2 Learning Goals – Composites List The CLASSES and TYPES of CompositesWhen to Use Composites Instead of Metals, Ceramics, or PolymersHow to Estimate Composite Stiffness & StrengthExamine some Typical Applications
3 Terms & Classifications Composite MultiPhase Material with Significant Proportions of Each PhasePhase ComponentsMATRIXDISPERSED PhaseMatrixThe CONTINUOUS PhaseThe Matrix Functiontransfer stress to other phase(s)Protect other phase(s) from the (corrosive) EnvironmentReprinted with permission fromD. Hull and T.W. Clyne, An Introduction to Composite Materials, 2nd ed., Cambridge University Press, New York, 1996, Fig. 3.6, p. 47.
6 Composite Survey – Particle-I Particle-reinforcedFiber-reinforcedStructuralExamples60Adapted from Fig , Callister 7e. (Fig is copyright United States Steel Corporation, 1971.)-Spheroiditesteelmatrix:ferrite (a)(ductile)particles:cementite(Fe3C(brittle)mAdapted from Fig. 16.4, Callister 7e. (Fig is courtesy Carboloy Systems, Department, General Electric Company.)-WC/Cocementedcarbidematrix:cobalt(ductile)particles:WC(brittle,hard)Vm:10-15vol%!600Adapted from Fig. 16.5, Callister 7e. (Fig is courtesy Goodyear Tire and Rubber Company.)-Automobiletiresmatrix:rubber(compliant)particles:C(stiffer)0.75m
7 ReInforced ConCrete Concrete is a PARTICLE ReInforced Composite Matrix = PortLand Cement3CaO-SiO2 + 2CaO-SiO2Dispersed PhasesSand+Gravel Aggregate60%-80% by VolSteel ReInforcing Bars (Rebar)A type of FIBER ReinforcementImproves Tensile & Shear Strength
8 More ReInforced Concrete Concrete ≡ gravel + SAND + cementWhy sand and gravel? → Sand packs into gravel VOIDSReinforced concrete - Reinforce with steel reBAR or reMESHIncreases TENSILE strength - even if Concrete matrix is crackedPreStressed concrete - reMesh under tension during setting of concrete. Tension release puts concrete under COMPRESSIVE StressConcrete is much stronger under compression.
9 Composite Survey – Particle-II Particle-reinforcedFiber-reinforcedStructuralComposite Material Elastic Modulus, EcTwo “Rule of Mixtures” ApproximationsData:Cu matrixw/tungstenparticles204681015025030350vol% tungstenE(GPa)lower limit:1Ec=Vm+pupperlimit:(Cu)(W)“rule of mixtures”←Springs in PARALLELUpper Limit is like Springs in PARALLEL: if Vm ~ Vp; then larger Ei dominatesLower limit => Ec = EmEp/ (VmEp + VpEm) => Then smaller Ei dominates←Springs in SERIESRule-of-Mixtures Applies to Other PropertiesElectrical conductivity, σelect: Replace E by σelectThermal conductivity, k: Replace E by k.
10 Composite Survey: Fiber-I Fibers very strongProvide significant strength improvement compared to pure matrix-materialExample: fiber-glassContinuous glass filaments in a polymer matrixStrength due to fibersPolymer simply holds them in place
11 Fiber MaterialsWhiskers - Thin single crystals - large length to diameter ratiographite, SiN, SiChigh crystal perfection – extremely strong, strongest knownvery expensiveTraditional Fiberspolycrystalline or amorphousGenerally polymers or ceramicsEx: Al2O3 , Aramid, E-glass, Boron, UHMWPEUltraHighMolecularWeightPolyEthylene
12 Composite Survey: Fiber-II Particle-reinforcedFiber-reinforcedStructuralFiber MaterialsWhiskers - Thin single crystals with large length to diameter ratiographite, SiN, SiChigh crystal perfection – extremely strong, strongest physical form knownvery expensive to produceFiberspolycrystalline or amorphousgenerally polymers or ceramicsEx: Al2O3 , Aramid, E-glass, Boron, UHMWPEWiresMetal – steel, Mo, W
13 Fiber Alignment aligned continuous aligned random discontinuous Adapted from Fig. 16.8, Callister 7e.alignedcontinuousaligned randomdiscontinuous
14 ISOstress & ISOstrainisoSTRAIN → Tensile strength and elastic modulus when fibers are parallel to the direction of stressisoSTRESS → Tensile strength and elastic modulus when fibers are perpendicular to the direction of stress
15 Composite Survey – Fiber-I Fiber-reinforcedParticle-reinforcedStructuralALIGNED, CONTINUOUS FibersExamplesMetal: g’ (Ni3Al)-a(Mo)by eutectic solidification.From W. Funk and E. Blank, “Creep deformation of Ni3Al-Mo in-situ composites", Metall. Trans. A Vol. 19(4), pp , Used with permission.matrix:a(Mo)(ductile)fibers:g’(Ni3Al)(brittle)2mGlass w/SiC fibersformed by glass slurryEglass = 76GPa; ESiC = 400GPa.(a)(b)From F.L. Matthews and R.L. Rawlings, Composite Materials; Engineering and Science, Reprint ed., CRC Press, Boca Raton, FL, (a) Fig. 4.22, p. 145 (photo by J. Davies); (b) Fig , p. 349 (micrograph by H.S. Kim, P.S. Rodgers, and R.D. Rawlings). Used with permission of CRCPress, Boca Raton, FL.
16 Composite Survey – Fiber-II Fiber-reinforcedParticle-reinforcedStructuralDISCONTINUOUS, RANDOM, 2D (Planer) FibersExample: Carbon-CarbonProcess: fiber/pitch, then burn out at up to 2500C.Uses: disk brakes, gas turbine exhaust flaps, rocket nose cones.Other variations:Discontinuous, random 3DDiscontinuous, 1DFully AlignedC fibers:very stiffverystrongC matrix:less stiffless strong(b)view onto planefibers liein plane(a)Adapted from F.L. Matthews and R.L. Rawlings, Composite Materials; Engineering and Science, Reprint ed., CRC Press, Boca Raton, FL, (a) Fig. 4.24(a), p. 151; (b) Fig. 4.24(b) p (Courtesy I.J. Davies) Reproduced with permission of CRC Press, Boca Raton, FL.
18 Fiber Lengths cont. Example: FiberGlass Need Fiber Lengh > 15mmReason for length Criteria → examine Extreme casesVery Short Fiber has very little hold-in force and would PULL-OUT (Fiber PULLS OUT before Fracture)Very Long Fiber would take almost all the axial load (Fiber FRACTURES before PullOut)Shorter, thicker fiber:Longer, thinner fiber:Poorer fiber efficiencyBetter fiber efficiencyAdapted from Fig. 16.7, Callister 6e.
19 Composite Survey – Fiber-IV Fiber-reinforcedParticle-reinforcedStructuralTypical Values for K:Aligned 1D: K = 1 (anisotropic)Random 2D: K = 3/8 2D isotropy)Random 3D: K = 1/5 (3D isotropy)TS in fiber direction (1D, Aligned) by VOLUME Weighted AverageEstimate Ec and TSValid for LONG Fiber Condition:The Elastic Modulus in Fiber Directionefficiency factor
20 Composite Survey – Structural Fiber-reinforcedParticle-reinforcedStacked and bonded fiber-reinforced sheetsOrthogonal stacking sequence: e.g., 0°/90°benefit: balanced, in-plane stiffnessSandwich panelslow density, honeycomb corebenefit: small weight, large bending stiffnesshoneycombadhesive layerface sheetThink PLYWOOD and LAMINATED BEAM tested in the LabSimilar to Composite Beam Lab Exercise
22 Composite Benefits cont.1 Polymer Matrix Composites → Better E:ρ (Stiffness:Weight) ratioE(GPa)G=3E8K=EDensity,r[Mg/m3].1.3110.012metal/metal alloyspolymersPMCsceramicsWant: HI Modulus; Lo density
23 Specific StrengthThe PRIMARY Motivation for the Use of Composites → Hi-Strength, Hi-Stiffness & Lo-WeightThus Two Important MetricsSpecific STRENGTHSimilarly The Specific STIFFNESSNow Specific WeightWhereρ Density in kg/m3g Acceleration of Gravity (9.81 m/s2)
24 Specific Strength cont.1 Now Determine Units for Sσ and SE by Way of ExamplesFor 7075 Al in the Heat treated Stateu = 83 ksi = lb/in3For Kevlar-49 (Aramid Fiber)E = 131 GPaρ = 1444 kg/m3Find Now Specific Stiffness
28 Summary – Composites cont.1 Composites enhance matrix properties:MMC: enhance sy, TS, creep performanceCMC: enhance KcPMC: enhance E, sy, TS, creep resistanceParticle ReInforcedElastic modulus can be estimated by the Rule of MixturesProperties are isotropic
29 Summary – Composites cont.2 Fiber ReInforced:Elastic modulus and TS can be estimated along fiber direction By Rule of MixturesProperties can be isotropic or anisotropicStructural:Based on build-up of sandwiches in layered formPlysHoneyCombs
30 WhiteBoard Work Prob 16.11 Where Given IsoStrain, Longitudinal Loading for a Continuous Fiber Composite:WhereF ForceE Elastic ModulusV Volume fractionSub-f → “fiber”Sub-m → “matrix”Sub-c → “composite”Then Show
32 E Glass - BackGround http://www.azom.com/details.asp?ArticleID=764 E-Glass or electrical grade glass was originally developed for stand off insulators for electrical wiring. It was later found to have excellent fibre forming capabilities and is now used almost exclusively as the reinforcing phase in the material commonly known as fibreglass.
33 E Glass - Composition Composition E-Glass is a low alkali glass with a typical nominal composition of SiO2 54wt%, Al2O3 14wt%, CaO+MgO 22wt%, B2O3 10wt% and Na2O+K2O less then 2wt%. Some other materials may also be present at impurity levels.
34 E Glass – Key Properties Properties that have made E-glass so popular in fibreglass and other glass fibre reinforced composite include:Low costHigh production ratesHigh strength, (see table on next slide)High stiffnessRelatively low densityNon-flammableResistant to heatGood chemical resistanceRelatively insensitive to moistureAble to maintain strength properties over a wide range of conditionsGood electrical insulation
35 E Glass – Fibre Strength Table 1. Comparison of typical properties for some common fibres.
36 E Glass – Use in Composites The use of E-Glass as the reinforcement material in polymer matrix composites is extremely common. Optimal strength properties are gained when straight, continuous fibres are aligned parallel in a single direction. To promote strength in other directions, laminate structures can be constructed, with continuous fibres aligned in other directions. Such structures are used in storage tanks and the like.Random direction matts and woven fabrics are also commonly used for the production of composite panels, surfboards and other similar devices.
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