Unit III- Composite Materials

Composite materials: Introduction to composite

materials – Properties and morphology – loading

characteristics Fibre reinforced compositescharacteristics - 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 Materialso Formed by the combination of

two or more constituent materials with significantly different physicalwith significantly different physicalor chemical properties.

o The constituent materials will remain separate and distinct on a macroscopic levelwithin 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 compositesNatural compositesWood: Cellulose fibres and lignin matrix

Animal body: bone fibres and tissues as matrix

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

Sea shells:Elephant tusk:

REQUIREMENTS OF COMPOSITE MATERIALS

S l i t f it t i lSome general requirements of composite materials

The second phase (fibres or particles) uniformly distributed

throughout the matrix and must not be in direct contact with onethroughout the matrix and must not be in direct contact with one

another

The constituents of the composite should not react with oneThe 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 compositeleading to premature failure of the composite

In no case should the second phase loose its strength, it should be

well bonded to the matrixwell bonded to the matrix

Matrix must have a lower modulus of elasticity than the fibre

In general, both the matrix and fibre should not have greatlyg , g y

different coefficient of linear expansion

Matrix Fibre Elastic Modulus (GPa)

Tensile st. (MPa)

long trans long translong trans long transAl B 210 150 1500 140Ti-6Al-4V SiC 300 150 1750 410Al-Li Al2O3 262 152 690 1802 3Epoxy E-glass 40 10 780 28Epoxy 2-D glass

cloth16.5 16.5 280 280

Epo Boron 215 24 2 1400 63Epoxy Boron 215 24.2 1400 63

Epoxy Carbon 145 9.4 1860 65Polyester Chopped

glass55-138 - 103-206 -

gAl2O3 - 350-700 2-5 Flexture

St (MPa)Fracture toughness (MPa m bar

MgO - 200-500 1-3gSiC - 500-800 3-6SiO2 glass - 70-150 1Al203 SiC

whiskers800 10

whiskersSiO2 glass SiC fibres 1000 ~ 20

Al203 BN particulates 350 7

Matrix binds the fibers together, holding them aligned in the ROLE OF MATRIX IN COMPOSITES

important stress direction

Loads applied to the composite and the fibers are the principal load

bearing component, through the matrix

This enables the composite to withstand compression, flexural

and shear forces as well as tensile loads.

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.

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 tAt 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 and3. 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 eliminate3. 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-homogeneousQuasi-isotropic

Mi fl k i f d ith l

Particulate composites

Mica flakes reinforced with glass(non-metallic particles in a non-metallic matrix)

Aluminium particles in polyurethane rubber(metallic particles in a non-metallic matrix)

Lead particles in copper alloys(metallic particles in a metallic matrix)(metallic particles in a metallic matrix)

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

Fibres of significant strength and stiffness embedded in a

matrix with distinct boundaries between them.

Both fibres and matrix maintain their physical and chemical

identities.

Combination performs a function which cannot be done

by each constituent acting singly.by each constituent acting singly.

Fibres of fibre reinforced plastic (FRP) may be short or

continuouscontinuous.

FRP having continuous fibres is more efficient.

Fibre reinforced composites

Constituents of composite

o Matrix 

o Dispersed phase/Reinforcement phaseo Dispersed phase/Reinforcement phase  

o Interface/inter‐phase

Interface

C iReinforcement

CompositeMatrix

Constituents of compositeo Matrix (Continuous phase) : Continuous or bulk material

o Reinforcement (Dispersed Phase) : Added primarily to increase thet th d tiff f t istrength 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 twopconstituent parts, one being a metal.The other material may be a different metal or another material such as a 

i i dceramic or organic compound. 

o Carbide drills are often made from a tough cobalt matrix with hard tungsten carbideparticles inside.

o Modern high‐performance sport cars, such as those built by Porsche, use rotorsmade 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 titaniummatrix for a structural component of the jet's landing gear.

o MMCs are nearly always more expensive than the more conventional materials theyo MMCs are nearly always more expensive than the more conventional materials theyare replacing.

o As a result, they are found where improved properties and performance can justifythe added cost.

o Today these applications are found most often in aircraft components, spacesystems 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 resistance3. Better fatigue resistance

4. Better elevated temperature properties

5 Higher strength5. 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 bilit1. 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 MMCs8. Fabric ability of whisker and particulate-reinforced MMCs

with conventional metal working equipment.

Some of the disadvantages of MMCs compared to monolithicSome of the disadvantages of MMCs compared to monolithic

metals and polymer matrix composites are:

1 Higher cost of some material systems1. 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:

There are local clouds (clusters) of the dispersed particles (fibers);

There may be gravity segregation of the dispersed phase due to aThere may be gravity segregation of the dispersed phase due to a

difference in the densities of the dispersed and matrix phase.

The technology is relatively simple and low costThe 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 compositesemi-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 dthe semi-solid matrix material enables better mixing of the dispersed

phase.

The most important MMC systems are:1. Aluminum matrix2 Continuous fibers: boron silicon carbide alumina graphite2. Continuous fibers: boron, silicon carbide, alumina, graphite3. Discontinuous fibers: alumina, alumina-silica4. Whiskers: silicon carbide5 P ti l t ili bid b bid5. Particulates: silicon carbide, boron carbide6. Magnesium matrix7. Continuous fibers: graphite, aluminag p ,8. Whiskers: silicon carbide9. Particulates: silicon carbide, boron carbide10 Titanium matrix10. Titanium matrix11. Continuous fibers: silicon carbide, coated boron12. Particulates: titanium carbide13 C t i13. Copper matrix14. Continuous fibers: graphite, silicon carbide15. Wires: niobium-titanium, niobium-tin16. 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 orchopped fibres particulates having compositions of Si N SiCchopped fibres, particulates having compositions of Si3N4, SiC,AlN, titanium diboride, boron carbide, and boron nitride orwith continuous fibres.

o The desirable characteristics of CMC includeHigh‐temperature stabilityHigh temperature stability

High thermal shock resistance

High hardness

Hi h i i tHigh 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 aggressivecomponents should withstand aggressive environments.In Aircraft engines - use of stater vanes formed of CMC in the hot section of the F136 turbofan engineis 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

FibresEg. Nylon, Sisal

Whiskers Eg. Graphite, SiC

Polymer matrix Compositeso 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 ThermoplasticThermosets Thermoplastic

Polymer matrix compositesThermoplastic polymer matrices‐

- Thermoplastics are incorporated in the composite system by melting and solidifying bycooling.

- The physical reaction being reversible in nature.

- Thermoplastics have low creep resistance and low thermal stability compared to thermosettingresins.

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.

Elastomer based composites‐

- The greater extensibility and high-energy storing capacity make them a suitable continuousThe greater extensibility and high energy storing capacity make them a suitable continuousphase for composite materials.

- Unlike plastics, a wide variety of flexible products can be made using elastomers as the matrixphase.

- They offer elastic strain higher than that of metals and can be stretched rapidly, even undersmall loads.

Polymer matrix compositeso Polymer resins like epoxies and polyesters have

desirable properties of easily forming into complexshapes.

o Materials like glass and boron have extremely highg y gtensile and compressive strength but on applicationof stress random surface flaws will cause the materialto crack even below breaking point.

o This problem can be overcome by producing thematerial in the fiber form since these flaws can bematerial in the fiber form since these flaws can bereduced.

o On mixing resin with glass, carbon and aramid,materials of exceptional properties are obtained.

o The resin matrix spreads the load applied to thecomposite between each of the individual fibers andalso protects the fibers from damage caused byabrasive.

o High strength and stiffness, ease of moulding complexshapes and high environmental resistance and lowdensities make these composites superior to evenmetals for many applications.

Fig.: The combined effect onmodulus of the additionof fibers to resin matrixof fibers to resin matrix.

Properties of composites

o The properties of the composite are determined by

a) properties of the fiberb) properties of the resinc) ratio of fibre to resin in the composite andd) geometry and orientation of the fibers in the composite.

o The higher the fiber volume fraction, the better will be the mechanicalproperties 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 tof t t i l h i 70% f fibmanufacture materials having 70% of fiber.

Properties of composites

o The geometry of the fibers in a composite is important since fibersh th i hi h t h i l ti l th i l th thhave their highest mechanical properties along their length thanacross 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 materialwhere loads will be applied and thus redundant material is avoided.

o The manufacturing processes, which are employed have critical partto 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) Compressionb) Compression

c) Shear  &

d) Flexured) Flexure. 

Loading characteristics of compositeso Tension

‐ The response of a composite material to tensile loads depends on thetensile stiffness and strength properties of the reinforcement fiberstensile stiffness and strength properties of the reinforcement fibers.

‐ These are far higher for fibre compared to the resin system.

o CompressionpThe adhesive and stiffness properties of the resin system are crucial, asthe resin has to maintain fibers as straight columns and prevent themfrom bucklingfrom buckling.

Shear strengtho 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 mustexhibit good mechanical properties and high adhesion to thereinforcement fiber.

o The inter‐laminar shear strength of a composite is often used to indicatethese 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 showno 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 lwith 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 thNanocomposites offer much different properties than

conventional composites. The most important ones are

enhanced mechanical strength

optical transparency

improved thermal stability

improved barrier propertiesimproved barrier properties

improved flexibility

novel electrical properties etcnovel 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 thesematerials into polymer matrices give property improvement remarkably.

o These can be incorporated into plastic foams to improve their inferiormechanical strength, poor surface quality and low thermal anddimensional stabilitydimensional stability.

o Nanocomposite foams based on the combination of functionalnanoparticles and super‐critical fluid forming technology may lead to anew class of materials that are light weight, high strength andmultifunctional.

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 improvedmechanical 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 inbet een the cla la ersbetween the clay layers.

b) Delaminated/exfoliated nanocomposites where thick layers of the nanofillers aredispersed 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 nanocompositesyp 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 inNanocomposite synthesis and processingp 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 nanoparticlesand dissolve the polymer matrix.

‐ Polymer chain is then adsorbed on the nanoparticles and solventis removed

Disadvantages:‐ Large amount of solvent required and product cost is high‐ The nanoparticles may re-agglomerateThe nanoparticles may re agglomerate

o Inorganic layered silicates are able to exfoliate in water and formcolloidal particles.

o Several polymer nanocomposites including polyethylene oxideo Several polymer nanocomposites, including polyethylene oxide,polyvinyl alcohol, polyacrylic acid are prepared using solutionblending.

Synthesis of nanocompositesb) M lt bl dib) Melt blending:

o Direct mixing of nanoparticles with a molten polymer.

Process eliminates the se of sol ento Process eliminates the use of solvent.

o Economically attractive route in fabricating polymer nanocomposites.

- Nylon 6, polystyrene and polypropylene composites are manufacturedy , p y y p yp py p fby 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 achievingp y y p y gparticle dispersion.

o For non polar polymers (polypropylene) a compatibilizer such as maleicanhydride modified polypropylene (PP‐MA) is commonly added to improve the

tibilit f l l d lcompatibility 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 disintegrateo Shear stress is needs to be controlled at an appropriate level to disintegrateand disperse nanoparticles.

Synthesis of nanocompositesc) 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 situo 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 foamsthermoplastics used in polymer foams

Synthesis of nanocompositesDuring in situ polymerization,

o Reactive groups containing carbon‐carbon double bonds were introduced

t th l f t i th l f li tito 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 bromidesurfactant 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 nanocompositeso 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

extrudersextruders.

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 crystallitedelamination of clay crystallite.

Intercalated and exfoliated PS/clay nanocompositesDimethyl dihydrogenated-tallowalkyl ammonium

hl idchloride

n-1n-1

Methacryloxyl-oxyethylHexadecyl-dimethylAmmonium bromide

DHTACAmmonium bromide

Synthesis of PVC nanocomposites1) 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 do Particles used include clay, calcium carbonate hydrosulphite, copper andantimony trioxide.

o The polar nature of the C‐Cl bond makes it possible to form exfoliatednanocomposites of PVC in melt blending.

o A plasticizer like dioctylphthalate may serve as a co‐intercalate toincrease clay dispersion in PVCincrease clay dispersion in PVC.

2) In situ polymerization:

l f h b d b h lo Clay nanocomposites of PVC have been prepared by either emulsionpolymerization or suspension polymerization.

o In general in situ polymerization methods can achieve much better clayg p y ydispersion.

Synthesis of PVC nanocompositeso Highly exfoliated PVC clay nanocomposites can also be produced by flocculating

a mixture of polymer and clay mineral dispersion.

(or) 

l i bl dio By solution blending.

‐ Organoclay tends to induce the degradation of PVC because of its low thermalstability.

o To reduce the degradation of PVC one of the following approaches is used:

i) Co‐intercalate dioctylphthalate into organoclay and then compound the mixturewith PVC Dioctylphthalate covers the quaternary amine groups preventing awith PVC. Dioctylphthalate covers the quaternary amine groups preventing acontact 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 pwhich has good miscibility with PVC, by in situ polymerization to get a layer ofepoxy or polycaprolactum which prevents the direct contact of organoclay withPVC in melt blending, inhibiting its degradation.

Biomedical Applications of Polymer Composites

o Biomaterials in the form of implants like sutures, bone plates, jointreplacement 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 lifeof the patients.

o Bio compatibility is measured to indicate the biological performance ofp y g pmaterials.

o Optimal interaction between biomaterial and host is reached when both thesurface 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 andg p yhigh compression resistance.

o Since the fiber reinforced polymers exhibit low elastic modulus and highstrength they are used in several orthopedic applicationsstrength, they are used in several orthopedic applications.

Composites in biomedical applications

o The composite materials offer several advantages over metals andalloys in biomedical applications such as:alloys in biomedical applications such as:

a) The radio transparency can be adjusted by adding contrast medium to thepolymer.

b) The polymer composite materials are fully compatible with the moderndiagnostic methods such as computer tomography and magnetic resonanceimaging as they are non‐magnetic.

o The applications include:

a) Hard tissue applications

b) Bone cement

c) Synthetic bone graft materials

Hard Tissue applicationsD i th t l fi ti f b i f f t ti t i lo During the external fixation of bones in case of fractures, casting materialused 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 activatedpolyurethanes are gaining popularity because ofp y g g p p y

‐ ease of handling‐ light weight‐ comfortable to anatomical shapep‐ strong and stiff‐water proof‐ radiolucent ‐ easy to remove‐ permeable to ventilation (to avoid the patient’s skin

getting scorched or weakened)

Fixations using nanocompositesg p

o External fixation made of stainless steel designs are beingo External fixation made of stainless steel designs are beingused which are heavy and cause discomfort to the patients.

o External fixations made using polymer composite materialso External fixations made using polymer composite materialsare gaining acceptance because of their light weight yetsufficient strength and stiffness.

o In the internal fixation approach bone fragments are heldtogether by different ways using these nanocompositei l b f h i fl ibili d bi ibiliimplants because of their flexibility and bio‐compatibility

Bone CementTh 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 MMAmonomermonomer.

o Fiber reinforcement with metal also reduces the peak temperature duringpolymerization of the cement and thus reducing tissue necrosis.

o The reinforced cement possesses higher fracture toughness, fatigue resistanceand damage energy absorption capabilities than the unreinforced cement.

o In another approach, bone particles or surface reactive glass powders are mixedi h PMMA b hi i di h i l fi i f PMMAwith PMMA bone cement to achieve immediate mechanical fixation of PMMA

with chemical bonding of bone particles or surface reactive glass powder with thebone.

o Formation of this chemical bond makes it possible for mechanical stresses to beo Formation of this chemical bond makes it possible for mechanical stresses to betransferred 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 mustmoulded or injected to conform to complex internalcavities in bone and it mustharden in situ.

Synthetic bone graft materialsSynthetic 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 tog pp , p p p y y

be enhanced.

o In order to improve the mechanical properties polyethylene iso 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 tS. No. Advantages Disadvantages1 Weight reduction

High strength or stiffness to weight ratio

Cost of raw materials and fabrication

ratio2 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 lt6 Inherent damping Analysis is difficult

7 Increased (or decreased) thermal orelectrical 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 fLighter, Stiffer and stronger

Boron, all carbon/ graphites, some aramid

Military aircraft, better performanceCommercial aircraft, operating costs

Lower inertia, faster startups,less deflection

High strengthcarbon/graphite, epoxy

Industrial rolls, for paper, filmsVery high modulus

Lightweight, damage tolerance

High strength carbon/graphite, fiberglass, (hybrids), epoxy

CNG tanks for ’green’ cars, trucksand busses to reduce environmentalpollution

More reproducible l f

High strength or highd l b hit /

High-speed aircraft. Metal skinst b f d t lcomplex surfaces modulus carbon graphite/

epoxycannot be formed accurately

Less pain and fatigue Carbon/graphite/epoxy Tennis, squash and racquetballRacquets. Metallic racquets are nolonger 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 industrialdrive shafts

Water resistance Fiberglass (woven fabric), polyester or isopolyester

Commercial boatsor isopolyester

Ease of field application Carbon/graphite, fiberglass- epoxy, tape and fabric

Freeway support structure repairafter 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 ofweight savings are significant ranging from 25 45% of the weight of

conventional metallic designs.

3 Directional tailoring capabilities to meet the design requirements3. 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 loadsto efficiently sustain the applied loads.

4. Composites offer improved torsional stiffness. This implies high

whirling speeds reduced number of intermediate bearings andwhirling speeds, reduced number of intermediate bearings and

supporting structural elements. The overall part count and

f t i & bl t th d dmanufacturing & 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 lconductivity 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 stressesrequirements 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 fortheir 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

Ultra-high-molecular-weight polyethylenebisphenol-A-glycidyl dimethacrylatePoly(methyl methacrylate)-grafted C fibrePoly(methyl methacrylate)-grafted C fibreKevlar fiber (KF) Polyethylene terephthalate (PET)

Thermoplastic matrices offer certain advantages of thermosetsp g

No chemical reaction that causes release of gas products or

exothermic heat

The materials can be reworkedThe materials can be reworked

Low processing time

At normal temperature they have an optimum combination of

toughness rigidity and creep resistancetoughness, rigidity and creep resistance

Nose landing gear doors: GraphiteWing to body fairings: graphite/kevlar/fiberglass and

List of composite parts in the main structure of the Boeing 757-200 aircraft

Wing-to-body fairings: graphite/kevlar/fiberglass and graphite/kevlar + non-woven kevlar mat

Body main landing gear doors: graphiteTrunnion fairings and wing landing gear doors: graphite/kevlarBrakes : structural carbonCowl components: graphiteSpoilers: graphiteWing leading edge lower panels: kevlar/fiberglassWing leading edge lower panels: kevlar/fiberglassFixed trailing edge panels: graphite/kevlar + non-woven kevlar matFixed trailing edge panels upper: graphite/fiberglass and

lower: graphite/kevlar + non-woven kevlar matEl hiElevators: graphiteFixed trailing edge panels: graphite/kevlar + non-woven kevlat matRudder: graphiteTip fairings : fiberglassTip fairings : fiberglassAft flaps: i) outboard: graphite ii) inboard: graphite/fiberglassFlap support fairings: i) Fwd segments: G/kevlar + non-woven k mat

ii) Aft segment: graphite/fiberglassAil hitAilerons: graphiteEngine strut fairings: kevlar/fiberglassEnvironmental control system ducts: kevlar

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