthepossibilityoftensilefailurecausedbydefects.
APFIS2017-6thAsia-PacificConferenceonFRPinStructuresSingapore,19-21stJuly20175HaiFang,HuiyuanShi,WeiqingLiu,YujunQi,andRuiliHuoAcknowledgmentsTheresearchdescribedherewassupportedbytheNationalNaturalScienceFoundationofChina(GrantNo.
51578285)andfundedbythePriorityAcademicProgramDevelopmentofJiangsuHigherEducationInstitutionsPAPD(GrantNo.
CE02-1-11).
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