AskelandPhuleNotes-CH16Printable

The Science and Engineering of Materials, 4th edDonald R. Askeland – Pradeep P. Phulé Chapter 16 – Composites: Teamwork and Synergy in Materials 1 Objectives of Chapter 16  Study different categories of composites: particulate, fiber, and laminar  Focus on composites used in structural or mechanical applications. 2 Chapter Outline          16.1 16.2 16.3 16.4 Dispersion-Strengthened Composites Particulate Composites Fiber-Reinforced Composites Characteristics of Fiber-Reinforced Composites 16.5 Manufacturing Fibers and Composites 16.6 Fiber-Reinforced Systems and Applications 16.7 Laminar Composite Materials 16.8 Examples and Applications of Laminar Composites 16.9 Sandwich Structures 3 (b) fiberglass is a fiber-reinforced composite containing stiff.1 Some examples of composite materials: (a) plywood is a laminar composite of layers of wood veneer. strong glass fibers in a softer polymer matrix ( 175). and (c) concrete is a particulate composite containing coarse sand or gravel in a cement matrix (reduced 50%).Figure 16. 4 . Tiny oxide particles formed in a metal matrix that interfere with dislocation movement and provide strengthening.Section 16. even at elevated temperatures. 5 .1 Dispersion-Strengthened Composites  A special group of dispersion-strengthened nanocomposite materials containing particles 10 to 250 nm in diameter is classified as particulate composites.  Dispersoids . Inc. A fiber-reinforced aluminum composite is shown for comparison. Thomson Learning ™ is a trademark used herein under license. The composite has benefits above about 300°C. 6 .2 Comparison of the yield strength of dispersionstrengthened sintered aluminum powder (SAP) composite with that of two conventional two-phase high-strength aluminum alloys. Figure 16. a division of Thomson Learning.©2003 Brooks/Cole. 7 . Gordon and Breach.Figure 16. p. © AIME.) 8 . 1968. 714. The dispersed ThO2 particles have a diameter of 300 nm or less ( 2000).3 Electron micrograph of TD-nickel. (From Oxide Dispersion Strengthening. 69 and 8.1 SOLUTION The densities of ThO2 and nickel are 9.9 g/cm3.1 TD-Nickel Composite Suppose 2 wt% ThO2 is added to nickel. How many particles are present in each cubic centimeter? Example 16. Each ThO2 particle has a diameter of 1000 Å.Example 16. The volume fraction is: 9 . respectively. The volume of each ThO2 sphere is: 10 . there is 0.Example 16.0184 cm3 of ThO2 per cm3 of composite.1 SOLUTION (Continued) Therefore.  Polymers . 11 .  Cemented carbides .The statement that the properties of a composite material are a function of the volume fraction of each material in the composite.  Electrical Contacts .2 Particulate Composites  Rule of mixtures .Particulate composites containing hard ceramic particles bonded with a soft metallic matrix.Materials used for electrical contacts in switches and relays must have a good combination of wear resistance and electrical conductivity.Section 16.Many engineering polymers that contain fillers and extenders are particulate composites. 8th Ed. 7. (From Metals Handbook..4 Microstructure of tungsten carbide—20% cobaltcemented carbide (1300).) 12 . American Society for Metals. 1972.Figure 16. Vol. 2 Cemented Carbides A cemented carbide cutting tool used for machining contains 75 wt% WC. 15 wt% TiC. Example 16.Example 16. The densities of the components of the composite are: 13 . we must convert the weight percentages to volume fractions. 5 wt% TaC. and 5 wt% Co. Estimate the density of the composite.2 SOLUTION First. 2 SOLUTION (Continued) From the rule of mixtures.Example 16. the density of the composite is 14 . Thomson Learning ™ is a trademark used herein under license. Inc. Figure 16. (b) a low-density compact is produced. (c) sintering joins the tungsten powders.©2003 Brooks/Cole. a division of Thomson Learning. 15 . and (d) liquid silver is infiltrated into the pores between the particles.5 The steps in producing a silver-tungsten electrical composite: (a) Tungsten powders are pressed. 3 Silver-Tungsten Composite A silver-tungsten composite for an electrical contact is produced by first making a porous tungsten powder metallurgy compact.3 SOLUTION From the rule of mixtures: 16 . Example 16. The density of the tungsten compact before infiltration is 14.Example 16. Calculate the volume fraction of porosity and the final weight percent of silver in the compact after infiltration. then infiltrating pure silver into the pores.5 g/cm3. 3 SOLUTION (Continued) After infiltration.Example 16. the volume fraction of silver equals the volume fraction of pores: 17 . ©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license. Figure 16.6 The effect of clay on the properties of polyethylene. 18 Example 16.4 Design of a Particulate Polymer Composite Design a clay-filled polyethylene composite suitable for injection molding of inexpensive components. The final part must have a tensile strength of at least 3000 psi and a modulus of elasticity of at least 80,000 psi. Polyethylene costs approximately 50 cents per pound and clay costs approximately 5 cents per pound. The density of polyethylene is 0.95 g/cm3 and that of clay is 2.4 g/cm3. Figure 16.6 The effect of clay on the properties of polyethylene. ©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license. 19 Example 16.4 SOLUTION In 1000 cm3 of composite parts, there are 350 cm3 of clay and 650 cm3 of polyethylene in the composite, or: The cost of materials is: 20 2 volume fraction clay.67 lb polyethylene.Example 16.4 SOLUTION (Continued) Suppose that weight is critical. then (using the same method as above) we find that we need 1. The composite’s density is: If we use only 0.06 lb clay and 1. The cost of materials is now: The density of the composite is: 21 . Figure 16.7 Microstructure of an aluminum casting alloy reinforced with silicon carbide particles. Lester B. In this case.) 22 . Knight Cost Metals Inc. the reinforcing particles have segregated to interdendritic regions of the casting ( 125). (Courtesy of David Kennedy. 23 .The tensile strength of a fiberreinforced composite (TSc) depends on the bonding between the fibers and the matrix.3 Fiber-Reinforced Composites  The Rule of Mixtures in Fiber-Reinforced Composites  Strength of Composites .Section 16. the modulus of elasticity is given by the rule of mixtures. Inc. Figure 16. 24 . a division of Thomson Learning. Thomson Learning ™ is a trademark used herein under license.8 The stress-strain curve for a fiber-reinforced composite. At low stresses (region l).©2003 Brooks/Cole. the matrix deforms and the rule of mixtures is no longer obeyed. At higher stresses (region ll). We use the symbol ‘‘  ’’ for stress to distinguish it from the symbol used for conductivity.5 Rule of Mixtures for Composites: Stress Parallel to Fibers Derive the rule of mixtures (Equation 16.Example 16.5) for the modulus of elasticity of a fiber-reinforced composite when a stress (  ) is applied along the axis of the fibers. Example 16.5 SOLUTION The total force acting on the composite is the sum of the forces carried by each constituent: Since F = σA: Fc = Fm + Ff 25 . σ = εE. Therefore: If the fibers are rigidly bonded to the matrix. the area fraction equals the volume fraction f : From Hooke’s law. both the fibers and the matrix must stretch equal amounts (isostrain conditions): 26 .Example 16.5 SOLUTION (Continued) If the fibers have a uniform cross-section. Example 16. instead.6 Modulus of Elasticity for Composites: Stress Perpendicular to Fibers Derive the equation for the modulus of elasticity of a fiberreinforced composite when a stress is applied perpendicular to the axis of the fiber (Equation 16-7). whereas the stresses in each component are equal (iso-stress conditions): 27 .Example 16. the weighted sum of the strains in each component equals the total strain in the composite.6 SOLUTION The strains are no longer equal. 28 .Example 16.7 Boron Aluminum Composites Boron coated with SiC(or Borsic) reinforced aluminum containing 40 vol% fibers is an important hightemperature. Estimate the density. and tensile strength parallel to the fiber axis. modulus of elasticity. lightweight composite material. Also estimate the modulus of elasticity perpendicular to the fibers. a division of Thomson Learning. 29 .9 The influence of volume percent boron-coated SiC (Borsic) fibers on the properties of Borsic-reinforced aluminum parallel to the fibers (for Example 16.©2003 Brooks/Cole.7). Inc. Figure 16. Thomson Learning ™ is a trademark used herein under license. Example 16. From the rule of mixtures: Perpendicular to the fibers: 30 .7 SOLUTION The properties of the individual components are shown below. Example 16. Also estimate the modulus of elasticity perpendicular to the fibers.Example 16. and tensile strength parallel to the fiber axis.4  106 psi 31 .5  106 psi Enylon = 0.8 SOLUTION The modulus of elasticity for each component of the composite is: Eglass = 10.8 Nylon-Glass Fiber Composites Boron coated with SiC(or Borsic) reinforced aluminum containing 40 vol% fibers is an important hightemperature. modulus of elasticity. Estimate the density. lightweight composite material. Example 16. 32 . so: Almost all of the load is carried by the glass fibers.8 SOLUTION (Continued) Both the nylon and the glass fibers have equal strain if bonding is good. diameter. and the bonding between the fibers and the matrix.Section 16.4 Characteristics of Fiber-Reinforced Composites  Many factors must be considered when designing a fiberreinforced composite.The length of a fiber divided by its diameter. including the length. 33 . and properties of the fibers. the properties of the matrix. amount.  Delamination . orientation.Separation of individual plies of a fiberreinforced composite.  Aspect ratio . Thomson Learning™ is a trademark used herein under license.5. 34 . Inc. the volume fraction of glass fibers is about 0.10 Increasing the length of chopped E-glass fibers in an epoxy matrix increases the strength of the composite. In this example. a division of Thomson Learning.©2003 Brooks/Cole. Figure 16. 35 Figure 16. a division of Thomson Learning. Thomson Learning ™ is a trademark used herein under license.©2003 Brooks/Cole.11 Effect of fiber orientation on the tensile strength of Eglass fiber-reinforced epoxy composites. Inc. . ©2003 Brooks/Cole. a division of Thomson Learning. Thomson Learning ™ is a trademark used herein under license. a 0°/+45°/90° composite is formed. In this case. 36 . Figure 16. Inc.12 (a) Tapes containing aligned fibers can be joined to produce a multi-layered different orientations to produce a quasi-isotropic composite. 37 .©2003 Brooks/Cole. Thomson Learning™ is a trademark used herein under license. Figure 16.13 A three-dimensional weave for fiberreinforced composites. Inc. a division of Thomson Learning. 38 . a division of Thomson Learning. . Thomson Learning ™ is a trademark used herein under license.14 Comparison of the specific strength and specific modulus of fibers versus metals and polymers. 39 Figure 16.©2003 Brooks/Cole. Inc. 15 The structure of KevlarTM.©2003 Brooks/Cole. Thomson Learning™ is a trademark used herein under license. Inc. a division of Thomson Learning. Figure 16. The fibers are joined by secondary bonds between oxygen and hydrogen atoms on adjoining chains. 40 . The specific modulus of the current 7075-T6 alloy is: 41 . Example 16.Example 16. yet maintain the same specific modulus. Design a material for the panel that will reduce weight.9 Design of an Aerospace Composite We are now using a 7075-T6 aluminum alloy (modulus of elasticity of 10  106 psi) to make a 500-pound panel on a commercial aircraft. Experience has shown that each pound reduction in weight on the aircraft reduces the fuel consumption by 500 gallons each year. and will be economical over a 10-year lifetime of the aircraft.9 SOLUTION let’s consider using a boron fiber-reinforced Al-Li alloy in the T6 condition. modulus of elasticity. 42 . about $375.Example 16.00 per gallon.500 gal per year. or $3.9 SOLUTION If we use 0. or (500 gal/lb)(375 lb) = 187. At about $2.75 million over the 10-year aircraft lifetime. and specific modulus of the composite are: If the specific modulus is the only factor influencing the design of the component. giving a component weight of 125 pounds rather than 500 pounds.000 in fuel savings could be realized each year. the thickness of the part might be reduced by 75%. then the density.6 volume fraction boron fibers in the composite. The weight savings would then be 375 pounds. 9. Vol. 1985. (From Metals Handbook. Poor bonding causes much of the fracture surface to follow the interface between the metal matrix and the carbon tows ( 3000). American Society for Metals..Figure 16.) 43 . 9th Ed.16 Scanning electron micrograph of the fracture surface of a silver-copper alloy reinforced with carbon fibers. Process for producing fiber-reinforced composites in which continuous fibers are wrapped around a form or mandrel.  Filament winding .5 Manufacturing Fibers and Composites  Chemical vapor deposition .A method for producing composites containing mats or continuous fibers. 44 .  Pultrusion . leaving behind a carbon fiber of high strength. Also known as pyrolizing.Driving off the non-carbon atoms from a polymer fiber.  Carbonizing .Section 16.Method for manufacturing materials by condensing the material from a vapor onto a solid substrate. Inc.©2003 Brooks/Cole. a division of Thomson Learning. Thomson Learning™ is a trademark used herein under license. Figure 16. 45 .17 Methods for producing (a) boron and (b) carbon fibers. 18 Photomicrographs of two fiber-reinforced composites: (a) In Borsic fiber-reinforced aluminum. R. 9th Ed.Figure 16.) 46 . American Society for Metals. (Courtesy of Dr. (From Metals Handbook.) (b) In this microstructure of a ceramic-fiber–ceramic-matrix composite. 9. silicon carbide fibers are used to reinforce a silicon nitride matrix. The SiC fiber is vapor-deposited on a small carbon precursor filament ( 125). Bhatt. Vol.. NASA Lewis Research Center. the fibers are composed of a thick layer of boron deposited on a smalldiameter tungsten filament ( 1000).T. 1985. . Thomson Learning ™ is a trademark used herein under license.©2003 Brooks/Cole. a division of Thomson Learning.19 The effect of heattreatment temperature on the strength and modulus of elasticity of carbon fibers. Inc. 47 Figure 16. ©2003 Brooks/Cole. Figure 16. Thomson Learning ™ is a trademark used herein under license. Inc. a division of Thomson Learning. 48 .20 A scanning electron micrograph of a carbon tow containing many individual carbon filaments (x200). 49 . a division of Thomson Learning. Inc. Thomson Learning ™ is a trademark used herein under license.21 Production of fiber tapes by encasing fibers between metal cover sheets by diffusion bonding.©2003 Brooks/Cole. Figure 16. (b) pressure bag molding.22 Producing composite shapes in dies by (a) hand lay-up. 50 . Figure 16. a division of Thomson Learning. Inc.©2003 Brooks/Cole. and (c) matched die molding. Thomson Learning™ is a trademark used herein under license. 23 Producing composite shapes by filament winding. a division of Thomson Learning.©2003 Brooks/Cole. Figure 16. Thomson Learning ™ is a trademark used herein under license. 51 . Inc. Thomson Learning ™ is a trademark used herein under license. 52 .24 Producing composite shapes by pultrusion. Inc. Figure 16. a division of Thomson Learning.©2003 Brooks/Cole. strengthened by metal or ceramic fibers. metal.  Ceramic-Matrix Composites . or ceramic fibers.The advanced composites normally are polymer–matrix composites reinforced with high-strength polymer.6 Fiber-Reinforced Systems and Applications  Advanced Composites .Section 16.These materials. 53 .Composites containing ceramic fibers in a ceramic matrix are also finding applications. provide hightemperature resistance.  Metal-Matrix Composites . a division of Thomson Learning. 54 .25 A comparison of the specific modulus and specific strength of several composite materials with those of metals and polymers. Thomson Learning™ is a trademark used herein under license. Inc. ©2003 Brooks/Cole.Figure 16. 55 . Thomson Learning ™ is a trademark used herein under license.26 The specific strength versus temperature for several composites and metals. Inc. 56 Figure 16. a division of Thomson Learning.©2003 Brooks/Cole. . 57 . (b) Tim is plated onto Nb-Cu composite wired. Thomson Learning™ is a trademark used herein under license.27 The manufacturer of composite super-conductor wires: (a) Niobium wire is surrounded with copper during forming. a division of Thomson Learning.©2003 Brooks/Cole. (c) Tin diffuses to niobium to produce the Nb3Sn-Cu composite. Figure 16. Inc. Thomson Learning ™ is a trademark used herein under license.©2003 Brooks/Cole. Figure 16.28 A comparison of the specific strength of various carbon-carbon composites with that of other hightemperature materials relative to temperature. 58 . a division of Thomson Learning. Inc. 59 . 1985.) (b) Bridging of some fibers across a crack enhances the toughness of a ceramic-matrix composite (unknown magnification). 9th Ed..Figure 16.29 Two failure modes in ceramic-ceramic composites: (a) Extensive pull-out of SiC fibers in a glass matrix provides good composite toughness (x20). Vol. (From Metals Handbook. (From Journal of Metals.) 60 . 9. May 1991. American Society for Metals. 000 psi. Epoxy costs about $0. The strut is 10 ft long and. it should stretch no more than 0.10 in.Example 16. the strut will stretch an extra amount but may not catastrophically fracture.80/lb and has a modulus of elasticity of 500. 61 . 12. If the fibers should happen to break.000 psi. when a force of 500 pounds is applied. We want to assure that the stress acting on the strut is less than the yield strength of the epoxy matrix.10 Design of a Composite Strut Design a unidirectional fiber-reinforced epoxy-matrix strut having a round cross-section. E = 77  106 psi. the density is 1. An area of 0.Example 16.10 SOLUTION For high modulus carbon fibers.5  106 psi is: The volume fraction of epoxy remaining is 0. The minimum volume fraction of carbon fibers needed to give a composite modulus of 14.817 times the total cross-sectional area of the strut must support a 500-lb load with no more than 12.000 psi if all of the fibers should fail: 62 .9 g/cm3 = 0. and the cost is about $30/lb.817.0686 lb/in.3. ) Our design. therefore.-diameter strut containing 0. (This calculation does not. they permit the lightest weight and the lowest material cost strut. is to use a 0.10 SOLUTION (Continued) Although the carbon fibers are the most expensive. 63 .255-in. take into consideration the costs of manufacturing the strut.183 volume fraction high modulus carbon fiber.Example 16. however. Some properties of the laminar composite materials parallel to the lamellae are estimated from the rule of mixtures.Section 16. 64 . (b) explosive bonding.7 Laminar Composite Materials  Rule of Mixtures .(a) roll bonding. and (d) brazing.  Producing Laminar Composites . (c) coextrusion. 65 . and (c) coextrusion. a division of Thomson Learning. Figure 16. Thomson Learning ™ is a trademark used herein under license. and (d) brazing.30 Techniques for producing laminar composites: (a) roll bonding. Inc.©2003 Brooks/Cole. (b) explosive bonding. 66 .8 Examples and Applications of Laminar Composites  Laminates .Section 16.  Cladding .A laminar composite material produced by joining two strips of metal with different thermal expansion coefficients.A laminar composite produced when a corrosion-resistant or high-hardness layer of a laminar composite formed onto a less expensive or higherstrength backing.  Bimetallic .Laminates are layers of materials joined by an organic adhesive. making the material sensitive to temperature changes. a division of Thomson Learning. which has potential for aerospace applications. Figure 16.©2003 Brooks/Cole.31 Schematic diagram of an aramid-aluminum laminate. Inc. Thomson Learning™ is a trademark used herein under license. Arall. 67 . A lightweight but stiff assembly of aluminum strip joined and expanded to form the core of a sandwich structure.Section 16. 68 .A composite material constructed of a lightweight. low-density material surrounded by dense. solid layers.  Honeycomb .9 Sandwich Structures  Sandwich . The sandwich combines overall light weight with excellent stiffness. Figure 16. (b) can be joined to two face sheets by means of adhesive sheets. strong honeycomb sandwich structure. 69 . a division of Thomson Learning. Thomson Learning™ is a trademark used herein under license. (c) producing an exceptionally lightweight yet stiff.©2003 Brooks/Cole. Inc.32 (a) A hexagonal cell honeycomb core. 70 .33 In the corrugation method for producing a honeycomb core. Inc.©2003 Brooks/Cole. The corrugated sheets are joined together with adhesive and then cut to the desired thickness. the material (such as aluminum) is corrugated between two rolls. 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