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  • IntroCompositeApplns.PropertiesVoigt, Reuss,Hill

    Anistrpy.CTECellularMatls.Wood

    1

    Microstructure-Properties:Composites

    Microstructure Properties

    Processing

    Performance27-301A.D.Rolle/,M.DeGraef

    Last modified: 2nd Nov. 15

    IntroCompositeApplns.PropertiesVoigt, Reuss,Hill

    Anistrpy.CTECellularMatls.Wood

    2

    Lecture Objectives: Composites Themainobjec?veofthislectureistointroduceyouto

    microstructure-propertyrela?onshipsincompositematerials.

    Compositematerialscons?tuteahugeclassofmaterials.Theobjec?veofthislecturewillthereforebetoprovidesomedefini?onsanddescribesomeofthebasicrela?onships.

    Cellularmaterialswillbeemphasizedbecauseoftheirconnec?ontonaturalmaterials(biomaterials)andespeciallywood,whichsomeofyouwillstudyinthesecondLab.

  • IntroCompositeApplns.PropertiesVoigt, Reuss,Hill

    Anistrpy.CTECellularMatls.Wood

    Questions & Answers for Part 11. Whatarethegeneraladvantagesofcomposite

    materialsovermonolithicmaterials?Givebothbiomaterialandman-madeexamples.Compositesgenerallyhavehigherspecificproper?es.Woodandcarbon-fiberreinforcedplas?csareexamples.

    2. Whatistheruleofmixturesasappliedtocomposites?Integratethepropertyofinterestoverthevolumeofthecomposite.

    3. Whatdothetermsisostressandisostrainmean?Asimplied,iso-stressmeanssamestressinallmaterials;iso-strainmeanssamestraininallmaterials.Foriso-stressyoucanthinkofthephasesasbeingconnectedinseriesbetweentheplanesacrosswhichtheloadistransmi/ed(andviceversaforiso-strain).

    4. Derivetheisostrainmodel.Seethenotes;deriva?onreliesonaveragingthestressesinthedifferentphases.

    5. Derivetheisostressmodel.Seethenotes;deriva?onreliesonaveragingthestrainsinthedifferentphases.

    6. Sketchthevaria?onsinmodulusexpectedforcompositesinwhichthecomponentshavestronglydifferentmoduli.Seethenotes;iso-strainmodelgiveslinearvaria?on(sameasRuleofMixturesinthiscase)whereasiso-stressmodelgivesnon-linearvaria?on.

    7. ExplainwhatismeantbytheVoigt,ReussandHillaveragemoduli.Voigt=iso-strain,Reuss=iso-stress,Hillaveragesthesetwo.

    8. Whichmodelfors?ffnessappliestoacompositematerialwithacompliantmatrixandawelldispersedpar?culatesecondphasethatiss?ffer(thanthematrix)?Inthiscase,theReuss(iso-stress)modelappliesbecausetheindividualpar?clesarenotconnectedandthusthereisli/leloadtransferbetweenthem.

    9. Whichmodelfors?ffnessappliestoacompositematerialwithacompliantmatrixandawelldispersed,parallel,s?fffibersthatisloadedalongthefiberdirec?on?Inthiscase,theVoigt(iso-strain)modelappliesbecausetheindividualfibersarestrainedequallywiththematrix.

    10. Whyarecellularorfoammaterialsusefulforachievinglowmodulus?Bymakingasubstan?alfrac?onofthematerialemptyspace(airortrappedgas),onecanreducethemodulustothevolumeaverageofthesolidmaterialandgas.Thisaccessesmodulusvaluesthatareinaccessibletofullydensematerials.

    3

    IntroCompositeApplns.PropertiesVoigt, Reuss,Hill

    Anistrpy.CTECellularMatls.Wood

    4

    Key points Compositesareregardedasar?ficial(man-made)mixturesof

    phases. Classifica?onofcompositesbyreinforcementtype(dimensionality)-

    par1cles,fibersandlaminated. Applica?onoftheRuleofMixtures. Dependenceofcompositeproper?esonthespa?alarrangementof

    thephases. Upperandlowerboundsonproper?es-exampleofelas?cmodulus,

    VoigtandReussapproxima?ons. Highproperty:densityra1osachievablewithcomposites. Engineeringwithresidualstressincomposites. Anisotropyofcompositeproper?es,e.g.elas?cmodulus. Proper?esofwoodasacellularmaterial. Cellular/foammaterialsasshockabsorbers.

    Examinable

  • IntroCompositeApplns.PropertiesVoigt, Reuss,Hill

    Anistrpy.CTECellularMatls.Wood

    5

    Examples

    IntroCompositeApplns.PropertiesVoigt, Reuss,Hill

    Anistrpy.CTECellularMatls.Wood

    6

    What are Composites? Compositematerialscontainmorethanonephase. Almostallmaterialscontainmorethanonephase,so

    whatsthedifference? Thetermcompositeistypicallyappliedtoamaterialwhen

    themul?-phasestructureisconstructedbydirectinterven?on(externaltothematerial).

    CompositeMaterialExamples:glassfiberreinforcedplas?c(GRP),wood,clamshell,Marsbar.

    Mul?-phaseMaterialExamples:precipita?onstrengthenedaluminumalloys,Ti-6Al-4V,dual-phasesteel,transforma?ontoughenedalumina(Al2O3-CeO2).

    Cau?on!Thereissomeoverlapbetweenthecategories!

    Examinable

  • IntroCompositeApplns.PropertiesVoigt, Reuss,Hill

    Anistrpy.CTECellularMatls.Wood

    7

    Properties Itisusefultoreviewthebasicproper?esofthedifferent

    typesofmaterialsthatareusedincomposites. Polymers-long[carbon]chainmoleculeswithanything

    fromvanderWaalsbondingbetweenthechains(thermoplas?cs)tocovalentlinks(thermosets).Lowdensity,lowmoduluscomparedtoothermaterials.Onenhighlyformable(duc?le).

    Ceramics-ionicorcovalentbonding,lowersymmetrycrystalstructures,highmel?ngpointandmodulus,resistanttodegrada?on,bri/le,highmodulus.

    Metals-metallicbonding,symmetriccrystalstructures,mediummel?ngpoint,mediummodulus,duc?le,formable,variableresistancetodegrada?on.

    Examinable

    IntroCompositeApplns.PropertiesVoigt, Reuss,Hill

    Anistrpy.CTECellularMatls.Wood

    8

    Why Use Composites? [Biomaterials] Innature,thebasicmaterialstendtobeweakand/orbri/le.

    Evolu?onhasresultedinstructuresthatcombinematerialstogetherforproper?esthatfarexceedthosethatcouldbeobtainedinthebasicmaterials.

    Thebasicinorganiccons?tuentofbone,forexample,iscalciumphosphateintheformofcrystallineCa10(PO4)6(OH)andamorphousCaPO3.Thisceramicisbri/leandnotpar?cularlys?ff.Thematrixoffibrouscollagenistoughbutevenlesss?ff.Whenembeddedarrangedintheformofacellularmaterial,however,remarkablevaluesofs?ffness:densityandtoughness:densityareachieved(andland-basedmul?-tonnecreaturesarepossiblesuchaselephants).

    Asimilarsitua?onexistsinwoodwherethebasicmaterialsarequitecompliantbutarrangedinthemul?-levelcompositeformsthatweknow,highvaluesofstrength:densityandtoughness:densityresult.

  • IntroCompositeApplns.PropertiesVoigt, Reuss,Hill

    Anistrpy.CTECellularMatls.Wood

    9

    Why Use Composites? [Man-made] Thebasicreasonfortheuseofcompositesisalwaysthe

    same:somecombina?onofproper?escanbeachievedthatisimpossibleinamonolithicmaterial[foragivencost].

    InSiC-reinforcedaluminumforbrakerotors,forexample,thecombina?onoflightweight,toughness(fromtheAlmatrixat~2.7Mgm/m3),ands?ffness(fromtheSiCaddi?ons)isnotpossibleineithercons?tuentbyitself.

    InCu-Nbforhighstrengthelectricalconductors,thecombina?onof>1GPayieldstrengthandhighelectricalconduc?vity(intheCu)couldneverbeachievedineithercons?tuentbyitself.Inthiscasethehighstrengthisasynergis?cpropertyofthecomposite.

    IntroCompositeApplns.PropertiesVoigt, Reuss,Hill

    Anistrpy.CTECellularMatls.Wood

    10

    Key aspects of composites

    Compositesareexpensivetomake,ascomparedtomonolithicmaterials,especiallyiftheshapeandarrangementofthephasesmustbecontrolled.

    Thereforetheremustbeastrongmo?va?onformakingacompositestructuretooffsetthecost.

    Thesimplestcompositesarepar?culatecomposites.Laminatesarenext,followedbyfibercomposites.Wovenstructuresarethemostcomplex.

    Examinable

  • IntroCompositeApplns.PropertiesVoigt, Reuss,Hill

    Anistrpy.CTECellularMatls.Wood

    11

    Typical Microstructures

    Weshownextsometypicalmicrostructures. Inbiomaterials,manyarecellularcompositesatsomelengthscale(typicallyaround1m).

    Man-madecompositesaremoreonenfullydense.Thethreemajor[structural]materialtypesareallusedsotheabbrevia?onsMMC[metalmatrixcomposite],CMC[ceramicmatrixcomposite],andPMC[polymermatrixcomposite]arecommonlyused.

    Examinable

    IntroCompositeApplns.PropertiesVoigt, Reuss,Hill

    Anistrpy.CTECellularMatls.Wood

    12 Cellular Biomaterials

    Gibson & Ashby: Cellular Solids

    Notethevaria?onindensity;alsothepresenceofdis?nctlayersofcellsinsomewoods,andinbone.Notealsothattheshapeofthecellsandtheirwallsmakesadifferencetotheirproper?es.

  • IntroCompositeApplns.PropertiesVoigt, Reuss,Hill

    Anistrpy.CTECellularMatls.Wood

    13

    Man-made Examples

    SiCfibersinTi3Almatrix

    SiCfibersinaCASceramicmatrixDowling: Mech. Behavior Materials

    Notethetypicallengthscaleof~100m,andtheuseoffibersforreinforcement.Thisbasictypeoffiber-reinforcedcompositeisstronglyanisotropic.ThetoughnessofsuchcompositesandtheneedforlimitedadhesionbetweenfiberandmatrixisdiscussedinthelectureonFracture.

    IntroCompositeApplns.PropertiesVoigt, Reuss,Hill

    Anistrpy.CTECellularMatls.Wood

    14

    Food!

    Fromlentoright,toptobo/om:a)Breadb)Meringuec)Chocolatebard)Chipe)Malteser(Candy)f)Jaffacake(cookie,seebelow)

    Gibson & Ashby: Cellular SolidsMaltesersimage:commons.wikimedia.org/MaltesersOpen.jpg

    Jaffa:thetas?ngbuds.com

  • IntroCompositeApplns.PropertiesVoigt, Reuss,Hill

    Anistrpy.CTECellularMatls.Wood

    15

    Food for Thought!

    Howdoesicecreamrepresentamaterialinwhichthethermal-mechanicalhistoryiscri?caltoitsmicrostructurewhich,inturn,controlsitsproper?es?

    Hint:thisinvolvesboththeproper?esofcompositematerials(ice,cream,voids)andpar?clecoarsening(theice).

    IntroCompositeApplns.PropertiesVoigt, Reuss,Hill

    Anistrpy.CTECellularMatls.Wood

    16

    Examples of composites Theclassicalexampleofacompositeisconcrete. Itismorecomplexthanitappears.Therearetypicallycoarse

    andfinepar?cles(rocks!)embeddedinamatrixofsilicatesandsulfates.Thereisahighfrac?onofporesofallsizes.Thisisanexampleofapar1culatecomposite.

    Ordinaryconcrete(properlymade)hasexcellentcompressivestrengthbutpoortensilestrength.Thusreinforcedconcretewasinventedtocombinethetensilestrengthofsteelwiththecompressivestrengthofconcrete.Thisisanexampleofamul?scalepar1culateandfiberreinforcedcomposite.Itispar1culatebecausetheaggregate(coarse

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