Revised Mini Project
Transcript of Revised Mini Project
INTRODUCTION
The aim of this project work is to experimentally investigate the
mechanical properties of ‘E’ Glass fiber reinforced Epoxy composite and compare
them with analytically derived properties in order to get an insight into their
behavior.
In its most basic form a composite material is one which is composed of at
least two elements working together to produce material properties that are
different to the properties of those elements on their own. In practice, most
composites consist of a bulk material (the 'matrix'), and a reinforcement of some
kind, added primarily to increase the strength and stiffness of the matrix. This
reinforcement is usually in fiber form.
Mankind has been aware composite materials for several hundred years
before Christ and applied innovation to improve the quality of life using these
materials. Although it is not clear as to how Man understood the fact that mud bricks
made sturdier houses if mingled with straw, he used them to make dwellings that
lasted. Ancient Pharaohs made their slaves use bricks with mud and straw to
enhance the structural integrity of their buildings, some of which testify to wisdom
of the dead civilization even today.
Composites could be natural or synthetic.
Traditional composites - composite materials that have been produced by
civilizations for many years
Examples: wood, concrete, asphalted roads
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- Naturally occurring composites include tendon, bone ,bamboo, rock, and
many other biological and geological materials. Wood is a good example of a
natural composite, combination of cellulose fiber and lignin. The cellulose
fiber provides strength and the lignin is the "glue" that bonds and stabilizes
the fiber.
Synthetic composites - modern material systems normally associated with the
manufacturing industries, in which the constituents are first produced separately
and then combined in a controlled way to achieve the desired structure,
properties, and part geometry
Contemporary composites resulted from research and innovation during
the past few decades and have progressed from glass fiber for automobile bodies to
modern, advanced composites with carbon aramid fibers for aerospace and a range
of other applications.
Ironically, despite the growing familiarity with composite materials and
ever-increasing range of applications, the term defies a clear definition. Loose terms
like “materials composed of two or more distinctly identifiable constituents” are
used to describe natural composites like timber, organic materials, like tissue
surrounding the skeletal system, soil aggregates, minerals and rock.
Constituents of composite materials
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Composites are combinations of two or more materials in which one of
the material is called the reinforcing phase, is in the form of fibers, sheets, or
particles, and is embedded in the other material called the matrix phase.
Typically, reinforcing materials are strong with low densities while the
matrix is usually a ductile or tough material. If the composite is designed and
fabricated correctly, it combines the strength of the reinforcement with the
toughness of the matrix to achieve a combination of desirable properties not
available in any single constituent material
Basic Components of composite materials:
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CLASSIFICATION OF COMPOSITES :
Composites that form heterogeneous structures which meet the
requirements of specific design function, imbued with desired properties limit the
scope for classification. However, this lapse is made up for, by the new types of
composites being innovated all the time, each with their own specific purpose like
the filled, flake, particulate and laminar composites.
Fibers or particles embedded in matrix of another material would be the
best example of modern-day composite materials, which are mostly structural.
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Composite materials are commonly classified at following two distinct levels:
matrix based classification
reinforcement based (on form of reinforcement) .
Composites based on matrix constituent :
The first level of classification is usually made with respect to
the matrix constituent. The major composite classes include Organic Matrix
Composites (OMCs), Metal Matrix Composites (MMCs) and Ceramic Matrix
Composites (CMCs). The term organic matrix composite is generally assumed
to include two classes of composites, namely Polymer Matrix Composites
(PMCs) and carbon matrix composites commonly referred to as carbon
carbon composites.
Today, the most common man-made composites can be divided into three
main groups:
Polymer Matrix Composites (PMC's) :These are the most common and will be the
main area of discussion in this investigation. Also known as FRP - Fibre
Reinforced Polymers (or Plastics) - these materials use a polymer-based resin as
the matrix, and a variety of fibers such as glass, carbon and aramid as the
reinforcement.
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Metal Matrix Composites (MMC's) - Increasingly used in the automotive industry.
These materials use a metal such as aluminum as the matrix, reinforced with
fibers such as silicon carbide.
Ceramic Matrix Composites (CMC's) - Used in very high temperature
environments, these materials use a ceramic as the matrix and reinforce it with
short fibres, or whiskers such as those made from silicon carbide and boron
nitride. Carbon-carbon composites( though OMC) also fall in this category
Composites based on reinforcement form
The second level of classification refers to the reinforcement form
- fibre reinforced composites, laminated composites and particulate composites.
Fibre reinforced composites can be further divided into those containing
discontinuous or continuous fibres.
Fibre Reinforced Composites are composed of fibres embedded in matrix
material. Such a composite is considered to be a discontinuous fibre or short
fibre composite if its properties vary with fibre length. On the other hand, when
the length of the fibre is such that any further increase in length does not further
enhance the elastic modulus of the composite, the composite is considered to be
continuous fiber reinforced. Fibres are small in diameter and when pushed
axially, they bend easily although they have very good tensile properties. These
fibres must be supported to keep individual fibres from bending and buckling.
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Laminated Composites are composed of layers of materials held together by
matrix.
Particulate Composites are composed of particles distributed or embedded in a
matrix body. The particles may be flakes or in powder form. Concrete and wood
particle boards are examples of this category.
REINFORCEMENTS:
Strong (high strength & modulus) materials bonded to or into a matrix
to improve mechanical properties are reinforcements. Materials, ranging from short
fibers through complex textile forms combined with a resin to provide the composite
with enhanced mechanical properties.
Reinforcements for the composites can be fibers, fabrics particles or
whiskers. Fibers are essentially characterized by one very long axis with other two
axes either often circular or near circular. Particles have no preferred orientation
and so does their shape. Whiskers have a preferred shape but are small both in
diameter and length as compared to fibers.
TYPES OF REINFOCEMENTS IN COMPOSITES:
Reinforcing constituents in composites, as the word indicates, provide
the strength that makes the composite what it is. But they also serve certain
additional purposes of heat resistance or conduction, resistance to corrosion and
provide rigidity. Reinforcement can be made to perform all or one of these functions
as per the requirements.
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A reinforcement that embellishes the matrix strength must be
stronger and stiffer than the matrix and capable of changing failure mechanism to
the advantage of the composite. This means that the ductility should be minimum or
even nil the composite must behave as brittle as possible.
Fiber Reinforcement :
Fibers are the important class of reinforcements, as they satisfy the
desired conditions and transfer strength to the matrix constituent influencing and
enhancing their properties as desired.
Glass fibers are the earliest known fibers used to reinforce materials.
Ceramic and metal fibers were subsequently found out and put to extensive use, to
render composites stiffer more resistant to heat
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Fibers fall short of ideal performance due to several factors. The
performance of a fiber composite is judged by its length, shape, orientation,
composition of the fibers and the mechanical properties of the matrix.
Types of Fibers : Organic and inorganic fibers are used to reinforce composite
materials. Almost all organic fibers have low density, flexibility, and elasticity.
Inorganic fibers are of high modulus, high thermal stability and possess greater
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rigidity than organic fibers and not withstanding the diverse advantages of organic
fibers which render the composites in which they are used.
Mainly, the following different types of fibers namely, glass fibers,
silicon carbide fibers, high silica and quartz fibers, aluminina fibers, metal fibers and
wires, graphite fibers, boron fibers, aramid fibers and multiphase fibers are used.
Among the glass fibers, it is again classified into E-glass, A-glass, R-glass etc.
There is a greater marker and higher degree of commercial movement of organic
fibers. The potential of fibers of graphite, silica carbide and boron are also exercising
the scientific mind due to their applications in advanced composites.
Glass fibers : Over 95% of the fibers used in reinforced plastics are glass fibers, as
they are inexpensive, easy to manufacture and possess high strength and stiffness
with respect to the plastics with which they are reinforced.
Their low density, resistance to chemicals, insulation capacity are other
bonus characteristics, although the one major disadvantage in glass is that it is
prone to break when subjected to high tensile stress for a long time.
However, it remains break-resistant at higher stress-levels in shorter time frames.
This property mitigates the effective strength of glass especially when glass is
expected to sustain loads for many months or years continuously.
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Period of loading, temperature, moisture and other factors also
dictate the tolerance levels of glass fibers and the disadvantage is further
compounded by the fact that the brittleness of glass does not make room for prior
warning before the catamorphic failure.
But all this can be easily overlooked in view of the fact the wide
range of glass fiber variety lend themselves amicably to fabrication processes like
matched die-moulding, filament winding lay-up and so on. Glass fibers are available
in the form of mates, tapes, cloth, continuous and chopped filaments, roving and
yarns.
Addition of chemicals to silica sand while making glass yields different types of
glasses
Carbon fibers also come in a variety of grades and sizes, and were once limited to
the aerospace industry due to their high cost. Carbon fiber imparts significantly
more stiffness to a composite than glass fibers, at a lower weight, and as the cost of
the fibers have decreased, the utilization of carbon fibers have made their way into
other industries.
Aramid fibers , recognized more commonly by their trade names of Kevlar and
Twaron, are very strong, lightweight, and heat resistant fibers. Aramid fibers are
most commonly used in high-end composites that require optimal strength-to-
weight performance.
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Thermoplastic fibers are strands of thermoplastic resin, from polypropylene to
ultra-high molecular weight polyethylene, that are lightweight, chemical resistant,
and very tough.
Natural Fibers have been in "composites" for thousands of years, dating back to the
use of straw in mud bricks for primitive buildings. In more recent times, with a focus
on renewable resources, there has been increased use of natural fibers in
composites, focused mostly in thermoplastic composites. As with any natural
resource there is natural variation in material and performance, variation that has
thus far been too great for many composite manufacturing processes. As agri-tech
and manufacturing process continue to evolve and expand with a focus on such.
Fabrics are produced from all of the above fibers in a multitude of weaves. These
fabrics, from unidirectional to three-dimensional weaves, are all designed and
engineered to optimize particular mechanical properties in specific directions
within the composite.
Cores are materials that have been encapsulated within a composite laminate,
typically designed to increase the stiffness or increase the insulative properties of
the composite, without significantly increasing the weight of the system. The use of
cores are even used to "tune" a composite's transparency to specific electromagnetic
radiation (i.e. various radar bands). Examples of core material include a wide range
of materials, from polyurethane foam to thermoplastic or even aluminum
honeycomb structures.
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Multiphase Fibers :
Spoolable filaments made by chemical vapour deposition processes are usually the
multiphase variety and they usually comprise materials like boron, silicon and their
carbides formed on surface of a very fine filament substrate like carbon or tungsten.
They are usually good for high temperature applications, due to their reduced
reaction with higher melting temperature of metals than graphite and other metallic
fibers. Boron filaments are sought after for structural and intermediate-temperature
composites.
A poly-phase fiber is a core-sheath fiber consisting of a poly-crystalline core.
Whiskers :
Single crystals grown with nearly zero defects are termed whiskers. They are
usually discontinuous and short fibers of different cross sections made from several
materials like graphite, silicon carbide, copper, iron etc. Typical lengths are in 3 to
55 N.M. ranges. Whiskers differ from particles in that, whiskers have a definite
length to width ratio greater than one. Whiskers can have extraordinary strengths
upto 7000 MPa.
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Matrix Materials
Although it is undoubtedly true that the high strength of composites is largely
due to the fibre reinforcement, the importance of matrix material cannot be
underestimated as it provides support for the fibres and assists the fibres in
carrying the loads. It also provides stability to the composite material. Resin matrix
system acts as a binding agent in a structural component in which the fibres are
embedded. When too much resin is used, the part is classified as resin rich. On the
other hand if there is too little resin, the part is called resin starved. A resin rich part
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is more susceptible to cracking due to lack of fibre support, whereas a resin starved
part is weaker because of void areas and the fact that fibres are not held together
and they are not well supported.
Functions of a Matrix
In a composite material, the matrix material serves the following functions:
• Holds the fibres together.
• Protects the fibres from environment.
• Distributes the loads evenly between fibres so that all fibres are subjected
to the same amount of strain.
• Enhances transverse properties of a laminate.
• Improves impact and fracture resistance of a component.
• Helps to avoid propagation of crack growth through the fibres by
providing alternate failure path along the interface between the fibres
and the matrix.
• Carry interlaminar shear.
The matrix plays a minor role in the tensile load-carrying capacity of a composite
structure. However, selection of a matrix has a major influence on the interlaminar
shear as well as in-plane shear properties of the composite material. The
interlaminar shear strength is an important design consideration for structures
under bending loads, whereas the in-plane shear strength is important under
torsion loads. The matrix provides lateral support against the possibility of fibre
buckling under compression loading, thus influencing to some extent the
compressive strength of the composite material.
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The interaction between fibres and matrix is also important in designing damage
tolerant structures. Finally, the processability and defects in a composite material
depend strongly on the physical and thermal characteristics, such as viscosity,
melting point, and curing temperature of the matrix. The fibres are saturated with a
liquid resin before it cures to a solid. The solid resin is then said to be the matrix for
the fibres
General types of Matrix Materials In general, following general following types of matrix materials are available:
• Thermosetting material;
• Thermoplastic material;
• Carbon;
• Metals;
• Ceramics;
• Glass Matrix.
A thermosetting material is the one which when cured by heat or chemical
reaction is changed into an infusible and insoluble material. Thermosetting resins
undergo irreversible chemical cross-linking reaction upon application of heat. On
the other hand, thermoplastics do not undergo a chemical reaction on application of
heat. They simply melt on application of heat and pressure to form a component.
Thermoplastics can be softened and they undergo large and rapid change in
viscosity with variation in temperature. Thermoplastics can be repeatedly softened
by heating and hardened by cooling. 15
Thermosetting Materials
The major group of materials used today in the industries contains thermosetting
matrix resins.
Thermoset Resin
Polyesters, epoxy and other resins in liquid form contain monomers
(consisting of simple molecules), which convert into polymers (complex cross-
linked molecules) when the resin is cured. The resulting solid .is called thermosets,
which is tough, hard, insoluble and infusible. The property of infusibility
distinguishes thermosets from the thermoplastics. Cure and polymerisation refer to
the chemical reactions that solidify the resin. Curing is accomplished by heat,
pressure and by addition of curing agents at room temperature.
Thermosetting materials can be further divided into two groups depending on
how they react to form their network structure. For example, epoxies and polyesters
react to form a network structure without formation of a volatile by-product.
Phenolics react to form a volatile by-product i.e., water. The fact that some
thermosets form volatile by-products means that high pressure laminating
techniques must be used to prevent the formation of voids or other defects. Epoxies
and polyesters can be cured at atmospheric pressures and also at ambient
temperatures.
Polyester matrices have been in use for the longest period in the widest range
of structures. Polyesters cure with the addition of a catalyst (usually a peroxide) 16
resulting in an exothermic reaction, which can be initiated at room temperature.
The most widely used matrices for advanced composites have been the epoxy
resins. These resins cost more than polyesters and do not have the high
temperature capability of the Bismaleimides or Polyimides. However, they are
widely used due to the following advantages.
• Adhesion to fibres and to resin
• No by-products formed during cure;
• Low shrinkage during cure;
• High or low strength and flexibility;
• Resistance to solvents and chemicals;
• Resistance to creep and fatigue;
• Wide range of curative options;
• Adjustable curing rate;
• Good electrical properties.
Epoxies do have few inherent disadvantages also, viz
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• Resins and curatives are somewhat toxic in uncured form;
• Moisture absorption resulting into change in dimensions and physical
properties;
• Limited to about 200°C (392°F) upper temperature use;
• Difficult to combine toughness and high temperature resistance;
• High thermal coefficient of expansion;
• High degree of smoke liberation in a fire;
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• May be sensitive to ultraviolet light degradation;
• Slow curing.
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Fibre Reinforced Polymer (FRP) Laminated Composites :
Laminate Lay-up :
A structural laminate is designed to have a specific lay-up or ply
arrangement, based on the various design criteria imposed on it. A laminate lay-up
definition refers to the fibre orientation of successive pies in a laminate with respect
to an established reference coordinate system.
Ply Orientation definition :
It designates the tape fibre direction or the warp
It is important that for positive and negative angles should be consistent with the
coordinate system chosen.
One of the advantages of using a modern composite is its potential to orient the
fibres to respond to the load requirement s. this means that the composite designer
must take into consideration the characteristics of the material including the aspects
of the fibre orientation in each ply and how the plies arte arranged.
Each ply (lamina) is defined by a number representing the direction of the fibre in
degrees with respect to the reference (x) axis. 0º fibres of both tape and fabric are
oriented at angles equal in magnitude but opposite in sign, (+) and (-) are used. Each
(+) or (-) sign represents one ply.
Criteria used during Ply Orientation
Following criteria should be used during ply orientation:
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• Attention to ply orientation on strength controlled laminates can prevent
matrix and stiffness degradation. The 0º ply orientation is used to carry the
longitudinal loading, the 90º ply orientation is suited to the transverse loading
and the ±45º ply orientation is for shear loading.
• In order to minimise the in-plane shear, place the ±45º and -45º plies
together; the in-plane shear is carried as tension and compression in the 45º
plies.
• To minimise warpage and interlaminar shear within a laminate, maintain the
symmetry about the centre line of the laminate.
• Stress orientation can be minimised by proper designing or by stepped
laminate thickness changes.
• The placement of specific ply orientations can influence the buckling strength
and damage tolerance. The outer ply orientations influence the laminate
bending characteristics more than plies placed at or near the laminate
bending characteristics more than the plies placed at or near the neutral axis.
Influence of Fibre Orientation :
Strength and stiffness of a composite laminate depends on the orientation of the plies
with reference to the load direction. Proper selection of ply orientation is necessary to
provide a structurally efficient design. As stated above, a composite part might require 0º
plies to react to the axial loads, ±45º to react to the shear loads and 90º plies to react to
the side loads. For example, a lay-up of 50% of 0º plies and 50% of ±45º plies will have
strength and stiffness equivalent to those of aluminium when loaded in the 0º direction.
Special classification of Laminates :
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The laminates also classified based on the symmetricity of Reinforced fibres, viz:
• Symmetric laminates
• Anti-symmetric laminates
• Non-symmetric laminates
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Designing the laminate :
Many structural materials generally have isotropic properties and they are
homogeneous, that is to say, they are uniform in all directions.
A composite material can take a number of different forms. The material
may be orthotropic, such as a unidirectionally reinforced polymer, where the
strength and stiffness in the fibre direction considerably exceeds that at 90° to the
fibre. It may be planar-isotropic, such as a random chopped strand glass mat
reinforced polymer. It may approach isotropy by the use of very short fibres
randomly, placed in a polymer by injection moulding. In all cases, though, composite
materials are inhomogeneous.
It is these anisotropic properties of composite materials that are the key
to developing highly efficient structures. Fibres can be strategically placed so that
they locally engineer the required strength and stiffness properties. Furthermore,
by combining different fibre types - glass, aramid, carbon, etc - the particular
properties of each fibre can be exploited. For instance, the low cost of glass, the
extreme toughness of aramid fibre and the high strength and stiffness of carbon can
all be used within a single laminate.
A composite material is not ductile like metal, and failure, when it occurs,
is abrupt. The stiffness properties are generally lower than those of steel, but the
lower weight of composite materials results in excellent specific strength and
stiffness properties, leading to reduced- weight components and structures.
The properties of the laminate are affected by the amount of fibre in the matrix,
which in turn is influenced by the manufacturing process.
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The principles of design analysis :
As in all structural designs the developed stress and strain levels in the
polymer composite when it is under load must be determined and the material designed.
The critical stress, strain and deformation values are then compared with the relevant
design criteria to ensure that the component satisfies product requirements and material
limitations. Polymer composites are usually macroscopically inhomogeneous and
anisotropic because of the reinforcing fibres and, in addition, have visco elastic properties
derived from the polymer matrix. Owing to the differing material descriptions between
composites, further material properties are required to characterise polymer composites
completely, consequently, more complex analysis procedures are required to determine
stress and deformation levels than are generally required for the more conventional
materials.
The three main aspects of material design which will be considered are:
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1. The analysis which considers the anisotropy and non-homogeneity in polymer
composites (the material properties & the fibre and matrix, ply orientation, layer
thicknesses, etc.).
2. The short term load condition, in which the elastic stress and analysis methods may
be used, provided anisotropy is taken into account.
3. The long term load conditions, in which viscoelastic and degradation effects may be
significant; in this case it would be necessary to modify the short term elastic
design procedures.
Requirements of materials’ design
Polymer composite materials generally consist of laminae of resin impregnated
fibres which are unidirectionally or orthogonally aligned, angle-ply or
randomly orientated systems. It is also possible to provide a mixture of fibre
arrays in adjacent laminae when fabricating a composite material to meet the
required loading situation. This freedom to tailor-make composite materials with
specific required properties introduces an additional complexity in the design
analyses of these systems over those of the conventional ones.
As the design of composite structures ideally involves the simultaneous analysis and
design of the material and the structural system, this approach may be undertaken
by the finite element analysis. It can be expensive for small jobs and is really
relevant only to the high technology of the aerospace industry; for the medium
technology applications a simpler approach is to consider the material design 24
independently from that of the structural one. Consequently, for the latter design
application, the properties of a chosen fibre/matrix array are calculated or
measured and are then utilised in the structural analyses.
The majority of polymer composite structural systems are composed of relatively
thin plates or shell laminates where the properties may be in terms of laminate structure
and ply thickness using laminated plate theory or by commercially available PC software.
Assuming that the laminates had orthotropic symmetry and that both in-plane direct and
shear loads as well as bending and twisting moments were acting on the plate,the element
properties would require two principal tensile stiffness, shear stiffness and two principal
flexural rigidities. In addition, the corresponding strength values in tension, flexure and
shear would be required; the latter three values would be obtained by either mechanical
tests or by undertaking a laminate analysis and thus the laminate stiffness and strength
characteristics would be known. To satisfy the necessary design criteria this relatively
small number of properties would then be used in the structural analysis and design for
the composite
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MANUFACTURING OR FABRICATION PROCESS OF COMPOSITE
LAMINATE:
Manufacturing Processes :
Manufacturing of composite materials involves distinct operations that may vary
depending upon available technology, existing facilities and personnel skill. The
manufacturing process may also vary due to wide variety of composite materials
and their application. Each of the fabrication processes has characteristics that
define the type of products to be produced. This is advantageous because this
expertise allows to produce the best composite. Factors considered for selection of
most efficient manufacturing process are as follows:
• User needs
• Total production volume
• Performai1ce requirements
• Economic targets
• Size of the product
• Labour
• Surface complexity
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• Materials
• Appearance
• Tooling/assembly
• Production rate
• Equipment
The goals of the composite manufacturing process are to:
• Achieve a consistent product by controlling
Fibre thickness
Fibre volume
Fibre direction
• Minimise voids
• Reduce internal residual stresses
• Process in the least costly manner
The procedure to achieve these goals involves series of actions to select the three
key components, viz.
• Composite material and its configuration
• Tooling
• Process
As reinforcement for composite material, the choice between unidirectional
tape and woven fabric is made on the basis of the greater strength and modulus
attainable with the tape particularly in applications in which compression strength
is important. Salient advantages and disadvantages of tape and fabric for their
selection are given below: 27
Tape Advantages
• Best modulus and strength efficiency
• High fibre volume achievable
• Low scrap rate
• Less tendency to trap volatiles
• Automated lay-up possible
• No discontinuities
Fabric Advantages
• Better drape for complex shapes
• Single ply is balanced and may be essentially symmetric
• Can be laid up without resin
• Plies stay in line better during cure
• Cured parts easier to machine
• Better impact resistance
• Many forms available
Fabric Disadvantages
• Fibre discontinuities (splices)
• Less strength and modulus
• Lower fibre volume than tape
• More costly than tape
• Greater scrap rates
• Warp and fill properties differ
• Fabric distortion can cause part warping
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Another aspect considered important for composite fabrication is appropriate lay-
up techniques along with composite cure control. Some of the considerations for
choosing lay-up techniques are given below:
Classification of Manufacturing Processes Most widely used manufacturing methods for laminated fibre composites are as follows:
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Open Mold Process :
• Spray lay-up - Chopped roving and resin sprayed simultaneously, rolled.
• Hand lay-up - Lay-up of fibres or woven cloth, impregnate, no heat or pressure.
• Filament winding.
• Sheet molding compound.
• Expansion tool molding.
• Contact molding.
Closed Mold Process :
• Compression molding – Load with raw material, press into shape.
• Vacuum bag, pressure bag, autoclave - Prepreg laid up, bagged, cured.
• Injection molding – Mold injected under pressure.
• Resin Transfer – Fibres in place, resin injected at low temperature.
Continuous Process :
• Pultrusion.
• Braiding.
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Open Mold Processes:
Open molding offers a number of process and product advantage over other high
volume and complex application methods. These include:.
• Freedom of design
• Easy to change design
• Low mold and/or tooling cost
-Tailored properties possible
• High strength large parts possible
• On-site production possible
Disadvantages associated with the open molding process include:
• Low to medium number of parts
• Long cycle times per molding
• Not the cleanest application process
• Only one surface has aesthetic appearance
• Operator skill dependent
As the resources are limited for us in our study of the composites ,we employed
hand lay up process for the fabrication of composite laminate
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Wet Lay-up/Hand Lay-up:
The hand (wet) lay-up is one of the oldest and most commonly used
methods for manufacture of composite parts. Hand lay-up composites are a case of
continuous fibre reinforced composites. Layers of unidirectional or woven
composites are combined to result in a material exhibiting desirable properties in
one or more directions. Each layer is oriented to achieve the maximum utilisation of
its properties. Layers of different materials (different fibres in different directions)
can be combined to further enhance the overall performance of the laminated
composite material. Resins are impregnated by hand into fibres, which are in the
form of woven, knitted, stitched or bonded fabrics. This is usually accomplished by
rollers or brushes, with an increasing use of nip-roller type impregnators for forcing
resin into the fabrics by means of rotating rollers and a bath of resin. Laminates are
left to cure under standard atmospheric conditions.
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Materials used for fabrication :
Resin: Epoxy resin( LY-556 BIFUNCTIONAL RESIN)
fibers: Woven Glass fibre reinforcement 13 mill cloth
ESTIMATING MATERIAL REQUIREMENT
Required size of the laminate = 350 x 300 mm.
Thickness of each 13 mill cloth layer = 13* (25.4/1000)= 0.3 mm
Total no. of layers reqd. in order to achieve a total thickness of 3 mm= 3/0.3=~ 9
layers.
Total no. of layers laid = 6 layers.
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Target vol. fraction = 60%
So weight fraction considered= 65%
Weight of 1 layer of 350x300 mm cloth = 48.3 gm.
Weight of total 6 layers = 290 gms.
Weight of total resin required=156.15 gms.
Amount of resin per lamina = 22.3 gms.
Amount of resin for gelcoat= 11.15gms.*2
STEPS INVOVLED IN HAND LAY UP PROCESS:
1. PREPARING THE MOLD
The mold plates are made up of the commercially available ¾ inch mild steel plates.
The surface of the plates is highly finished by milling up to order of micron. The
plates are then cleaned using zero-grade emery sheets to obtain a smooth finish and
surface accuracy.
The plates are then cleaned with acetone to dissolve any remaining dirt or oil from
the surface. The plates are then allowed to dry.
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Once the plates are dried, a layer of soft wax polish is applied using a soft towel
made in form of a buff. The entire surfaces of the plates are covered with wax, and
then it is allowed to dry. Two layers of wax are applied to ensure proper parting,
while removing the laminate after curing.
2. PREPARATION OF THE RESIN SOLUTION
The resin and the constituent hardener and the diluents are to be mixed in the
prescribed proportion of 100:24:24.
That implies that for every 100 units of resin, we add 24 parts of hardener and 24
parts of diluents.
We make up the resin solution as per the above given ratio, as per our requirements.
3. LAYING OF LAMINATE
The 6 layers of glass cloth are cut to the required dimensions of 350X300 mm.
The resin is divided into 7 equal parts that are to be evenly applied on 6 fibre glass
layers.
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The 1st part of the resin is spread evenly on the mold plate using a smooth
brush. Then the glass cloth is placed on the wetted part of mold and rolled using a
roller. So that the resin percolates upwards through the fabric and the wets the
cloth.
Then the 2nd part of the resin is spread on the glass fabric layer and nicely
rolled and another layer of fabric layer is placed on it and the process is repeated
again for all the 6 layers.
Any remaining resin is to be spread evenly on the top and the freshly laid laminate is
to be rolled for few minutes so as to remove any air bubbles trapped in between.
Any fiber loosely hanging from the laminate are to be cut using a sharp razor blade
or pulled towards the laminate.
4. COVERING THE MOLD
The mold plate upon which the laminate is laid is again covered with a top plate.
The surface of the top plate is also equally prepared as the bottom plate.Care has to
be taken so as not to disturb the laminate while putting the top plate. Then the mold
is kept in the oven for curing
Main Advantages of Hand Layup Process:
Low capital Investment.
Simple principles to fabricate the part.
Low cost tooling, if room-temperature cure resins are used.
36
Wide choice of suppliers and material types
Disadvantages:
• Only one molded surface is obtained.
• Quality is related to the skill of the operator.
• Low volume process.
• Longer cure times required.
• Resins need to be low in viscosity to be workable by hand. This generally
compromises their mechanical/thermal properties.
• The waste factor can be high.
CURING OF COMPOSITES:
DEFINITION OF CURING:
Curing is a term in polymer chemistry and process engineering that refers
to the toughening or hardening of a polymer material by cross-linking of polymer
chains, brought about by chemical additives, ultraviolet radiation, electron beam or
heat. In rubber, the curing process is also called vulcanization.
Resin curing:37
Despite the wide variety of thermoset resin formulations (epoxy, vinylester,
polyester, etc.), their cure behavior is qualitatively identical. The resin viscosity
drops initially upon the application of heat, passes through a region of maximum
flow and begins to increase as the chemical reactions increase the average length
and the degree of cross-linking between the constituent oligomers. This process
continues until a continuous 3-dimensional network of oligomer chains is created –
this stage is termed gelation. In terms of process ability of the resin this marks an
important watershed: before gelation the system is relatively mobile, after it the
mobility is very limited, the micro-structure of the resin and the composite material
is fixed and severe diffusion limitations to further cure are created. Thus in order to
achieve vitrification in the resin, it is usually necessary to increase the process
temperature after gelation.
A very important aspect of thermo set resins is their cure cycle. Unsaturated
polyester and vinyl ester, along with epoxy, require time and temperature in order
to achieve what we call “Cross linking.” This is the “set” part of thermo set, and is the
permanent and irreversible chemical bonds in the resin. The amount of time and
temperature is dependent upon the formulation of the resin, the ratio of resin-to-
hardener, and the presence of additional chemicals used to modify the properties.
Curing Mechanisms
Temperature plays an important role in the curing process of the resins used in
composites. Many of the resins are setup for room-temperature curing. This
38
requires that the temperature is ideally set between 65 and 75oC. And that the resin
itself is near this temperature.
Some resins cure with time and elevated temperatures, which are achieved with the
use of ovens. These allow for nearly unlimited open working time before cure. When
things are satisfactorily placed, the temperatures are elevated to start the cure
process.
COMPOSITE MACHINING:
Due to the toughness and abrasive nature of modern composites, there is a
need for harder and longer lasting cutting tools. A large variety
of machining methods are available for machining metal, wood and some
thermoplastics. However, much of this methods cannot be applied to machining
composites . Modern composites like graphite-epoxy, aramid-epoxy and carbon
carbon each have their own machining characteristics.
Composites are not homogeneous or isotropic, therefore the machining
characteristics are dependent on the tool path in relation
to the direction of the reinforcing fibers. Metals or metal alloys have nearly
homogeneous properties throughout the work piece, but each material in a
composite retains its individual properties.
39
Advantages of machining composites are:
improved surface finish unless part surface was directly in contact with the
mold surface;
machined surfaces provide accurate mating surfaces for parts to be
assembled;
eliminates the majority of the problems associated with part shrinkage and
insert movement during the fabrication processes
DISADVANTAGES:
The disadvantages associated with machining of composites include controlling dust
particles produced due to machining, confining them to a small area and having an
adequate collection system.
A second problem is controlling the outer layers of the composite so that the fibers
will shear instead of lifting up under the force of the cutting action and leaving
extended fibers beyond the cut surface.
Also when cutting perpendicular to the lay of composite fibers, edge break-out can
occur. This can be controlled by designing a backup structure in the tool.
Delamination of composite is also another major disadvantage while
machining .The fiber glass reinforcement tend to separate from the matrix material
due to delamination .This tend to happen during machining due to improper curing
and insufficient compaction pressure .If the curing temperature is not maintained
properly then there will be weak cross linking40
Of the resin with the reinforcement .Therefore care should be taken while
Curing the composites and machining of the composites.
SAFETY WHILE MACHINING OF COMPOSITES:
Safety is something that needs lots of attention. The processes are very operator
dependent and we are working with chemicals here, so workers must be protected.
Many of these chemicals are regulated by several government agencies. This is why
these chemicals are generally difficult to obtain on the street.
The styrene-based polyesters and vinylesters require respiratory protection and
skin protection, as styrene is considered by some to be a possible carcinogen. There
is a time weighted average for breathing the esters, specific to the percentage of
styrene in the mixture. Excessive inhalation can lead to headaches, sinus irritation,
and watering eyes. Skin contact is permissible, but can be difficult to remove and
can enter the bloodstream.
The epoxy-based resins are more forgivable with regards to respiratory issues, but
dermal protection is much more important. Short term occasional exposure is not
serious, but can develop into allergic reactions.
Therefore while machining of the composites a lot of dust is generated and must be
eliminated in order for the safety of the workers .For this, a vaccum pump is
41
provided while machining process so that the dust produced is eliminate by vacuum
pump by sucking of the dust produced while machining process ensuring the safety
of the workers. As a safety measure very every worker need to wear a protective
mask around his face and cover his body with a apron to prevent any health
problems.
MACHINING PROCESS:
Due to the toughness and abrasive nature of the modern composites it is not
possible to machine the composites through the conventional methods as the tool
wear out is at a larger scale. So , non conventional machining process are employed
for the machining of the composites.
The various non convectional machining process employed are
ABRASIVE WATER JET MACHINING
WATER JET MACHINING
LASER MACHINING
ELECTRIC DISCHARGE MACHINING
ULTRASONIC MACHINING
MACHINING OF THE PREPARED LAMINATE
42
A TUNGSTEN CARBIDE CUTTING TOOL is employed for the machining process. The
tool is mounted on to a flat table with a suitable position and is connected to a
electric motor. The tool is made to rotate at a speed of 12000 RPM and the
machining of the composite is done. The high shear action is required to machine
the composites.
The dust produced from the glass fiber composite is much higher compared to other
composites. so to prevent the dust to disperse water is used a preventive measure
so that the dust get mixed in the water and does get dispersed into air. The operator
should wear a protective mask and an apron to cover his body to prevent any health
problems.
The machining should be done very skillfully and precaution should be taken while
machining to avoid delamination.
ASTM D3039
Standard Test Method for
Tensile Properties of Polymer Matrix Composite Materials
This test method determines the in-plane tensile properties of polymer matrix
composite materials reinforced by high-modulus fibers. The composite material
forms are limited to continuous fiber or discontinuous fiber-reinforced composites
in which the laminate is balanced and symmetric with respect to the test direction.
Test method43
The specimen machined as per above shown dimensions is mounted on to Universal
Testing Machine (UTM).
The specimen is subjected to static loading under a constant cross head speed of
2mm/min.
The values of the load and the corresponding extensions within the specimen is
recorded and the values of tensile stress and the tensile modulus is computed.
The extension is measured using an extenso-meter .
CALCULATIONS
Load applied = P Newton (N)
Change in length = ∆L mm
Original length (Gauge length) =L mm
Width = W mm
Thickness = T mm
Cross sectional area = W*T mm2
Stress developed ( ) = Load/CS area N/mmσ 2 (or) MPa
Strain ( ) = ∆L/LЄ
Youngs modulus (E) = Stress/Strain = / GPaσ Є
44
STRESS v/s. STRAIN curve for E-glass/epoxy specimen.- A
45
Length = 250 mm. Strain rate = 2 mm/min.
Width = 18 m Extensometer length = 60 mm.
Thickness= 3 mm. Gripping length = 50 mm
SCALE:
X-Axis : 1unit = 0.005 mm/mm
Y-Axis : 1unit = 50 N/mm2
46
0
50
100
150
200
250
0 0.005 0.01 0.015 0.02
S.No. Load(N) Extension(micron) Corrected strain(mm) Strain (mm/mm) Stress(N/mm2) Modulous (GPa)
1 1000 60 0.06 0.001 18.51851852 18.51851852
2 1500 90 0.09 0.0015 27.77777778 18.51851852
3 2000 140 0.14 0.002333333 37.03703704 15.87301587
4 2500 190 0.19 0.003166667 46.2962963 14.61988304
5 3000 230 0.23 0.003833333 55.55555556 14.49275362
6 3500 270 0.27 0.0045 64.81481481 14.40329218
7 4000 310 0.31 0.005166667 74.07407407 14.33691756
8 4500 350 0.35 0.005833333 83.33333333 14.28571429
47
9 5000 390 0.39 0.0065 92.59259259 14.24501425
10 5500 430 0.43 0.007166667 101.8518519 14.2118863
11 6000 480 0.48 0.008 111.1111111 13.88888889
12 6500 530 0.53 0.008833333 120.3703704 13.62683438
13 7000 560 0.56 0.009333333 129.6296296 13.88888889
14 7500 620 0.62 0.010333333 138.8888889 13.44086022
15 8000 650 0.65 0.010833333 148.1481481 13.67521368
16 8500 700 0.7 0.011666667 157.4074074 13.49206349
17 9000 750 0.75 0.0125 166.6666667 13.33333333
18 9500 800 0.8 0.013333333 175.9259259 13.19444444
19 10000 840 0.84 0.014 185.1851852 13.22751323
20 10500 880 0.88 0.014666667 194.4444444 13.25757576
21 11000 930 0.93 0.0155 203.7037037 13.14217443
22 11500 960 0.96 0.016 212.962963 13.31018519
23 11700 1020 1.02 0.017 216.6666667 12.74509804
48
SPECIMEN-A
STRESS v/s. STRAIN curve for E-glass/epoxy specimen.- B
Length = 250 mm. Strain rate = 2 mm/min.
Width = 18 m Extensometer length = 60 mm.
Thickness= 3 mm. Gripping length = 50 mm
SCALE:
X-Axis : 1unit = 0.005 mm/mm
49
0
50
100
150
200
250
300
0 0.002 0.004 0.006 0.008 0.01 0.012 0.014 0.016 0.018
Y-Axis : 1unit = 50 N/mm2
S.No. Load(N) Extension(micron) Corrected
strain(mm)
Strain
(mm/mm)
Stress(N/mm2) Modulous
(GPa)
1 1000 30 0.03 0.0005 18.51851852 37.03703704
2 1500 40 0.04 0.000666667 27.77777778 41.6666666750
3 2000 50 0.05 0.000833333 37.03703704 44.44444444
4 2500 70 0.07 0.001166667 46.2962963 39.68253968
5 3000 90 0.09 0.0015 55.55555556 37.03703704
6 3500 100 0.1 0.001666667 64.81481481 38.88888889
7 4000 140 0.14 0.002333333 74.07407407 31.74603175
8 4500 180 0.18 0.003 83.33333333 27.77777778
9 5000 210 0.21 0.0035 92.59259259 26.45502646
10 5500 250 0.25 0.004166667 101.8518519 24.44444444
11 6000 300 0.3 0.005 111.1111111 22.22222222
12 6500 330 0.33 0.0055 120.3703704 21.88552189
13 7000 380 0.38 0.006333333 129.6296296 20.46783626
14 7500 430 0.43 0.007166667 138.8888889 19.37984496
15 8000 450 0.45 0.0075 148.1481481 19.75308642
16 8500 510 0.51 0.0085 157.4074074 18.51851852
17 9000 560 0.56 0.009333333 166.6666667 17.85714286
18 9500 610 0.61 0.010166667 175.9259259 17.30418944
19 10000 650 0.65 0.010833333 185.1851852 17.09401709
20 10500 700 0.7 0.011666667 194.4444444 16.66666667
21 11000 750 0.75 0.0125 203.7037037 16.2962963
22 11500 780 0.78 0.013 212.962963 16.38176638
51
23 12000 830 0.83 0.013833333 222.2222222 16.06425703
2412500 890 0.89 0.014833333 231.4814815 15.60549313
25 13000 930 0.93 0.0155 240.7407407 15.53166069
26 13500 970 0.97 0.016166667 250 15.46391753
27 13700 1020 1.02 0.017 253.7037037 14.92374728
Specimen-B
STRESS v/s. STRAIN curve for E-glass/epoxy specimen.- C
52
Length = 250 mm. Strain rate = 2 mm/min.
Width = 18 m Extensometer length = 60 mm.
Thickness= 3 mm. Gripping length = 50 mm
SCALE:
X-Axis : 1unit = 0.002 mm/mm
Y-Axis : 1unit = 50 N/mm2
53
0
50
100
150
200
250
-0.002 0 0.002 0.004 0.006 0.008 0.01 0.012 0.014 0.016 0.018
S.No. Load(N) Extension(micron) Corrected
strain(mm)
Strain
(mm/mm)
Stress(N/mm2) Modulous
(GPa)
1 1000 0 0 0 18.51851852 0
2 1500 0 0 0 27.77777778 0
3 2000 10 0.01 0.000166667 37.03703704 222.2222222
4 2500 40 0.04 0.000666667 46.2962963 69.44444444
5 3000 70 0.07 0.001166667 55.55555556 47.61904762
6 3500 120 0.12 0.002 64.81481481 32.40740741
7 4000 150 0.15 0.0025 74.07407407 29.62962963
8 4500 190 0.19 0.003166667 83.33333333 26.31578947
9 5000 250 0.25 0.004166667 92.59259259 22.22222222
10 5500 280 0.28 0.004666667 101.8518519 21.82539683
11 6000 320 0.32 0.005333333 111.1111111 20.83333333
12 6500 370 0.37 0.006166667 120.3703704 19.51951952
13 7000 400 0.4 0.006666667 129.6296296 19.44444444
14 7500 450 0.45 0.0075 138.8888889 18.51851852
15 8000 500 0.5 0.008333333 148.1481481 17.77777778
16 8500 540 0.54 0.009 157.4074074 17.48971193
54
17 9000 590 0.59 0.009833333 166.6666667 16.94915254
18 9500 630 0.63 0.0105 175.9259259 16.75485009
19 10000 670 0.67 0.011166667 185.1851852 16.58374793
20 10500 710 0.71 0.011833333 194.4444444 16.43192488
21 11000 760 0.76 0.012666667 203.7037037 16.08187135
22 11500 810 0.81 0.0135 212.962963 15.77503429
23 12000 860 0.86 0.014333333 222.2222222 15.50387597
24 12500 920 0.92 0.015333333 231.4814815 15.09661836
25 12700 950 0.95 0.015833333 235.1851852 14.85380117
Specimen-C
55
STRESS v/s. STRAIN curve for E-glass/epoxy specimen.- D
Length = 250 mm. Strain rate = 2 mm/min.
Width = 18 m Extensometer length = 60 mm.
Thickness= 3 mm. Gripping length = 50 mm
SCALE:
X-Axis : 1unit = 0.005 mm/mm
Y-Axis : 1unit = 50 N/mm2
56
0
50
100
150
200
250
0 0.005 0.01 0.015 0.02
S.No. Load(N) Extension(micron) Corrected
strain(mm)
Strain
(mm/mm)
Stress(N/mm2) Modulous
(GPa)
1 1000 30 0.03 0.0005 18.51851852 37.03703704
2 1500 70 0.07 0.001166667 27.77777778 23.80952381
3 2000 100 0.1 0.001666667 37.03703704 22.22222222
4 2500 140 0.14 0.002333333 46.2962963 19.84126984
5 3000 180 0.18 0.003 55.55555556 18.51851852
6 3500 225 0.225 0.00375 64.81481481 17.28395062
7 4000 265 0.265 0.004416667 74.07407407 16.77148847
8 4500 310 0.31 0.005166667 83.33333333 16.12903226
9 5000 330 0.33 0.0055 92.59259259 16.83501684
57
10 5500 390 0.39 0.0065 101.8518519 15.66951567
11 6000 430 0.43 0.007166667 111.1111111 15.50387597
12 6500 480 0.48 0.008 120.3703704 15.0462963
13 7000 540 0.54 0.009 129.6296296 14.40329218
14 7500 580 0.58 0.009666667 138.8888889 14.36781609
15 8000 630 0.63 0.0105 148.1481481 14.10934744
16 8500 690 0.69 0.0115 157.4074074 13.68760064
17 9000 740 0.74 0.012333333 166.6666667 13.51351351
18 9500 790 0.79 0.013166667 175.9259259 13.36146273
19 10000 830 0.83 0.013833333 185.1851852 13.38688086
20 10500 870 0.87 0.0145 194.4444444 13.40996169
21 11000 930 0.93 0.0155 203.7037037 13.14217443
22 11500 990 0.99 0.0165 212.962963 12.90684624
23 12000 1030 1.03 0.017166667 222.2222222 12.94498382
24 12500 1100 1.1 0.018333333 231.4814815 12.62626263
25 12700 1130 1.13 0.018833333 235.1851852 12.48770895
Length = 250 mm. Strain rate = 2 mm/min.
Width = 18 m Extensometer length = 60 mm.
Thickness= 3 mm. Gripping length = 50 mm 58
STRESS v/s. STRAIN curve for E-glass/epoxy specimen.- E
SCALE:
X-Axis : 1unit = 0.005 mm/mm
Y-Axis : 1unit = 50 N/mm2
59
0
50
100
150
200
250
0 0.005 0.01 0.015 0.02
S.No. Load(N) Extension(micron) Corrected strain(mm)
Strain (mm/mm)
Stress(N/mm2) Modulous (GPa)
1 1000 30 0.03 0.0005 18.51851852 37.03703704
2 1500 70 0.07 0.001166667 27.77777778 23.80952381
3 2000 100 0.1 0.001666667 37.03703704 22.22222222
4 2500 140 0.14 0.002333333 46.2962963 19.84126984
5 3000 180 0.18 0.003 55.55555556 18.51851852
6 3500 225 0.225 0.00375 64.81481481 17.28395062
7 4000 265 0.265 0.004416667 74.07407407 16.77148847
8 4500 310 0.31 0.005166667 83.33333333 16.12903226
9 5000 330 0.33 0.0055 92.59259259 16.83501684
10 5500 390 0.39 0.0065 101.8518519 15.66951567
60
11 6000 430 0.43 0.007166667 111.1111111 15.50387597
12 6500 480 0.48 0.008 120.3703704 15.0462963
13 7000 540 0.54 0.009 129.6296296 14.40329218
14 7500 580 0.58 0.009666667 138.8888889 14.36781609
15 8000 630 0.63 0.0105 148.1481481 14.10934744
16 8500 690 0.69 0.0115 157.4074074 13.68760064
17 9000 740 0.74 0.012333333 166.6666667 13.51351351
18 9500 790 0.79 0.013166667 175.9259259 13.36146273
19 10000 830 0.83 0.013833333 185.1851852 13.38688086
20 10500 870 0.87 0.0145 194.4444444 13.40996169
21 11000 930 0.93 0.0155 203.7037037 13.14217443
22 11500 990 0.99 0.0165 212.962963 12.90684624
23 12000 1030 1.03 0.017166667 222.2222222 12.94498382
Specimen-E
61
STRESS v/s. STRAIN curve for E-glass/epoxy specimen.- F
Length = 250 mm. Strain rate = 2 mm/min.
Width = 18 m Extensometer length = 60 mm.
Thickness= 3 mm. Gripping length = 50 mm
SCALE:
X-Axis : 1unit = 0.002 mm/mm
Y-Axis : 1unit = 50 N/mm2
62
0
50
100
150
200
250
0 0.002 0.004 0.006 0.008 0.01 0.012 0.014 0.016 0.018
S.No. Load(N) Extension(micron) Corrected
strain(mm)
Strain
(mm/mm)
Stress(N/mm2) Modulous
(GPa)
1 1000 30 0.03 0.0005 18.51851852 37.03703704
2 1500 70 0.07 0.001166667 27.77777778 23.80952381
3 2000 100 0.1 0.001666667 37.03703704 22.22222222
4 2500 140 0.14 0.002333333 46.2962963 19.84126984
5 3000 180 0.18 0.003 55.55555556 18.51851852
6 3500 225 0.225 0.00375 64.81481481 17.28395062
7 4000 265 0.265 0.004416667 74.07407407 16.77148847
8 4500 310 0.31 0.005166667 83.33333333 16.12903226
9 5000 330 0.33 0.0055 92.59259259 16.83501684
10 5500 390 0.39 0.0065 101.8518519 15.66951567
11 6000 430 0.43 0.007166667 111.1111111 15.50387597
12 6500 480 0.48 0.008 120.3703704 15.0462963
13 7000 540 0.54 0.009 129.6296296 14.40329218
14 7500 580 0.58 0.009666667 138.8888889 14.36781609
15 8000 630 0.63 0.0105 148.1481481 14.10934744
16 8500 690 0.69 0.0115 157.4074074 13.6876006463
17 9000 740 0.74 0.012333333 166.6666667 13.51351351
18 9500 790 0.79 0.013166667 175.9259259 13.36146273
19 10000 830 0.83 0.013833333 185.1851852 13.38688086
20 10500 870 0.87 0.0145 194.4444444 13.40996169
21 11000 930 0.93 0.0155 203.7037037 13.14217443
22 11500 990 0.99 0.0165 212.962963 12.90684624
23 12000 1030 1.03 0.017166667 222.2222222 12.94498382
24 12500 1100 1.1 0.018333333 231.4814815 12.62626263
Specimen-F
Specimen A
Max load sustained: 11700 N
Max deflection seen: 1.02 mm
Peak tensile stress: 216 Mpa
Avg. modulus: 14.05 GPa
Remarks: failure at lower end of the specimen. Delamination is observed of two
layers in front.
Specimen B
Max load sustained: 13700 N
Max deflection seen: 1.02 mm
64
Peak tensile stress: 253.7 MPa
Avg. modulus: 24.09 GPa
Conclusion: fracture originating from upper grip. Delamination is seen at the gauge
length.
Specimen C
Max load sustained:12700 N
Max deflection seen: 0.95 mm
peak tensile stress:235.18 MPa
Avg. modulus: 29.17 GPa
Conclusion: fracture at lower grip ends. Delamination is seen in gauge length.
Specimen D
Max load sustained:12700 N
Max deflection seen: 1.13 mm
Peak tensile stress:235.18 MPa
Avg. modulus: 16.36 GPa
Conclusion: fracture at upper grip ends.65
Specimen E
Max load sustained:12000 N
Max deflection seen: 1.05 mm
Peak tensile stress:222.22 MPa
Avg. modulus: 15.325 GPa
Conclusion: fracture at lower grip ends. Delamination is seen in gauge length
Specimen F
Max load sustained:12300 N
Max deflection seen: 1 mm
Peak tensile stress:227.77 MPa
Avg. modulus: 18.81 GPa
Conclusion: fracture at lower grip ends. Delamination is seen in gauge length.
Rule of Mixtures
Ec = Ef Vf + Em Vm
66
Ec = Youngs modulus of composite
Ef = Youngs modulus of fiber
Em = Youngs modulus of matrix material
Vm = Volume fraction of matrix
Vf = Volume fraction of fiber
67
ASTM D 3171
STANDARD TEST METHOD FOR DETERMINATION OF CONSTITUENT MATERIAL
FRACTIONS IN POLYMER MATRIX COMPOSITE
We use the resin burn test to eliminate matrix from the composite system.
In this method we burn a know mass of a sample in furnace to an elevated
temperatures of 5000 C for about 3 hours.
The epoxy resin completely burns of from the system leaving behind the glass fibres
which are resistant to elevated temperatures.
The left over fiber is weighed and suitably the weight of matrix is computed.
The volume is computed from densities and mass obtained
Calculation:
Vf = 55%
Vm =45%
68
Em = 30MPa
Ef = 70 GPa
Ec = Ef Vf + Em Vm
= (0.55 x 70) + (0.45 x 0.03) GPa
Ec = 38.51 GPa
Conclusion & discussions
It is observed that most of the specimens develop fracture at the lower grip
ends.
Delamination is prominently seen. This indicates a poor inter-laminar matrix
inter face.
the peak strengths are ranging between a min of 216 MPa to a max of 253
MPa with an average of 225 MPa.
The average modulus value also tends to be around 19.6 GPa
The modulus value obtained from the law of mixtures is observed to be
around 22 GPa for the 55% fibre vol. fraction
The variation is results can be attributed to a variety of reasons
(i) non uniform spreading of resin.
69
(ii) presence of void pockets with in the laminate, which brought down
The modulus value obtained from the law of mixtures is observed to be
around 38.51 GPa for the 55% fiber vol. fraction
The variation is results can be attributed to a variety of reasons
(i) non uniform spreading of resin.
(ii) presence of void pockets with in the laminate, which brought down
The strength of the FRP
(iii) parallality of the machining axis with warp direction.
(iv) sundry losses
70
71