compos manufac_prof. balasubramanian

7/24/2019 Compos Manufac_Prof. Balasubramanian

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Manufacturing Methods ofComposites

Dr. M. BalasubramanianDept. of Metallurgical & Materials Engg.

Indian Institute of Technology

Chennai - 600 036


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Constituents of Composites

Discontinuous phase - Reinforcement

Continuous phase - Matrix

SEM micrograph of a fractured composite

15 m


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Constituents

Reinforcements

Principal load bearing member

Matrix provides a medium for binding and holding the

reinforcements together into a solid

protects the reinforcement from environmental

degradation serves to transfer load from one insert to the other

Provides finish, colour, texture, durability and

other functional properties


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Fibres: Important Characteristics

A small diameter

Allows a higher fractionof the theoreticalstrength to be achieved

A high aspect ratio

Allows effective loadtransfer to fibres

A very high degree offlexibility

Permits the use of avariety of techniques formaking composites


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Synthetic Fibres

Glass

Carbon

AramidPolyethylene

Alumina

Silicon carbide


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Types of Glass Fibres

%by of

constituents

E Glass A Glass C Glass S Glass Z Glass M Glass

SiO2 52.4-53.2 72.5 65.0 64.0-65.0 60.0 53.7

Al2O3 14.4-14.8 0.7-1.5 4.0 25.0-26.0 - -

B2O3 8.0-10.0 - 6.0 - - -

MgO 4.5 2.5 3.0 10.0 - 9.0

CaO 17.5 10.0 14.0 - - 12.9

Na2 * K2O 0.5 13.5-14.0 8.0 - 20.0 -

Fe2O3 0.4 - - - - -

F2 0.0 - - - - -

SO3 - 0.7 - - - -

BeO - - - - - 8.0

TiO2 - - - - 5.0 7.9

CeO2 - - - - - 3.0

Li2O - - - - - 3.0

ZrO2 - - - - 15.0 2.0


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Commercial forms of Glass F ibres

Rovings

Chopped Strand Mat

Yarn


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Chopped Strands

Woven Rovings

Commercial forms of Glass F ibres (contd.,)


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Carbon fibre

Made from organic precursor fibre

Commonly used precursor fibre is

polyacrylonitrile (PAN)Other precursor fibres

Rayon

Pitches Polyvinyl alcohol

Polyimides

Phenolics


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Processing of Carbon Fibre fromPAN


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Two Approaches to Make High

Modulus Polymer FibresProcess a polymer with highly

oriented and extended chain

arrangement Polyethylene fibre

Synthesis followed by extrusion of anew class of polymers, called liquidcrystal polymers

These have a rigid rod molecularstructure

Aramid fibre


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Comparison of fibres


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Properties of ReinforcementFibresProperties PAN-Based

CarbonKevlar

49E

GlassSiC Al2O3 Boron

(W)

HM HS CVD Nicalon

Diameter (m) 7-10 7.6-8.6

12 8-14 100-200

10-20 20 100-200

Density (g cm-3) 1.95 1.75 1.45 2.55 3.3 2.6 3.95 2.6

Youngs Modulus (GPa)Parallel to fibre axisPerpendicular to fibreaxis

39012

25020

125-

7070

430-

180-

379-

385-

Tensile strength (GPa) 2.2 2.7 2.8-

3.5

1.5-

2.5

3.5 2 1.4 3.8

Strain to fracture (%) 0.5 1.0 2.2-2.8

1.8-3.2

- - - -

Coefficient of thermalexpansion (10-6K-1)Parallel to fibre axis

Perpendicular to fibreaxis

-0.5 --1

7-12

0.1--0.5

7-12

-2- -5

59

4.7

4.7

5.7

-

-

-

7.5

-

8.3

-


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Natural Fibres

Natural fibres are also used for makingFRP products.

Some of the common natural fibres Jute

Banana

Sisal Pineapple

Coir


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Natural Fibres

The primary driving force for these naturalfibre are low cost and recyclable nature.

Other reasons for their increasing use Weight reduction

these fibres are half the weight of fibre-glass

Green movement

desire for natural products

Major draw back

they absorb moisture because of inherent

porosity


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Comparison of Natural FibresProperty Jute Banana Sisal Pineapple Coir

Width or Diameter(micron )

20-60 80-250 50-200 20-80 100-450

Density (gms./cc) 1.3 1.35 1.45 1.44 1.15

Elastic Modulus(GN/m2)

- 8-20 9-16 34-82 4-6

Elongation (%) 1-1.2 1.0-3.5 3-7 0.8-1.6 15-40

Cellulose/LigninContent (%)

61 /12 65 /5 67 /12 81 /12 43 /45

REINFORCEMENTS MATRICES


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REINFORCEMENTS MATRICES

GLASS FIBRE(1940)

THERMOSETPLASTICS

BASALT FIBRE

(1965)

THERMO-

PLASTICS

NATURALFIBRES

RUBBER ANDELASTOMERS

CARBON FIBRE(1960)

METALS &ALLOYS

ARAMID FIBRE(1972)

CEMENTS

BORON FIBRE(1959)

CARBON

ALUMINA FIBRE(1962)

STRUCTURALCERAMICS

SiC FIBRES &WHISKERS

GLASS

Si3N4FIBRES


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Polymer Matrix

A polymer is defined as a long-chainmolecule containing one or morerepeating units of atoms, joinedtogether by strong covalent bonds

A polymeric material is a collection of alarge number of polymer molecules ofsimilar chemical structure

These molecules are frozen in space,

either in random fashion or in amixture of random and orderlyfashions


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Thermoset Polymers (Resins)

Epoxies principally used in aerospace

applications

Polyester, vinyl esters commonly used in automotive, marine,

chemical and electrical applications

Phenolics

used in bulk moulding compounds

Polyimides, polybenzimidazoles (PBI),polyphenylquinoxaline (PPQ)

high temperature aerospace applications


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ThermoplasticsNylons, thermoplastic polyesters,

polycarbonate, polyacetals

used with discontinuous fibres in injection

moulded articles

Polyamide-imide (PAI), polyether-etherketone (PEEK), polysulphone (PSUL),

polyphenylene sulphide (PPS), polyetherimide (PEI)

suitable for moderately high temperatureapplications with continuous fibres


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Processing of PolymerComposites

Hand lay-up

Resin transfer moulding (RTM)

Filament winding

Pultrusion

Autoclave processCompression moulding


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Hand Lay-up


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Hand Lay-up

Cover bench with release sheet Spread Resin base


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Apply surfacing veil Add more resin

Apply the layer of chopped strand mat Add resin and apply second mat

Hand Lay-up


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Apply woven roving Roll roving into resin

Add final chopped strand mat Finish with wax topcoat

Hand Lay-up


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Hand Lay-up

Advantages

Widely used

Low tooling cost Custom shape

Larger and complex

items can be produced

Problems

Labour intensive

Low-volume process

Longer cure time requireddue to lack of hightemperatures andpressures to accelerate

the curing Good surface finish on

only one side

Quality is purelydependent on fabricator


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Spray-up


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Resin transfer molding (RTM)

Closed mold, low pressuretechnique

Place the fibre preform in a mold

Inject the liquid resin into the moldby a pump

Low polymer viscosity, < 1 Pa s(thermosets such epoxy, polyester)

Thermoplastics have high viscosity difficult to process by RTM.


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Resin Transfer Moulding

Vacuum infusion: Instead of applying pressure, vacuum is applied to draw resin


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Resin Transfer Moulding

Advantages:

Low skill labour required

Low tooling cost

Low volatile emission

Required design

tailorability

Problems:

Control of resin flow

Kinking of fibres

Criticality in mould

design


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Pultrusion


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Pultrusion

Can producecontinuously at a rate of10 to 200 cm/min.

Pultruded profiles as

wide as 1.25 m withmore than 60 vol. %fibre can be made.

Example:

A helicopter windshieldpost (carbon fiber/vinylester), 1.5 m long.


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Pultrusion

Advantages:

Minimal kinking of

fibres/fabricsRapid processing

Low material scrap

rate

Good quality control

Problems:

Improper fibre wet-

outFibre breakage

Inadequate cure

Die jamming

Complex die design


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Filament winding

Resin-impregnated continuous fiberor tape is wound on a mandrel in aprecise geometric pattern.

Rotate the mandrel while a deliveryhead precisely positions fibers froma creel on the mandrel surface.


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Filament Winding


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Filament wound pressurebottles for gas storage


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Prepregs

Pre-impregnated fibres

A thin sheet or lamina of unidirectional fibre/polymercomposite protected on both sides with easilyremovable separators

An intermediate stage in the fabrication

Partially cured state with a moderately self-adhesivetack

Easily obtained with epoxies


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Autoclave Process

Very high quality productHeat & pressure are applied

Removes the entrapped air and helps curing

Generally prepregs are usedChopped fibres with resin can also be used

Hybrid composites can be produced

High fibre volume fractions can be obtained


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a) Autoclave process to make a laminated compositeb) Prepregs of different orientations stacked to form a laminated composite

a)

b)


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Sheet Moulding Compounds

Consists of apolyester resin plusadditives

Additives are

generally fine calciumcarbonate and shortglass fibres

Used in auto body

parts (bumper beams,radiator supportpanels, etc.)

Schematic of compressionmoulding


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Thermoplastic Matrix Composites

Advantages

Refrigeration is not necessary with a thermoplasticmatrix

Parts can be made & joined by heating

Parts can be remoulded and any scrap can berecycled

Better toughness & impact resistanceDisadvantages

Processing temperatures are generally higher

Stiff and boardy


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Injection Moulding

Generally discontinuous fibres are

used

Mixed with molten matrix materialand injected into the die

Recent development is reinforced

reaction injection moulding


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Film Stacking

Fibres with very low resin content are usedStacked with pure polymer layer

Consolidated by heat & pressure

Pressure is 6-12 MPa & temperature is 275-350C for polysulphones and polyetheretherketone

Moulding cycle with thermoplastic is less

Alternative is to use continuous tows ofcommingled carbon fibre/PEEK


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Commingled Fibres

Matrix fibre and reinforcement fibre

commingled to produce yarn

Yarn can be woven, knit or filamentwound

Subjected to heat and pressure


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Thermoplastic Tape Laying

A controllable tape

head has the tape

dispensing reels and

shoes

Hot shoes heat the tape

to molten state

Cold shoes cool the

tape instantly to solidstate


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Thermoforming


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Diaphragm Forming

Involves the sandwiching of freely

floating thermoplastic prepreg layers

between two diaphragms

Components with double curvatures

can be formed


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Constituents of MMC

Metal matrix composites consistof a metal or an alloy as the

continuous matrix and areinforcement that can beparticle, short fibre or whiskeror continuous fibre.


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Typical reinforcements used inmetal matrix composites

Type Aspect

Ratio

Diameter

(m)

Examples

Particle ~ 1-4 1-25 SiC, Al2O3, BN,

B4C, Fly ash

Short fibre or

whisker

~ 10-1000 0.1-25 SiC, Al2O3,

Al2O3+SiO2, C

Continuous

fibre

> 1000 3-150 SiC, Al2O3, C, B,

W


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Important Metallic Matrices

Aluminium Alloys

Titanium Alloys

Magnesium Alloys

Copper

Intermetallic Compounds


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Processing of MMCs

Many processes for fabricating metalmatrix composites are available.

These processes involve processing

in the liquid and solid state.Some processes involve a variety of

deposition techniques

A recent processing method is in-situprocess of incorporating areinforcement phase.


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Duralcan ProcessA stir casting process

8-12 m particles are used

Too small particles, e.g. 2-3 m,

Will result in a very large interface region and

thus a very viscous meltFoundry-grade MMCs

High silicon aluminium alloys (e.g., A356)

Alumina particles

Wrought MMCs

Al-Mg-type alloys (e.g., 6061)

Silicon carbide particles


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Stir Casting

Stirring of composite melt with ceramic particles to minimize

settling of the particles during processing.


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Squeeze Infiltration

The molten metal is infiltrated into the

reinforcement preform under pressure

This method obviates the requirement ofgood wettability

Have minimal reaction between the

reinforcement and molten metal

Short dwell time at high temperature

Free from common casting defects, such

as porosity and shrinkage cavities

Preform Manufacturing


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Preform Manufacturing

Press Forming of Preform


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Squeeze infiltration technique of composite fabrication


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Diesel engine piston

Saffil alumina fibre/Al composite)

Made by squeeze casting


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Powder Metallurgy

TechniqueMixing

Compaction

Sintering/hot pressing

Powder metallurgy and extrusion


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Powder metallurgy and extrusionprocessing of Al/SiCpcomposites

Vacuum degassing

Hot pressing

Pressure

Graphite die

Particle reinforcedmetal matrix composite

P/M Al SiCp

Blending of gasatomized powders

Cold Isostatic Compaction

Extrusion

Diff i B di P


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Diffusion Bonding Process

A solid state processing method

Schematic of diffusion bonding process


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The microstructure of SiC fibre/titanium matrix composite

made by diffusion bonding


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In-situ Process

Composite material is produced in onestep from an appropriate starting alloy

Reinforcement phase is formed in-situ

Avoiding the difficulties inherent incombining the separate components

The solidification rate in practice,however, is limited to a range of

1-5 cm/h for fibre-reinforcedcomposites

Many particulate reinforced compositesare now-a-days made with this process


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Transverse section of in-situ

composites obtained at different

solidification rates

Solidification rates indicated in left-hand top corners (cm/h)

T f C i C it


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Types of Ceramic Composites

Oxide and Non-oxide Ceramic composites Silica, alumina, SiC, Si3N4and other ceramics

are reinforced with carbon, silicon nitride orsilicon carbide fibres/whiskers

Used for temperatures up to 2000C

Carbon fibre reinforced carbon

Used as a high temperature resistant material

for heat shields, rocket nozzles, etc. and asbody implants

Can be used up to 1500C under inertconditions

T f C i C it


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Types of Ceramic Composites

Glass and Glass ceramic composites Glass and glass ceramics can be

reinforced with carbon or metallic fibres

for improving their impact resistanceCement composites

Portland cement can be reinforced with

glass, plastics, asbestos or steel fibresfor building and construction industry

P i M h d f CMC


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Processing Methods of CMCs

Cold pressing and Sintering

Hot pressing & Hot isostatic pressing

Reaction bonding process

Direct oxidation process Chemical vapour impregnation process

Sol-gel process

Polymer infiltration & pyrolysis

Cold Pressing & Sintering


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Cold Pressing & Sintering

Li it ti f C ld P i &


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Limitations of Cold Pressing &Sintering

The reinforcement phase can form aconnective network throughout thecomposite.

This network will resist densification and leadsto a porous microstructure.

Large residual stresses can develop incomposites during sintering due to thermalexpansion mismatch between the

constituent phases. These stresses can sometimes be large

enough to cause cracking in the composite.

Hot pressing


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Hot pressing

Simultaneous application ofpressure and high temperature

Pore-free and fine grained compact

Limitations

Difficult to produce complex shapes

Very high pressure can easily damagefibres

Low production rate

Hot pressing


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Hot pressing

Similar to diecompaction

But, the whole die set-upis heated

Die is usually made fromgraphite

Allows external inductionheating

Other common diematerials

Refractory metals & theiralloys

If the compact exhibitsincompatible thermalexpansion

Ejected at high

temperature

A cross-sectional view of the uniaxial hotpressing operation

Hot Isostatic Pressing


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Hot Isostatic Pressing

To produce near full density parts and

complex shapes

Performed in a pressurized fluid

High pressure argon or nitrogen is used to

transfer heat & pressure

Flexible dies are used

Glass, steel, stainless steel & tantalum

Temperatures up to 2200C & pressuresup to 200 MPa are possible

Useful for large components, where full

density & isotropic properties are required


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Hot isostatic pressing


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Hot isostatic pressing

One variant is to use previouslysintered compacts

Component already has the desiredshape

Densities over 92% TD

Closed pores allow for HIP

Widely used to consolidatecemented carbides, ceramiccomposites, and wear resistantmaterials

Reaction bonding process


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act on on ng proc ss

Process steps

A composite is made with silicon powder Heated to a high temperature in the presence

of reactive gases

Matrix shrinkage during densification can

be avoided Large volume fractions of whiskers or

fibres can be used

Multidirectional, continuous fibre preforms

can be used Low temperature processing

Great disadvantage of this process

high porosity

Directed Oxidation


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Directed Oxidation

Schematic diagram of directed metal oxidation process of Lanxide Corp.


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Chemical Vapour Impregnation

Advantages

Good mechanical properties at hightemperatures

Large, complex shapes can beproduced to a near-net shape

Considerable flexibility in the fibresand matrices

Disadvantages

Process is slow and expensive

I th l h i l


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Isothermal chemical vapour

infiltration process


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Schematic diagram of a chemical vapour infiltration process with pressureand temperature gradients (Chawla, Composite Materials)


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Sol-gel Processing


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Sol-gel Processing

Advantages

lower processing temperatures

greater compositional homogeneity

potential for producing unique multiphasematrix materials

allows processing via liquids of low viscosity

Disadvantages

high shrinkage

results in a large density of cracks in thematrix

generally, repeated impregnations arerequired to produce a substantially densematrix

P l I filt ti &


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Polymer Infiltration &Pyrolysis (PIP)

Formation of ceramic matrixmaterials by high temperature

pyrolysis of polymeric materialscontaining the constituentelements.


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References

1. Chawla, K.K. (2012) CompositeMaterials: Science and Engineering,3rdEdition, Springer Verlag.

2. Mallick, P.K. (2008) Fiber-reinforcedComposites, 3rdEdition, CRC Press,Boca Raton.

3. Balasubramanian, M. (2013)Composite Materials and Processing,CRC Press, Boca Raton.


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Thank You

compos manufac_prof. balasubramanian

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