is an example of a short-fibre composite Sanjay, 2011. This reinforcement is done to improve performance.
The main concept of a composite is that it contains matrix materials. Generally, composite material is formed by reinforcing fibres in matrix resin. The
reinforcements can be made from polymers, ceramics, and even metals. The fibres can be continuous, long, or short. The reinforcing fibre or fabric provides strength and
stiffness to the composites, whereas the matrix gives rigidity and environmental resistance. The properties mainly depends on the orientation of the fibres that are laid
in the composites. The main idea about composites are that the fibre carries the load and its strength is greatest along the axis of the fibre. Long continuous fibres in the
direction of the load result in a composite with properties far exceeding the matrix resin itself. The same material chopped into short lengths yields lower properties than
continuous fibres. Depending on the application of the composite materials, the fibre forms can be selected Swift K.G., 2013.
2.4 CARBON FIBRE
Carbon fibre, or alternatively known as graphite fibre or CF, are materials made
of fibres of carbon atoms ranging from 5–10 μm in diameter. Carbon fibre is widely used in applications requiring outstanding mechanical properties associated to a low
density Vautard F., 2014. The production of carbon fibre, is carried by bonding crystals are mostly aligned parallel to the longitudinal axis of the fibre. Due to the
structural alignment of the crystals, it allows the fibre to have high strength to volume ratio which allows high strength relative to its size. These fibres would then be bundled
up together in to several thousand to form what is called a tow. This tow can be used by itself or woven to form a carbon fibre fabric.
Carbon fibre is usually supplied in the form of a continuous tow that has been wounded onto a reel. The tow which consists of thousands of continuous individual
carbon filaments are held together and protected by an organic coating such as polyethylene oxide PEO or polyvinyl alcohol PVA. The tow can be unwounded
from the reel for convenience. The carbon filament has a cylindrical shape with a
diameter of 5–8 micrometres. Some of earliest carbon fibre produced such as T300, HTA and AS4 had diameters of 16–22 micrometres Cantwell W.J., September 1991.
During the carbonization and graphitization process, precursors go through chemical changes that yield high stiffness to weight and strength to weight properties.
The successive surface treatment and sizing process improves it’s to resin compatibility and handle ability Ronald, 2011
The atomic structure of carbon fibre is almost the same than that of graphite. It consists of sheets of carbon atoms arranged in a hexagonal pattern which are known
as graphene sheets. The difference here is being how these sheets of graphene sheets interlock. Graphite is a crystalline material whereby the sheets are stacked parallel to
one another in a regular and repeating pattern. The intermolecular forces Van der Waals forces between the sheets are relatively weak allowing graphite to be soft but
brittle at the same time.
Depending on the type of fibre required, carbon fibre can be turbostratic or graphitic, or a hybrid structure with both turbostratic and graphitic parts present. For
the turbostratic carbon fiber, the sheets of carbon atoms are folded, or crumpled, together. Turbostatic carbon fibres are derived from Polyacrylonitrile PAN, whereas
graphitic carbon fibres are derived from mesophase pitch after heat treatment at temperatures in excess of 2200 °C. Turbostratic carbon fibres are generally having
higher tensile strength, whereas heat-treated mesophase-pitch derived carbon fibres have higher Youngs modulus and higher thermal conductivity.
Carbon fibres in general have high stiffness and tensile strength, have low weight, high resistance to chemical attacks, able to withstand high temperature and
have low thermal expansion. These properties make carbon fibre the material or choice and has been proven to be very popular especially in the aerospace civil engineering
industry, military application, as well as motorsports other competition sports industry. However, they are relatively expensive when compared to similar fibres, such as glass
fibres or plastic fibres.
Carbon fibres combined with other materials to form a composite. Usually, carbon fibre is combined with a plastic resin to form carbon-fibre-reinforced polymer.
This will give the composite a very high strength-to-weight ratio, very rigid but brittle. However, carbon fibres are could also be composited with other materials, such as
graphite to form carbon-carbon composites which would result in very high tolerance to heat.
Non-polymer materials can be used as the matrix for carbon fibre composites. However, the formation of metal carbides and corrosion concerns, carbon fibre has not
been successful in metal matrix composite applications. Reinforced carbon-carbon RCC is a carbon fibre-reinforced graphite, is mainly use in structural applications in
high temperature conditions. Carbon fibre is also sometimes used to filter high- temperature gases, as an electrode that has high surface area and corrosion resistance,
and as an anti-static component. In addition, moulding a thin layer of carbon fibres can improve fire resistance of any polymers or thermoset composites because a layer of
compact carbon fibre can act as a heat reflector Zhongfu Z., 2009.
Carbon fibre composites are quickly replacing aluminium especially from the automotive, aviation and aerospace space industry instead of other metals due to
galvanic corrosion issues David B.. Galvanic corrosion can be defined as damage caused when electrochemical process occurs whereby one metal corrodes when both
metals different metals are in electrical contact and in the presence of an electrolyte.
Carbon fibre composites global demand was valued to be at almost US10.8 billion in the year 2009. This however is expected to reach US13.2 billion by 2012
and would grow to US18.6 billion by 2015 with an annual growth rate of 7 or more Acmite Market Intelligence, February 2014. Some of the highest demands is from
the aircraft aerospace industry, wind energy production, as well as from the automotive industry who are using the resin matric systems Roman W.H., 2012.
2.5 EPOXY
