CHAPTER. Composite Materials

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1 CHAPTER 16 Composite Materials 1

2 Chapter 16: Composites ISSUES TO ADDRESS... What are the classes and types of composites? What are the advantages of using composite materials? How do we predict the stiffness and strength of the various types of composites? 2

3 Content 16.1 Introduction 16.2 Large-Particle Composites 16.3 Dispersion-Strengthened Composites 16.4 Influence of Fiber Length 16.5 Influence of Fiber Orientation and Concentration 16.6 The Fiber Phase 16.7 The Matrix Phase 16.8 Polymer-Matrix Composites 16.9 Metal-Matrix Composites Ceramic-Matrix Composites Carbon Carbon Composites Hybrid Composites Processing of Fiber-Reinforced Composites Laminar Composites Sandwich Panels

4 1. Introduction Every material is composite at one or the other level 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. Reinforcement + matrix Properties of composite materials can be superior to its individual components. Examples: Fiber reinforced plastics, concrete, asphalt, wood etc.

5 Composite Combination of two or more individual materials Composite materials (or composites for short) are engineered materials made from two or more constituent materials with significantly different physical or chemical properties and which remain separate and distinct on a macroscopic level within the finished structure. Design goal: obtain a more desirable combination of properties (principle of combined action) e.g., low density and high strength 5

7 Terminology/Classification Composite: -- Multiphase material that is artificially made. Phase types: -- Matrix - is continuous -- Dispersed - is discontinuous and surrounded by matrix 7

phase: -- Purpose: MMC: increase s y, TS, creep resist.

8 Terminology/Classification Matrix phase: -- Purposes are to: - transfer stress to dispersed phase - protect dispersed phase from environment -- Types: MMC, CMC, PMC metal ceramic polymer Dispersed phase: -- Purpose: MMC: increase s y, TS, creep resist. CMC: increase K Ic PMC: increase E, s y, TS, creep resist. -- Types: particle, fiber, structural woven fibers cross section view 0.5 mm 0.5 mm 8

9 Classification of Composites Composites Particle-reinforced Fiber-reinforced Structural Largeparticle Dispersionstrengthened Continuous (aligned) Discontinuous (short) Laminates Sandwich panels Aligned Randomly oriented 9

(brittle) - WC/Co cemented carbide matrix: cobalt (ductile,

10 Classification: Particle-Reinforced (i) Particle-reinforced Fiber-reinforced Structural Examples: - Spheroidite steel matrix: ferrite (a) (ductile) 60 mm particles: cementite ( Fe 3 C ) (brittle) - WC/Co cemented carbide matrix: cobalt (ductile, tough) : particles: WC (brittle, hard) 600 mm - Automobile tire rubber matrix: rubber (compliant) 0.75 mm particles: carbon black (stiff) 10

11 Classification: Particle-Reinforced (ii) 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 nut threaded rod 11

12 Classification: Particle-Reinforced (iii) Particle-reinforced Fiber-reinforced Structural Elastic modulus, E c, of composites: -- two rule of mixture extremes: upper limit: E c = V m E m + V p E p Data: Cu matrix w/tungsten particles E(GPa) lower limit: 1 = V m + V p E c E m E p (Cu) ( W) vol% tungsten Application to other properties: -- Electrical conductivity, s e : Replace E s in equations with s e s. -- Thermal conductivity, k: Replace E s in equations with k s. 12

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14 Concrete Flexible, economical, fire resistant, durable, fabricated on site. Low tensile strength, less ductile and shrinkable. Concrete is a ceramic composite composed of coarse granular material embedded in hard matrix of cement paste. Concrete = 7-15% Portland cement, 14-21% water, ½ - 8% air, 24-30% fine aggregate and 31-51% coarse aggregate.

15 4. Classification: Fiber-Reinforced (i) 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 15

w/sic fibers formed by glass slurry E glass

16 Classification: Fiber-Reinforced (iii) Particle-reinforced Fiber-reinforced Structural Aligned Continuous fibers Examples: -- Metal: g'(ni 3 Al)-a(Mo) by eutectic solidification. matrix: a (Mo) (ductile) -- Ceramic: Glass w/sic fibers formed by glass slurry E glass = 76 GPa; E SiC = 400 GPa. (a) fracture surface 2 mm fibers: g (Ni 3 Al) (brittle) (b) 16

2500ºC. -- uses: disk brakes, gas turbine exhaust flaps, missile nose cones.

17 Classification: Fiber-Reinforced (iv) Particle-reinforced Fiber-reinforced Structural Discontinuous fibers, random in 2 dimensions Example: Carbon-Carbon -- fabrication process: - carbon fibers embedded in polymer resin matrix, - polymer resin pyrolyzed at up to 2500ºC. -- uses: disk brakes, gas turbine exhaust flaps, missile nose cones. Other possibilities: -- Discontinuous, random 3D -- Discontinuous, aligned (b) (a) 500 mm view onto plane C fibers: very stiff very strong C matrix: less stiff less strong fibers lie in plane 17

18 Classification: Fiber-Reinforced (v) Particle-reinforced Fiber-reinforced Structural Critical fiber length for effective stiffening & strengthening: fiber ultimate tensile strength s fiber length 2 f d c fiber diameter shear strength of 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: s fiber length 2 f d c Long, thin fibers: s fiber length 2 f d c Low fiber efficiency High fiber efficiency 18

19 Longitudinal direction 5. Fiber Alignment Transverse direction aligned continuous aligned random discontinuous 19

21 5. Composite Stiffness: Longitudinal Loading Continuous fibers - Estimate fiber-reinforced composite modulus of elasticity for continuous fibers Longitudinal deformation s c = s m V m + s f V f and c = m = f volume fraction isostrain E cl = E m V m + E f V f E cl = longitudinal modulus c = composite f = fiber m = matrix 21

22 Composite Stiffness: Transverse Loading In transverse loading the fibers carry less of the load c = m V m + f V f and s c = s m = s f = s 1 E ct V E m m Vf E f E E ct m E f V m E f V f E m isostress E ct = transverse modulus c = composite f = fiber m = matrix 22

23 Composite Stiffness Particle-reinforced Fiber-reinforced Structural Estimate of E cd for discontinuous fibers: -- valid when fiber length < 15 s fd c -- Elastic modulus in fiber direction: E cd = E m V m + KE f V f efficiency factor: -- aligned: K = 1 (aligned parallel) -- aligned: K = 0 (aligned perpendicular) -- random 2D: K = 3/8 (2D isotropy) -- random 3D: K = 1/5 (3D isotropy) 23

24 Composite Strength Particle-reinforced Fiber-reinforced Structural Estimate of * s cd for discontinuous fibers: 1. When l > l c * s cd s f* V f 1 l c s m (1 V f ) 2 l 2. When l < l c s c d * l c d V s (1 V ) f m f 24

25 6. Classification: Fiber-Reinforced (ii) Particle-reinforced Fiber-reinforced Structural Fiber Types Whiskers - thin single crystals - large length to diameter ratios graphite, silicon nitride, silicon carbide high crystal perfection extremely strong, strongest known very expensive and difficult to disperse Fibers polycrystalline or amorphous generally polymers or ceramics Ex: alumina, aramid, E-glass, boron, UHMWPE Wires metals steel, molybdenum, tungsten 25

26 table_16_04

27 Fibers for Reinforced-Plastic Composite Materials Three main types of synthetic fibers are used Glass: widely used, low cost Carbon: high strength, low density, high cost Aramid: aromatic polyamide fibers, high strength, low density, high cost

28 Glass Fibers for Reinforced Plastic Composite Materials Glass fiber reinforced plastic composite materials have high strength-weight ratio, good dimensional stability, good temperature and corrosion resistance and low cost E (electrical) Glass : 52-56% SiO 2, % Al 2 O 3, 16-25% CaO % B 2 O 3 Tensile strength = 3.44 GPa, E = 72.3 GPa S (high-strength) Glass : Used for military and aerospace application. 65% SiO % Al 2 O % MgO Tensile strength = 4.48 GPa, E = 85.4 GPa

29 Production of Glass Fibers Produced by drawing monofilaments from a furnace and gathering them to form a strand. Strands are held together with resinous binder. Properties: Density and strength are lower than carbon and aramid fibers. Higher elongation. Low cost and hence commonly used. 粗紗 ; 粗紡

30 Carbon Fibers for Reinforced Plastics Light weight, very high strength and high stiffness micrometer in diameter. Produced from polyacrylonitrile (PAN) and pitch. Steps: Stabilization: PAN fibers are stretched and oxidised in air at about C. Carbonization: Stabilized carbon fibers are heated in inert atmosphere at C which results in elimination of O,H and N resulting in increase of strength. Graphitization: Carried out at C and increases modulus of elasticity at the expense of strength Tensile strength = GPa, E = GPa, density = g/cc.

Aramid Fibers for Reinforcing Plastic Resins Aramid = aromatic polyamide fibers. Trade name is Kevlar Kevlar 29:- Low density, high strength, and used for ropes and cables.

31 Aramid Fibers for Reinforcing Plastic Resins Aramid = aromatic polyamide fibers. Trade name is Kevlar Kevlar 29:- Low density, high strength, and used for ropes and cables. Kevlar 49:- Low density, high strength and modulus and used for aerospace and auto applications. Hydrogen bonds bond fiber together. Used where resistance to fatigue, high strength and light weight is important.

32 7. The Matrix Phase All three basic material types are used for matrices, but the most common are polymers and metals Matrix phase normally performs three functions: binds the fibers together and transmits an externally applied load to the fibers protects the individual fibers from surface damage. prevents the propagation of cracks from fiber to fiber Fibrous reinforced composites are sometimes classified according to matrix type; within this scheme are three classifications: polymer-, metal-, and ceramic-matrix

Polyester resins: Cheaper than epoxy resins Applications: Boat hulls, auto and

33 Matrix Materials Unsaturated polyester and epoxy resins are the two important matrix materials. Polyester resins: Cheaper than epoxy resins Applications: Boat hulls, auto and aircraft applications Epoxy resins: Good strength, low shrinkage Commonly used matrix materials for carbon and aramid-fiber composite Fiberglass-polyester

34 8. Polymer-Matrix Composites (PMC) PMCs consist of a polymer resin as the matrix with fibers as the reinforcement medium. Polymer-matrix composites are the most common; they may be reinforced with glass, carbon, and aramid fibers.

35 Fiber Reinforced-Plastic Composites Fiber glass-reinforced polyester resins (GFRP): Higher the wt% of glass, stronger the reinforced plastic is. Nonparallel alignment of glass fibers reduces strength. Carbon fiber reinforced epoxy resins (CFRP): Carbon fiber contributes to rigidity and strength while epoxy matrix contributes to impact strength Polyimides, polyphenylene sulfides are also used. Exceptional fatigue properties. Carbon fiber epoxy material is laminated to meet strength requirements.

Example:- Aluminum alloy Boron fiber composite Boron fiber is made by depositing boron vapor on tungsten

37 9. Metal Matrix Composites (MMCs) Continuous fiber reinforced MMCs: Continuous fibers are reinforced in metal matrix used in aerospace, auto industry and sports equipments. Example:- Aluminum alloy Boron fiber composite Boron fiber is made by depositing boron vapor on tungsten substrate. Boron fibers are hotpressed between aluminum foils. Tensile strength of Al6061 increases from 310 to 1417GPa and E increases from 69 to 231 GPa Tungsten filament Boron

Discontinuous fiber and particulate reinforced MMCs Particulate reinforced MMCs: Irregular shaped alumina and silicon carbide particulate are used.

38 Discontinuous fiber and particulate reinforced MMCs Particulate reinforced MMCs: Irregular shaped alumina and silicon carbide particulate are used. Particulate is mixed into molten aluminum and cast into ingots or billets. Al % SiC Tensile strength increased to 496 MPa E increased to 103 GPa Discontinuous fiber reinforced MMcs: Needle like SiC whiskers (1-3 micron diameter, micron in length) are mixed with metal powder. Mixture is consolidated by hot pressing and then forged or extruded. Tensile strength of Al 6061 increases to 480 MPa and E increases to 115 GPa

39 10. Ceramic-Matrix Composites (CMCs) Continuous fiber reinforced CMCs: SiC fibers are woven into mat and SiC is impregnated into fibrous mat by chemical vapor deposition. SiC fibers can be encapsulated by a glass ceramic. Used in heat exchanger tube and thermal protection system. Discontinuous and particulate reinforced CMCs: Fracture toughness is significantly increased. Fabricated by common process such as hot isolatic pressing.

40 Toughening Mechanisms in CMCs Toughening is due to fibers interfering with crack propagation. Crack deflection: Up on encountering reinforcement, crack is deflected making propagation more meandering. Crack bridging: Fibers bridge the crack and help to keep the cracks together. Fiber pullout: Friction caused by pulling out the fiber from matrix results in higher toughness.

41 11. Carbon-Carbon Composites Carbon carbon composites are composed of carbon fibers embedded in a pyrolyzed carbon matrix These materials are expensive and used in applications requiring high strengths and stiffness (that are retained at elevated temperatures), resistance to creep, and good fracture toughness

42 Carbon fibre-reinforced Carbon (abbreviated C/C) is a composite material consisting of carbon fibre reinforcement in a matrix of graphite. Carbon-carbon composites have a combination of properties that renders them uniquely superior in operating temperatures as high as 2800 C. The combination of these properties make this material suitable for re-entry applications, rocket motors, and aircraft brakes. The more commercial application of this material is in the brake pads or racing cars.

43 12. Hybrid Composites The hybrid composites contain at least two different fiber types. Using hybrids it is possible to design composites having better all-around sets of properties.

13. Composite Production Methods (i) Pultrusion Continuous fibers pulled through resin tank to impregnate fibers with thermosetting resin Impregnated fibers pass through steel die that preforms

44 13. Composite Production Methods (i) Pultrusion 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 curing die that is precision machined to impart final shape heated to initiate curing of the resin matrix Fig , Callister & Rethwisch 8e.

45 Closed Mold Process Compression and injection molding: Same as in polymers except that the fiber reinforcement is mixed with resin. Sheet molding compound process: Highly automated continuous molding process. Continuous strand fiberglass roving is chopped and deposited on a layer of resin-filler paste. Another layer of paste is deposited on first layer. Sandwich is compacted and rolled into rolls.

Sheet Molding (Cont..) The rolled up sheet is stored in a maturation room for 1-4 days. The sheets are cut into proper size and pressed in hot mold (149 0 C) to form final product.

46 Sheet Molding (Cont..) The rolled up sheet is stored in a maturation room for 1-4 days. The sheets are cut into proper size and pressed in hot mold (149 0 C) to form final product. Efficient, quick, good quality and uniformity. Continuous protrusion: Continuous strand fibers are impregnated in resin bath, fed into heated die and drawn. Used to produce beams, channels, and pipes.

Composite Production Methods (ii) Filament Winding Continuous reinforcing fibers are accurately positioned in a predetermined pattern to form a hollow (usually cylindrical) shape Fibers are fed

47 Composite Production Methods (ii) Filament Winding Continuous reinforcing fibers are accurately positioned in a predetermined pattern to form a hollow (usually cylindrical) shape Fibers are fed through a resin bath to impregnate with thermosetting resin Impregnated fibers are continuously wound (typically automatically) onto a mandrel After appropriate number of layers added, curing is carried out either in an oven or at room temperature The mandrel is removed to give the final product

Open Mold Process for Fiber Reinforced Plastics Hand lay-up process: Gel coat is applied to open mold. Fiberglass reinforcement is placed in the mold.

48 Open Mold Process for Fiber Reinforced Plastics Hand lay-up process: Gel coat is applied to open mold. Fiberglass reinforcement is placed in the mold. Base resin mixed with catalysts is applied by pouring brushing or spraying. Spray-up process: Continuous strand roving is fed by chopper and spray gun and chopped roving and catalyst resin is deposited in the mold.

Vacuum Bag-Autoclave and Filament Winding Vacuum bag-autoclave process: Long thin sheet or prepeg carbon-fiber epoxy material is laid on the table. The sheet is cut and laminate is constructed.

49 Vacuum Bag-Autoclave and Filament Winding Vacuum bag-autoclave process: Long thin sheet or prepeg carbon-fiber epoxy material is laid on the table. The sheet is cut and laminate is constructed. Laminate is put in vacuum bag to remove entrapped air and cured in autoclave. Filament winding: Fiber reinforcement is fed through resin bath and wound around suitable mandrel. Mandrel is cured and mold part is stripped from mandrel.

14. 15. Classification: Structural Particle-reinforced Fiber-reinforced Structural Laminates - -- stacked and bonded fiber-reinforced sheets - stacking

50 Classification: Structural Particle-reinforced Fiber-reinforced Structural Laminates - -- stacked and bonded fiber-reinforced sheets - stacking sequence: e.g., 0º/90º - benefit: balanced in-plane stiffness Sandwich panels -- honeycomb core between two facing sheets - benefits: low density, large bending stiffness face sheet adhesive layer honeycomb 50

51 Sandwich Structure Composite materials are also made by sandwiching a core material between two thin outer layers. Honeycomb sandwich: Fabricated by adhesively bonding aluminum alloy face sheets to aluminum alloy honeycomb core sections. Stiff, rigid strong and used in aerospace applications. Clad metal structure: Metal core and thin outer layer of other metal are bonded by hot rolling. Example: 10 cent and 25 cent coins have cladding of Cu -25% Ni alloy over less expensive Cu core.

52 CMCs: Increased toughness Force particle-reinf un-reinf fiber-reinf Bend displacement MMCs: Increased creep resistance Composite Benefits ss (s -1 ) Al Al w/sic whiskers E(GPa) PMCs: Increased E/r PMCs ceramics metal/ metal alloys polymers Density, r [mg/m 3 ] s (MPa) 52

53 Nanocomposites in tennis balls

54 Summary 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 K Ic -- PMC: enhanced E/r, s y, TS/r 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 54

55 upper lower tableun_16_p666

56 Common use and natural composites Concrete Asphalt and asphalt mixes Wood Sandwich structures Bone: a natural composite material

57 Portland Cement Production: Lime (CaO), Silica (SiO 2 ), alumina (Al 2 O 3 ) and iron oxide (Fe 2 O 3 ) are raw materials. Raw materials are crushed, ground and proportional for desired composition and blended. Mixture is fed into rotary kiln and heated to C and then cooled and pulverized. Chemical Composition:

58 Asphalt and Asphalt Mixes Asphalt is a bitumen Hydrocarbon % C, 9-10% H, 2-8% O, 0.5-7% sulfur and traces of impurities. Asphalt + Aggregate Asphalt mixture used primarily for paving roads. Obtained primarily from petroleum refining but also from rocks and surface deposits. Angular aggregate bonds better with asphalt and produces better skid resistance on pavements.

Wood Wood is naturally occurring composite with polymeric material lignin and other organic compounds. Nonhomogenous and highly anisotropic.

59 Wood Wood is naturally occurring composite with polymeric material lignin and other organic compounds. Nonhomogenous and highly anisotropic. Consists of layers: Outer bark provides protection Inner bark moist and soft, carries food Cambium layer forms wood and bark cells Sapwood carries wood and sap. Heartwood dead, dark and provides strength Pith Soft tissue at the center

Macrostructure Bone: a Natural Composite Material - The microstructure of bone is complex, containing many constituents in both the micro- and the nanorange

- Although different bones in the body have different properties and structure, the structure of all bones at the macroscopic level may be divided into two

49) - The cortical portion is dense (ivory like) and comprises the outer structure or cortex of the bone (Fig. 12.

60 Macrostructure Bone: a Natural Composite Material - The microstructure of bone is complex, containing many constituents in both the micro- and the nanorange scale. - Although different bones in the body have different properties and structure, the structure of all bones at the macroscopic level may be divided into two distinct types of osseous (bony) tissues: (1) cortical or compact and (2) cancellous or trabecular (Fig ) - The cortical portion is dense (ivory like) and comprises the outer structure or cortex of the bone (Fig a) - The internal portion of the bone consists of the cancellous tissue, which is composed of thin plates or trabeculae loosely meshed and porous (Fig b). The pores in the cancellous region are filled with red marrow. (a) Fig A longitudinal section through an adult femur. Fig (a) The SEM image of the cortical bone from a human tibia. (b) A photomicrograph of cancellous bone (b)

Chapter 16: Composites

Chapter 16: Composites ISSUES TO ADDRESS... What are the classes and types of composites? What are the advantages of using composite materials? How do we predict the elastic modulus for composites with