Composite Materials Composites Classification

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Composites ClassificationComposite Materials Composites: Multiphase material with significant proportions of each phase.Matrix: The continuous phase Purpose is to:- transfer stress to other phasesISSUES TO ADDRESS. What are the classes and types of composites?- protect phases from environment Classification: MMC, CMC, PMC Why are composites used instead of metals,ceramics, or polymers?Mech. Eng. Dept. - Concordia UniversityMECH 321 Lecture 7/1 Examples: Spheroidite steelFiber-reinforced0.5 mmMECH 321 Lecture 7/2Particulates x:Ferrite ( )ductilecrosssectionviewMech. Eng. Dept. - Concordia UniversityDr. M. MedrajParticulates CompositesParticle-reinforced0.5 mm . . .Dispersed phase: Purpose: enhance matrix properties.- MMC: increase y, TS, creep resist.- CMC: increase Kc- PMC: increase E, y, TS, creep resist. Classification: Particle, fiber, structural How do we estimate composite stiffness & strength?Dr. M. MedrajwovenfibersProperties of particulates composites depend on:brittle60 mm WC/Cocemented carbidematrix: cobaltductileparticles: WCbrittle, hardconcentrationsize .Vm:10-15vol%!600 mm Automobile tiresmatrix: rubbercompliantparticles: Cstifferdistribution0.75 mmDr. M. MedrajMech. Eng. Dept. - Concordia UniversityMECH 321 Lecture 7/3Dr. M. Medraj .Mech. Eng. Dept. - Concordia UniversityMECH 321 Lecture 7/4

Particulates CompositesFiber Composites Elastic modulus of composites, Ec:Particle-reinforced two approaches:(1) Aligned Continuous fibersupper limit: Rule of Mixtures (ROM)E c VmE m Vp E pE(GPa)35030 0Cu matrix/tungsten 250particles20 0150 Glass reinforced with SiC fibers Examples: Metal: '(Ni3Al)- (Mo)lower limit:1 Vm VpEC Em Epformed by glass slurryEglass 76GPa; ESiC 400GPa.matrix: (Mo) fracturesurface020 4 060 80Cu10 0 vol% tungstenW Application to other properties:This failure is not catastrophic- because not all fibers fail at thesame time, and- even after fibers failure thematrix is still intact until it isstrained to its fracture point.2 m- Electrical conductivity, e: Replace E by e.fibers: ’ (Ni 3 Al) - Thermal conductivity, k: Replace E by k.Dr. M. MedrajStructuralfiber-reinforcedMech. Eng. Dept. - Concordia UniversityMECH 321 Lecture 7/5Mech. Eng. Dept. - Concordia UniversityDr. M. MedrajFiber CompositesMECH 321 Lecture 7/6Fiber Composites Critical fiber length for effective stiffening & strengthening:(2) Discontinuous, random 2D fibersFiber strength in tension Example: Carbon-CarbonC fibers: very stiffvery strong- uses: disk brakes, gasturbine exhaust flaps, nosecones.view onto planeC matrix: less stiffless strongfibers liein plane Other variations: Discontinuous, random 3D Discontinuous, 1DDr. M. MedrajMech. Eng. Dept. - Concordia UniversityFiber diametershear strength offiber-matrix interfaceFor glass and carbon composites, lc is often around 1mm (20 - 150 x df)Fibers need to be long enough to carry load.How does fiberstrengthening work?Transfer load frommatrix to strong/stifffiber. Requires agood .MECH 321 Lecture 7/7 fdlc 2 cDr. M. MedrajNo load is transferredat fiber endsMech. Eng. Dept. - Concordia UniversityLoad is transferredalong fiber sidesMECH 321 Lecture 7/8

Fiber CompositesRule of Mixtures (RoM)Volume of composite Vol. of fibers Vol. of matrixVolume fraction of fibers: Vf vol. of fibers/vol. of compositeVolume fraction of matrix: Vm vol. of matrix/vol. of compositeVf Vm 1Vm (1-Vf)Thus density of composite can be written as:ρc Vf ρf Vm ρmorρc Vf ρf (1-Vf)ρmElastic Properties: Longitudinal loadingcontinuousdiscontinousrandomly orientedWhen: c Ac m Am f Afl 15 lc "continuous" fibersl lc not acting as fibers (particles).Area fraction vol. fraction (ifall fibers have the same length) c mVm σ f V f .(aligned)Mech. Eng. Dept. - Concordia UniversityMECH 321 Lecture 7/9 c Ac m Am f Af c mσ V fV c m m f fbut or Ec Em (1 V f ) E f V faDr. M. MedrajFmMECH 321 Lecture 7/10Isostress case c f mAll stretch by same amount c mVm σ f V fAnd ratio of loads in fibre and matrix :ε1 εf εmElastic Properties: Transverse loading c m fFfIsostrain caseMech. Eng. Dept. - Concordia UniversityDr. M. MedrajElastic Properties: Longitudinal loadingEc EmVm E f V fDivide by AcA c m Am f fAcAcl 10 lc "discontinuous" fibersDr. M. Medrajload carried by composite loads carried bytwo phases:Fc Fm Ff since F A E fV fEmVmbMech. Eng. Dept. - Concordia University Ect mEmFrom RoMEVm σfEfVfwhere E ct is the transverse modulus.(recall c f m )(a) brittle fiber and ductilematrix.(b) stress–strain curve for analigned fiber-reinforcedcomposite that is exposed toa uniaxial stress applied inthe direction of alignment.MECH 321 Lecture 7/11E(GPa)350111 Vm VfE ctEmEf300250200which can be rearranged to:Ect Dr. M. Medraj150Em E fEm E f Vm E f V f Em (1 V f ) E f V f EmMech. Eng. Dept. - Concordia University0Cu204060 80vol% W10 0WMECH 321 Lecture 7/12

Strength of Aligned Cont. Fiber CompositesMatrixFiber}Transverse StrengthSame strainFiber-Matrix interfaceComposite will fail at lower fracture strainBrittle matricesMatrix fails firsteg. epoxiesSo, eitherDuctilematrixOr, fiber fails firsteg. thermoplastic polymerIf we assume that strain-to-failure of fiber is less than strain-to-failure ofmatrix as is most common: i.e. *f m* The transverse strength of unidirectional composites is usually very low. Fibers can actually act as . rather than as reinforcements. Transverse strength can be approximated as . the matrix strength inmany cases.The Fiber Content forEach is Approximately50 Vol%Then we can estimate the longitudinal strength of the compositeas: cl* m' (1 V f ) *f V fWhere ’m is the stress in the matrixwhen the fibers fail.Mech. Eng. Dept. - Concordia UniversityDr. M. MedrajMECH 321 Lecture 7/13Discontinuous & Aligned Fiber CompositesReinforcement efficiency is lower than that for continuous fibers but thecomposites are common for .- Modulus of elasticity can be up to . of continuous fiber compositeTypical Longitudinal and Transverse Tensile Strengths for three UnidirectionalFiber-Reinforced Composites.Dr. M. MedrajMech. Eng. Dept. - Concordia UniversityMECH 321 Lecture 7/14Discontinuous & Randomly Oriented Fiber CompositesWhen fiber orientation is random and the fibers are short, a “RoM”expression is used for the elastic modulus using an .factor, K (which is less than unity- usually between 0.1 - 0.6)).- Tensile strength can be up to . of continuous fiber composite*when c , the longitudinal strength, cdis given by :Ecd K Ef Vf EmVm cd* f*V f 1 c m' 1 Vf 2 where f* and m' represent the fiber fracture strength and the matrix stressat fiber failure respective ly.If the fiber length is less than the critical length, c , then :* cd' c V f m' 1 Vf dDr. M. Medrajwhere,d fiber diameter c the of either fiber – matrixbond strength or matrix shear strengthMech. Eng. Dept. - Concordia UniversityMECH 321 Lecture 7/15Dr. M. MedrajMech. Eng. Dept. - Concordia UniversityMECH 321 Lecture 7/16

Structural leStructural Stacked and bonded fiber-reinforced sheets stacking sequence: e.g., 0/90A continuous and aligned carbon fiber-epoxy composite consists of 60vol% fibers. The moduli of elasticity are 700GPa and 3GPa for the fiberand the matrix respectively. Calculate the longitudinal and transversecomposite modulus of elasticity? Compare the result with that of steel(E 207 Gpa)? Calculate the density of the composite if the density ofcarbon fiber is 1.8 g/cm3 and of the epoxy is 1.2 g/cm3? benefit: balanced, in-plane stiffness Sandwich panels low density, honeycomb core benefit: small weight, large bending stiffnessface sheetadhesive layerhoneycombDr. M. MedrajMech. Eng. Dept. - Concordia UniversityMECH 321 Lecture 7/17Next time:Fracture MechanicsDr. M. MedrajMech. Eng. Dept. - Concordia UniversityMECH 321 Lecture 7/19Dr. M. MedrajMech. Eng. Dept. - Concordia UniversityMECH 321 Lecture 7/18

Volume fraction of fibers: Vf vol. of fibers/vol. of composite Volume fraction of matrix: Vm vol. of matrix/vol. of composite Rule of Mixtures (RoM) Volume of composite Vol. of fibers Vol. of matrix Vf Vm 1 Vm (1-Vf) Thus density of composite can be written as: ρc Vf ρ

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