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International Journal of Mechanical Engineering and Technology (IJMET)
Volume 10, Issue 03, March 2019, pp. 1263–1274, Article ID: IJMET_10_03_129
Available online at http://www.iaeme.com/ijmet/issues.asp?JType=IJMET&VType=10&IType=3
ISSN Print: 0976-6340 and ISSN Online: 0976-6359
© IAEME Publication Scopus Indexed
A LITERATURE REVIEW ON PROCESSING
AND TESTING OF MECHANICAL PROPERTIES
OF HYBRID COMPOSITES USING
GRAPHENE/EPOXY WITH ALUMINA
Divakara Shetty S
Dean (Academics), Mangalore Institute of Technology & Engineering (MITE),
Badaga Mijar, Near Moodabidre- 574 225, Mangalore, Karnataka, India
Nagaraja Shetty*
Assistant Professor-Senior Scale, Department of Mechanical and Manufacturing Engineering,
Manipal Institute of Technology, Manipal Academy of Higher Education (MAHE),
Manipal- 576 104, Karnataka, India
ABSTRACT
Epoxy has been often used with reinforcements due to its brittle nature. Various
reinforcing agents have provided a multitude of composites with their own unique
characteristics. Graphene is perhaps one of the most inspiring discoveries in the field
of science and technology since its potential applications are limitless due to its
admirable properties. It is basically an allotrope of carbon, a single layer of atoms
bonded in a honeycomb lattice. Among the various other nano fillers, graphene has
been used as reinforce epoxy which is then further strengthened with alumina.
Composites have been designed and redesigned throughout the years, developing more
and more advanced materials for engineering applications. But there’s always a need
for a material with higher performance at lower cost in every aspect of technology. The
aim of this review is to put forth information regarding the materials used for developing
a hybrid composite using alumina, graphene and epoxy. This is done in order to boost
the performance of the existing epoxy resin, which will be then tested for its mechanical
characteristics. The result of the experiment will be compared with a standard specimen
consisting of graphene and epoxy. The materials and their properties, along with tests
conducted on them are covered in this paper.
Key words: Alumina, Epoxy, Graphene, Mechanical properties, Nanocomposite,
Synthesis.
Cite this Article: Divakara Shetty S and Nagaraja Shetty, A Literature Review on
Processing and Testing of Mechanical Properties of Hybrid Composites Using
Graphene/Epoxy with Alumina, International Journal of Mechanical Engineering and
Technology 10(3), 2019, pp. 1263–1274.
http://www.iaeme.com/IJMET/issues.asp?JType=IJMET&VType=10&IType=3
A Literature Review on Processing and Testing of Mechanical Properties of Hybrid Composites
Using Graphene/Epoxy with Alumina
http://www.iaeme.com/IJMET/index.asp 1264 editor@iaeme.com
1. INTRODUCTION
1.1. Composites
Composites consist of fibers which serve as the backbone, and matrix, which holds the fibers
together. The advantages of composites are their high strength and stiffness, along with low
density which results in reduced weight of the component (Madhujit, 2005). Every combination
doesn’t work out and each combination of materials has its own pros and cons. That’s why
research on composites will never come to a halt. The main composition of a composite consists
of a matrix and reinforcement. Reinforcement can be of different types. Based on their shapes,
they can be fibers, particulate, flakes, skeletal or laminar. Considering the direction and
placement of fibers, reinforcement can also be classified as continuous fiber composite, woven
fiber composite, chopped fiber composite and hybrid composite (Agarwal, 2018; Vijay et al.,
2017).
There are 5 forms of composites, namely, Polymer Matrix Composites (PMCs), Metal
Matrix Composites (MMCs), Ceramic Matrix Composites (CMCs), Carbon-Carbon (CC) and
Hybrid Composites (HCs) which is a combination of the earlier mentioned composite types.
According to studies, the most prominently used fibers in 2001 were glass fibers. E-glass fibers
were the most commonly used glass fibers and accounted for 90% of the total glass fibers used.
S-glass fibers constituted the rest 10% and are typically 50-70% stronger than E-glass fibers,
which made them the ideal reinforcement in military applications. Recent years have seen a lot
of changes in composites. Aramid fibers and carbon are two other types of fibers which are
growing in popularity and usage due to their excellent properties and feasibility. Matrix is the
binding material which holds the fiber together in the composite, providing it support and
protection (Madhujit, 2005). It also helps to evenly distribute the load that falls on the composite
onto the fibers. Some of the most commonly used matrix materials are epoxy, polyester, nylon,
PVC and polyethylene. A comparison between their properties is shown in Table 1.
Table 1 Properties of common matrix materials
Material
Density
(kg/m3)
Et
(GPa)
Ec
(GPa)
σt
(MPa)
σc
(MPa)
v
α (10-6/°C)
PVC
1400
2.8
---
58
---
---
50
Polyester
1200-1400
2.5-4.0
---
45-90
100-250
0.37-0.40
100-200
Epoxy
1100-1350
3.0-5.5
---
40-100
100-200
0.38-0.40
45-65
NARMCO 2387
(Epoxy)
1210
3.38
3.86
29
158
---
---
Nylon
1140
2.8
---
70
---
---
100
Polyethylene
960
1.2
---
32
---
---
120
Where, Et and Ec are the moduli of elasticity for tensile and compression respectively, σt
and σc are the ultimate strengths, v is the Poisson’s ratio and α is the coefficient of thermal
expansion.
1.2. Synthesis
Fabrication of composites involves wetting, mixing or saturating the reinforcement with the
matrix. This causes the matrix to stick together and become rigid. There are multiple techniques
to fabricating a composite. The type of materials used for the composite also is a factor in
Divakara Shetty S and Nagaraja Shetty
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determining the process of fabrication. Some of the prominent techniques used for fabricating
the composite are:
The Lamination technique is usually used for materials like glass fiber, wood, foil and
plastic which are coated with thermoset or thermoplastic resin. There are 4 types of lamination
techniques – the overlay method, vacuum bagging, pressure molds and hybrid method. Picking
a technique for fabricating a composite depends on the number of identical products you need,
how much time can be allotted for the fabrication, and the cost of production (Sanjay 2001).
Pultrusion is a closed mold, continuous process that is very cost effective for high volumes
of production. This technique mainly deals with parts which have a constant cross section. As
shown in Figure 1, the this process is generally contains pulling of continuous fibers through a
bath of resin, blended with a catalyst and then into pre-forming fixtures where the section is
partially pre-shaped & excess resin is removed. It is then passed through a heated die, which
determines the sectional geometry and finish of the final product (Joshi, 2012)
Figure 1 Pultrusion process flow diagram
Filament winding is another popular fabrication technique where reinforcements are
continuous in the form of rovings or monofilaments, and are would over cylindrical a rotating
mandrel (Cohen, 1997). This is a fairly simple technique used to manufacture structures like
pipes, pressure vessels, etc. a number of rovings are pulled from multiple creels and are spread
our using combs. Then they are sent through a resin bath after which they are grouped back up
into a band. This band passes through a fiber feed which moves back and forth along the length
of the mandrel. Multiple layers of fiber can be stacked to provide the necessary thickness for
the part to be manufactured (Giacoletto, 2002).
1.3. Current applications
Due to their high strength to weight ratio and cost effectiveness, along with a set of other
beneficial properties, composites have found their applications in almost every sector of the
technological field. Their applications range from fuselages and propellers for aerospace to
everyday items like fishing rods and baseball bats. For example, companies like Tata Auto
Comp Systems Limited – Composites Division use reinforced plastics in truck bodies and
trailers, which are very light and have low heat transfer coefficient. This makes the
manufacturing substantially economical. Carbon fibers have found their applications in luxury
and sports cars due to their lightweight and high strength to weigh ratio (Compos, 2013). Kevlar
is used for military applications due to its very high strength and lightweight, used to reinforce
vehicles and body suits (Tham et al., 2008). It is also used in pipes and fittings for various
purposes like transportation of water for sewage or irrigation. There are numerous types of
composites being produced and the possibilities are endless.
2. GRAPHENE
A Literature Review on Processing and Testing of Mechanical Properties of Hybrid Composites
Using Graphene/Epoxy with Alumina
http://www.iaeme.com/IJMET/index.asp 1266 editor@iaeme.com
Carbon has many allotropes, some that were discovered long ago (diamond and graphite) and
some discovered 10-20 years ago (fullerenes and nanotubes). Interestingly, the two-
dimensional form (graphene) was only obtained very recently, bringing about a great deal of
change in our current science (Mikhail, 2007). Graphene has a number of remarkable
mechanical and electrical properties. It is significantly stronger than steel, and it is very flexible.
The thermal and electrical conductivity is very high. Graphene’s excellent thermal, mechanical,
and electronic properties make it one of the most favored materials for filling agents in
composite materials and its applications. Graphene nanocomposites show substantial
enhancements in their multifunctional aspects at low loading, in comparison with conventional
composites and materials (Vivek Dhand et al., 2013). This makes the material lighter with
simple processing, as well as increasing mechanical strength for various applications. Figure 2,
shows an interpretation of graphene's uniform structure at the molecular scale
Figure 2 A rendering of graphene's uniform structure, at the molecular scale.
2.1. Tests Conducted on Graphene
The physical and chemical properties of the host matrix are upgraded upon embedding due to
the exceptional properties of graphene. This leads to enhancement of strength and bonding
between layers of graphene and host matrix, which in turn develops the cumulative properties
of graphene in its nanocomposites (Kuilla et al., 2010). Jang and Zhamu (2008) reviewed the
paper about processing of graphene nanoplatelets (GNPs) to create composite materials. It
describes the earlier processes used to produce multilayer nanoscale graphene platelets and their
composites, followed by recent developments in preparation of single layered nanoscale
graphene platelets and their composites (Jang & Zhamu, 2008). Mack et al. (2005) developed
nanocomposites of polyacrylonitrile (PAN) nanofibers reinforced by GNP, which they
exhibited to increased mechanical properties (Mack & Viculis, 2005).
Yu et al. (2007) spotted that graphene nanocomposites containing epoxy resin shows
interesting characteristics for the electronic industries. This means thermal interface based
materials is favored for fabrication (Yu et al., 2007). Research by Hansma et al. (2007)
demonstrated successfully to create graphene-based nanocomposites. They maximized the
amount and combination of adhesives and high-strength nanostructures (i.e. graphene) needed
to yield a strong, lightweight, low-density, and to resist damage of composite material (Hansma
et al., 2007). Dikin et al. (2007) prepared a graphene oxide paper which was fabricated by flow
directed assembly of single layers of graphene oxide sheets and characterization was performed.
The graphene oxide sheets clearly outclassed almost every other paper-like material when it
came to stiffness and strength (Dikin et al., 2007).
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Chen et al. (2008) fabricated graphene paper with a layered structure using vacuum filtration
of well-dispersed graphene dispersion. This was then treated to thermal annealing that resulted
in greater electrical conductivity and mechanical properties (Chen et al., 2008). Tests conducted
by Changgu Lee. et al. (2008) reveal some interesting values when monolayer graphene was
tested for its elastic properties and intrinsic strength. The breaking strength was found to be 42
Nm-1, Young’s modulus of 1 terapascal, inherent strength of 130 GPa and 3rd order elastic
stiffness of -2 terapascals. The fact that graphene is one of the strongest, if not the strongest
material, to have been measured, was set in stone (Changgu Lee. et al., 2008). A study
conducted by M. A. Rafiee et al. (2009) consisted of measurement of mechanical properties of
nanocomposites at low graphene content. The results showed that the Young’s modulus of the
nanocomposite was around 31% more than pristine epoxy, 40% increase in tensile strength and
53% increase in fracture toughness. This stands to prove graphene’s claim as one of the most
exciting material discovered yet (Rafiee et al., 2009). Diana Berman et al. added small amounts
of ethanol solution which contained graphene onto sliding steel surfaces. This resulted in
reduction of friction coefficient and wear by a huge amount, thus concluding graphene
incorporation to reduce wear is very efficient (Diana Berman et al., 2013). Lee et al. (2013)
adopted cryomilling to fabricate tiny particulate graphene and chitosan. A composite material
was formed when a mixture of these two were formed by sonication and reinforcement. The
graphene particles exhibited a progressive nature which resulted in development of the
mechanical properties of the composite. A decrease in lumping of graphene while mixing was
also seen (Lee et al., 2013).
2.2. Fabrication of Graphene
There are plenty of methods to fabricate graphene, but two main techniques have been debated
here, namely, mechanical exfoliation of graphene from bulk graphite and graphitization of
epitaxially grown SiC crystals. Graphene obtained from these two techniques are similar to
each other but their physical properties tend to differ, although not by a huge margin. But since
exact specifications are needed for work regarding the material, it is necessary to indicate the
type of graphene being used (Xinran wang & Yi Shi, 2014).
2.2.1. Exfoliation Technique
Exfoliation is one of the most commonly used methods to obtain graphene from graphite, and
it includes extracting a single layer of carbon atoms through various means. Some of these
developments are discussed below.
2.2.1.1. Adhesive Tape
Adhesive tapes were used to separate layers of graphite into graphene. Multiple exfoliations
were needed to obtain single layers. Each exfoliation produced a slice with fewer layers, until
only one remains. Crystallites large enough to be seen by the naked eye are obtained (Geim &
Macdonald, 2007). The schematic representation of exfoliation process is shown in Fig. 3.