Introduction to Composite Materials

The world of materialsThe world of materialsSteels

Cast ironsAl-alloys

PE, PP, PC

y

MetalsCu-alloysNi-alloysTi-alloys

, ,PA (Nylon)

Polymers,elastomers

Butyl rubberN

GFRPCFRP

AluminaSi-Carbide

Ceramics,glasses

S d l NeopreneCompositesKFRP

Plywood

Soda-glassPyrex

Polymer foamsMetal foams

FoamsCeramic foams

Glass foams

Woods

Naturalmaterials

Natural fibres:Glass foams Hemp, Flax, Cotton

CompositesCompositesComposites are formed from two or more typesof materials Examples polymer/ceramic andof materials. Examples polymer/ceramic andmetal/ceramic composites.

Composites are used because overall propertiesof the composites are superior to those of theindividual components.For example: polymer/ceramic composites have agreater modulus than the polymer componentgreater modulus than the polymer component,but aren't as brittle as ceramics.

• Definition: a material composed of 2 or more pconstituents– Reinforcement phase (e.g., Fibers)

Bi d h ( li t t i )– Binder phase (e.g., compliant matrix)

• Advantages• Advantages– High strength and stiffness– Low weight ratio– Material can be designed in addition to the structure

InterfaceInterface merupakan permukaan antarareinforcement dan matriks yang menentukanproses transfer tegangan dari matrik-reinforcement-matrik, yang berpengaruhkepada :- spesific strength- spesific stiffnes- fracture toughness- ketahanan creep

Macam-macam interfacial bonding :Macam macam interfacial bonding :• Molecule entanglement → adanya ikatan

antar molekul di permukaan fiber danantar molekul di permukaan fiber dan matrik.

• Electrostatic → adanya perbedaan muatan• Electrostatic → adanya perbedaan muatanlistrik secara atomik antara reinforce danmatrik di permukaan interface yangmatrik di permukaan interface yang mengakibatkan tarik-menarik, bila adagas, ikatan melemah.g

• Reaksi kimia →pada interface terdapatReaksi kimia →pada interface terdapatkumpulan gugus kimia yang saling berikatan antara fiber dan matrikberikatan antara fiber dan matrik.

• Mechanical bonding → adanyamekanisme interlocking pada permukaanmekanisme interlocking pada permukaansehingga semakin kasar permukaan ikatan yang terjadi makin kuatikatan yang terjadi makin kuat.

• Reaction & Interdiffusion bonding- Reaction → terjadi pada material polimerReaction → terjadi pada material polimerdimana terjadi penjalinan rantai-rantaiI t diff i b di t j di di- Interdiffusion bonding → terjadi di interface logam dan keramik dimanak b t k l i di kakan membentuk lapisan di permukaan

yang berbeda

Two types of composites are: yp pFiber Reinforced

CompositesParticle Reinforced

Compositesp p

Particle reinforced composites support higher tensile, compressive and shear stresses.

Figure 1. Examples for particle-reinforced composites. (S h idi d t l d t bil(Spheroidized steel and automobile

The following are some of the reasons why g ycomposites are selected for certain applications:

High strength to weight ratio (low density high tensile strength)strength)

High creep resistance

High tensile strength at elevated temperatures

High toughness

Examples of CompositesExamples of Composites• NaturalNatural

– Wood• flexible cellulose fibers held together with stiff lignin• flexible cellulose fibers held together with stiff lignin

– Bone• strong protein collagen and hard brittle apatitestrong protein collagen and hard, brittle apatite

• Artificial (man-made)constituent phases are chemically distinct– constituent phases are chemically distinct

DefinitionsDefinitions

• Composites often have only two phasesComposites often have only two phases• Matrix phase

ti d th h– continuous - surrounds other phase• Dispersed phase

– discontinuous phase

Matrix (light)Dispersed phase (dark)

ObjectivesObjectives• Definitions in composite materialsDefinitions in composite materials

– dispersed phase, matrixStructure of composites• Structure of composites– particle-reinforced

f f– fiber reinforced– structural composites

• Engineering applications often require unusual bi ti f ticombinations of properties

– esp. aerospace, underwater, and transportationcan’t be achieved with a single material– can t be achieved with a single material

– e.g. - aerospace requires strong, stiff, light, and abrasion resistant materialabrasion resistant material• most strong, stiff materials are dense and

heavy• most light materials are not abrasion resistant

Classification of Artificial Composites

Composites

Particulate Fiber Structural

Continuous Discontinuous

Laminates SandwichPanels

LargeParticle

DispersionStrengthened

Aligned Random

Properties of CompositesProperties of CompositesDependent on:Dependent on:• constituent phases

l ti t• relative amounts• geometry of dispersed phase

– shape of particles– particle sizep– particle distribution– particle orientationp

C it P tComposite ParametersFor a given matrix/dispersed phase system:• Concentration• Size• Shape• Distribution• Orientation

ParametersParametersParametersParameters

ConcentrationDistribution OrientationConcentrationDistribution Orientation

SizeShape

Classification of Artificial Composites

Composites

Particulate Fiber Structural

Continuous Discontinuous

Laminates SandwichPanels

LargeParticle

DispersionStrengthened

Aligned Random

Particle-Reinforced Composites

Divided into two classes(based on strengthening mechanism)• Large particle

– interaction between particles and matrix pare not on the atomic or molecular level

– particle/matrix interface strength is criticalp g• Dispersion strengthened

– 0 01-0 1 μm particles0.01 0.1 μm particles– inhibit dislocation motion

Large Particle CompositesLarge Particle CompositesExamples:Examples:• Some polymers with added fillers are

really large particle compositesreally large particle composites• Concrete (cement with sand or gravel)

– cement is matrix, sand is particulate

CERMET Cutting Tool

Light phase - Matrix (Cobalt)

CERMET Cutting Tool

Dark phase- Particulate (WC)

Large Particle CompositesLarge Particle CompositesDesired CharacteristicsDesired Characteristics• Particles should be approximately

equiaxedequiaxed• Particles should be small and evenly

di t ib t ddistributed• Volume fraction dependent on desired

properties

Large-Particle Composite Materials

• All three material typesAll three material types– metals, ceramics, and polymers

CERMET (ceramic metal composite)• CERMET (ceramic-metal composite)– cemented carbide (WC, TiC embedded in Cu

or Ni)or Ni)– cutting tools (ceramic hard particles to cut, but

a ductile metal matrix to withstand stresses)a ductile metal matrix to withstand stresses)– large volume fractions are used (up to 90%!)

Large Particle CompositesConcrete

• Concrete is not cement)Concrete is not cement)– Concrete is the composite of cement and an

aggregate (fine sand or coarse gravel)aggregate (fine sand or coarse gravel)• Reinforced concrete

a composite (large particle composite) with a– a composite (large particle composite) - with a matrix which is a compositesteel rods wires bars (sometimes stretched– steel rods, wires, bars (sometimes stretched elastically while concrete dries to put system in compression)in compression)

Dispersion Strengthened CompositesDispersion Strengthened Composites• Metals and metal alloys

– hardened by uniform dispersion of fine particles of a very hard material (usually ceramic)

• Strengthening occurs through the interactions• Strengthening occurs through the interactions of dislocations and the particulates

• ExamplesExamples• Thoria in Ni• Al/Al2O3 sintered aluminum powder SAP

Classification of ArtificialClassification of Artificial Composites

Composites

Particulate Fiber Structural

Continuous Discontinuous

Laminates SandwichPanels

LargeParticle

DispersionStrengthened

Aligned Random

Fiber sebagai reinforcedFiber sebagai reinforced

Fiber yang digunakan harus:Fiber yang digunakan harus: • Mempunyai diameter yang lebih kecil dari

diameter bulknya (matriksnya) namundiameter bulknya (matriksnya) namun harus lebih kuat dari bulknyaH i t il t th• Harus mempunyai tensile strength yang tinggi

Matriks yang dipadukan dengan fiber berfungsi sebagai :

• Penjepit fiber• Melindungi fiber dari kerusakan permukaan• Pemisah antara fiber dan juga mencegah

timbulnya perambatan crack dari suatu fiber ke fiber lain

• Berfungsi sebagai medium dimana eksternal t di lik ik k k itstress yang diaplikasikan ke komposit,

ditransmisikan dan didistribusikan ke fiber.

Matriks yang digunakan harus :Matriks yang digunakan harus :• Ductility tinggi

M iliki d l l ti it l bih d h• Memiliki modulus elastisitans lebih rendah daripada fiber

• Mempunyai ikatan yang bagus antara matriks dan fiber

• Biasanya secara umum yang digunakan adalah polimer dan logamp g

Sh t(di ti ) fib i f d ita. Short(discontinuous) fiber reinforced composites

Aligned Random

b. Continuous fiber (long fiber) reinforced composites

Fiber yang biasa digunakan antara lain :Fiber yang biasa digunakan antara lain :

Fibers – Glass– Sangat umun digunakan, fiber yang murah adalah

glass fiber yang sering digunakan untuk reinforcement dalam matrik polimerreinforcement dalam matrik polimer

– Komposisi umum adalah 50 – 60 % SiO2 dan paduan lain yaitu Al, Ca, Mg, Na, dll.

– Moisture dapat mengurangi kekuatan dari glass fiber

– Biasanya digunakan untuk: piping, tanks, boats, y g p p g, , ,alat-alat olah raga

Sifat-Sifatnyay• Densitasnya cukup rendah ( sekitar 2.55 g/cc)• Tensile strengthnya cukup tinggi (sekitar 1.8 g y p gg (

GPa)• Biasanya stiffnessnya rendah (70GPa)• Stabilitas dimensinya baik• Resisten terhadap panas

R i h d di i• Resisten terhadap dingin• Tahan korosi

Keuntungan :• Biaya murah• Tahan korosi• Biayanya relative lebih rendah dari komposit

lainnyaKerugianKerugian

• Kekuatannya relative rendah • Elongasi tinggiElongasi tinggi• Keuatan dan beratnya sedang (moderate)

Jenis-jenisnya antara lain :j y– E-Glass - electrical, cheaper– S-Glass - high strength

Fibers - Aramid (kevlar Twaron)Fibers - Aramid (kevlar, Twaron)Biasanya digunakan untuk : Armor, protective clothing industrial sportingprotective clothing, industrial, sporting goodsK t k k t k ti i dKeuntungan :kekutannya cukup tinggi, dan lebih ductile dari carbon

Carbon Fibers• Densitas karbon cukup ringan yaitu sekitar 2.3

g/cc• Struktur grafit yang digunakan untuk membuatStruktur grafit yang digunakan untuk membuat

fiber berbentuk seperti kristal intan.• Karakteristik komposit dengan serat karbon :

– ringan;– kekuatan yang sangat tinggi;– kekakuan (modulus elastisitas) tinggi.( ) gg

• Diproduksi dari poliakrilonitril (PAN), melalui tiga tahap proses :

Stabilisasi = peregangan dan oksidasi;• Stabilisasi = peregangan dan oksidasi;• Karbonisasi= pemanasan untuk mengurangi O, H,

N;G fiti i i k tk d l l ti it• Grafitisasi = meningkatkan modulus elastisitas.

Flat flakes sebagai penguat (Flake composites)Flat flakes sebagai penguat (Flake composites)

Fillers sebagai penguat (Filler composites)Fillers sebagai penguat (Filler composites)

Fiber Reinforced CompositesFiber-Reinforced Composites• Technologically the most important typeTechnologically, the most important type

of composite• Characterized in terms of specific strength• Characterized in terms of specific strength

or specific modulus = strength (or E) per weightweight– usually want to maximize specific strength

and modulusand modulus• Subclasses:

– Short fiber and continuous fiber lengths

Fiber PhaseFiber PhaseRequirements for the fiberRequirements for the fiber• The small diameter fiber must be much

stronger than the bulk materialg• High tensile strengthDifferent classificationsDifferent classifications• whiskers (single crystal - large aspect ratio)• fibers (polycrystalline or amorphous)fibers (polycrystalline or amorphous)• wires (large diameters - usually metal)

Matrix PhaseMatrix PhaseFunctionFunction• Binds fibers together• Acts as a medium through which• Acts as a medium through which

externally applied stress is transmitted and distributed to the fibersand distributed to the fibers

• Protects fiber from surface damage• Separates fibers and prevents a crack• Separates fibers and prevents a crack

from one fiber from propagating through anotheranother

Matrix PhaseMatrix PhaseRequirementsRequirements• Ductile• Lower E than for fiber• Lower E than for fiber• Bonding forces between fiber and

matrix must be highmatrix must be high– otherwise fiber will just “pull-out” of matrix

G ll l l d t l• Generally, only polymers and metals are used as matrix material (they are d til )ductile)

Influence of Fiber LengthInfluence of Fiber Length• Mechanical properties depend on:p p p

• mechanical properties of the fiber• how much load the matrix can transmit to the

fiberfiber– depends on the interfacial bond between the fiber

and the matrix

• Critical fiber length depends on• Critical fiber length - depends on• fiber diameter, fiber tensile strength• fiber/matrix bond strength

Influence of Fiber LengthInfluence of Fiber Length

• Critical fiber length• Critical fiber length -lc– “Continuous” fibers l >>– Continuous fibers l >>

15 lc– “Short” fibers are anything

shorter 15 ll d/2shorter 15 lclc = σfd/2τc

where No Reinforcement

d = fiber diameterτc = fiber-matrix bond strengthstrengthσf = fiber yield strength

Influence of Fiber OrientationInfluence of Fiber Orientation• Fiber parametersFiber parameters

– arrangement with respect to each other– distributiondistribution– concentration

• Fiber orientationFiber orientation– parallel to each other– totally randomy– some combination

Influence of Fiber OrientationInfluence of Fiber Orientation

• Stage I - elastic deformation with intermediate • Stage II - matrix yieldsg y• Failure - Non-catastrophic. When fibers fracture, you now have new fiber

length and matrix is still present

Aligned FibersAligned Fibers• When fibers are alignedWhen fibers are aligned

– properties of material are highly anisotropicmodulus in direction of alignment is a function– modulus in direction of alignment is a function of the volume fraction of the E of the fiber and matrixmatrix

– modulus perpendicular to direction of alignment is considerably less (the fibers do g y (not contribute)

Randomly Oriented FibersRandomly Oriented Fibers• Properties are isotropicProperties are isotropic

– not dependent on directionUltimate tensile strength is less than for• Ultimate tensile strength is less than for aligned fibers

f f• May be desirable to sacrifice strength for the isotropic nature of the composite

Fiberglass Reinforced Composites

Glass is a common reinforcementGlass is a common reinforcement• it is easily drawn into fibers

it i h d dil il bl• it is cheap and readily available• it is easy to process into composites• it can produce very strong, very light

composites (high specific strength)p ( g p g )• it is usually chemically inert (does not

degrade in harsh environments)degrade in harsh environments)

Volume Fraction in Fiber Composites

Elastic modulus is dependent on the volume• Elastic modulus is dependent on the volume fraction of fibers“R l f i t ” ti ( i )• “Rule of mixtures” equation (again)– E - elastic modulus, V- volume fraction, m- matrix, f- fiber– upper boundpp

lower bound

Ec =EmVm +E fVf(iso(iso--strain)strain)

– lower bound

Ec =EmE f

(iso(iso--stress)stress) Ec = EfVm +EmVf

Rule of MixturesRule of Mixtures

*

Upper bound(iso-strain)

Ec =EmVm +E fVf

* **

***

* f f

EEmE f

conc of fibersx er

Lower bound(iso-stress)

Ecf

EfVm +EmVf=

Actual

conc. of fibers

E-m

atri

E -

fibe

ValuesE

ExampleExample• Calculate the composite modulus forCalculate the composite modulus for

polyester reinforced with 60 vol% E-glass under iso-strain conditionsunder iso strain conditions.

• Epolyester = 6.9 x 103 MPa• EE glass = 72.4 x 10 3 MPaEE-glass 72.4 x 10 MPa

Ec = (0.4)(6.9x103 MPa) + (0.6)(72.4x103 MPa) = 46.2 x 103 MPa

Other Composite PropertiesOther Composite Properties

• In general, the rule of mixtures (for upperand lower bounds) can be used for any property Xc - thermal conductivity,density, electrical conductivity…etc.

Xc = XmVm + XfVf

Xc = XmXf/(VmXf + VfVm)

Fiber and Matrix PhasesFiber and Matrix Phases • Fibers

• whiskers: flawless, large l/d ratio, very strong• fiber• wires

• Matrix– polymer or metal-matrix: used for their ductility

• bind fibers, transmits load to fibers• matrix should be more ductile, fiber should have higher E• matrix protects fibers from surface damage (cracks)

t i t k ti f fib t th t hi h ld• matrix prevents cracks propagating from one fiber to the next which could cause catastrophic failure.

– ceramics-matrix: used to increase fracture t h f itoughness of ceramic

• Essential that Fiber-Matrix bond be strong

Fiber and Matrix PhasesFiber and Matrix Phases

Polymer Matrix CompositesPolymer-Matrix Composites • Fibers

• Glass Fiber - fiberglass• Carbon fiber - graphitic and amorphous C• Aramid fiber - Kevlar, highly linear polymer chain

• Matrix• polyester and vinyl esters - fiberglass• epoxies - aerospace applications, stronger,

resistant to moist reresistant to moisture• polyimides - high temperature• high temperature thermoplastics - PEEK PPShigh temperature thermoplastics PEEK, PPS,

PEI, aerospace

Metal-Matrix Composites

Ceramic-Matrix Composites

Employed to increase the fracture toughness of the ceramicEmployed to increase the fracture toughness of the ceramicExample: Transformation toughened zirconia

Other CompositesOther Composites

Carbon-Carbon Compositescarbon fiber in pyrolyzed carbon matrixhigh tensile strength and modulus at high temperature (2000ºC)g g g p ( )low coefficient of thermal expansionhigh thermal conductivitieslow thermal shock potentialApplications include; rocket motors, friction materials in aircraft,

advanced turbine engine components, ablative shields for reentry vehicles

Hybrid compositestwo or more different kinds of fibers.

Classification of Artificial Composites

Composites

Particulate Fiber Structural

Continuous Discontinuous

Laminates SandwichPanels

LargeParticle

DispersionStrengthened

Aligned Random

Structural CompositesStructural Composites• DefinitionDefinition

– composed of both homogeneous and composite materialscomposite materials

– properties depend on constituent materials and on geometrical design of the elementsand on geometrical design of the elements

• Typeslaminar composites– laminar composites

– sandwich panels

Laminar CompositesLaminar Composites

T di i l h t• Two dimensional sheets or panels with a preferred high-strength directiong

• Q. What is a natural example of this?

• A. Wood• Q. What is a man made example• A. Plywood - Layers are stacked

and subsequently bonded together h h hi h h di iso that the high strength direction

varies

Sandwich PanelsSandwich Panels• Two strong outer sheets (called faces)Two strong outer sheets (called faces)

separated by a layer of less dense material or core (which has lower E andmaterial or core (which has lower E and lower strength)

• Core• Core– separates faces

i t d f ti di l t th– resists deformation perpendicular to the facesoften hone comb str ct res– often honeycomb structures

• Used in roofs, walls, wings

Sandwich PanelSandwich Panel

Structurtal Compositep