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INTRODUCTION
Composite materials are considered the most advanced
and adaptable engineering materials known to man.
A composite material is the combination of 2 or more
distinct materials into one engineering material where
the phases are still significantThe word composite is derived from the latin word
componere which means to put together .
The components are put together in order to suppress
their undesirable properties in favor of their desirable
properties.
This does not include metal alloys or polymer blends
which combines at an atomic level.
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Evolution of Material
During the stone age, flint was used as cutting material.Metals were then least important.
At that time, natural polymers (wood, skins, fibers) dominated
in the engineering applications. (house, weapons, boats)
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Later, metal working evolved and development dominatesengineering achievement until into 20th century.
In 1960s the use of metal in engineering material declined.Polymers, composites and ceramics regaining the relativeimportance to man. However these are synthetic materials.
Examples of natural composites are trees, wood, bone ormollusk shell. Natural composites tend to be weaker and lessstiff than synthetic composites, but are often superior in termsof design and manufacture. E.g: Spider Web
Natural composites are also smart materials in that theyadapt to the environment.
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Synthetic composites- first composites are
believed to be made by the Egyptians who used
straw to reinforce clay to make brick.
They use papyrus reeds (placed parallel to each
other forming layers, and then stacked
perpendicular to each other in alternate directions,
dried under pressure to form paper like sheets.
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-Composites in most cases comprisesof a bulk phase enclosing a fibrousreinforcing phase; called matrix andreinforcement.
Matrix
Gives shape to the composites
Bind the reinforcement together
Introduce external loads to the
reinforcement Protect it from environmental effects(hightemperature, water, UV light, etc)
Fiber Reinforcement
Carries, the structural loads Dictates microscopic stiffness & strength
The Composite Concept
Fiber reinforcement
Matrix
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BASIC KNOWLEDGE Most impressive mechanical properties are found in composites with
continuous and aligned reinforcement.
Why polymer composites are used in most structural applications?
-they offer a given property
-often excellent stiffness and strength at a lower weight than the competition(steel, concrete, wood).
Properties of composite materials:
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Properties of Polymer Composites
Advantages Disadvantages
- corrosion resistance - high raw material cost
- electrical insulation - difficult manufacturing
- reduction in tool and assembly cost - lack of knowledge/experience
- decrease in maintenance cost
- exceptional formability
Composites are therefore certainly not appropriate in
all applications;
a critical assessment of the material alternativesmust always be made in term ofperformance- cost
ratio.
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Transport Applications Is a dominant sector of
composites and the fastestgrowing.
High specific stiffness andstrength but lighter parts can
be exploited to reduce fuelconsumption or to increasepayload. (commercialvehicles)
Better feasible mold designgeometrically can beachieved by usingcomposites
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In some truck and bus
applications, usually body panels
and dashboards are designed
from composites.
Composites also turn up in an
increasing number of non-
structural or semi- structuralunder the hood applications,
where temperatures are of the
order of 150oC or higher.
More applications such as noiseshields, heat shields, air intake
manifold, engine top cover etc.
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In F1 and motorcycle racing,they use composites:
-save weight and thus gainperformance.
Carbon fiber and Kevlar arebeing used as they arelightweight, high in strength
with good heat resistance.
Body parts of sports cars aredesigned as composite bodypanel fastened to a
conventional steel spaceframe like dodge viper,skyline and the newMercedes CLK.
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Boat Building
By the 1950's, boat buildersbegan the transition to fiberglasshulls. Such designs are:
-easier to build
-significantly lower in cost
-complex shapes were easily formedin fiberglass when compared towood or metal.
Buyers got attractive new stylesthat were lower cost, easier totransport, extremely durable andeasy to maintain, since fiberglassdoes not rust like steel nor rot likewood.
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In the Defense world, marinecomposites offer similaradvantages.
Steel ships rust, requiringconstant maintenance.
The heavy weight of steelships also places limits on theirspeed and increases fuelconsumption: heavy ships takea lot of fuel to move. Becausewarships often have to worryabout explosive mines, themagnetic signature of ships is
a concern to all sailors.
Composites are non-magneticand make an ideal material forany ship expected to face minewarfare conditions. (MCMV)
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Aerospace and MilitaryApplications
The main reason to use composites:
-high profile material is needed
-the ultimate in performance
-saved weight is seen as increase inload carrying capability or a matter oflife and death.
The less insignificant fact is thatcomposites can lower manufacturingcost, better fatigue resistance thanlight metal.
Recently, glass reinforcedcomposites have been used inaircraft radomes (nose cones) andstealth properties (although most ofthe stealth technique depends on theangular geometry to reflect minimumof radiation).
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In commercial and civilian
aircraft applications,
potential weight saving is
highly valued.
Here, the use of carbon
reinforced epoxy sandwich
with honeycomb core as areplacement of metal rudder,
clearly resulted in a
reduction of 22 percent
weight and number of partsfrom 17000 to 4800 (since
bonding eliminates rivets)
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In aerospace, weightreduction by usingcomposites can be seenclearly from the launch of
The Pegasus XL, where analmost composite completestructure can be seen.
Composites are well suitedto applications where
primary load case is(internal) pressure.
For launching, manycomponents are exposed tosuch high temperatures
where compositescontaining ceramic andcarbon matrices are used.
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Construction Applications
Composites inconstruction come underindustrial and agriculturalequipment and corrosionresistant equipment.
The most significantexample of application isthe bridge building. The
Aberfeldy footbridge inScotland utilizes smallamount of heavymachinery and concrete.
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- In other industries such as
chemical plants, waste water
treatment plants,
composites are used in
construction applications
such as handrails, watertanks and silos to eliminate
corrosion issues and reduce
maintenance costs in
replacing steel components.
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Electrical and Sanitary Applications
In electrical applications, dielectricstrength of the glass-reinforcedcomposites is more important thanthe structural capabilities.
This includes circuit boards,equipment housings, transformerspacers and cable trays.
Ladder rail is a common example
where direct electrical contactbetween electrician and potentiallyhot wires and ground is obvious.
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- In sanitary applications suchas shower enclosures, bathtubs, spas, sinks and cabinets
composites are used as theypossess design freedom andeconomically proven on theproduction and maintenanceconsiderations.
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Sports Applications
In some applications whereperformance and weight isthe deciding factor, it is vitalto use composites to enhance
the properties
In ski, tennis, golf and squashapplications, the use of
Kevlar, graphite or carbonreinforcement is vital as theyactually change the traditionalapproach of the game aswell.
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Other Applications
The first one is medicine, wherecomposites for quite some time havebeen used in patient support tables inX-ray machines. These tables offergreat stiffness while still beingtransparent to the radiation in order notto obscure the radiograph.
- Composites are also beinginvestigated for artificial joints toreplace the more conventional metalcomponents used in, for example,artificial hip joints.
- A problem with inserting a titanium hipimplant into the femur is that thestiffness of the implant is so muchgreater than that of the bone, whichgradually leads to bone deterioration.
- With composites the stiffness can betailored to that of the bone to eliminate
this problem.
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A somewhat unusual composite application is in musical
instrument where string instruments so far have receivedthe most attention.
With careful design and manufacture an acoustic guitar,or for that matter any string instrument, can be made tosatisfy the pickiest musician.
Advantages:
-possibility of tailoring the instrument to whatever the
customer wants-the instrument is not sensitive to climate changes ortransportation damage
-no rare woods on the brink extinction are used.
Other Usage
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