Carbon fibres its applications

Document Sample
Carbon fibres its applications Powered By Docstoc
					Carbon fibres & its applications                              Page 1

                                    CHAPTER 1

        W hen you go to a sports shop you are inundated with new
"graphite" based materials for sports equipment: golf clubs,
tennis rackets, bicycles (frames and wheel disks), ultra light
airframes feature these new lightweight materials. Bu t, we are
also familiar with graphite as being a very common and mundane
substance. Graphite has long been a component of pencil lead,
and is used as a basic lubricant. How is it that graphite is both a
hi-tech and low-tech material? It would seem as if th ere are two
different kinds of graphite. In fact, this is true. W hen vendors
market "graphite fib re" products they are usually selling a "carbon
fibre" product. The correct name for the fib res used in all
strengthening and reinforcing applications is carbo n fibres. But,
there is more to the story than just a general misconception over
the term "graphite fib res." Surprisingly, if we look at a small
section of graphite and carbon fib res on the atomic level they
appear to be identical.

Department of Mechanical engineering                           AJCE
carbon fiber & its applications                                      Page2

                                   CHAPTER 2

                                  CARBON FIBRE


        Carbon Fib re is one of the most recent developments in the
field of composite materials and is one of the strongest fibers
known to man. It is usually the first choice of fibre if something
very strong and very light is req uired. Carbon fibre was originally
developed in space technology, but has now been adopted in
many other areas of manufacture. Generally the term "carbon
fibre" is used to refer to carbon filament thread. Carbon fibre is
one of the latest reinforcement materials used in composites. It's
a real hi-tech material, which provides very good structural
properties, better than those of any metal . This material is known
for its high specific stiffness and strength. The material has an
advantageous combination of good mechanical properties and low
weight. It is fast becoming one of the leading materials in many
areas,       including        performance   sport   equipment,   transport,
scientific experiments and even wallets a nd watches!

Department of Mechanical engineering                                 AJCE
carbon fiber & its applications                                                          Page3

                                  Table2.1: Key benefits of carbon fibre

                                   Fine Grained             Unidirectional
        Property                                                               3-D Fibres
                                      Graphite                   Fibres

Elastic Modulus
                             10-15                       120-150              40-100

Tensile Strength
                             40-60                       600-700              200-350

Compressive Strength
                             110-200                     500-800              150-200

Fracture Energy
                             0.07-0.09                   1.4-2.0              5-10

                                                                              better than
Oxidation resistance         Very low                    poor

                           Table2.2: comparison b/w carbon fibre & steel

                            TENSILE                      DENSITY SPECIFIC
                            STRENGTH                                   STRENGTH

     CARBON FIBRE 3.50                                   1.75          2.00

     STEEL                  1.30                         7.90          0.17

        Carbon fibre has a tensile strength almost 3 times greater
than that of steel, and have 4.5 times less dense.

Department of Mechanical engineering                                                     AJCE
carbon fiber & its applications                 Page4


       high tensile strength
       low thermal expansion
       Resistance to corrosion and fire
       High stress tolerance levels
       electrically and thermally conductive
       Chemical inertness
       light weight and low density
       very hard and brittle
       high abrasion and wear resistance

Department of Mechanical engineering            AJCE
carbon fiber & its applications                                             Page5

                                   CHAPTER 3

                        PRODUCTION PROCESSES


        Carbon fibres are long bundles of linked graphite plates,
forming a crystal structure layered parallel to the fiber axis. This
crystal structure makes the fibers highly anisotropic, with an
elastic modulus of up to 5000GPa. Fibres can be made from
several       different      precursor      materials,     and   the   method    of
production is essentially the same for each precursor: a polymer
fibre undergoes pyrolysis under well -controlled heat, timing and
atmospheric conditions, and at some point in the process it is
subjected to tensio n. The resulting fiber can have a wide range of
properties, based on the orientation, spacing, and size of the
graphite chains produced by varying these process conditions.

        Precursor material is drawn or spun into a thin filament. The
filament is then heat ed slowly in air to stabilize it and prevent it
from melting at the high temperatures used in the following steps.
The stabilized fibre is placed in an inert atmosphere and heated
to approximately 1500°C to drive out the non -carbon constituents
of the precursor material. This pyrolysis process, known as
carbonization, changes the fibre from a bundle of polymer chains
into a bundle of "ribbons" of linked hexagonal graphite plates,
oriented somewhat randomly through the fibre. The length of the
ribbons can be increased and their axial orientation improved
through further heating steps up to 3000°C, a process called
graphitization. Because the graphite ribbons are bonded to each
other perpendicular to the fibres only by weak Van der W aals
bonds, the ribbons mus t be reoriented to increase the tensile
strength of the fibre to a useful level. This is accomplished
through       the    application       of   tension   at    some   point   in   the

Department of Mechanical engineering                                        AJCE
carbon fiber & its applications                                         Page6

stabilization or pyrolysis phases, the exact time depending on the
precursor material. Increased a xial orientation increases the
fibre's tensile strength by making better use of the strong
covalent bonds along the ribbons of graphite plates.

        Polyacrylonitrile (PAN ) and rayon are the most commonly
used precursors. PAN is stretched during the stabilizati on phase,
and heated to 250°C in air. The tension is then removed, and the
fibre is heated slowly in an inert nitrogen atmosphere to 1000 -
1500°C. Slow heating maintains the molecular ordering applied by
tension       during       the    stabilization   phase.   Graphitizatio n   at
temperatures up to 3000°C then follows. Applying tension at
2000°C further increases the proper ordering of graphite ribbons.
Rayon, a cellulose -based fibre made from wood pulp, is spun into
a filament from a melt, and stabilized without tension up to
400°C. It is then carbonized without tension up to 1500°C, and is
stretched in the graphitization phase up to 2500°C.


Department of Mechanical engineering                                    AJCE
carbon fiber & its applications                                             Page7


                             Carbon fibre perform structure

           Liquid impregnation                        Chemical vapour deposition
           Thermosetting resin                            Hydrocarbon Gas
                   pitch                                    1000 – 1200°C

                                                    1-3 times

                          1-5 times

                                   Heat treatment

                                  Carbon – Carbon

                             FIG 3.2: LAYOUT DIAGRAM

Department of Mechanical engineering                                         AJCE
carbon fiber & its applications                                                  Page8

                                     CHAPTER 4


        A wide range of different processes have developed for
molding of composites parts ranging from very simple manual
processes         such     as     hand   lay    to        very   sophisticated   highly
industrialized processes Each process has its own particular
benefits      and      limitations     making        it    applicable   for   particular
applications. The choice of process is important in order to
achieve the required technical performance at an economic cost .

        The main technical factors that                      govern the choice        of
process are the size and shape of the part, the mechanical and
environmental perf ormance and aesthetics. The main economic
factor is the number of identical parts required. Most processes
will have an initial investment or set up cost. This is a major
factor in the choice of process.

Some of the common methods are:

 Open molding - hand and spray lamination
 Vacuum Infusion
 Resin injection
 Vacuum Bag and Press Molding
 Pultrusion

Department of Mechanical engineering                                              AJCE
carbon fiber & its applications                      Page9

                                  CHAPTER 5


   Very low weight
   High impact tolerance
   Insensitive to climate and temperature changes
   Reduced maintenance costs
   Long service life

Department of Mechanical engineering                 AJCE
carbon fiber & its applications                                                      Page10

                                         CHAPTER 6



        Carbon fiber -reinforced polymer is used extensively in high -
end automobile racing. The high cost of carbon fiber is mitigated
by the material's unsurpassed strength -to-weight ratio, and low
weight      is    essential        for   high -performance      automobile        racing.
Racecar manufacturers have also developed methods to give
carbon fiber pieces strength in a certain direction, making it
strong in a load -bearing direction, but weak in directions where
little or no load would be placed on the member. On the converse,
manufacturers developed unidirectional carbon fiber weaves that
apply     strength       in   all    directions.     This   type      of    carbon     fiber
assembly is most widely used in the "safety cell" monologue
chassis assembly of high -performance racecars.


        Carbon fiber reinforced polymer has over the past two
decades          become       an     increasingly     notable      material     used      in
structural engineering applications. It has proved itself cost -
effective in a number of field applications strengthening concrete,
masonry, steel, cast iron, and timber structures. Carbon fiber-
reinforced polymer (CFRP) can applied to enhance shear strength
of reinforced concrete by wrapping fabrics or fibers around the
section      to    be     strengthened.        And    it    greatly        increases    the
resistance to collapse under earthquake loading.

Department of Mechanical engineering                                                 AJCE
carbon fiber & its applications                                           Page11

        Its major application is in earthquake -prone areas, since it
is much more economic than alternative methods. It also includes
strengthening the old structures (such as bridges) and repair of
damaged structures. CFRP is one of the few practical methods of
strengthening cast -iron beams. W hen used as a replacement for
steel, CFRP bars could be used to reinforce concrete structures,
however the applications are not common. CFRP could be used
as materials due to their high strength. The advantages of CFRP
over steel as a pre -stressing material, namely its light weight and
corrosion resistance, should enable the material to be used for
niche applications such as in offshore environments.


        Carbon fiber -reinforced polymer has found a lot of use in
high-end sports equipment such as racing bicycles. For the same
strength, a carbon -fiber frame weighs less than a bicycle tubing
of aluminum or steel. Carbon fibe r-reinforced polymer frames,
forks, handlebars, seat posts, and crank arms . Carbon fiber-
reinforced polymer forks are used on most new racing bicycles.
Other sporting goods applications include fishing rods, long
boards,       and      rowing     shells.   This   material   is   used   when
manufacturing squash, tennis and badminton racquets.

        Much of the fuselage of the new aircrafts will be composed
of CFRP, making the aircraft lighter than a comparable aluminum
fuselage, with the added benefit of less maintenance because of
CFRP's superior fatigue resistance. Due to its high ratio of
strength to weight, CFRP is widely used in micro air vehicles
(MAVs). CFRP has also found application in the construction of
high-end audio components such as turntables and loudspeakers,
again due to its stiffness.

Department of Mechanical engineering                                      AJCE
carbon fiber & its applications                                Page12

        It is used for parts in a variety of musical instruments,
including violin bows, guitar pick guards etc. Shoe manufacturers
may use carbon fiber as a shank plate to keep the foot stable.
CFRP is used, either as standard equipment or in aftermarket
parts, in high-performance radio -controlled vehicles and aircraft.
i.e. for the main rotor blades of radio controlled helicopters --
which should be light and stiff to p erform 3D maneuvers.

        Fire resistance of polymers or thermo set composites is
significantly improved if a thin layer of carbon fibers is molded
near the surface -- dense, compact layer of carbon fibers
efficiently reflects heat.

Carbon fibres are cutting edges in:

 Aerospace and aircraft industry
 Sports equipment
 Automotive parts
 Small consumer goods like laptops, watches etc.
 Air filtration
 Fishing rods and tripods
 Acoustics
 As a microelectrode in extracellular recording in medicine

Department of Mechanical engineering                           AJCE
carbon fiber & its applications                                        Page13

                                   CHAPTER 7


        The chief drawback of carbon fibre composites is that they
oxidize readily at temperatures between 600 -700°C, especially in
the presence of atomic oxygen. A protective coatin g (usually
silicon carbide) must be applied to prevent high -temperature
oxidation, adding an additional manufacturing step and additional
cost to the production process. The high electrical conductivity of
airborne graphite particles creates an unhealthy e nvironment for
electrical       equipment        near   machining   areas.   Carbon    fibre
composites are currently very expensive and complicated to
produce, which limits their use mostly to aerospace and defense

Department of Mechanical engineering                                   AJCE
carbon fiber & its applications                                                     Page14

                                        CHAPTER 8

                                   FUTURE SCOPE


         Carbon fiber -reinforced polymers (CFRPs) have an almost
infinite service lifetime when protected from the sun, but, unlike
steel alloys, have no endurance limit when exposed to cyclic
loading. W hen it is time to decommission CFRPs, they c annot be
melted down in air like many metals. W hen free of vinyl (PVC or
polyvinyl chloride ) and other halogenated polymers , CFRPs can
be thermally decomposed via thermal depol ymerization in an
oxygen-free environment. This can be accomplished in a refinery
in a one -step process. Capture and reuse of the carbon and
monomers is then possible.

         CFRPs can also be milled or shredded at low temperature
to reclaim the carbon fiber                 however this process shortens the
fibers     dramatically.          Just    as   with        down   cycled    paper,     the
shortened fibers cause the recycled material to be weaker than
the original material. There are still many industrial applications
that     do    not    need        the    strength     of    full -length   carbon    fiber
reinforcement. For example, chopped reclaimed carbon fiber can
be used in consumer electronics, such as laptops. It provides
excellent reinforcement of the polymers used even if it lacks the
strength -to-weight ratio of an aerospace component

Department of Mechanical engineering                                                AJCE
carbon fiber & its applications                                            Page15


           Researches on wind power turbine with turbine blades
            longe r, stronger and more efficient.
           Composite components for a new generation of fuel -
            saving commercial aircraft.
           Developing earth conscious material.
           For structural or semi-structural components in automobiles.

Department of Mechanical engineering                                       AJCE
carbon fiber & its applications                            Page16

                                  CHAPTER 9


        Carbon f ibre is now an engineering material that must be
designed, engineered and manufactured to the same standards of
precision and quality control as any other engineering material.
Carbon fib re thus has revolutionized the field of light weig ht
materials. This can be used as a substitute for steel without the
most of latter’s difficulties like high weight, lack of corrosion
resistance etc. This is thus one of the future manufacturing

Department of Mechanical engineering                        AJCE
carbon fiber & its applications                                  Page17


     ASME Journal of Engineering Materials and Technology APRIL
        2010, Vol. 132 / 021005-7
     Hancox, N. L., 1981, Fibre Composite Hybrid Materials, MacMillan,
        New York.

Department of Mechanical engineering                             AJCE