Chapter 16: Composite Materials

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Chapter 16: Composite MaterialsISSUES TO ADDRESS. What are the classes and types of composites? Why are composites used instead of metals,ceramics, or polymers? How do we estimate composite stiffness & strength? What are some typical applications?Chapter 16 - 1

Composites Combine materials with the objective of getting amore desirable combination of properties– Ex: get flexibility & weight of a polymer plus thestrength of a ceramic structure materials for aircraft engine:low densities, strong, stiff, abrasion and impact resistant andcorrosion resistant.GE http://www.geae.com/education/theatre/ge90/ Principle of combined action– Mixture gives “averaged” propertiesbetter property combinations are fashioned by thecombination of 2 or more distinct materials.Chapter 16 - 2

Composite is considered to be any multiphase materials that exhibits asignificant proportion of the properties of both constituent phases suchthat a better combination of properties is realized.Schematic representations of the various geometrical and spatialcharacteristics of particles of the dispersed phase that may influence theproperties of composites: (1) concentration, (b) size, shape, (d)distribution, and (e) orientation.Chapter 16 - 3

Terminology/Classification Composites:-- Multiphase material w/significantproportions of each phase.wovenfibers Matrix:-- The continuous phase-- Purpose is to:0.5 mm-- Classification:crosssectionview- transfer stress to other phases- protect phases from environmentmetalMMC, CMC, PMCceramicpolymer Dispersed phase:-- Purpose: enhance matrix properties.MMC: increase σy, TS, creep resist.CMC: increase KcPMC: increase E, σy, TS, creep resist.-- Classification: Particle, fiber, structural0.5 mmReprinted with permission fromD. Hull and T.W. Clyne, AnIntroduction to Composite Materials,2nd ed., Cambridge University Press,New York, 1996, Fig. 3.6, p. 47.Chapter 16 - 4

Composite chpanels10-100nmAlignedRandomlyorientedAdapted from Fig.16.2, Callister 7e.Chapter 16 - 5

Composite Survey: Particle-IParticle-reinforced Examples:- Spheroidite matrix:ferrite (α)steelFiber-reinforced(ductile)60 µm- WC/Cocementedcarbidematrix:cobalt(ductile)Vm :10-15 vol%!Structuralparticles:cementite(Fe3 C)(brittle)Adapted from Fig.10.19, Callister 7e.(Fig. 10.19 iscopyright UnitedStates SteelCorporation, 1971.)particles:WC(brittle,hard)Adapted from Fig.16.4, Callister 7e.(Fig. 16.4 is courtesyCarboloy Systems,Department, GeneralElectric Company.)600 µm- Automobile .75 µmAdapted from Fig.16.5, Callister 7e.(Fig. 16.5 is courtesyGoodyear Tire andRubber Company.)Chapter 16 - 6

Composite Survey: cturalConcrete – gravel sand cement- Why sand and gravel?Sand packs into gravel voidsReinforced concrete - Reinforce with steel rerod or remesh- increases strength - even if cement matrix is te forming system showing reinforced concrete housing/Prestressed concrete - remesh under tension during setting ofconcrete. Tension release puts concrete under compressive force- Concrete much stronger under compression.- Applied tension must exceed compressive forcePost tensioning – tighten nuts to put under tensionthreadedrodnutChapter 16 - 7

Fractured reinforced concreteChapter 16 - 8

Chapter 16 - 9

How prestressed concrete is made ?High strength steelThe prestressing strand isstretched across the casting bed,30000 pounds of tension will beappliedA tarp is placed over and heat is appliedThe prestressingstrands are cutand removedfrom the castingbedCement, sand, stone, and watermake up concreteChapter 16 - 10

Post-tensioning Post-tensioning is the method of achieving pre-stressingafter the concrete has hardened and takes advantage ofconcrete's inherent compressive strength. Concrete is exceptionally strong in compression, butgenerally weak when subjected to tension forces or forcesthat pull it apart. These tension forces can be created byconcrete shrinkage caused during curing or by flexuralbending when the foundation is subjected to design loads(dead and live loads from the structure and/or expansivesoil induced loads). This tension can result in crackingwhich can lead to large deflections that can cause distressin the building's structure. The application of an external force into the concrete,recompressing it before it is subjected to the design loads,makes the foundation less likely to crack.http://www.youtube.com/watch?v d51lciZRwF0Chapter 16 - 11

Composite Survey: uctural Elastic modulus, Ec, of composites:-- two approaches.E(GPa)350Data:Cu matrix 300w/tungsten 250particles2001500upper limit: “rule of mixtures”Ec VmEm VpEp(Cu)lower limit:1 Vm Vp Ec Em Ep20 40 60 80Adapted from Fig. 16.3,Callister 7e. (Fig. 16.3 isfrom R.H. Krock, ASTMProc, Vol. 63, 1963.)10 0 vol% tungsten(W) Application to other properties:-- Electrical conductivity, σe: Replace E in equations with σe.-- Thermal conductivity, k: Replace E in equations with k.Chapter 16 - 12

Composite Survey: al Fibers very strong– Provide significant strength improvement tomaterial– Ex: fiber-glass Continuous glass filaments in a polymer matrix Strength due to fibers Polymer simply holds them in placeInfluence of fiber materials, orientation, concentration, length, etcChapter 16 - 13

Composite Survey: ral Fiber Materials– Whiskers - Thin single crystals - large length to diameter ratio graphite, SiN, SiC high crystal perfection – extremely strong, strongest known very expensive– Fibers polycrystalline or amorphous generally polymers or ceramics Ex: Al2O3 , Aramid, E-glass, Boron, UHMWPE– Wires Metal – steel, Mo, WChapter 16 - 14

Fiber AlignmentAdapted from Fig.16.8, Callister ter 16 - 15

Composite Survey: Fiber-IIIParticle-reinforcedFiber-reinforced Aligned Continuous fibers Examples:-- Metal: γ'(Ni3Al)-α(Mo)by eutectic solidification.-- Ceramic: Glass w/SiC fibersformed by glass slurryEglass 76 GPa; ESiC 400 GPa.matrix: α (Mo) (ductile)(a)2 µmfibers: γ ’ (Ni3Al) (brittle)From W. Funk and E. Blank, “Creepdeformation of Ni3Al-Mo in-situcomposites", Metall. Trans. A Vol. 19(4), pp.987-998, 1988. Used with permission.Structural(b)fracturesurfaceFrom F.L. Matthews and R.L.Rawlings, Composite Materials;Engineering and Science, Reprinted., CRC Press, Boca Raton, FL,2000. (a) Fig. 4.22, p. 145 (photo byJ. Davies); (b) Fig. 11.20, p. 349(micrograph by H.S. Kim, P.S.Rodgers, and R.D. Rawlings). Usedwith permission of CRCPress, Boca Raton, FL.Chapter 16 - 16

Composite Survey: Fiber-IVParticle-reinforcedFiber-reinforced Discontinuous, random 2D fibers Example: Carbon-Carbon-- process: fiber/pitch, thenburn out at up to 2500ºC.-- uses: disk brakes, gasturbine exhaust flaps, nosecones.(b) Other variations:-- Discontinuous, random 3D-- Discontinuous, 1DStructuralC fibers:very stiffvery strongC matrix:less stiffview onto plane less strong(a)Boeing 787fibers liein planeAdapted from F.L. Matthews and R.L. Rawlings,Composite Materials; Engineering and Science,Reprint ed., CRC Press, Boca Raton, FL, 2000.(a) Fig. 4.24(a), p. 151; (b) Fig. 4.24(b) p. 151.(Courtesy I.J. Davies) Reproduced withpermission of CRC Press, Boca Raton, FL.Carbon fiber-reinforced polymer compositesChapter 16 - 17

Composite Survey: al Critical fiber length for effective stiffening & strengthening:fiber strength in tensionσf dfiber length 15τcfiber diametershear strength offiber-matrix interface Ex: For fiberglass, fiber length 15 mm needed Why? Longer fibers carry stress more efficiently!Shorter, thicker fiber:σf dfiber length 15τcσ(x)Longer, thinner fiber:σf dfiber length 15τcσ(x)Adapted from Fig.16.7, Callister 7e.Poorer fiber efficiencyBetter fiber efficiencyChapter 16 - 18Load transmittance: the magnitude of the interfacial bond between the fiber and matrix phase

Composite Strength:Longitudinal LoadingContinuous fibers - Estimate fiber-reinforced compositestrength for long continuous fibers in a matrix Longitudinal deformationσc σmVm σfVfModulus of elasticity volume fractionEce Em Vm EfVfFfEfVf Fm E mVmbutεc εm εfisostrainlongitudinal (extensional)modulusf fiberm matrixChapter 16 - 19

Composite Strength:Transverse Loading In transverse loading the fibers carry less of the load- isostressσc σm σf σεc εmVm εfVf 1Vm Vf Ect E m Eftransverse modulusChapter 16 - 20

Composite ral Estimate of Ec and TS for discontinuous fibers:σf d-- valid when fiber length 15τc-- Elastic modulus in fiber direction:Ec EmVm KEfVfefficiency factor:-- aligned 1D: K 1 (aligned )-- aligned 1D: K 0 (aligned )-- random 2D: K 3/8 (2D isotropy)-- random 3D: K 1/5 (3D isotropy)Values from Table 16.3, Callister 7e.(Source for Table 16.3 is H. Krenchel,Fibre Reinforcement, Copenhagen:Akademisk Forlag, 1964.)-- TS in fiber direction:(TS)c (TS)mVm (TS)fVf(aligned 1D)Chapter 16 - 21

Composite Production Methods-I Pultrusion– Continuous fibers pulled through resin tank, thenperforming die & oven to cureAdapted from Fig.16.13, Callister 7e.Chapter 16 - 22

Composite Production Methods-II Filament Winding– Ex: pressure tanks– Continuous filaments wound onto mandrelAdapted from Fig. 16.15, Callister 7e. [Fig.16.15 is from N. L. Hancox, (Editor), FibreComposite Hybrid Materials, The MacmillanCompany, New York, 1981.]Chapter 16 - 23

Composite Survey: turalA structural composite is normally composed of both homogeneousand composite materials. Stacked and bonded fiber-reinforced sheets-- stacking sequence: e.g., 0º/90º-- benefit: balanced, in-plane stiffness Sandwich panelsAdapted fromFig. 16.16,Callister 7e.-- low density, honeycomb core-- benefit: small weight, large bending stiffnessface sheetadhesive layerhoneycombAdapted from Fig. 16.18,Callister 7e. (Fig. 16.18 isfrom Engineered MaterialsHandbook, Vol. 1, Composites, ASM International, Materials Park, OH, 1987.)Chapter 16 - 24

Composite Benefits CMCs: Increased toughnessForce103particle-reinf1un-reinf MMCs:10 -410 -810 -10metal/metal alloys.1 G 3E/8 polymers.01 K E.1 .3 1 3 10 30Density, ρ [mg/m3]6061 Alεss (s-1)10 iber-reinfBend displacement PMCs: Increased E/ρ6061 Alw/SiCwhiskers20 30 50Adapted from T.G. Nieh, "Creep rupture of asilicon-carbide reinforced aluminumcomposite", Metall. Trans. A Vol. 15(1), pp.139-146, 1984. Used with permission.σ(MPa)100 200Chapter 16 - 25

Summary Composites are classified according to:-- the matrix material (CMC, MMC, PMC)-- the reinforcement geometry (particles, fibers, layers). Composites enhance matrix properties:-- MMC: enhance σy, TS, creep performance-- CMC: enhance Kc-- PMC: enhance E, σy, TS, creep performance Particulate-reinforced:-- Elastic modulus can be estimated.-- Properties are isotropic. Fiber-reinforced:-- Elastic modulus and TS can be estimated along fiber dir.-- Properties can be isotropic or anisotropic. Structural:-- Based on build-up of sandwiches in layered form.Chapter 16 - 26

and composite materials. Chapter 16 -24-- low density, honeycomb core-- benefit: small weight, large bending stiffness honeycomb adhesive layer face sheet Adapted from Fig. 16.18, Callister 7e. (Fig. 16.18 is from Engineered Materials Handbook, Vol. 1, Co