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CHAPTER-1
INTRODUCTION
Fiber-reinforced composite materials consist of fibers of high strength and modulus embedded in
or bonded to a matrix with distinct interfaces (boundaries) between them. In this form, both
fibers and matrix retain their physical and chemical identities, yet they produce a combination of
properties that cannot be achieved with either of the constituents acting alone. In general, fibers
are the principal load-carrying members, while the surrounding matrix keeps them in the desired
location and orientation, acts as a load transfer medium between them, and protects them from
environmental damages due to elevated temperatures and humidity. Thus, even though the fibers
provide reinforcement for the matrix, the latter also serves a number of useful functions in a fiber
reinforced composite material. The principal fibers in commercial use are various types of glass
and carbon as well as Kevlar 49. Other fibers, such as boron, silicon carbide, and aluminum
oxide, are used in limited quantities. All these fibers can be incorporated into a matrix either in
continuous lengths or in discontinuous (short) lengths. The matrix material may be a polymer, a
metal, or a ceramic. Various chemical compositions and microstructural arrangements are
possible in each matrix category. The most common form in which fiber-reinforced composites
are used in structural applications is called a laminate, which is made by stacking a number of
thin layers of fibers and matrix and consolidating them into the desired thickness. Fiber
orientation in each layer as well as the stacking sequence of various layers in a composite
laminate can be controlled to generate a wide range of physical and mechanical properties for the
composite laminate. Historical examples of composites are abundant in the literature. Significant
examples include the use of reinforcing mud walls in houses with bamboo shoots, glued
laminated wood by Egyptians (1500 B. C.), and laminated metals in forging swords (A.D. 1800).
In the 20th century, modern composites were used in the 1930s when glass fibers reinforced
resins were used. Boats and aircraft were built out of these glass composites, commonly called
fiberglass. Since the 1970s, application of composites has widely increased due to development
of new fibers such as carbon, boron, and aramids and new composite systems with matrices
made of metals and ceramics.
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1.1COMPOSITESA composite is a structural material that consists of two or more combined constituents that are
combined at a macroscopic level or microscopic level and are not soluble in each other. One
constituent is called the reinforcing phase and the one in which it is embedded is called the
matrix. The reinforcing phase material may be in the form of fibers, particles, or flakes. The
matrix phase materials are generally continuous. Examples of composite systems include
concrete reinforced with steel and epoxy reinforced with graphite fibers, etc. For years,
composite materials have growing applications in different industries. In many cases, using
composites is more efficient. For example, in the highly competitive airline market, one is
continuously looking for ways to lower the overall mass of the aircraft without decreasing the
stiffness and strength of its components. This is possible by replacing conventional metal alloyswith composite materials. Even if the composite material costs may be higher, the reduction in
the number of parts in an assembly and the savings in fuel costs make them more profitable.
Reducing one 0.453 kg of mass in a commercial aircraft can save up to 1360 liter of fuel per year
and fuel expenses are 25% of the total operating costs of a commercial airline. Composites offer
several other advantages over conventional materials. These may include improved strength,
stiffness, fatigue and impact resistance, thermal conductivity, corrosion resistance, etc. The
mechanical advantage of composite can be measured by specific modulus and specific strength.
The axial deflection Y, of a prismatic rod under an axial load P, is given by
PLY =
AE, (1.1)
Where
L = length of the rod,
E= Youngs modulus of elasticity of the material of the rod.
Now the mass, M, of the rod is given by
M = AL (1.2)
Where = density of the material of the rod,
From equations 1.1 and 1.2 we have,
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2PL 1
M =EY
(1.3)
This implies that the lightest beam for specified deflection under a specified load is one with the
highest (E/) value. Thus, to measure the mechanical advantage, the (E/) ratio is calculated andis called the specific modulus (ratio between the Youngs modulus (E) and the density () of the
material). The other parameter is called the specific Strength and is defined as the ratio between
the strength ( ult) the density () of the material that is,
Specific modulus =E
,
Specific strength =
ult
.
The two ratios are high in composite materials. For example, the strength of a graphite/epoxy
unidirectional composite could be the same as steel, but the specific strength is three times that
of steel. For any rod cross-section of graphite/epoxy would be same as that of the steel, but the
mass of graphite/epoxy rod would be one third of the steel rod. This reduction in mass translates
to reduced material and energy costs. Figure 1.1 shows how composites and fibers rate with
other traditional materials in terms of specific strength over the years. Values of specific
modulus and strength are given in Table 1.1 for typical composite fibers and other materials.
Fibers such as graphite, aramid, and glass have a specific modulus which is several times that of
metals, such as steel and aluminum. This gives a false impression about the mechanical
advantages of composites because they are made not only of fibers, but also of fibers and matrix
combined; matrices generally have lower modulus and strength than fibers. Due to this overall
strength of the composites decreases. Composites have distinct advantages over metals but there
are many drawbacks and limitations in use of composite which mainly includes:
High cost of fabrication of composites. Material characterization is complex as composites are not isotropic. Repairing of composite material is difficult. They do not have a high combination of strength and fracture toughness compared to
metals and many more.
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Figure 1.1: Specific strength as a function of time of use of materials
Table 1.1: Specific Modulus and Specific Strength of Typical Fibers, Composites, and Bulk Metals
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1.2CLASSIFICATION OF COMPOSITESBased on the types of reinforcement used, the composites are classified as:
1.2.1 PARTICULATE REINFORCED COMPOSITES
A composite whose reinforcement is a particle with all the dimensions roughly equal are called
particulate reinforced composites. Particulate fillers are employed to improve high temperature
performance, reduce friction, increase wear resistance and to reduce shrinkage. The particles will
also share the load with the matrix, but to a lesser extent than a fiber. A particulate reinforcement
will therefore improve stiffness but will not generally strengthen.
1.2.2 Fiber reinforced composites
Fiber reinforced composites contain reinforcements having lengths higher than cross sectional
dimension. Fibrous reinforcement represents physical rather than a chemical means of changing
a material to suit various engineering applications. These can be broadly classified as:
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Reinforcing fiber in a single layer composite may be short or long based on its overall
dimensions. Composites with long fibers are called continuous fiber reinforcement and
composite in which short or staple fibers are embedded in the matrix are termed as discontinuous
fiber reinforcement (short fiber composites). In continuous fiber composites fibers are oriented in
one direction to produce enhanced strength properties. In short fiber composites, the length of
short fiber is neither too high to allow individual fibers to entangle with each other nor too small
for the fibers to loss their fibrous nature. The reinforcement is uniform in the case of composites
containing well dispersed short fibers. There is a clear distinction between the behavior of short
and long fiber composites.
1.2.3 HYBRID COMPOSITES
Composite materials incorporated with two or more different types of fillers especially fibers in a
single matrix are commonly known as hybrid composites. Hybridisation is commonly used for
improving the properties and for lowering the cost of conventional composites. There are
different types of hybrid composites classified according to the way in which the component
materials are incorporated. Hybrids are designated as i) sandwich type ii) interply iii) intraply
and iv) intimately mixed. In sandwich hybrids, one material is sandwiched between layers of
another, whereas in interply, alternate layers of two or more materials are stacked in regular
manner. Rows of two or more constituents are arranged in a regular or random manner in
intraply hybrids while in intimately mixed type, these constituents are mixed as much as possible
so that no concentration of either type is present in the composite material.
1.2.4 LAMINATES
A laminate is fabricated by stacking a number of laminae in the thickness direction. Generally
three layers are arranged alternatively for better bonding between reinforcement and the polymer
matrix, for example plywood and paper. These laminates can have unidirectional or bi-
directional orientation of the fiber reinforcement according to the end use of the composite. A
hybrid laminate can also be fabricated by the use of different constituent materials or of the same
material with different reinforcing pattern. In most of the applications of laminated composite,
man made fibers are used due to their good combination of physical, mechanical and thermal
behavior.
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1.3FIBER REINFORCEMENTFiber is defined as any single unit of matter characterized by flexibility, fineness and high
aspect ratio. It is a slender filament that is longer than 100 m or the aspect ratio greater than 10.
Fibers have a fine hair like structure and they are of animal, vegetable, mineral or synthetic
origin. Fibers are broadly classified into types as natural and man made or synthetic.
1.3.1 SYNTHETIC FIBERSGLASS FIBER
Glass fiber is the best known reinforcement in high performance composite applications due to its
appealing combination of good properties and low cost. The major ingredient of glass fiber is silica which
is mixed with varying amounts of other oxides. The different types of glass fibers commercially available
are E and S glass. The letter E stands for electrical as the composition has a high electrical resistance
and S stands for strength. Glass fibers are used successfully for reinforcing the plastic s and therefore,
the suitability of this fiber as a reinforcing material for rubbers has been studied. High initial aspect ratio
can be obtained with glass fibers, but brittleness causes breakage of fibers during processing.
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CHAPTER-2
LITERATURE REVIEW
Many researchers have proposed their theories, numerical results and experimental results
regarding damping behavior of various composite materials under various types of loading.
Damping behavior is related to the analysis of composite for finding the lag of response for given
force. The detailed literature survey related to current work is stated under:
C. T. Sun et. al.(1985) provided an analytical study to optimize the internal damping of short
fiber polymer matrix composites. Two different analytical methods-force balance model and
finite-element numerical scheme were used to obtain numerical results. The loss factor was
optimized in terms of many important parameters such as; fiber aspect ratio, the angle between
the applied tensile load and the fiber direction, stiffness ratio between the fiber and matrix
materials and the damping ratio between the fiber and matrix materials. The numerical results
showed that, for given fiber and matrix materials and given fiber volume fraction, there exists an
optimum fiber aspect ratio and an optimum angle for maximum damping of the composite.
Shive K. Chaturvedi et. al.(1991) investigated that discontinuous fibers in composite make it
theoretically possible to improve and optimize the damping properties in composites. The effects
of the fiber aspect ratio, and damping and stiffness properties of fiber, matrix and interphase (a
distinctive third phase in between the fibers and the bulk matrix with its own viscoelastic
properties) on the composite damping and stiffness were analyzed and discussed.
I. Lee et. al.(1993) investigated the dynamic characteristics of carbon fiber/ polyetheretherketone
(CF/PEEK) composites have been investigated by the impact test and the sinusoidal free
vibration test. Using a cantilevered beam with rectangular cross-section, the natural frequenciesand damping properties were measured. In addition to CF/PEEK composites, experiments have
been performed for CF/epoxy composites. The damping of CF/epoxy is much larger than that of
CF/PEEK.
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R. Chandra et. al.(1999) The status of research on damping in fiber-reinforced composite
materials and structures with emphasis on polymer composites was reviewed in this paper. As a
first step, composite damping mechanisms and methodology applicable to damping analysis was
described. Further, the paper presents damping studies involving macromechanical,
micromechanical and viscoelastic (relaxation and creep) approaches; models for interphase
damping, damping and damage in composites. Some important works related to improved
damping models for thick laminates, improvement of laminate damping and optimization for
damping in fiber reinforced composites/structures were critically reviewed.
Ioana C. Finegan et. al.(2003) worked on analytical and experimental investigations of the
dynamic mechanical properties of carbon nanofiber/polypropylene composites. In this case, the
carbon nanofibers are vapor grown carbon fibers (VGCF) which are grown catalytically from
gaseous hydrocarbons using metallic catalyst particles. The mechanical damping and storage
modulus of these materials are measured by using a Dynamic Mechanical Thermal Analyzer.
C. Subramanian et. al.(2009) investigated the results on composite leaf spring confirmed that
long glass fibre reinforced PP leaf spring is able to carry three times the load for a design
deflection than short glass fibre reinforced PP leaf spring. This improved spring rate behavior
results in significant improvement of the energy-absorbing capability. The influence of strain
rate over the load deflection behavior of long fibre reinforced leaf spring is found to be less than
that of short fibre reinforced leaf spring. However, the damping behavior of short glass fibre
reinforced leaf spring is found to be superior to that of long glass fibre reinforced leaf springs.
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CHAPTER-3
PRESENT WORK
3.1 PROBLEM FORMULATION
Composites are used everywhere nowadays. Their increased utilization necessitates detailed
study before putting them in actual use. Vibration characteristics are one of the important
parameters which have to be studied for safe utilization of composites in various field specially
related to antivibration applications. Damping behavior directly relates materials ability to absorb
shocks and vibrations without getting damaged. Phase Lag gives the measure of damping
capacity of any material. Reinforcement types also contribute towards damping behavior. In
present work damping behavior of unreinforced epoxy, long copper fiber reinforced and short
copper fiber reinforced epoxy material are studied.
From literature survey it was observed that damping behavior of various fiber reinforced
composites were studied using finite element method and experimental analysis, but hardly any
work was reported on damping behavior of epoxy composite reinforced with cooper fibers.
3.2 RESEARCH GAP IN THE EXISTING LITERATURES
Following research gaps are reported on the basis of study of existing literature:
1. It is observed that very little work has been reported on material characterization ofcopper fiber reinforced composites of epoxy thermosetting.
2. Very few efforts have been made to understand the effect of fiber length on dampingbehavior of polypropylene composite. Many researchers have related strength of
composites with length of reinforcement fibers by considering the effect of critical
length but no one studied the effect ofdifferent fiber length on damping behavior.
3. Very few efforts were made to relate the damping behavior of polypropylenecomposites with different orientation angles of reinforcement fibers.
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3.3 OBJECTIVES OF PROPOSED STUDY
To fill these research gaps following objectives are carried out:
1. To prepare the unreinforced epoxy, short fiber and long fiber copper reinforced epoxycomposite model using die and punch technique with different orientations.
2. To evaluate the mechanical properties of unreinforced, short and long fibersreinforced composite.
3. To analyze all the composites for damping behavior and to obtain the best compositefrom the damping and strength point of view.
3.4 WORK JUSTIFICATION
With the advancement in composite sciences, their field of utilization has increased manifolds.
Commercial and industrial applications of fiber reinforced polymer composites are so varied that
it is impossible to list them all. One of the examples is the Lear Fan 2100, a business aircraft
built in 1983, in which carbon fiber epoxy and Kevlar 49 fiberepoxy accounted for ~70% of the
aircrafts airframe weight. Fiber- reinforced polymers are used in many military and commercial
helicopters for making baggage doors, fairings, vertical fins, tail rotor spars etc. Such
combination of high specific strength and low mass is possible only by composites. Since
composites are mainly used in structural elements and many parts of automobile and aerospace
industry, which are subjected to lot of vibrations and shocks. So their damping behavior
significantly contributes to their usefulness in industrial applications.
3.5 METHODOLOGY
Present work is accomplished through following major steps:
1. In first phase, unreinforced epoxy, short cooper fiber and long cooper fiber will be handmolded using punch and die technique. Various orientations of fibers will be incorporated
in preparation of composite work pieces.
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2. In second phase of work these composite will be analyzed for various mechanicalproperties (tensile test and impact test).
3. In third phase, these materials will be analyzed for damping behavior.4. Comparisons will be made for strength test, impact test and damping behavior, in order to
obtain best composite in terms of strength and damping capacity.