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Foundations of 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 is a material system, a 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: reinforced plastics, , , etc. Composite Characteristics

• Matrix: – softer, more flexible and continuous part that surrounds the other phase. – transfer to other phases – protect phases from environment

• Reinforcement (dispersed phase): – stiffer, high strength part (particles or are the most common). – enhances matrix properties

matrix: particles: ferrite (a) cementite (Fe C) (ductile) 3 (brittle) 60mm

Spheroidite Composite

Natural composites:

- Wood: strong & flexible cellulose fibers in stiffer (surrounds the fibers).

- Bone: strong but soft (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 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 and fibers are used to produce forks with different stiffness

Weight Reduction Design Flexibility Cost Composite

Synthetic composites:

Pole-vaulting

Lightweight : low Buckling resistance : stiffness Strong : 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, , or . • typically 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 .

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 + + water - Why sand and gravel? Sand fills voids between gravel particles – 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

• , 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: , SiC, silicon nitride, aluminum oxide. Fibers – polycrystalline or amorphous. – typically: polymers or ceramics (polymer , glass, carbon, , 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 - 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 , 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 2c 2c

Low fiber efficiency High fiber efficiency Classification of Fiber-Reinforced Composites

Composite Production Methods (i) • Continuous fibers pulled through resin tank to impregnate fibers with thermosetting resin • Impregnated fibers pass through steel die that preforms to the desired shape • Preformed stock passes through a die that is – precision machined to impart final shape – heated to initiate curing of the resin matrix Composites

• Composites types are designated by: -- the matrix material (CMC, MMC, PMC) -- the reinforcement (particles, fibers, structural) • Composite property benefits: -- MMC: enhanced E, s, creep performance -- CMC: enhanced KIc -- PMC: enhanced E/, sy, TS/ • Particulate-reinforced: -- Types: large-particle and dispersion-strengthened -- Properties are isotropic • Fiber-reinforced: -- Types: continuous (aligned) discontinuous (aligned or random) -- Properties can be isotropic or anisotropic • Structural: -- Laminates and sandwich panels Composite Benefits

• CMCs: Increased toughness • PMCs: Increased E/r Force 3 ceramics particle-reinf 10 E(GPa) PMCs 10 2 10 fiber-reinf metal/ 1 metal alloys un-reinf 0.1 polymers 0.01 Bend displacement 0.1 0.3 1 3 10 30 3 10 -4 Density, r [mg/m ] 6061 Al ess (s-1) • MMCs: 10 -6 Adapted from T.G. Nieh, "Creep rupture of a silicon- Increased carbide reinforced aluminum composite", Metall. Trans. A Vol. 15(1), pp. 139-146, 1984. Used with creep permission. 10 -8 6061 Al resistance w/SiC whiskers -10 s 10 (MPa) 20 30 50 100 200 Glass Fibers for Reinforced Plastic Composite Materials

• reinforced plastic composite materials have high strength-weight ratio, good dimensional stability, good temperature and corrosion resistance and low cost.

 ‘E’ Glass : 52-56% SiO2, + 12-16% Al2O3, 16-25% CaO + 8-13% B2O3  Tensile strength = 3.44 GPa, E = 72.3 GPa  ‘S” Glass : Used for military and aerospace application.

 65% SiO2 + 25% Al2O3 + 10% MgO  Tensile strength = 4.48 GPa, E = 85.4 GPa Production of Glass Fibers

• Produced by drawing monofilaments from a furnace and gathering them to form a strand. • Strands are held together with resinous . • Properties: Density and strength are lower than carbon and fibers. • Higher elongation. • Low cost and hence commonly used. Carbon Fibers for Reinforced Plastics

• Light weight, very high strength and high stiffness. • 7-10 micrometer in diameter. • Produced from polyacrylonitrile (PAN) and pitch. • Steps:  Stabilization: PAN fibers are stretched and oxidised in air at about 2000C.  Carbonization: Stabilized carbon fibers are heated in inert atmosphere at 1000-15000C which results in elimination of O,H and N resulting in increase of strength.  Graphitization: Carried out at 18000C and increases modulus of elasticity at the expense of strength • Tensile strength = 3.1-4.45 GPa, E = 193-241 GPa, density = 1-7-2.1 g/cc.