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Unit III- Composite Materials
Composite materials: Introduction to composite
materials – Properties and morphology – loading
characteristics Fibre reinforced composites
characteristics - Fibre reinforced composites,
Types of composite materials: metal matrix
composites, ceramic composites – properties and
specific applications in industries and aerospace;
specific applications in industries and aerospace;
Nanocomposites: Classification, properties and
applications.

Composite Materials
o Formed by the combination of
two or more constituent materials
with significantly different physical
with significantly different physical
or chemical properties.
o The constituent materials will remain separate and distinct on a macroscopic level
within the finished structure.
o The main components of composite materials are fibers and matrix.
‐ fiber provides most of the stiffness and strength
‐ matrix binds and holds the fibers together.
o Other substances are added to improve the specific properties
‐ Eg. fillers to reduce the cost and improve processability
and dimensional stability.

Natural composites
Natural composites
ƒ Wood: Cellulose fibres and lignin matrix
ƒ Animal body: bone fibres and tissues as matrix
ƒ Bone: inorganic and organic components
. Org. components like carbohydrates, fats and proteins giving
pliability and toughness to the bone
. Ing. components as calcium phosphates giving rigidity and
strength to the bones
ƒ Sea shells:
ƒ Elephant tusk:

REQUIREMENTS OF COMPOSITE MATERIALS
S l i t f it t i l
Some general requirements of composite materials
ƒ The second phase (fibres or particles) uniformly distributed
throughout the matrix and must not be in direct contact with one
throughout the matrix and must not be in direct contact with one
another
ƒ The constituents of the composite should not react with one
ƒ The constituents of the composite should not react with one
another at high temp; otherwise interfacial bond will become weak
leading to premature failure of the composite
leading to premature failure of the composite
ƒ In no case should the second phase loose its strength, it should be
well bonded to the matrix
well bonded to the matrix
ƒ Matrix must have a lower modulus of elasticity than the fibre
ƒ In general, both the matrix and fibre should not have greatly
g , g y
different coefficient of linear expansion

Matrix Fibre Elastic
Modulus
(GPa)
Tensile
st. (MPa)
long trans long trans
long trans long trans
Al B 210 150 1500 140
Ti-6Al-4V SiC 300 150 1750 410
Al-Li Al2O3 262 152 690 180
2 3
Epoxy E-glass 40 10 780 28
Epoxy 2-D glass
cloth
16.5 16.5 280 280
Epo Boron 215 24 2 1400 63
Epoxy Boron 215 24.2 1400 63
Epoxy Carbon 145 9.4 1860 65
Polyester Chopped
glass
55-138 - 103-206 -
g
Al2O3 - 350-700 2-5 Flexture
St (MPa)
Fracture
toughness
(MPa m bar
MgO - 200-500 1-3
g
SiC - 500-800 3-6
SiO2 glass - 70-150 1
Al203 SiC
whiskers
800 10
whiskers
SiO2 glass SiC fibres 1000 ~ 20
Al203 BN particulates 350 7

ƒ Matrix binds the fibers together, holding them aligned in the
ROLE OF MATRIX IN COMPOSITES
important stress direction
ƒ Loads applied to the composite and the fibers are the principal load
bearing component, through the matrix
ƒ This enables the composite to withstand compression, flexural
and shear forces as well as tensile loads.
ƒ The matrix isolates the fibers, so that they can act as separate
entities and cracks are unable to pass unimpeded/unrestricted
through sequences of fibers in contact.
ƒ The matrix protects the reinforcing filaments from mechanical
damage (e.g., abrasion) and from environmental attack.
At l t d ti t t th t i t t
ƒ At elevated operating temperature, the matrix protects
the fibers from oxidative attack.

The functions & requirements of the matrix are to:
The functions & requirements of the matrix are to:
1. Keep the fibers in place in the structure;
2. Help to distribute or transfer loads;
3 Protect the filaments both in the structure and
3. Protect the filaments, both in the structure and
before and during fabrication;
4. Control the electrical and chemical properties of
the composite;
the composite;
5. Carry interlaminar shear.

Specific Properties for Selection of Matrix to a Specific Application
1 Minimize moisture absorption and have low shrinkage;
1. Minimize moisture absorption and have low shrinkage;
2. Low coefficient of thermal expansion;
3 Must flow to penetrate the fiber bundles completely and eliminate
3. Must flow to penetrate the fiber bundles completely and eliminate
voids during the compacting/curing process; have reasonable
t th d l d l ti ( l ti h ld b >fib )
strength, modulus and elongation (elongation should be >fiber);
4. Must be elastic to transfer load to fibers;
5 H t th t l t d t t (d di li ti )
5. Have strength at elevated temperature (depending on application);
6. Have low temperature capability (depending on application);
7. Have excellent chemical resistance (depending on application);
8. Be easily processable into the final composite shape;
9. Have dimensional stability (maintain its shape).

Key Factors needed for selection of Matrix
1. The matrix must have a mechanical strength commensurate
with that of the reinforcement i.e. both should be compatible.
2. Thus, if a high strength fibre is used as the reinforcement, there
is no point using a low strength matrix, which will not transmit
stresses efficiently to the reinforcement.
3. The matrix must stand up to the service conditions, viz.,
temperature, humidity, exposure to UV environment, exposure
to chemical atmosphere, abrasion by dust particles, etc.
4. The matrix must be easy to use in the selected fabrication
process and life expectancy.
5. The resultant composite should be cost effective.

(i)P ti l t it d (ii) fib i f d it
Two-phase composite materials are classified into two broad categories:
(i)Particulate composites and (ii) fibre reinforced composites
‰ Quasi-homogeneous
‰ Quasi-isotropic
Mi fl k i f d ith l
Particulate composites
ƒ Mica flakes reinforced with glass
(non-metallic particles in a non-metallic matrix)
ƒ Aluminium particles in polyurethane rubber
(metallic particles in a non-metallic matrix)
ƒ Lead particles in copper alloys
(metallic particles in a metallic matrix)
(metallic particles in a metallic matrix)
ƒ Silicon carbide particles in aluminium
(non-metallic particles in a metalIic matrix)

Fib f i ifi t t th d tiff b dd d i
Fibre reinforced composites
ƒ Fibres of significant strength and stiffness embedded in a
matrix with distinct boundaries between them.
ƒ Both fibres and matrix maintain their physical and chemical
identities.
ƒ Combination performs a function which cannot be done
by each constituent acting singly.
by each constituent acting singly.
ƒ Fibres of fibre reinforced plastic (FRP) may be short or
continuous
continuous.
ƒ FRP having continuous fibres is more efficient.

Constituents of composite
o Matrix
o Dispersed phase/Reinforcement phase
o Dispersed phase/Reinforcement phase
o Interface/inter‐phase
Interface
C i
Reinforcement
Composite
Matrix

Constituents of composite
o Matrix (Continuous phase) : Continuous or bulk material
o Reinforcement (Dispersed Phase) : Added primarily to increase the
t th d tiff f t i
strength and stiffness of matrix
o The reinforcement is generally can be in the form of fibres, particles,
whiskers or flakes
The most common man made composites can be divided into three main
groups based on the matrix
Matrix
Polymer Ceramic Metal

o Metal‐ matrix composites (MMC)
Composite material with at least two
p
constituent parts, one being a metal.
The other material may be a different
metal or another material such as a
i i d
ceramic or organic compound.
o Carbide drills are often made from a tough cobalt matrix with hard tungsten carbide
particles inside.
o Modern high‐performance sport cars, such as those built by Porsche, use rotors
made of carbon fiber within a silicon carbide matrix.
o Ford offers a Metal Matrix Composite (MMC) driveshaft upgrade
o The F‐16 Fighting Falcon uses monofilament silicon carbide fibres in a titanium
matrix for a structural component of the jet's landing gear.
o MMCs are nearly always more expensive than the more conventional materials they
o MMCs are nearly always more expensive than the more conventional materials they
are replacing.
o As a result, they are found where improved properties and performance can justify
the added cost.
o Today these applications are found most often in aircraft components, space
systems and high‐end or "boutique" sports equipment.

Compared to monolithic metals, MMCs have the following
improved properties:
1. Higher strength-to-density ratios
2. Higher stiffness-to-density ratios
3. Better fatigue resistance
3. Better fatigue resistance
4. Better elevated temperature properties
5 Higher strength
5. Higher strength
6. Lower creep rate
7. Lower coefficients of thermal expansion
8. Better wear resistance

The advantages of MMCs over polymer matrix composites are:
1 Hi h t t bilit
1. Higher temperature capability
2. Fire resistance
3. Higher transverse stiffness and strength
4. No moisture absorption
5. Higher electrical and thermal conductivities
6. Better radiation resistance
7. No out gassing
8 Fabric ability of whisker and particulate reinforced MMCs
8. Fabric ability of whisker and particulate-reinforced MMCs
with conventional metal working equipment.

Some of the disadvantages of MMCs compared to monolithic
Some of the disadvantages of MMCs compared to monolithic
metals and polymer matrix composites are:
1 Higher cost of some material systems
1. Higher cost of some material systems
2. Relatively immature technology
3. Complex fabrication methods for fiber-reinforced systems
(except for casting)
4. Limited service experience

Stir Casting is characterized by the following features:
1. Content of dispersed phase is limited (usually <30% v/v).
1. Content of dispersed phase is limited (usually 30% v/v).
2. Distribution of dispersed phase throughout the matrix is not
perfectly homogeneous:
perfectly homogeneous:
¾ There are local clouds (clusters) of the dispersed particles (fibers);
¾ There may be gravity segregation of the dispersed phase due to a
¾ There may be gravity segregation of the dispersed phase due to a
difference in the densities of the dispersed and matrix phase.
¾The technology is relatively simple and low cost
¾The technology is relatively simple and low cost.
™ Distribution of dispersed phase may be improved if the matrix is in
semi solid condition The method using stirring metal composite
semi-solid condition. The method using stirring metal composite
materials in semi-solid state is called rheocasting. High viscosity of
th i lid t i t i l bl b tt i i f th di d
the semi-solid matrix material enables better mixing of the dispersed
phase.

The most important MMC systems are:
1. Aluminum matrix
2 Continuous fibers: boron silicon carbide alumina graphite
2. Continuous fibers: boron, silicon carbide, alumina, graphite
3. Discontinuous fibers: alumina, alumina-silica
4. Whiskers: silicon carbide
5 P ti l t ili bid b bid
5. Particulates: silicon carbide, boron carbide
6. Magnesium matrix
7. Continuous fibers: graphite, alumina
g p ,
8. Whiskers: silicon carbide
9. Particulates: silicon carbide, boron carbide
10 Titanium matrix
10. Titanium matrix
11. Continuous fibers: silicon carbide, coated boron
12. Particulates: titanium carbide
13 C t i
13. Copper matrix
14. Continuous fibers: graphite, silicon carbide
15. Wires: niobium-titanium, niobium-tin
16. Particulates: SiC, boron carbide, titanium carbide.
17. Superalloy matrices

o Ceramic Matrix composite (CMC)
o A given ceramic matrix can be reinforced with either
discontinuous reinforcements, such as particles, whiskers or
chopped fibres particulates having compositions of Si N SiC
chopped fibres, particulates having compositions of Si3N4, SiC,
AlN, titanium diboride, boron carbide, and boron nitride or
with continuous fibres.
o The desirable characteristics of CMC include
™ High‐temperature stability
™ High temperature stability
™ High thermal shock resistance
™ High hardness
™ Hi h i i t
™ High corrosion resistance
™ Light weight
™ Nonmagnetic and nonconductive properties
™ Versatility in providing unique engineering solutions

Applications:
™ CMCs find promising applications in the area of
cutting tools and in heat engines where the
components should withstand aggressive
components should withstand aggressive
environments.
™ In Aircraft engines - use of stater vanes formed of
CMC in the hot section of the F136 turbofan engine
is under consideration.

Reinforcement (Dispersed Phase)
o The dispersed phase can be any material in the form of fibres, particles,
whiskers or flakes
Flakes
Eg. Mica
Particles
Eg. Carbon black, talc
Dispersed Phase
p
Fibres
Eg. Nylon, Sisal
Whiskers
Eg. Graphite, SiC

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Polymer matrix Composites
o Polymers constitute the most important matrix materials and are used
in more than 95% of the composite products in use today.
Polymer
Resin Elastomer
Thermosets Thermoplastic
Thermosets Thermoplastic

Polymer matrix composites
¾ Thermoplastic polymer matrices‐
- Thermoplastics are incorporated in the composite system by melting and solidifying by
cooling.
- The physical reaction being reversible in nature.
- Thermoplastics have low creep resistance and low thermal stability compared to thermosetting
resins.
¾ Thermoset polymer matrices‐
- Thermosetting resins are more common for the development of composite systems.
- Solidification from the liquid phase takes place by the action of an irreversible chemical cross-
- Solidification from the liquid phase takes place by the action of an irreversible chemical cross-
linking reaction, generally in the presence of heat and pressure.
¾ Elastomer based composites‐
- The greater extensibility and high-energy storing capacity make them a suitable continuous
The greater extensibility and high energy storing capacity make them a suitable continuous
phase for composite materials.
- Unlike plastics, a wide variety of flexible products can be made using elastomers as the matrix
phase.
- They offer elastic strain higher than that of metals and can be stretched rapidly, even under
small loads.

Polymer matrix composites
o Polymer resins like epoxies and polyesters have
desirable properties of easily forming into complex
shapes.
o Materials like glass and boron have extremely high
g y g
tensile and compressive strength but on application
of stress random surface flaws will cause the material
to crack even below breaking point.
o This problem can be overcome by producing the
material in the fiber form since these flaws can be
material in the fiber form since these flaws can be
reduced.
o On mixing resin with glass, carbon and aramid,
materials of exceptional properties are obtained.
o The resin matrix spreads the load applied to the
composite between each of the individual fibers and
also protects the fibers from damage caused by
abrasive.
o High strength and stiffness, ease of moulding complex
shapes and high environmental resistance and low
densities make these composites superior to even
metals for many applications.
Fig.: The combined effect on
modulus of the addition
of fibers to resin matrix
of fibers to resin matrix.

Properties of composites
o The properties of the composite are determined by
a) properties of the fiber
b) properties of the resin
c) ratio of fibre to resin in the composite and
d) geometry and orientation of the fibers in the composite.
o The higher the fiber volume fraction, the better will be the mechanical
properties of the resultant composite.
‐ However, the fibers need to be fully coated in resin to be effective.
‐ The inclusion of fiber in the manufacturing process leads to
imperfections and air inclusions.
E.g.. a) In boat‐ building industry fiber level will be 30 – 40 %.
b) In aerospace industry precise processes are used to
f t t i l h i 70% f fib
manufacture materials having 70% of fiber.

Properties of composites
o The geometry of the fibers in a composite is important since fibers
h th i hi h t h i l ti l th i l th th
have their highest mechanical properties along their length than
across width.
o This leads to the highly anisotropic properties of composites.
o This leads to the highly anisotropic properties of composites.
o This is very advantageous since it is only necessary to put material
where loads will be applied and thus redundant material is avoided.
o The manufacturing processes, which are employed have critical part
to play in determining the performance of the resultant structure.

Loading Characteristics of composites
o There are four main direct loads that any
material in a structure has to withstand
a) Tension
b) Compression
b) Compression
c) Shear &
d) Flexure
d) Flexure.

Loading characteristics of composites
o Tension
‐ The response of a composite material to tensile loads depends on the
tensile stiffness and strength properties of the reinforcement fibers
tensile stiffness and strength properties of the reinforcement fibers.
‐ These are far higher for fibre compared to the resin system.
o Compression
p
The adhesive and stiffness properties of the resin system are crucial, as
the resin has to maintain fibers as straight columns and prevent them
from buckling
from buckling.

Shear strength
o Under shear loads the resin plays a major role in transferring the
stresses across the composite.
o For the good shear strength of composite material, the resin must
exhibit good mechanical properties and high adhesion to the
reinforcement fiber.
o The inter‐laminar shear strength of a composite is often used to indicate
these properties in a multiplayer composite (laminate).
Fig. : The shear load applied to a composite body

Flexure
o Flexural loads are a combination of tensile, compressive and shear loads.
o In the figure shown
o In the figure shown,
‐ the upper face experiences compression,
‐ the lower face experiences tension and
‐ central portion of the laminate experiences shear.
Fig. :The loading due to flexure on a composite body

Comparison with other structural materials
o The composite properties can vary by a factor of 10 with
a) the range of fiber contents and
b) orientation of the fibre commonly achieved.
y
o The lowest properties for each material are associated
ith i l f t i d t i l
with simple manufacturing processes and material
forms.
o The higher properties are associated with higher
technology manufacturing like aerospace industry.

Properties of nanocomposites
™ N it ff h diff t ti th
™ Nanocomposites offer much different properties than
conventional composites. The most important ones are
¾ enhanced mechanical strength
¾ optical transparency
¾ improved thermal stability
¾ improved barrier properties
¾ improved barrier properties
¾ improved flexibility
¾ novel electrical properties etc
¾ novel electrical properties etc.
‰ Since a lower degree of swelling indicates better curing, it is obvious
that the sample with 50% nanosilica stands out as less cured.
‰ Tg proportional to concentration of fillers, but curing is less

Polymer nanocomposites
o Polymer nanocomposites find importance since incorporation of these
materials into polymer matrices give property improvement remarkably.
o These can be incorporated into plastic foams to improve their inferior
mechanical strength, poor surface quality and low thermal and
dimensional stability
dimensional stability.
o Nanocomposite foams based on the combination of functional
nanoparticles and super‐critical fluid forming technology may lead to a
new class of materials that are light weight, high strength and
multifunctional.
o Polymer composites are widely used in automotive, aerospace,
o Polymer composites are widely used in automotive, aerospace,
constructions and electronic industries because of their improved
mechanical properties and physical properties over pure polymers.
Poly(dimethylsiloxane) >>>> PDMS

Types of polymer nanocomposites
o Polymer nanocomposites are divided into two general types:
a) Intercalated nanocomposites consisting of a regular penetration of the polymer in
bet een the cla la ers
between the clay layers.
b) Delaminated/exfoliated nanocomposites where thick layers of the nanofillers are
dispersed in the matrix forming a monolithic structure on the microscale.
o Exfoliation (material science) is the process responsible for breaking up
particle aggregates.
INTERCALATED EXFOLIATED

Types of nanocomposites
yp p
o Nanocomposites are usually divided as:
a) Platelet like nano structure (clay)
b) Nanotubes & nanofibers (CNF)
c) Spherical nanoparticles (ceramics metals block copolymers)
c) Spherical nanoparticles (ceramics, metals block copolymers)
o All three types of nanomaterials have been used in
Nanocomposite synthesis and processing
p y p g
o The following nanoparticles have attracted much attention:
a) plate‐like clay nanoparticles
b) carbon nanofibers and
c) carbon nanotubes

Synthesis of nanocomposites
Methods are:
a) Solution blending
b) Melt blending &
c) In situ polymerization
a) Solution blending:
S l t l t i t i d t di th ti l
- Solvent or solvent mixture is used to disperse the nanoparticles
and dissolve the polymer matrix.
‐ Polymer chain is then adsorbed on the nanoparticles and solvent
is removed
Disadvantages:
‐ Large amount of solvent required and product cost is high
‐ The nanoparticles may re-agglomerate
The nanoparticles may re agglomerate
o Inorganic layered silicates are able to exfoliate in water and form
colloidal particles.
o Several polymer nanocomposites including polyethylene oxide
o Several polymer nanocomposites, including polyethylene oxide,
polyvinyl alcohol, polyacrylic acid are prepared using solution
blending.

b) M lt bl di
b) Melt blending:
o Direct mixing of nanoparticles with a molten polymer.
Process eliminates the se of sol ent
o Process eliminates the use of solvent.
o Economically attractive route in fabricating polymer nanocomposites.
- Nylon 6, polystyrene and polypropylene composites are manufactured
y , p y y p yp py p f
by this method.
o This melt intercalation gives a simple way of preparing nanocomposites.
o Polar interactions of polymer and clay surface play a critical role in achieving
p y y p y g
particle dispersion.
o For non polar polymers (polypropylene) a compatibilizer such as maleic
anhydride modified polypropylene (PP‐MA) is commonly added to improve the
tibilit f l l d l
compatibility of polypropylene and clay.
o Polymers and carbon nanofibers, nanocomposites are also synthesized through this
method.
o Shear stress is needs to be controlled at an appropriate level to disintegrate
o Shear stress is needs to be controlled at an appropriate level to disintegrate
and disperse nanoparticles.

c) In situ polymerization:
c) In situ polymerization:
o Only viable method for most thermoset polymer to prepare
nanocomposites.
[
o By tailoring the interactions between the monomer, the surfactants and
the clay surface, exfoliated nanocomposites e.g. nylon 6,
polycaprolactum, epoxy, polycarbonate have been synthesized via the
ring opening polymerization.
o Carbon nanotubes and nanofibers have also been synthesized via in situ
o Carbon nanotubes and nanofibers have also been synthesized via in situ
polymerization. 10 wt% of polystyrene was added into the mixture of
styrene and carbon nanofibers to achieve a higher initial viscosity and
consequently a more stable fiber suspension.
o Polystyrene, polyvinyl chloride and polyolefins are three primary
thermoplastics used in polymer foams
thermoplastics used in polymer foams

During in situ polymerization,
o Reactive groups containing carbon‐carbon double bonds were introduced
t th l f t i th l f li ti
to the clay surface to increase the clay exfoliation.
o A nanoclay was prepared by the ion exchange of a reactive cationic
surfactant 2‐methacryloxyethyl hexadecyldimethyl ammonium bromide
surfactant 2 methacryloxyethyl hexadecyldimethyl ammonium bromide
(MHAB) with cations on the montmorillonite surface.
o Closite is a clay containing non polar aliphatic chain with the anchored
organic surfactant with polymerizable groups on MHAB provides an
additional kinetic driving force for layer separation.
o Complex exfoliation was reported for polystyrene nanocomposites
o Complex exfoliation was reported for polystyrene nanocomposites
synthesized with this reactive nanoclay at a clay concentration of 20 wt
%.

Synthesis of PS nanocomposites
o Polystyrene clay nanocomposites were synthesized in both
intercalated and exfoliated structures.
o To prepare the nanocomposites, organo‐nanoclay particles are pre‐
mixed with PS and then mechanically blended in single or twin screw
extruders
extruders.
o The formation of nanocomposites depends on the penetration of
polymer chains into the interlayer regions to separate the layers.
polymer chains into the interlayer regions to separate the layers.
o In situ polymerization has also been used to prepare PS
nanocomposites.
o By using reactive surfactants, the copolymerization of the interlayer
surfactant and styrene monomer provides the driving force for
delamination of clay crystallite
delamination of clay crystallite.

Intercalated and exfoliated PS/clay nanocomposites
Dimethyl dihydrogenated
-tallowalkyl ammonium
hl id
chloride
n-1
n-1
Methacryloxyl-oxyethyl
Hexadecyl-dimethyl
Ammonium bromide
DHTAC
Ammonium bromide

Synthesis of PVC nanocomposites
1) By melt blending:
o Used to prepare exfoliated nanocomposites of PVC.
P ti l d i l d l l i b t h d l hit d
o Particles used include clay, calcium carbonate hydrosulphite, copper and
antimony trioxide.
o The polar nature of the C‐Cl bond makes it possible to form exfoliated
nanocomposites of PVC in melt blending.
o A plasticizer like dioctylphthalate may serve as a co‐intercalate to
increase clay dispersion in PVC
increase clay dispersion in PVC.
2) In situ polymerization:
l f h b d b h l
o Clay nanocomposites of PVC have been prepared by either emulsion
polymerization or suspension polymerization.
o In general in situ polymerization methods can achieve much better clay
g p y y
dispersion.

Synthesis of PVC nanocomposites
o Highly exfoliated PVC clay nanocomposites can also be produced by flocculating
a mixture of polymer and clay mineral dispersion.
(or)
l i bl di
o By solution blending.
‐ Organoclay tends to induce the degradation of PVC because of its low thermal
stability.
o To reduce the degradation of PVC one of the following approaches is used:
i) Co‐intercalate dioctylphthalate into organoclay and then compound the mixture
with PVC Dioctylphthalate covers the quaternary amine groups preventing a
with PVC. Dioctylphthalate covers the quaternary amine groups preventing a
contact between amine and active chlorine atoms.
(or)
ii) Intercalate or exfoliate nanoclay in a polymer such as epoxy or polycaprolactum
) y p y p y p y p
which has good miscibility with PVC, by in situ polymerization to get a layer of
epoxy or polycaprolactum which prevents the direct contact of organoclay with
PVC in melt blending, inhibiting its degradation.

Biomedical Applications of Polymer Composites
o Biomaterials in the form of implants like sutures, bone plates, joint
replacement ligaments, vascular grafts, heart valves, intraocular lenses,
dental implants etc. and medical devices like pacemakers, bio sensors,
artificial hearts and blood tubes are widely used to improve the quality of life
of the patients.
o Bio compatibility is measured to indicate the biological performance of
p y g p
materials.
o Optimal interaction between biomaterial and host is reached when both the
surface and the structural compatibilities are met.
surface and the structural compatibilities are met.
o A large number of polymers are used in various biomedical applications.
o Ceramics are known for their good bio compatibility, corrosion resistance and
g p y
high compression resistance.
o Since the fiber reinforced polymers exhibit low elastic modulus and high
strength they are used in several orthopedic applications
strength, they are used in several orthopedic applications.

Composites in biomedical applications
o The composite materials offer several advantages over metals and
alloys in biomedical applications such as:
alloys in biomedical applications such as:
a) The radio transparency can be adjusted by adding contrast medium to the
polymer.
b) The polymer composite materials are fully compatible with the modern
diagnostic methods such as computer tomography and magnetic resonance
imaging as they are non‐magnetic.
o The applications include:
a) Hard tissue applications
b) Bone cement
c) Synthetic bone graft materials

Hard Tissue applications
D i th t l fi ti f b i f f t ti t i l
o During the external fixation of bones in case of fractures, casting material
used includes fabrics of glass and polyester fibers.
o However, plaster of Paris has many disadvantages like heaviness,
bulkiness, and low fatigue strength radio opaque and long setting time.
o Casts made of glass or polyester fiber fabrics and water activated
polyurethanes are gaining popularity because of
p y g g p p y
‐ ease of handling
‐ light weight
‐ comfortable to anatomical shape
p
‐ strong and stiff
‐ water proof
‐ radiolucent
‐ easy to remove
‐ permeable to ventilation (to avoid the patient’s skin
getting scorched or weakened)

Fixations using nanocomposites
g p
o External fixation made of stainless steel designs are being
o External fixation made of stainless steel designs are being
used which are heavy and cause discomfort to the patients.
o External fixations made using polymer composite materials
o External fixations made using polymer composite materials
are gaining acceptance because of their light weight yet
sufficient strength and stiffness.
o In the internal fixation approach bone fragments are held
together by different ways using these nanocomposite
i l b f h i fl ibili d bi ibili
implants because of their flexibility and bio‐compatibility

Bone Cement
Th t id l d b t i b d Pol (meth l methacr late)
o The most widely used bone cement is based on Poly(methyl methacrylate)
(PMMA), also called acrylic bone cement.
o It is self polymerizing and contains solid PMMA powder and liquid MMA
monomer
monomer.
o Fiber reinforcement with metal also reduces the peak temperature during
polymerization of the cement and thus reducing tissue necrosis.
o The reinforced cement possesses higher fracture toughness, fatigue resistance
and damage energy absorption capabilities than the unreinforced cement.
o In another approach, bone particles or surface reactive glass powders are mixed
i h PMMA b hi i di h i l fi i f PMMA
with PMMA bone cement to achieve immediate mechanical fixation of PMMA
with chemical bonding of bone particles or surface reactive glass powder with the
bone.
o Formation of this chemical bond makes it possible for mechanical stresses to be
o Formation of this chemical bond makes it possible for mechanical stresses to be
transferred across the cement/bone interface.
o For developing new bone cements the requirements are that it can be shaped,
moulded or injected to conform to complex internalcavities in bone and it must
moulded or injected to conform to complex internalcavities in bone and it must
harden in situ.

Synthetic bone graft materials
Synthetic bone graft materials
o The bone graft material must be sufficiently strong and stiff and
also capable of bonding to the residual bones.
o Polyethylene is considered biocompatible for satisfactory usage
in hip and knee joint replacement for many years.
o For load bearing applications, properties of polyethylene need to
g pp , p p p y y
be enhanced.
o In order to improve the mechanical properties polyethylene is
o In order to improve the mechanical properties polyethylene is
reinforced with hydroxyapatite [Ca5(PO4)3(OH)] to get a
composite material.

Advantages/disadvantages of advanced composites:
S N Ad t Di d t
S. No. Advantages Disadvantages
1 Weight reduction
High strength or stiffness to weight
ratio
Cost of raw materials and fabrication
ratio
2 Tailorable properties
Can tailor strength or stiffness to be
in the load direction
Transverse properties may be weak
3 Redundant load paths (fiber to fiber) Matrix is weak, low toughness
4 Longer life (no corrosion) Reuse and disposal may be difficult
5 Lower manufacturing costs because
of less part count
Difficult to attach
6 I h t d i A l i i diffi lt
6 Inherent damping Analysis is difficult
7 Increased (or decreased) thermal or
electrical conductivity
Matrix subject to environmental
degradation

Some typical Industrial Applications and reasons for using composites
Reason for use Material selected Application
Li ht Stiff d B ll b / hit Milit i ft b tt f
Lighter, Stiffer and
stronger
Boron, all carbon/ graphites, some
aramid
Military aircraft, better performance
Commercial aircraft, operating costs
Lower inertia,
faster startups,
less deflection
High strength
carbon/graphite, epoxy
Industrial rolls, for paper, films
Very high modulus
Lightweight,
damage tolerance
High strength carbon/graphite,
fiberglass, (hybrids), epoxy
CNG tanks for ’green’ cars, trucks
and busses to reduce environmental
pollution
More reproducible
l f
High strength or high
d l b hit /
High-speed aircraft. Metal skins
t b f d t l
complex surfaces modulus carbon graphite/
epoxy
cannot be formed accurately
Less pain and fatigue Carbon/graphite/epoxy Tennis, squash and racquetball
Racquets.
Metallic racquets are no
longer available.
Tailorability of bending
& twisting response
Carbon/graphite-epoxy Golf shafts, fishing rods
Transparency to radiation Carbon/ graphite-epoxy X-ray tables
Crashworthiness Carbon/ graphite-epoxy Racing cars
Higher natural frequency,
lighter
Carbon/ graphite-epoxy Automotive and industrial
drive shafts
Water resistance Fiberglass (woven fabric), polyester
or isopolyester
Commercial boats
or isopolyester
Ease of field application Carbon/graphite, fiberglass
- epoxy, tape and fabric
Freeway support structure repair
after earthquake

Advantages of Composite materials
1. High resistance to fatigue and corrosion degradation.
1. High resistance to fatigue and corrosion degradation.
2. High ‘strength or stiffness to weight’ ratio. As enumerated above,
weight savings are significant ranging from 25-45% of the weight of
weight savings are significant ranging from 25 45% of the weight of
conventional metallic designs.
3 Directional tailoring capabilities to meet the design requirements
3. Directional tailoring capabilities to meet the design requirements.
The fibre pattern can be laid in a manner that will tailor the structure
to efficiently sustain the applied loads
to efficiently sustain the applied loads.
4. Composites offer improved torsional stiffness. This implies high
whirling speeds reduced number of intermediate bearings and
whirling speeds, reduced number of intermediate bearings and
supporting structural elements. The overall part count and
f t i & bl t th d d
manufacturing & assembly costs are thus reduced.
5. High resistance to impact damage.

6. Composites are dimensionally stable i.e. they have low thermal
d ti it d l ffi i t f th l i C it t i l
conductivity and low coefficient of thermal expansion. Composite materials
can be tailored to comply with a broad range of thermal expansion design
requirements and to minimize thermal stresses
requirements and to minimize thermal stresses.
7. The improved weatherability of composites in a marine environ. as well as
their corrosion resistance and durability reduce the down time for
their corrosion resistance and durability reduce the down time for
maintenance.
8. Material is reduced because composite parts and structures are frequently
p p q y
built to shape rather than machined to the required configuration, as is
common with metals.
9. Excellent heat sink properties of composites, especially C-C, combined
with their lightweight have extended their use for aircraft brakes.
10. Improved friction and wear properties.

Disadvantage of Composites
Some of the associated disadvantages of advanced composites are
as follows:
1. High cost of raw materials and fabrication.
2. Transverse properties may be weak.
3. Reuse and disposal may be difficult.
4. Difficult to attach.
5. Hot curing is necessary in many cases requiring special tooling.
6. Hot or cold curing takes time and analysis is difficult.
7. Matrix is subject to environmental degradation

para-aramid synthetic fiber : kevlar

ƒUltra-high-molecular-weight polyethylene
ƒbisphenol-A-glycidyl dimethacrylate
ƒPoly(methyl methacrylate)-grafted C fibre
ƒPoly(methyl methacrylate)-grafted C fibre
ƒ Kevlar fiber (KF)
ƒPolyethylene terephthalate (PET)

Thermoplastic matrices offer certain advantages of thermosets
p g
¾ No chemical reaction that causes release of gas products or
exothermic heat
¾ The materials can be reworked
¾ The materials can be reworked
¾ Low processing time
¾ At normal temperature they have an optimum combination of
toughness rigidity and creep resistance
toughness, rigidity and creep resistance

¾ Nose landing gear doors: Graphite
¾ Wing to body fairings: graphite/kevlar/fiberglass and
List of composite parts in the main structure of the Boeing 757-200 aircraft
¾ Wing-to-body fairings: graphite/kevlar/fiberglass and
graphite/kevlar + non-woven kevlar mat
¾ Body main landing gear doors: graphite
¾ Trunnion fairings and wing landing gear doors: graphite/kevlar
¾ Brakes : structural carbon
¾ Cowl components: graphite
¾ Spoilers: graphite
¾ Wing leading edge lower panels: kevlar/fiberglass
¾ Wing leading edge lower panels: kevlar/fiberglass
¾ Fixed trailing edge panels: graphite/kevlar + non-woven kevlar mat
¾ Fixed trailing edge panels upper: graphite/fiberglass and
¾ lower: graphite/kevlar + non-woven kevlar mat
¾El hi
¾Elevators: graphite
¾Fixed trailing edge panels: graphite/kevlar + non-woven kevlat mat
¾ Rudder: graphite
¾ Tip fairings : fiberglass
¾ Tip fairings : fiberglass
¾ Aft flaps: i) outboard: graphite ii) inboard: graphite/fiberglass
¾ Flap support fairings: i) Fwd segments: G/kevlar + non-woven k mat
¾ ii) Aft segment: graphite/fiberglass
¾ Ail hit
¾ Ailerons: graphite
¾ Engine strut fairings: kevlar/fiberglass
¾ Environmental control system ducts: kevlar

sity
ngth/den
astic
stre
ngth
=
ela
units)
nsile
stren
arbitrary
Ti>Steel>Mg>Al
pecific
ten
(in
g
Specific tensile modulus = elastic modulus/density
(in arbitrary units)
Sp

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