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Foundations of Materials Science and Engineering Lecture Note 7(Chapter 12 Composite Materials) May 6, 2013

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Foundations of Materials Science and Engineering Lecture Note 7(Chapter 12 Composite Materials) May 6, 2013 Foundations of Materials Science and Engineering Lecture Note 7(Chapter 12 Composite Materials) May 6, 2013 Kwang Kim Yonsei University [email protected] 39 8 7 34 53 Y O N Se I 88.91 16.00 14.01 78.96 126.9 Introduction • What are the classes and types of composites? • What are the advantages of using composite materials? • Mechanical properties of composites • How do we predict the stiffness and strength of the various types of composites? • Applications Introduction • Combination of two or more individual materials • A composite material is a material system, a mixture or combination of two or more micro or macroconstituents that differ in form and composition and do not form a solution. • Multiphase materials with chemically different phases and distinct interfaces • Design goal: obtain a more desirable combination of properties (principle of combined action) e.g., High-strength/light-weight, low cost, environmentally resistant • Properties of composite materials can be superior to its individual components. • Examples: Fiber reinforced plastics, concrete, asphalt, wood etc. Composite Characteristics • Matrix: – softer, more flexible and continuous part that surrounds the other phase. – transfer stress to other phases – protect phases from environment • Reinforcement (dispersed phase): – stiffer, high strength part (particles or fibers are the most common). – enhances matrix properties matrix: particles: ferrite (a) cementite (Fe C) (ductile) 3 (brittle) 60mm Spheroidite steel Composite Natural composites: - Wood: strong & flexible cellulose fibers in stiffer lignin (surrounds the fibers). - Bone: strong but soft collagen (protein) within hard but brittle apatite (mineral). - Certain types of rocks can also be considered as composites. Composite Synthetic composites: • Matrix phase: -- Purposes are to: woven - transfer stress to dispersed phase fibers - protect dispersed phase from environment -- Types: MMC, CMC, PMC 0.5 mm metal ceramic polymer cross section view • Dispersed phase: -- Purpose: 0.5 mm MMC: increase sy, TS, creep resist. CMC: increase K Reprinted with permission from Ic D. Hull and T.W. Clyne, An PMC: increase E, s , TS, creep resist. Introduction to Composite Materials, y 2nd ed., Cambridge University Press, -- Types: particle, fiber, structural New York, 1996, Fig. 3.6, p. 47. Composite Synthetic composites: Braided and High Strength unidirectional S-2 Glass and carbon fibers are used to produce forks with different stiffness Weight Reduction Design Flexibility Cost Performance Composite Synthetic composites: Pole-vaulting Lightweight : low density Buckling resistance : stiffness Strong : yield strength Minimal twisting Cost Composite Synthetic composites: Composite • Composite: -- Multiphase material that is artificially made. • Phase types: -- Matrix - is continuous -- Dispersed - is discontinuous and surrounded by matrix Composite Depends on: - properties of the matrix material. - properties of reinforcement material. - ratio of matrix to reinforcement. - matrix-reinforcement bonding/adhesion. - mode of fabrication. Classification of Composites Matrix-based: – Metal Matrix Composites (MMC) – Ceramic Matrix Composites (CMC) – Polymer Matrix Composites (PMC) Classification of Composites Reinforcement-based Classification of Composites Matrix of Composites Matrix Phase • can be metal, polymers, or ceramics. • typically metals and polymer because some ductility is often desired. • main functions of the matrix: -Hold fibers together. -Transmit and distribute external stress to the fibers. -Protect fibers from surface damage: abrasions, chemical reactions in CMCs, reinforcements are usually added to improve fracture toughness . Matrix-based: – Metal Matrix Composites (MMC) – Ceramic Matrix Composites (CMC) – Polymer Matrix Composites (PMC) Matrix of Composites Fiber-Matrix Interface 1. Molecular entanglement (interdiffusion): • Entanglement of molecules at the interface. • Especially important in fibers that are precoated with polymers. • Molecular conformation/structural and chemical aspects. 2. Electrostatic attraction • Depends on surface charge density. • e.g. glass fibers, polymers with chargeable groups. 3. Covalent bonding • Usually the strongest fiber matrix fiber-interaction. • The most important in many composites. 4. Mechanical adhesion • Interlocking of 2 rough surfaces • e.g. thermosetting resins Particle-Reinforced Composites Particle-reinforced Fiber-reinforced Structural • Examples: - Spheroidite matrix: particles: steel ferrite (a) cementite (Fe C) (ductile) 3 (brittle) 60mm - WC/Co matrix: particles: cemented cobalt WC (ductile, carbide (brittle, tough): hard) 600mm - Automobile matrix: particles: tire rubber rubber carbon (compliant) black (stiff) 0.75mm Particle-Reinforced Composites Particle-reinforced Fiber-reinforced Structural Concrete – gravel + sand + cement + water - Why sand and gravel? Sand fills voids between gravel particles Reinforced concrete – Reinforce with steel rebar or remesh - increases strength - even if cement matrix is cracked Prestressed concrete - Rebar/remesh placed under tension during setting of concrete - Release of tension after setting places concrete in a state of compression - To fracture concrete, applied tensile stress must exceed this compressive stress Posttensioning – tighten nuts to place concrete under compression threaded nut rod Particle-Reinforced Composites Particle-reinforced Fiber-reinforced Structural • Elastic modulus, Ec, of composites: -- two “rule of mixture” extremes: upper limit: Ecmm= VE + VpEp E(GPa) Data: 350 lower limit: Cu matrix 30 0 1 V V w/tungsten 250 = m + p particles 20 0 Ec Em Ep 150 020406080100vol% tungsten (Cu) (W) • Application to other properties: -- Electrical conductivity, e: Replace E’s in equations with e’s. -- Thermal conductivity, k: Replace E’s in equations with k’s. Fiber-Reinforced Composites Particle-reinforced Fiber-reinforced Structural • Fibers very strong in tension – Provide significant strength improvement to the composite – Ex: fiber-glass - continuous glass filaments in a polymer matrix • Glass fibers – strength and stiffness • Polymer matrix – holds fibers in place – protects fiber surfaces – transfers load to fibers Fiber-Reinforced Composites Particle-reinforced Fiber-reinforced Structural Fiber Phase – Smaller diameter fiber is stronger than bulk in most materials Whiskers – very thin single crystals that have extremely large aspect ratios. – high degree of crystallinity and virtually flaw free – exceptionally high strength. – usually extremely expensive. – some whisker materials: graphite, SiC, silicon nitride, aluminum oxide. Fibers – polycrystalline or amorphous. – typically: polymers or ceramics (polymer aramids, glass, carbon, boron, SiC… Fine Wires – relatively large diameter, often metal wires. – e.g. steel, molybdenum, Fiber-Reinforced Composites Particle-reinforced Fiber-reinforced Structural Fiber-Reinforced Composites Particle-reinforced Fiber-reinforced Structural • Aligned Continuous fibers • Examples: -- Metal: g'(Ni3Al)-a(Mo) -- Ceramic: Glass w/SiC fibers by eutectic solidification. formed by glass slurry matrix: a (Mo) (ductile) Eglass = 76 GPa; ESiC = 400 GPa. (a) fracture surface 2mm From F.L. Matthews and R.L. Rawlings, Composite Materials; Engineering and fibers: g’ (Ni Al) (brittle) Science, Reprint ed., CRC Press, Boca 3 (b) Raton, FL, 2000. (a) Fig. 4.22, p. 145 (photo by J. Davies); (b) Fig. 11.20, p. 349 From W. Funk and E. Blank, “Creep deformation of (micrograph by H.S. Kim, P.S. Rodgers, and Ni3Al-Mo in-situ composites", Metall. Trans. A Vol. R.D. Rawlings). Used with permission of 19(4), pp. 987-998, 1988. Used with permission. CRC Press, Boca Raton, FL. Fiber-Reinforced Composites Particle-reinforced Fiber-reinforced Structural • Discontinuous fibers, random in 2 dimensions • Example: Carbon-Carbon C fibers: -- fabrication process: very stiff - carbon fibers embedded very strong (b) in polymer resin matrix, 500 m C matrix: less stiff - polymer resin pyrolyzed view onto plane less strong at up to 2500ºC. fibers lie -- uses: disk brakes, gas (a) in plane turbine exhaust flaps, missile nose cones. Adapted from F.L. Matthews and R.L. Rawlings, Composite Materials; Engineering and Science, Reprint ed., CRC • Other possibilities: Press, Boca Raton, FL, 2000. (a) Fig. 4.24(a), p. 151; (b) Fig. 4.24(b) p. 151. (Courtesy I.J. Davies) Reproduced with -- Discontinuous, random 3D permission of CRC Press, Boca Raton, FL. -- Discontinuous, aligned Fiber-Reinforced Composites Fiber-Reinforced Composites Fiber-Reinforced Composites Fiber-Reinforced Composites Fiber-Reinforced Composites Fiber-Reinforced Composites Fiber-Reinforced Composites Fiber-Reinforced Composites Fiber-Reinforced Composites Fiber-Reinforced Composites Fiber-Reinforced Composites Fiber-Reinforced Composites Fiber-Reinforced Composites Fiber-Reinforced Composites Fiber-Reinforced Composites Particle-reinforced Fiber-reinforced Structural • Critical fiber length for effective stiffening & strengthening: fiber ultimate tensile strength fiber diameter d fiber length f 2 shear strength of c fiber-matrix interface • Ex: For fiberglass, common fiber length > 15 mm needed • For longer fibers, stress transference from matrix is more efficient Short, thick fibers: Long, thin fibers: d d fiber length f fiber length f 2c 2c Low fiber efficiency High fiber efficiency Classification of Fiber-Reinforced Composites Composite Production Methods (i) Pultrusion • Continuous fibers pulled through resin tank to impregnate
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