Textile Structural Composites

Yiping Qiu

College of TextilesDonghua University

Spring, 2006

Reading AssignmentTextbook chapter 1 General Information.High-Performance Composites: An Overview, High-Performance Composites, 7-19, 2003 Sourcebook.FRP Materials, Manufacturing Methods and Markets, Composites Technology, Vol. 6(3) 6-20, 2000.

ExpectationsAt the conclusion of this section, you should be able to:Describe the advantages and disadvantages of fiber reinforced composite materials vs. other materialsDescribe the major applications of fiber reinforced compositesClassification of composites

IntroductionWhat is a composite material?Two or more phases with different propertiesWhy composite materials?SynergyHistoryCurrent Status

IntroductionApplicationsAutomotive MarineCivil engineeringSpace, aircraft and militarySports

Applications in plane

Fiber reinforced composite materialsClassifications according to:MatricesPolymer ThermoplasticThermosetMetalCeramicOthers

Fiber reinforced composite materialsClassificationsFibersLengthshort fiber reinforcedcontinuous fiber reinforcedCompositionSingle fiber typeHybridMechanical propertiesConventionalFlexible

Fiber reinforced composite materialsAdvantagesHigh strength to weight ratioHigh stiffness to weight ratioHigh fatigue resistanceNo catastrophic failureLow thermal expansion in fiber oriented directions Resistance to chemicals and environmental factors

02468Specific gravity (g/cc)SteelAl alloyTi alloyCarbon/epoxyKevlar/epoxymaterialsComparison of specific gravities

Fiber reinforced composite materialsDisadvantagesGood properties in one direction and poor properties in other directions.High cost due to expensive material and complicated fabrication processes.Some are brittle, such as carbon fiber reinforced composites.Not enough data for safety criteria.

Design of Composite MaterialsProperty MapsMerit index

Design of Composite MaterialsMerit indexExample for tensile stiffness of a beam

However, for a given tensile sample, tensile stiffness has nothing to do with length or L = 1 may be assumed

Design of Composite MaterialsHow about for torsion beams and bending plates? Lets make the derivation of these our first homework.

Major components for fiber-reinforced compositesReading assignment:Textbook Chapter 2 Fibers and matricesFibers Share major portion of the loadMatrix To transfer stress between the fibersTo provide a barrier against an adverse environmentTo protect the surface of the fibers from mechanical abrasion

Major components for fiber reinforced compositesCoupling agents and coatings to improve the adhesion between the fiber and the matrixto protect fiber from being reacted with the matrix or other environmental conditions such as water moisture and reactive fluids. Fillers and other additives: to reduce the cost,to increase stiffness,to reduce shrinkage,to control viscosity,to produce smoother surface.

Materials for fiber reinforced compositesMainly two components:Fibers Matrices

Materials for fiber reinforced compositesFibersInfluences:Specific gravity,Tensile and compressive strength and modulus,Fatigue properties,Electrical and thermal properties,Cost.

Materials for fiber reinforced compositesFibersFibers used in compositesPolymeric fibers such as PE (Spectra 900, 1000) PPTA: Poly(para-phenylene terephthalamide) (Kevlar 29, 49, 149, 981, Twaron) Polyester (Vectran or Vectra)PBZT: Poly(p-phenylene benzobisthiozol)

Materials for fiber reinforced compositesFibersInorganic fibers: Glass fibers: S-glass and E-glassCarbon or graphite fibers: from PAN and PitchCeramic fibers: Boron, SiC, Al2O3Metal fibers: steel, alloys of W, Ti, Ni, Mo etc. (high melting temperature metal fibers)

Materials for fiber reinforced compositesMost frequently used fibersGlassCarbon/graphitePPTA (Kevlar, etc.)Polyethylene (Spectra)Polyester (Vectra)

Materials for fiber reinforced compositesCarbon fibersManufacturing processesStructure and properties

Materials for fiber reinforced compositesCarbon fibersManufacturing processesThermal decomposition of fibrous organic precursors:PAN and RayonExtrusion of pitch fibers

Materials for fiber reinforced compositesCarbon fiber manufacturing processesThermal decomposition of fibrous organic precursorsRayon fibersRayon based carbon fibersStabilization at 400C in O2, depolymerization & aromatization Carbonization at 400-700C in an inert atmosphereStretch and graphitization at 700-2800C (improve orientation and increase crystallinity by 30-50%)

Materials for fiber reinforced compositesCarbon fiber manufacturing processesThermal decomposition of fibrous organic precursorsPAN (polyarylonitrile) based carbon fibersPAN fibers (CH2-CH(CN))Stabilization at 200-300C in O2, depolymerization & aromatization, converting thermoplastic PAN to a nonplastic cyclic or ladder compound (CN groups combined and CH2 groups oxidized)Carbonization at 1000-1500C in an inert atmosphere to get rid of noncarbon elements (O and N) but the molecular orientation is still poor.Stretch and graphitization at >1800C, formation of turbostratic structure

Materials for fiber reinforced compositesPitch based carbon fiberspitch - high molecular weight byproduct of distillation of petroleumheated >350C, condensation reaction, formation of mesophase (LC)melt spinning into pitch fibersconversion into graphite fibers at ~2000C

Materials for fiber reinforced compositesCarbon fibersAdvantagesHigh strengthHigher modulusNonreactiveResistance to corrosionHigh heat resistancehigh tensile strength at elevated temperatureLow density

Materials for fiber reinforced compositesCarbon fibersDisadvantagesHigh costBrittle

Materials for fiber reinforced compositesCarbon fibersOther interesting propertiesLubricating propertiesElectrical conductivityThermal conductivityLow to negative thermal expansion coefficient

Materials for fiber reinforced compositesCarbon fibersheat treatment below 1700Cless crystalline and lower modulus (365GPa)

Materials for fiber reinforced compositesGlass fibersCompositions and propertiesAdvantages and disadvantages

Materials for fiber reinforced compositesGlass fibersCompositions and StructuresMainly SiO2 +oxides of Ca, B, Na, Fe, AlHighly cross-linked polymerNoncrystalineNo orientationSi and O form tetrahedra with Si centered and O at the corners forming a rigid networkAddition of Ca, Na, & K with low valency breaks up the network by forming ionic bonds with O strength and modulus

Microscopic view of glass fiberCross polarFirst order red plate

Materials for fiber reinforced compositesGlass fibersTypes and PropertiesE-glass (for electric)draws well good strength & stiffnessgood electrical and weathering properties

Materials for fiber reinforced compositesGlass fibersTypes and PropertiesC-glass (for corrosion)good resistance to corrosion low strength

Materials for fiber reinforced compositesGlass fibersTypes and PropertiesS-glass (for strength)high strength & modulus high temperature resistancemore expensive than E

Materials for fiber reinforced compositesProperties of Glass fibers

Materials for fiber reinforced compositesGlass fibersProductionMelt spinning

Materials for fiber reinforced compositesGlass fiberssizing:purposesprotest surfacebond fibers togetheranti-staticimprove interfacial bondingNecessary constituentsa film-forming polymer to provide protectinge.g. polyvinyl acetatea lubricanta coupling agent: e.g. organosilane

Materials for fiber reinforced compositesGlass fibersAdvantageshigh strengthsame strength and modulus in transverse direction as in longitudinal directionlow cost

Materials for fiber reinforced compositesGlass fibersdisadvantagesrelatively low modulushigh specific density (2.62 g/cc)moisture sensitive

Materials for fiber reinforced compositesKevlar fibersStructurePolyamide with benzene rings between amide groupsLiquid crystallinePlanar array and pleated system

Materials for fiber reinforced compositesKevlar fibersTypesKevlar 29, E = 50 GPaKevlar 49, E = 125 GPaKevlar 149, E = 185 GPa

Materials for fiber reinforced compositesKevlar fibersAdvantageshigh strength & moduluslow specific density (1.47g/cc)relatively high temperature resistance

Materials for fiber reinforced compositesKevlar fibersDisadvantagesEasy to fibrillatepoor transverse propertiessusceptible to abrasion

Materials for fiber reinforced compositesSpectra fibersStructure: (CH2CH2)nLinear polymer - easy to packNo reactive groupsAdvantageshigh strength and moduluslow specific gravityexcellent resistance to chemicalsnontoxic for biomedical applications

Materials for fiber reinforced compositesSpectra fibersDisadvantagespoor adhesion to matrixhigh creeplow melting temperature

Materials for fiber reinforced compositesOther fibersSiC and BoronProductionChemical Vapor Deposition (CVD)MonofilamentCarbon or Tungsten core heated by passing an electrical currentGaseous carbon containing silane

Materials for fiber reinforced compositesSiCProductionPolycarbosilane (PCS)Multi-filamentspolymerization process to produce precursorPCS pyrolised at 1300CWhiskersSmall defect free single crystal

Materials for fiber reinforced compositesParticulatesmall aspect ratiohigh strength and modulusmostly cheap

Materials for fiber reinforced compositesThe strength of reinforcementsCompressive strengthFiber fracture and flexibilityStatistical treatment of fiber strength

Materials for fiber reinforced compositesThe strength of reinforcementsCompressive strength(Mainly) Euler Buckling

Materials for fiber reinforced compositesThe strength of reinforcementsFactors determining compressive strengthMatrix materialFiber diameter or aspect ratio (L/d)fiber propertiescarbon & glass >> Kevlar

Materials for fiber reinforced compositesThe strength of reinforcementsFiber fractureMostly brittle e.g. Carbon, glass, SiCSome ductilee.g. Kevlar, SpectraFibrillatione.g. Kevlar

Materials for fiber reinforced compositesThe strength of reinforcementsFiber flexibilityHow easy to be bent Moment required to bend a round fiber:

E = Youngs Modulus d = fiber diameter = curvature

Materials for fiber reinforced compositesThe strength of reinforcementsFiber failure in bendingStress on surface Tensile stress:

E = Youngs Modulus d = fiber diameter = curvature

Materials for fiber reinforced compositesThe strength of reinforcementsFiber failure in bendingStress on surface Maximum curvature

* = fiber tensile strength

Materials for fiber reinforced compositesThe strength of reinforcementsFiber failure in bendingWhen bent, many fibers fail in compressionKevlar forms kink bands

Materials for fiber reinforced compositesStatistical treatment of fiber strengthBrittle materials: failure caused by random flawdont have a well defined tensile strengthpresence of a flaw populationStatistical treatment of fiber strengthPeirce (1928): divide a fiber into incremental lengths

Materials for fiber reinforced compositesStatistical treatment of fiber strengthPeirces experimentHypothesis:The longer the fiber length, the higher the probability that it will contain a serious flaw.Longer fibers have lower mean tensile strength.Longer fibers have smaller variation in tensile strength.

Materials for fiber reinforced compositesStatistical treatment of fiber strengthPeirces experimentExperimental verification:

Materials for fiber reinforced compositesStatistical treatment of fiber strengthWeakest Link Theory (WLT)define n = No. of flaws per unit length causing failure under stress .For the first element, the probability of failureThe probability for the fiber to survive

Materials for fiber reinforced compositesStatistical treatment of fiber strengthWeakest Link Theory (WLT)If the length of each segment is very small, then Pfi are all very small, Therefore (1-Pfi) exp(-Pfi)The probability for the fiber to survive

Materials for fiber reinforced compositesStatistical treatment of fiber strengthWeibull distribution of fiber strengthWeibulls assumption:m = Weibull shape parameter (modulus).0 = Weibull scale parameter, characteristic strength.L0 = Arbitrary reference length.

Materials for fiber reinforced compositesStatistical treatment of fiber strengthWeibull distribution of fiber strengthThus

Materials for fiber reinforced compositesStatistical treatment of fiber strengthWeibull distribution of fiber strengthDiscussion:Shape parameter ranges 2-20 for ceramic and many other fibers.The higher the shape parameter, the smaller the variation. When

Materials for fiber reinforced compositesStatistical treatment of fiber strengthWeibull distribution of fiber strengthPlot of fiber strength or failure strain datalet

Statistical treatment of fiber strengthExampleEstimate number of fibers fail at a gage length twice as much as the gage length in single fiber testL/L0 = 2

MatricesAdditional reading assignment:Jones, F.R., Handbook of Polymer-Fiber Composites, sections:2.4-2.6, 2.9, 2.10, 2.12.

MatricesPolymerMetalCeramic

MatricesPolymerThermosetting resinsEpoxyUnsatulated polyesterVinyl esterhigh temperature: PolyimidesPhenolic resins

MatricesPolymerTarget net resin properties

Epoxy resinsStarting materials:Low molecular weight organic compounds containing epoxide groups

Epoxy ResinsTypes of epoxy resins

Epoxy resinsTypes of epoxy resinbifuctional: diglycidyl ether of bisphenol Aa distribution of monomers n is fractional: effect of n molecular weight viscosity curing temp. distance between crosslinks Tg & ductility -OH moisture absorption

Epoxy resinsTypes of epoxy resin (cont.)Trifunctional (glycidyl amines)Tetrafunctionalhigher functionalitypotentially higher crosslink densitieshigher TgLess -OH groups moisture absorption

Epoxy resinsCuringCopolymerization: A hardener required: e.g. DDS, DICYHardeners have two active H atoms to add to the epoxy groups of neighboring epoxy molecules, usually from -NH2Formation of -OH groups: moisture sensitiveAddition polymerization: No small molecules formed no volatile formationStoichiometric concentration used, phr: part per hundred (parts) of resin

Epoxy resinMajor ingredients: epoxy resin and curing agent

Epoxy resinChemical reactions

Epoxy resinChemical reactions

Epoxy resinsCuringHomopolymerization: Addition polymerization: a catalyst or initiator required: eg. Tertiary amines and BF3 compoundsLess -OH groups formedTypical properties of addition polymersCombination of catalyst with hardeners

Epoxy ResinsReaction of homopolymerization

Epoxy resinsEpoxy resinsMechanical and thermomechanical propertiesEffect of curing agent on mechanical propertiesHeat distortion temperature (HDT)measured as temperature at which deflection of 0.25 mm of 100 mm long bar under 0.455 MPa fiber stress occurs.related but TgMoisture absorption: 1% decrease Tg by 20K

PolyimidesLargest class of high temperature polymers in compositesTypesPMR (polymerization of monomeric reactants) polyimides are insoluble and infusible. in situ condensation polymerization of monomers in a solvent2 stage process: first stage to form imidized prepolymer of oligomer and volatile by-products removed using autoclave or vacuum oven.Second stage: prepolymer is crosslinked via reaction of the norbornene end cap under high pressure and temperature (316C and 200 psi)

PolyimidesTypesbis-imides (derived from monomers with 2 preformed imide groups).Typical BMI (bismaleimides)Used for lower temperature range ~ 200C

PolyimidesProperties (show tables)

PolyimidesAdvantages:Heat resistantDrawbacks: toxicity of constituent chemicals (e.g. MDA)microcracking of fibers on thermal cyclinghigh processing temperature Typical ApplicationsEngine parts in aerospace industry

Phenolic resinsPrepared through condensation polymerization between phenol and formaldehyde.Large quantity of Water generated (up to 25%) leading to high void content

Phenolic resinsAdvantages:High temperature stabilityChemical resistanceFlame retardantGood electrical propertiesTypical applicationsOffshore structuresCivil engineeringMarineAuto parts: water pumps, brake componentspan handles and electric meter cases

Time-temperature-transformation diagrams for thermosets resins

Additional reading assignment:reserved: Gillham, J.K., Formation and Properties of Thermosetting and High Tg Polymeric Materials, Polymer Engineering and Science, 26, 1986, p1429-1431

Time-temperature-transformation diagrams for thermosets resins

Time-temperature-transformation diagrams for thermosets resins

Important conceptsGelation formation of an infinite networksol and gel coexist VitrificationTg rises to isothermal temperature of cureTcure > Tg, rubbery material Tcure < Tg, glassy materialAfter vitrification, conversion of monomer almost ceases.

Time-temperature-transformation diagrams for thermosets resins

Important conceptsDevitrificationTg decreases through isothermal temperature of cure due to degradationdegradation leads to decrosslink and formation of plasticizing materialsChar or vitrificationdue to increase of crosslink and volatilization of low molecular weight plasticizing materials

Time-temperature-transformation diagrams for thermosets resins

Important conceptsThree critical temperatures:Tg - Tg of cured systemgelTg - Tg of gelTgo - Tg of reactants

Time-temperature-transformation diagrams for thermosets resins

DiscussionUngelled glassy state is good for commercial molding compoundsTgo > Tprocessing, processed as solidTgo < Tprocessing, processed as liquidStore temperature < gelTg to avoid gelationResin fully cured when Tg = Tg Tg > Tcure about 40CFull cure is achieved most readily by cure at T > Tg and slowly at T < Tg.

Unsaturated polyesterReading assignmentMallick, P.K., Fiber Reinforced Composites . Materials, Manufacturing and Design, pp56-64.Resin: Products of condensation polymerization of diacids and diolse.g. Maleic anhydride and ethylene glycolStrictly alternating polymers of the type A-B-A-B-A-BAt least one of the monomers is ethylenically unsaturated

Unsaturated polyester

Unsaturated polyester

Unsaturated polyesterCross-linking agentReactive solvent of the resin: e.g. styreneAddition polymerization with the resin molecules: initiator needed, e.g. peroxideApplication of heat to decompose the initiator to start addition polymerizationan accelerator may be added to increase the decomposition rate of the initiator.

Unsaturated polyester

Unsaturated polyesterFactors to control propertiesCross-linking density:addition of saturated diacids as part of the monomer for the resin: e.g phthalic anhydrid, isophthalic acid and terephthalic acidas ratio of saturated acids to unsaturated acids increases, strength and elongation increase while HDT decreases

Unsaturated polyesterFactors controlling propertiesType of acidsTerephthalic acids provide higher HDT than the other two acids due to better packing of moleculesnonaromatic acid: adipic acid HOOC(CH2)4COOH, lowers stiffnessResin microstructure: local extremely high density of cross-links.Type of diolslarger diol monomer: diethylene glycol bulky side groups

Unsaturated polyesterFactors to control propertiesType of crosslinking agentamount of styrene: more styrene increases the distance of the space of neighboring polyester molecules lower modulusExcessive styrene: self-polymerization formation of polystyrene polystyrene-like properties

Unsaturated polyesterAdvantagesLow viscosityFast cureLow costDisadvantageslower properties than epoxylarge mold shrinkage sink marksan incompatible thermoplastic mixed into the resin to form a dispersed phase in the resin low profile system

Vinyl ester Resin:Products of addition polymerization of epoxy resin and an unsaturated carboxylic acid (vinyl)unsaturated C=C bonds are at the end of a vinyl ester molecule fewer cross-links more flexibleCross-linking agentThe polymer is dissolved in styreneAddition polymerization to form cross-links Formation of a gigantic moleculeSimilar curing reaction as unsaturated polyester resin

Vinyl ester

Vinyl ester

Vinyl ester Advantagesepoxy-like: excellent chemical resistancehigh tensile strengthpolyester-like:Low viscosityFast curingless expensivegood adhesion to glass fibers due to existence of -OHDisadvantages:Large volumetric shrinkage (5 10 %)

Vinyl ester

Advantages of thermosetting resinsHigh strength and modulus.Less creep and stress relaxationGood resistance to heat and chemicalsBetter wet-out between fibers and matrix due to low viscosity before cross-linking

Disadvantages of thermosetting resinsLimited storage lifeLong time to cureLow strain to failureLow impact resistanceLarge shrinkage on curing

Thermoplastic matricesReading assignment:Mallick, P.K., Fiber Reinforced Composites . Materials, Manufacturing and Design, section 2.4 pp 64-69.Types: Conventional: no chemical reaction during processingSemi-crystallineLiquid crystalAmorphousPseudothermoplastics: molecular weight increase and expelling volatiles

Thermoplastic matricesexamples:ConventionalNylonPolyethylenePolypropylenePolycarbonatePolyesterPMMA

Thermoplastic matricesexamples:Advanced (e.g.)

Thermoplastic matricesexamples:Advanced (e.g.)Polyimide

Thermoplastic matrices

Thermoplastic matricesMain descriptors: LinearRepeatedly meltableProperties and advantages of thermoplastic matrices High failure strainHigh impact resistanceUnlimited storage life at room temperatureShort fabrication timePostformability (thermoforming)Ease of repair by welding, solvent bondingEase of handling (no tackiness)

Thermoplastic matrices

Disadvantages of thermoplastic matrices High melt or solution viscosity (high MW)Difficult to mix them with fibersRelatively low creep resistanceLow heat resistance for conventional thermoplastics

Metal Matrices ExamplesAl, Ti, Mg, Cu and Super alloysReinforcements: Fibers: boron, carbon, metal wiresWhiskersParticulate

Metal MatricesFiber matrix interaction Fiber and matrix mutually nonreactive and insolubleFiber and matrix mutually nonreactive but solubleFiber and matrix react to form compounds at interface

Metal MatricesAdvantage of metal matrix composites (MMC)Versus unreinforced metals higher strength to density ratiobetter properties at elevated temperaturelower coefficient of thermal expansionbetter wear characteristicsbetter creep performance

Metal MatricesAdvantage of MMCVersus polymeric matrixbetter properties at elevated temperaturehigher transverse stiffness and strengthmoisture insensitivityhigher electrical and thermal conductivitybetter radiation resistanceless outgassing contamination

Metal MatricesDisadvantage of MMChigher costhigh processing temperaturerelatively immature technologycomplex and expensive fabrication methods with continuous fiber reinforcementshigh specific gravity compared with polymercorrosion at fiber matrix interface (high affiliation to oxygen)limited service experience

Ceramic MatricesGlass ceramicsglass forming oxides, e.g. Borosilicates and aluminosilicates semi-crystalline with lower softening temperature Conventional ceramicsSiC, Si3N4, Al2O3, ZrO2fully crystallineCement and concreteCarbon/carbon

Ceramic MatricesIncreased toughness through deflected crack propagation on fiber/matrix interface.Example: Carbon/carbon composites