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