Carbon Fibre Reinforced Composite1
CARBON FIBRE REINFORCED COMPOSITE
Name
Cleophas Chebii
Technical University of Mombasa
Mombasa, Kenya
12/06/2019
Carbon Fibre Reinforced Composite2
Carbon Fibre Reinforced Composite
Currently, the development of composite materials is based on the need to obtain
materials with better properties, where good resistance and toughness are combined. The use of
composite materials is growing rapidly, implanting itself in a wide variety of industrial sectors,
this is attributable to its magnificent mechanical properties, such as its low density, light-weight,
resistant, ductile and high temperature resistant materials. Composite carbon fiber materials in
polymeric matrix, currently have a wide field of applications, in the aeronautical, automotive and
medical industries. Taking into account that every day the opportunity to optimize the design of
composite materials grows, it can be affirmed that it is necessary to know the mechanical
properties of the materials to be built. In recent years, carbon fibers have been used in different
applications, where their mechanical properties and lightness are very important. Likewise,
polymer matrix composites are increasingly used as they have excellent mechanical properties
with respect to a high strength-to-weight ratio.
Carbon Reinforced Fibre composite is mostly applied in the automotive industry to
construct high power racing vehicles, powerboats and motorbikes. For example, formula 1 cars
are lightweight racing vehicles with excellent protection capabilities. CRFC is also widely used
in the manufacture of sporting equipment like golf club shaft because of lightweight and low
torque. Rackets used in tennis sport are also fabricated using carbon composites. Further, carbon
composites are also used in making musical instruments, space ships and planes.
Sandwich and Plain Structure Composite
Sandwich composite structure is made by connecting two thin rigid skins to a core that is
light and thick. The thick primary element offers the sandwich structure with high stiffness of
bending and reduced density. Core materials used in fabricating sandwich structures include
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foams such as polyethylene, balsa wood, polyvinylchloride among others. Glass laminates,
thermoplastics or thermosets are commonly used as skins in making sandwich composites.
Adhesives are used to connect the skins to the core materials.
Figure 1: Sandwich structure composite
Type of sandwich structure composites include Metal Composite Material (MCM) and recycled
paper. Sandwich composites can be classified according to the type of core material. Classes of
sandwich composites according to the core material, include locally reinforced, homogeneously,
regionally, unidirectional or bi-directionally supported. Sandwich composite’s strength depends
on two main factors; the external skins and the boundary between the skin and the core material.
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Sandwich composite structures are applied in sandwich panels. Examples of sandwich
panels include Fibre Reinforced Polymer (FRP) sandwich panel or aluminium composite panel.
Sandwich structures are also used in aerospace industries, automotive parts, sport equipment,
construction materials. Carbon sandwich composite structures are also used in the manufacturing
industry. The structured composites are used where fatigue resistance, electrical conductivity
moderate strength and lightweight components are required. Plain CRFC structures are used in
semi-structural building and manufacturing various structural components e.g. aileron, flaps, and
landing gear doors. Plain composite structures are two-dimensional built by front stitches only.
Plain structures have excellent tensile characteristics because of minimal isotropic fibre
alignment. Plain structure composites are applied in making blankets and canvas.
Types of Carbon Weave Fibre
Carbon fibre weaves offer additional structural strength in the composite. Types of
carbon weaves include twill, plain and Harness Satin. Carbon fibre with plain weave have an
appearance of a small checkerboard. In plain weaves, tows are woven in an under/over pattern.
Plain weave fibres are suitable for tubes, flat sheets and 2D curves.
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Figure 2: Plain weave Fibre
Twill weave fibre acts as a bridge between plain and satin weaves. The under/over pattern makes
a diagonal arrowhead look also called twill line. Twill weaves have enhanced flexibility and can
make complex shapes. Twill weaves can be either 2*2 or 4*4.
Figure 3: 2*2 Twill Carbon Weave
Satin fibre weave was used to make silk fabrics in the past. Satin fibre weave have good draping
properties thus can easily make complex shapes. Types of satin weaves include 4 harness satin,
5 harness satin and 8 harness (Ogasawara et al., 2018).
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Figure 4: 4 harness satin weave (Ogasawara et al., 2018).
Characterization of Carbon Fibre Reinforced Composite
The carbon fibre structure is either continuous or short. The fibre can be amorphous,
crystalline or in partly crystalline form and possess the graphite crystal structure. The layer has
carbon atoms joined by covalent bonds and metallic bonds. The layer bonding is always by
Vander Waals forces which enables sliding of carbon layers with respect to each other. Graphite
has a difference in the in-face and out-of face connection thus possesses great elastic modulus
parallel and low elastic modulus perpendicular to the planes (Ogasawara et al., 2018). Therefore,
graphite is highly anisotropic because of the variations across the parallel and perpendicular
planes. During carbon fibre manufacture, surface treatments e.g. oxidation, wetting agent,
couplings and coating, enhance the bonding between fibres and polymer matrix.
The tensile strength of carbon fibre declines with growing modulus. Tminimizedd
strength of the fibre causes the rupture strain to be minimised. Carbon fibre displays brittle
materials at greater modulus thus crucial in manufacture and connection of joints in high stress
concentration (Ogasawara et al., 2018). Thus, laminates of the carbon composite become more
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efficient with resin adhesive bonding. The table 1 shown below illustrates the mechanical
properties of various grades of carbon fibre.
Table 1: Mechanical properties of various carbon fibre grades (Ogasawara et al., 2018).
Fibre Grade
Carbon, High strength
Carbon, ultra High
Modulus
Carbon, High Modulus
Elastic Modulus
(GPa)
230
520-620
Tensile Strength
(MPa)
2480
1030-1310
Density
(gr/cm3)
1.8
2.0-2.1
370
1790
1.9
Fibre-reinforced composites have excellent in-face properties with weak through-thickness
behaviour observed at the inter-laminar delamination. Such properties of fibres poses a major
difficulty in the composite structures design. Laminates delamination occurs as a result of fragile
matrix-fibre boundary and the resins’ brittle nature. Improvement of matrix-fibre boundary is
done through various ways including braiding, stitching and z-pinning. Fibre-matrix boundary
improvement has limitations. The enhancement process may damage the main fibre thus causing
decreased in-face performance characteristics. The enhancement process is also costly thus not
economical for simple processes of manufacturing. However, development of modern methods
of boundary enhancement improves the fibre-matrix interfacial adhesion. Modern enhancement
methods increase the reactivity functionalizationof the fibre through plasma treatment, chemical
functionalization and thermal alteration.
Resin in Carbon Fibre Reinforced Composite
Resins are used in the matrix phase of carbon composites. The resins help fibre bonding
and protection from environmental and mechanical damage. Polymer resins are of two types,
thermoplastics and thermosets. After heating, thermoplastic resins melt and remain as solids
when cooled. Thermoplastic resins do not cure permanently. Thermoset resins cure permanently
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after being subjected to heat. Examples of resins used in composite applications include
epoxies, vinyl esters and unsaturated polyesters. Epoxies have more strength and costlier than
polyesters.
The matrix element of carbon composites is made of epoxy resins because of their
different functionalities. Usually, epoxies like glycidyl ethers and amines are used in the matrix
of carbon composites. The material characteristics and cure rates of epoxy can be altered to meet
the composite requirements. Epoxies add to the durability, strength and chemical resistance of a
carbon composite. At elevated temperature, epoxies provide high performance with wet/hot
service temperatures up to 121o C. Carbon composite epoxy resin are in the form of either solid,
liquid or viscous states and are cured by a hardener in an addition reaction.
Characterisation of Carbon Fibre Reinforced Composite with Epoxy Resin
Design of composite materials is such that the reinforced element positions on the load
direction. In case the direction of the load is invariable and not parallel to the fibre, the
composite design may consider the composite’s laminate mechanical behaviour. The fibre should
therefore be arranged at different alignments like ±30o, ±45o or ±90o. Fibre alignment
significantly affects the composite’s flexural and tensile property. For example, fibre alignment
of 90o causes the tensile load to be uniformly distributed on all fibres and transmitted along the
fibre’s axis. Non-parallel fibre axes leads to elevated concentration of stress resulting to
laminates failure.
Tensile property of epoxy resin
Mechanical test of CFRC with epoxy resin shows the following tensile properties in
various fibre alignments.

Flexural and tensile strength is higher at 90o fibre alignment.
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
Deflection and extensions are reduced in 90o alignment

Deflection and extension are at maximum in 30o alignment thus increased strain.

In 90o alignment, more load is required to fracture CFRC.
Epoxy Resin Flexural Property
Carbon fibre epoxy resin subjected to mechanical tests shows the following properties
before yielding:

The flexural strength is maximum at 90o alignment of fibre.

There is increased stiffness property at 90o alignment.

Force at maximum point of yield is superior at 90o alignment
 There is more deflection at 45o alignment lesser than in 90o orientation.
Vacuum Assisted Resin Transfer Molding (VARTM)
Vacuum Assisted Resin Transfer Molding (VARTM) is used in the fabrication of high-quality
composite elements. VARTM process of low cost involve the following steps:
o Material and tooling preparation,
o The infusion
o
The post-infusion
Material and tool Preparation
Metal (aluminium) or vinyl coated wooden plates are used as molds in the composite
fabrication process. MYLAR film of 25 micron is used in protecting the mold surface and
facilitates easy panel removal from the mold. Carbon fibres are then cut into plies of size 24’’x
36’’ and arranged in the 0o direction. The fibre is then kept in a room with dry atmospheric
conditions and regulated temperature to prevent impurities from the environment (Bhatta, 2018).
After component stacking, a vacuum bag is then used to cover the mold plate and sealed. The
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mold plate is therefore tested for leakages through creation of a vacuum of 2 torr. The catalyst is
added to the resin to speed up reactions with chemicals and make it aerated. After aeration of the
resin, degassing is required before it is injected into the mold.
Infusion
When the resin is ready, injection into the mold is done gently. The resin flow is regulated using
a peristaltic pump (Bhatta, 2018). Vacuum pressure present in VARTM offers a driving force for
the resin flow into the mold. Finite element analytical tools are used to capture the process of
resin flow.
Post-Infusion Process
Resin infused into the mold has low viscosity. Bleeding is done to remove excess resin
from a location of low vacuum pressure. Bleeding leads to reduction in resin volume thus
decreasing its thickness which subsequently improves the fraction of fiber volume.
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Figure 5: Steps in VARTM Process
Figure 5: VARTM composite fabrication process
Fibre Reinforced Composite Testing
Charpy impact test uses a horizontal simply supported beam.
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Figure 6: Charpy impact test of carbon composite
The carbon composite is first prepared and should be in a rectangular shape with a notch cut as
shown above. (Bulut et al., 2020). The notch permits pre-set location of crack initiation. The
specimen is first placed into a big apparatus that consist of pendulum with a specified weight.
The pendulum swings, and the impacts and breaks the carbon fibre and then raises to a measured
height as illustrated below (Bulut et al., 2020).
Figure 7: Charpy impact test process
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The original height (ho) and final heights (hf) of the pendulum are recorded. The change in height
is proportional to the quantity of energy loss resulting from the fracture of the specimen. The
overall energy from the fracture is given by the formula:
𝑇 = 𝑚𝑔(ℎ𝑜 − ℎ𝑓 )
(2)
Where
T = total energy
g = gravitational acceleration
m= mass
Three Point Bending Test for CFRC
Three point bending test is carried out to investigate the bending and flexural stress plus
strain of composite materials (Liu et al., 2016). The machine used in the experiment is known as
an Instron Testing Machine shown below. Preparation of test samples follows the guidelines on
ASTM 790 standard. An electrical power saw is used to cut strips from a rectangular composite
plate. The strips are then polished with emery paper to smoothen its edges.
Figure 8: Three Point Bending Test Machine
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References
Bhatta, R.K., 2018. Investigating the electrical behaviour of nanoparticle infused holes on
carbon fibre reinforced composites during fatigue loading (Doctoral dissertation, Wichita
State University).
Bulut, M., Bozkurt, Ö.Y., Erkliğ, A., Yaykaşlı, H. and Özbek, Ö., 2020. Mechanical and
Dynamic Properties of Basalt Fiber-Reinforced Composites with Nanoclay Particles.
Arabian Journal for Science and Engineering, 45(2), pp.1017-1033.
Chawla, K.K., 2019. Carbon Fiber/Carbon Matrix Composites. In Composite Materials (pp. 297311). Springer, Cham.
Liu, C., Du, D., Li, H., Hu, Y., Xu, Y., Tian, J., Tao, G. and Tao, J., 2016. Interlaminar failure
behavior of GLARE laminates under short-beam three-point-bending load. Composites Part B:
Engineering, 97, pp.361-367.
Ogasawara, T., Ayabe, S., Ishida, Y., Aoki, T. and Kubota, Y., 2018. Heat-resistant sandwich
structure with carbon fiber-polyimide composite faces and a carbon foam core. Composites Part
A: Applied Science and Manufacturing, 114, pp.352-359.