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