Composite Materials

Composite MaterialsComposite Materials

Ahmed W. MoustafaAhmed W. Moustafa

Lecture (1)Lecture (1)

COMPOSITE COMPOSITE MATERIALSMATERIALS Technology and Classification of Technology and Classification of

Composite MaterialsComposite Materials Metal Matrix CompositesMetal Matrix Composites Ceramic Matrix CompositesCeramic Matrix Composites Polymer Matrix CompositesPolymer Matrix Composites Guide to Processing Composite Guide to Processing Composite

MaterialsMaterials

Classification Scheme Classification Scheme for for Composite MaterialsComposite Materials1.1. Metal Matrix CompositesMetal Matrix Composites (MMCs) ‑ mixtures (MMCs) ‑ mixtures

of ceramics and metals, such as cemented of ceramics and metals, such as cemented carbides and other cermets carbides and other cermets

2.2. Ceramic Matrix CompositesCeramic Matrix Composites (CMCs) ‑ Al (CMCs) ‑ Al22OO33 and SiC imbedded with fibers to improve and SiC imbedded with fibers to improve properties, especially in high temperature properties, especially in high temperature applications applications – The least common composite matrixThe least common composite matrix

3.3. Polymer Matrix CompositesPolymer Matrix Composites (PMCs) ‑ (PMCs) ‑ thermosetting resins are widely used in PMCs thermosetting resins are widely used in PMCs – Examples: epoxy and polyester with fiber Examples: epoxy and polyester with fiber

reinforcement, and phenolic with powders reinforcement, and phenolic with powders

The Reinforcing Phase The Reinforcing Phase (Secondary Phase)(Secondary Phase) Function is to reinforce the primary phase Function is to reinforce the primary phase Imbedded phase is most commonly one of Imbedded phase is most commonly one of

the following shapes: the following shapes: – FibersFibers– ParticlesParticles– Flakes Flakes

In addition, the secondary phase can take In addition, the secondary phase can take the form of an infiltrated phase in a the form of an infiltrated phase in a skeletal or porous matrix skeletal or porous matrix – Example: a powder metallurgy part infiltrated Example: a powder metallurgy part infiltrated

with polymerwith polymer

Figure 9.1Figure 9.1 ‑ Possible physical shapes of imbedded phases in ‑ Possible physical shapes of imbedded phases in composite materials: (a) fiber, (b) particle, and (c) flakecomposite materials: (a) fiber, (b) particle, and (c) flake

FibersFibers

Filaments of reinforcing material, usually Filaments of reinforcing material, usually circular in cross‑sectioncircular in cross‑section

Diameters range from less than 0.0025 mm Diameters range from less than 0.0025 mm to about 0.13 mm, depending on material to about 0.13 mm, depending on material

Filaments provide greatest opportunity for Filaments provide greatest opportunity for strength enhancement of composites strength enhancement of composites – The filament form of most materials is The filament form of most materials is

significantly stronger than the bulk form significantly stronger than the bulk form – As diameter is reduced, the material becomes As diameter is reduced, the material becomes

oriented in the fiber axis direction and oriented in the fiber axis direction and probability of defects in the structure decreases probability of defects in the structure decreases significantlysignificantly

Continuous vs. Continuous vs. Discontinuous FibersDiscontinuous Fibers Continuous fibersContinuous fibers - very long; in theory, - very long; in theory,

they offer a continuous path by which a they offer a continuous path by which a load can be carried by the composite part load can be carried by the composite part

Discontinuous fibersDiscontinuous fibers (chopped sections of (chopped sections of continuous fibers) - short lengths (L/D = continuous fibers) - short lengths (L/D = roughly 100) roughly 100) – Important type of discontinuous fiber are Important type of discontinuous fiber are

whiskerswhiskers ‑ hair-like single crystals with ‑ hair-like single crystals with diameters down to about 0.001 mm (0.00004 diameters down to about 0.001 mm (0.00004 in.) with very high strength in.) with very high strength

Fiber Orientation – Fiber Orientation – Three CasesThree Cases One‑dimensionalOne‑dimensional reinforcement, in reinforcement, in

which maximum strength and stiffness which maximum strength and stiffness are obtained in the direction of the fiberare obtained in the direction of the fiber

PlanarPlanar reinforcement, in some cases in reinforcement, in some cases in the form of a two‑dimensional woven the form of a two‑dimensional woven fabricfabric

RandomRandom or three‑dimensional in which or three‑dimensional in which the composite material tends to the composite material tends to possess isotropic properties possess isotropic properties

Figure 9.3 ‑ Fiber orientation in composite materials: Figure 9.3 ‑ Fiber orientation in composite materials:

(a) one‑dimensional, continuous fibers; (b) planar, continuous (a) one‑dimensional, continuous fibers; (b) planar, continuous fibers in the form of a woven fabric; and (c) random, fibers in the form of a woven fabric; and (c) random,

discontinuous fibersdiscontinuous fibers

Materials for FibersMaterials for Fibers

Fiber materials in fiber‑reinforced Fiber materials in fiber‑reinforced composites: composites: – Glass – most widely used filamentGlass – most widely used filament– Carbon – high elastic modulusCarbon – high elastic modulus– Boron – very high elastic modulusBoron – very high elastic modulus– Polymers - KevlarPolymers - Kevlar

– Ceramics – SiC and AlCeramics – SiC and Al22OO33

– Metals - steelMetals - steel The most important commercial use of The most important commercial use of

fibers is in polymer composites fibers is in polymer composites

Particles and FlakesParticles and Flakes

A second common shape of imbedded phase is A second common shape of imbedded phase is particulateparticulate, ranging in size from microscopic to , ranging in size from microscopic to macroscopic macroscopic

FlakesFlakes are basically two‑dimensional particles ‑ are basically two‑dimensional particles ‑ small flat platelets small flat platelets

The distribution of particles in the composite The distribution of particles in the composite matrix is random, and therefore strength and matrix is random, and therefore strength and other properties of the composite material are other properties of the composite material are usually isotropic usually isotropic

Strengthening mechanism depends on particle Strengthening mechanism depends on particle size size

The InterfaceThe Interface There is always an There is always an interfaceinterface between constituent between constituent

phases in a composite material phases in a composite material For the composite to operate effectively, the For the composite to operate effectively, the

phases must bond phases must bond wherewhere they join at the interface they join at the interface

Figure 9.4 ‑ Interfaces between phases in a composite material: (a) direct bonding between primary and secondary phases

InterphaseInterphase In some cases, a third ingredient must be added In some cases, a third ingredient must be added

to achieve bonding of primary and secondary to achieve bonding of primary and secondary phases phases

Called an Called an interphaseinterphase, this third ingredient can be , this third ingredient can be thought of as an adhesive thought of as an adhesive

Figure 9.4 ‑ Interfaces between phases: (b) addition of a third ingredient to bond the primary phases and form an interphase

Figure 9.4 ‑ Interfaces and interphases between phases in a Figure 9.4 ‑ Interfaces and interphases between phases in a composite material: (c) formation of an interphase by solution composite material: (c) formation of an interphase by solution of the primary and secondary phases at their boundaryof the primary and secondary phases at their boundary

Another InterphaseInterphase consisting of a solution of primary and secondary phases

Properties of Properties of Composite MaterialsComposite Materials

In selecting a composite material, an In selecting a composite material, an optimum combination of properties is optimum combination of properties is usually sought, rather than one particular usually sought, rather than one particular property property – Example: fuselage and wings of an aircraft must Example: fuselage and wings of an aircraft must

be lightweight and be strong, stiff, and tough be lightweight and be strong, stiff, and tough Several fiber‑reinforced polymers possess this Several fiber‑reinforced polymers possess this

combination of propertiescombination of properties

– Example: natural rubber alone is relatively weakExample: natural rubber alone is relatively weak Adding significant amounts of carbon black to NR Adding significant amounts of carbon black to NR

increases its strength dramatically increases its strength dramatically

Properties are Properties are Determined by Three Determined by Three Factors: Factors: 1.1. The materials used as component The materials used as component

phases in the compositephases in the composite

2.2. The geometric shapes of the The geometric shapes of the constituents and resulting structure constituents and resulting structure of the composite systemof the composite system

3.3. The manner in which the phases The manner in which the phases interact with one another interact with one another

Figure 9.5 ‑ (a) Model of a fiber‑reinforced composite material Figure 9.5 ‑ (a) Model of a fiber‑reinforced composite material showing direction in which elastic modulus is being showing direction in which elastic modulus is being estimated by the rule of mixtures (b) Stress‑strain estimated by the rule of mixtures (b) Stress‑strain relationships for the composite material and its relationships for the composite material and its constituents. The fiber is stiff but brittle, while the matrix constituents. The fiber is stiff but brittle, while the matrix (commonly a polymer) is soft but ductile. (commonly a polymer) is soft but ductile.

Figure 9.6 ‑ Variation in elastic modulus and tensile strength Figure 9.6 ‑ Variation in elastic modulus and tensile strength as a function of direction of measurement relative to as a function of direction of measurement relative to longitudinal axis of carbon fiber‑reinforced epoxy composite longitudinal axis of carbon fiber‑reinforced epoxy composite

Fibers Illustrate Fibers Illustrate Importance of Geometric Importance of Geometric ShapeShape Most materials have tensile strengths several Most materials have tensile strengths several

times greater as fibers than in bulk times greater as fibers than in bulk By imbedding the fibers in a polymer matrix, By imbedding the fibers in a polymer matrix,

a composite material is obtained that avoids a composite material is obtained that avoids the problems of fibers but utilizes their the problems of fibers but utilizes their strengths strengths – The matrix provides the bulk shape to protect the The matrix provides the bulk shape to protect the

fiber surfaces and resist buckling fiber surfaces and resist buckling – When a load is applied, the low‑strength matrix When a load is applied, the low‑strength matrix

deforms and distributes the stress to the deforms and distributes the stress to the high‑strength fibershigh‑strength fibers

Other Composite Other Composite StructuresStructures Laminar composite structure – Laminar composite structure –

conventionalconventional Sandwich structureSandwich structure Honeycomb sandwich structureHoneycomb sandwich structure

Laminar Composite StructureLaminar Composite Structure Two or more layers bonded together in an integral Two or more layers bonded together in an integral

piecepiece Example: Example: plywoodplywood in which layers are the same in which layers are the same

wood, but grains are oriented differently to wood, but grains are oriented differently to increase overall strength of the laminated piece increase overall strength of the laminated piece

Figure 9.7 ‑ Laminar composite structures: (a) conventional laminar structure

Sandwich Structure – Foam CoreSandwich Structure – Foam CoreConsists of a relatively thick core of low Consists of a relatively thick core of low

density foam bonded on both faces to thin density foam bonded on both faces to thin sheets of a different material sheets of a different material

Figure 9.7 ‑ Laminar composite structures: (b) sandwich structure using foam core

Sandwich Structure – Honeycomb CoreSandwich Structure – Honeycomb Core An alternative to foam coreAn alternative to foam core Either foam or honeycomb achieves high Either foam or honeycomb achieves high

strength‑to‑weight and stiffness‑to‑weight ratiosstrength‑to‑weight and stiffness‑to‑weight ratios

Figure 9.7 ‑ Laminar composite structures: (c) sandwich structure using honeycomb core

Other Laminar Other Laminar Composite StructuresComposite Structures

Automotive tiresAutomotive tires - consists of multiple layers - consists of multiple layers bonded togetherbonded together

FRPsFRPs - multi‑layered fiber‑reinforced plastic panels - multi‑layered fiber‑reinforced plastic panels for aircraft, automobile body panels, boat hullsfor aircraft, automobile body panels, boat hulls

Printed circuit boardsPrinted circuit boards - layers of reinforced plastic - layers of reinforced plastic and copper for electrical conductivity and and copper for electrical conductivity and insulation insulation

Snow skisSnow skis - composite structures consisting of - composite structures consisting of layers of metals, particle board, and phenolic layers of metals, particle board, and phenolic plasticplastic

Windshield glassWindshield glass - two layers of glass on either - two layers of glass on either side of a sheet of tough plasticside of a sheet of tough plastic

Metal Matrix Metal Matrix Composites (MMCs)Composites (MMCs)

A A metalmetal matrix reinforced by a second matrix reinforced by a second phase phase

Reinforcing phases:Reinforcing phases:1.1. ParticlesParticles of ceramic (these MMCs are of ceramic (these MMCs are

commonly called commonly called cermetscermets))

2.2. FibersFibers of various materials: other metals, of various materials: other metals, ceramics, carbon, and boron ceramics, carbon, and boron

CermetsCermets

MMC with MMC with ceramicceramic contained in a contained in a metallic metallic matrixmatrix

The ceramic often dominates the mixture, The ceramic often dominates the mixture, sometimes up to 96% by volume sometimes up to 96% by volume

Bonding can be enhanced by slight Bonding can be enhanced by slight solubility between phases at elevated solubility between phases at elevated temperatures used in processing temperatures used in processing

Cermets can be subdivided into Cermets can be subdivided into 1.1. Cemented carbides – most commonCemented carbides – most common

2.2. Oxide‑based cermets – less commonOxide‑based cermets – less common

Cemented CarbidesCemented CarbidesOne or more One or more carbidecarbide compounds bonded in a compounds bonded in a

metallicmetallic matrixmatrix The term The term cermetcermet is not used for all of these is not used for all of these

materials, even though it is technically correct materials, even though it is technically correct Common cemented carbides are based on Common cemented carbides are based on

tungsten carbide (WC), titanium carbide (TiC), tungsten carbide (WC), titanium carbide (TiC), and chromium carbide (Crand chromium carbide (Cr33CC22) )

Tantalum carbide (TaC) and others are less Tantalum carbide (TaC) and others are less common common

Metallic binders: usually cobalt (Co) or nickel Metallic binders: usually cobalt (Co) or nickel (Ni) (Ni)

Figure 9.8 ‑ Photomicrograph (about 1500X) of cemented Figure 9.8 ‑ Photomicrograph (about 1500X) of cemented carbide with 85% WC and 15% Co (photo courtesy of carbide with 85% WC and 15% Co (photo courtesy of

Kennametal Inc.)Kennametal Inc.)

Figure 9.9 ‑ Typical plot of hardness and transverse Figure 9.9 ‑ Typical plot of hardness and transverse rupture strength as a function of cobalt contentrupture strength as a function of cobalt content

Applications of Applications of Cemented CarbidesCemented Carbides TungstenTungsten carbidecarbide cermets (Co binder) - cutting cermets (Co binder) - cutting

tools are most common; other: wire drawing tools are most common; other: wire drawing dies, rock drilling bits and other mining tools, dies, rock drilling bits and other mining tools, dies for powder metallurgy, indenters for dies for powder metallurgy, indenters for hardness testers hardness testers

Titanium carbideTitanium carbide cermets (Ni binder) - high cermets (Ni binder) - high temperature applications such as gas‑turbine temperature applications such as gas‑turbine nozzle vanes, valve seats, thermocouple nozzle vanes, valve seats, thermocouple protection tubes, torch tips, cutting tools for protection tubes, torch tips, cutting tools for steels steels

Chromium carbidesChromium carbides cermets (Ni binder) - gage cermets (Ni binder) - gage blocks, valve liners, spray nozzles, bearing seal blocks, valve liners, spray nozzles, bearing seal rings rings

Ceramic Matrix Ceramic Matrix Composites (CMCs)Composites (CMCs)A A ceramicceramic primary phase imbedded with a primary phase imbedded with a

secondary phase, which usually consists of fiberssecondary phase, which usually consists of fibers Attractive properties of ceramics: high stiffness, Attractive properties of ceramics: high stiffness,

hardness, hot hardness, and compressive hardness, hot hardness, and compressive strength; and relatively low density strength; and relatively low density

Weaknesses of ceramics: low toughness and bulk Weaknesses of ceramics: low toughness and bulk tensile strength, susceptibility to thermal cracking tensile strength, susceptibility to thermal cracking

CMCs represent an attempt to retain the CMCs represent an attempt to retain the desirable properties of ceramics while desirable properties of ceramics while compensating for their weaknessescompensating for their weaknesses

Polymer Matrix Polymer Matrix Composites (PMCs)Composites (PMCs)A A polymerpolymer primary phase in which a secondary primary phase in which a secondary

phase is imbedded as fibers, particles, or phase is imbedded as fibers, particles, or flakes flakes

Commercially, PMCs are more important than Commercially, PMCs are more important than MMCs or CMCs MMCs or CMCs

Examples: most plastic molding compounds, Examples: most plastic molding compounds, rubber reinforced with carbon black, and rubber reinforced with carbon black, and fiber‑reinforced polymers (FRPs) fiber‑reinforced polymers (FRPs)

FRPs are most closely identified with the FRPs are most closely identified with the term compositeterm composite

Fiber‑Reinforced Fiber‑Reinforced Polymers (FRPs)Polymers (FRPs)A PMC consisting of a A PMC consisting of a polymerpolymer matrixmatrix

imbedded with high‑strength imbedded with high‑strength fibersfibers Polymer matrix materials:Polymer matrix materials:

– Usually a Usually a thermosettingthermosetting (TS) plastic such as (TS) plastic such as unsaturated polyester or epoxyunsaturated polyester or epoxy

– Can also be Can also be thermoplasticthermoplastic (TP), such as (TP), such as nylons (polyamides), polycarbonate, nylons (polyamides), polycarbonate, polystyrene, and polyvinylchloride polystyrene, and polyvinylchloride

– Fiber reinforcement is widely used in Fiber reinforcement is widely used in rubberrubber products such as tires and conveyor belts products such as tires and conveyor belts

Fibers in PMCsFibers in PMCs

Various forms: discontinuous (chopped), Various forms: discontinuous (chopped), continuous, or woven as a fabric continuous, or woven as a fabric

Principal fiber materials in FRPs are glass, Principal fiber materials in FRPs are glass, carbon, and Kevlar 49 carbon, and Kevlar 49

Less common fibers include boron, SiC, and Less common fibers include boron, SiC, and AlAl22OO33, and steel , and steel

Glass (in particular E‑glass) is the most Glass (in particular E‑glass) is the most common fiber material in today's FRPs; its common fiber material in today's FRPs; its use to reinforce plastics dates from around use to reinforce plastics dates from around 1920 1920

Common FRP StructureCommon FRP Structure

Most widely used form of FRP is a Most widely used form of FRP is a laminar laminar structurestructure, made by stacking and bonding thin , made by stacking and bonding thin layers of fiber and polymer until desired layers of fiber and polymer until desired thickness is obtained thickness is obtained

By varying fiber orientation among layers, a By varying fiber orientation among layers, a specified level of anisotropy in properties can specified level of anisotropy in properties can be achieved in the laminate be achieved in the laminate

Applications: parts of thin cross‑section, such Applications: parts of thin cross‑section, such as aircraft wing and fuselage sections, as aircraft wing and fuselage sections, automobile and truck body panels, and boat automobile and truck body panels, and boat hulls hulls

FRP PropertiesFRP Properties High strength‑to‑weight and High strength‑to‑weight and

modulus‑to‑weight ratiosmodulus‑to‑weight ratios Low specific gravity - a typical FRP weighs only Low specific gravity - a typical FRP weighs only

about 1/5 as much as steel; yet, strength and about 1/5 as much as steel; yet, strength and modulus are comparable in fiber directionmodulus are comparable in fiber direction

Good fatigue strengthGood fatigue strength Good corrosion resistance, although polymers Good corrosion resistance, although polymers

are soluble in various chemicalsare soluble in various chemicals Low thermal expansion - for many FRPs, Low thermal expansion - for many FRPs,

leading to good dimensional stabilityleading to good dimensional stability Significant anisotropy in properties Significant anisotropy in properties

FRP ApplicationsFRP Applications

AerospaceAerospace – much of the structural weight of – much of the structural weight of todays airplanes and helicopters consist of todays airplanes and helicopters consist of advanced FRPsadvanced FRPs

AutomotiveAutomotive – somebody panels for cars and – somebody panels for cars and truck cabstruck cabs– Continued use of low-carbon sheet steel in cars is Continued use of low-carbon sheet steel in cars is

evidence of its low cost and ease of processingevidence of its low cost and ease of processing Sports and recreationSports and recreation

– Fiberglass reinforced plastic has been used for boat Fiberglass reinforced plastic has been used for boat hulls since the 1940shulls since the 1940s

– Fishing rods, tennis rackets, golf club shafts, Fishing rods, tennis rackets, golf club shafts, helmets, skis, bows and arrows.helmets, skis, bows and arrows.

Figure 9.11 ‑ Composite materials in the Boeing 757 Figure 9.11 ‑ Composite materials in the Boeing 757 (courtesy of Boeing Commercial Airplane Group)(courtesy of Boeing Commercial Airplane Group)

Other Polymer Matrix Other Polymer Matrix CompositesComposites

In addition to FRPs, other PMCs contain In addition to FRPs, other PMCs contain particles, flakes, and short fibers as the particles, flakes, and short fibers as the secondary phasesecondary phase

Called Called fillersfillers when used in molding when used in molding compounds compounds

Two categories: Two categories: 1.1. Reinforcing fillersReinforcing fillers – used to strengthen or – used to strengthen or

otherwise improve mechanical properties otherwise improve mechanical properties Examples: wood flour in phenolic and amino resins; Examples: wood flour in phenolic and amino resins;

and carbon black in rubberand carbon black in rubber

2.2. ExtendersExtenders – used to increase bulk and reduce – used to increase bulk and reduce cost per unit weight, but little or no effect on cost per unit weight, but little or no effect on mechanical properties mechanical properties

Guide to Processing Guide to Processing Composite MaterialsComposite Materials The two phases are typically produced The two phases are typically produced

separately before being combined into the separately before being combined into the composite partcomposite part

Processing techniques to fabricate MMC and Processing techniques to fabricate MMC and CMC components are similar to those used CMC components are similar to those used for powdered metals and ceramics for powdered metals and ceramics

Molding processes are commonly used for Molding processes are commonly used for PMCs with particles and chopped fibersPMCs with particles and chopped fibers

Specialized processes have been developed Specialized processes have been developed for FRPs for FRPs