ED8073-COMPOSITE MATERIALS AND MECHANICS

1. ED8073-COMPOSITE MATERIALS AND MECHANICS
NOTES
R-2013
YEAR: ME I YEAR SEM : I
KALAIGNAR KARUNANIDHI INSTITUTE OF TECHNOLOGY
KANNAMPALAYAM, COIMBATORE-641 402.

2. UNIT I
INTRODUCTION TO COMPOSITE MATERIALS
MATRIX MATERIALS
A fiber-reinforced composite (FRC) is a high-performance composite material made up
of three components - the fibers as the discontinuous or dispersed phase, the matrix acts as the
continuous phase, and the fine interphase region or the interface.
The matrix is basically a homogeneous and monolithic material in which a fiber system
of a composite is embedded. It is completely continuous. The matrix provides a medium for
binding and holding reinforcements together into a solid. It offers protection to the
reinforcements from environmental damage, serves to transfer load, and provides finish, texture,
color, durability and functionality.
Types of Composite Matrix Materials
There are three main types of composite matrix materials:
 Ceramic matrix - Ceramic matrix composites (CMCs) are a subgroup of composite
materials. They consist of ceramic fibers embedded in a ceramic matrix, thus forming a
ceramic fiber reinforced ceramic (CFRC) material. The matrix and fibers can consist of
any ceramic material. CMC materials were designed to overcome the major
disadvantages such as low fracture toughness, brittleness, and limited thermal shock
resistance, faced by the traditional technical ceramics.
 Metal matrix - Metal matrix composites (MMCs) are composite materials that contain at
least two constituent parts – a metal and another material or a different metal. The metal
matrix is reinforced with the other material to improve strength and wear. Where three or
more constituent parts are present, it is called a hybrid composite. In structural
applications, the matrix is usually composed of a lighter metal such as magnesium,
titanium, or aluminum. In high temperature applications, cobalt and cobalt-nickel alloy
matrices are common. Typical MMC's manufacturing is basically divided into three

3. types: solid, liquid, and vapor. Continuous carbon, silicon carbide, or ceramic fibers are
some of the materials that can be embedded in a metallic matrix material. MMCs are fire
resistant, operate in a wide range of temperatures, do not absorb moisture, and possess
better electrical and thermal conductivity. They have also found applications to be
resistant to radiation damage, and to not suffer from outgassing. Most metals and alloys
make good matrices for composite applications.
 Polymer matrix - Polymer matrix composites (PMCs) can be divided into three sub-
types, namely, thermoset, thermoplastic, and rubber. Polymer is a large molecule
composed of repeating structural units connected by covalent chemical bonds. PMC's
consist of a polymer matrix combined with a fibrous reinforcing dispersed phase. They
are cheaper with easier fabrication methods. PMC's are less dense than metals or
ceramics, can resist atmospheric and other forms of corrosion, and exhibit superior
resistance to the conduction of electrical current.
Composite Matrix Material Applications
The following are common application areas of composite matrix materials:
 Electrical moldings
 Decorative laminates
 High performance Cookware
 Sealants and gaskets
 Heat shield systems (capable of handling high temperatures, thermal shock conditions
and heavy vibration)
 Components for high-temperature gas turbines such as combustion chambers, stator
vanes and turbine blades
 Brake disks and brake system components used in extreme thermal shock environments
 Components for slide bearings under heavy loads requiring high corrosion and wear
resistance
 Carbide drills are made from a tough cobalt matrix with hard tungsten carbide particles
inside

4.  Components for burners, flame holders, and hot gas ducts
POLYMERS
Polymers are substances whose molecules have high molar masses and are composed of a
large number of repeating units. There are both naturally occurring and synthetic polymers.
Among naturally occurring polymers are proteins, starches, cellulose, and latex.
METALS
Metals are opaque, lustrous elements that are good conductors of heat and electricity.
Most metals are malleable and ductile and are, in general, denser than the other elemental
substances
CERAMICS
A ceramic is an inorganic, nonmetallic solid material comprising metal, nonmetal or
metalloid atoms primarily held in ionic and covalent bonds. The crystallinity of ceramic
materials ranges from highly oriented to semi-crystalline, and often completely amorphous (e.g.,
glasses). Varying crystallinity and electron consumption in the ionic and covalent bonds cause
most ceramic materials to be good thermal and electrical insulators and extensively researched in
ceramic engineering. Nevertheless, with such a large range of possible options for the
composition/structure of a ceramic (e.g. nearly all of the elements, nearly all types of bonding,
and all levels of crystallinity), the breadth of the subject is vast, and identifiable attributes (e.g.
hardness, toughness, electrical conductivity, etc.) are hard to specify for the group as a whole.
However, generalities such as high melting temperature, high hardness, poor conductivity, high
moduli of elasticity, chemical resistance and low ductility are the norm,[1]
with known exceptions
to each of these rules (e.g. piezoelectric ceramics, glass transition temperature, superconductive
ceramics, etc.). Many composites, such as fiberglass and carbon fiber, while containing ceramic
materials, are not considered to be part of the ceramic family.
REINFORCEMENT
In behavioral psychology, reinforcement is a consequence that will strengthen an
organism's future behavior whenever that behavior is preceded by a specific antecedent stimulus.

5. This strengthening effect may be measured as a higher frequency of behavior (e.g., pulling a
lever more frequently), longer duration (e.g., pulling a lever for longer periods of time), greater
magnitude (e.g., pulling a lever with greater force), or shorter latency (e.g., pulling a lever more
quickly following the antecedent stimulus). Although in many cases a reinforcing stimulus is a
rewarding stimulus which is "valued" or "liked" by the individual (e.g., money received from a
slot machine, the taste of the treat, the euphoria produced by an addictive drug), this is not a
requirement. Indeed, reinforcement does not even require an individual to consciously perceive
an effect elicited by the stimulus.[1]
Furthermore, stimuli that are "rewarding" or "liked" are not
always reinforcing: if an individual eats at a fast food restaurant (response) and likes the taste of
the food (stimulus), but believes it is bad for their health, they may not eat it again and thus it
was not reinforcing in that condition. Thus, reinforcement occurs only if there is an observable
strengthening in behavior.
PARTICLE
A particle is a minute fragment or quantity of matter. In the physical sciences, the word
is used to describe a small localized object to which can be ascribed several physical or chemical
properties such as volume or mass; subatomic particles such as protons or neutrons; and other
elementary particles. The word is rather general in meaning, and is refined as needed by various
scientific fields. Something that is composed of particles may be referred to as being particulate.
However, the term particulate is most frequently used to refer to pollutants in the Earth's
atmosphere, which are a suspension of unconnected particles, rather than a connected particle
aggregation.
INORGANIC FIBERS
The inorganic fibers are constituted mainly by inorganic chemicals, based on natural
elements such as carbon, silicon and boron, that, in general, after receiving treatment at elevated
temperatures are transformed into fibers.
Inorganic fibers, also sometimes dubbed high performance fibers or super-fibers, have
characteristics and properties that differ from other non-natural fibers and therefore rarely find
applications in the field of conventional textiles.

6. Effectively, these fibers have general characteristics as high thermal and mechanical
resistance, which makes them especially in engineering solutions applied in many cases in
combination with other materials – composites.
In these applications, they compete normally with conventional materials, replacing them
often due to their ease of processing, thermal resistance, resistance to chemical agents and
especially due to the excellent weight/mechanical properties correlation.
In general, the inorganic fibers are difficult to process by conventional textile techniques,
such as weaving or knitting, due to the fact that easily break in flexure (weak), presenting low
elongation at break and possess high coefficients of friction with metals , forcing many times to
its surface lubrication.
CERAMIC MATRIX COMPOSITES
Ceramic matrix composites (CMCs) are a subgroup of composite materials as well as a
subgroup of technical ceramics. They consist of ceramic fibres embedded in a ceramic matrix,
thus forming a ceramic fibre reinforced ceramic (CFRC) material. The matrix and fibres can
consist of any ceramic material, whereby carbon and carbon fibres can also be considered a
ceramic material.
Ceramic fibres in CMCs can have a polycrystalline structure, as in conventional ceramics. They
can also be amorphous or have inhomogeneous chemical composition, which develops upon
pyrolysis of organic precursors. The high process temperatures required for making CMCs
preclude the use of organic, metallic or glass fibres. Only fibres stable at temperatures above
1000 °C can be used, such as fibres of alumina, mullite, SiC, zirconia or carbon. Amorphous SiC
fibres have an elongation capability above 2% – much larger than in conventional ceramic
materials (0.05 to 0.10%).[1]
The reason for this property of SiC fibres is that most of them
contain additional elements like oxygen, titanium and/or aluminium yielding a tensile strength
above 3 GPa. These enhanced elastic properties are required for various three-dimensional fibre
arrangements (see example in figure) in textile fabrication, where a small bending radius is
essential.

7. NATURAL FIBRES
The use of composite materials dates from centuries ago, and it all started with natural
fibres. In ancient Egypt some 3 000 years ago, clay was reinforced by straw to build walls. Later
on, the natural fibre lost much of its interest. Other more durable construction materials like
metals were introduced. During the sixties, the rise of composite materials began when glass
fibres in combination with tough rigid resins could be produced on large scale. During the last
decade there has been a renewed interest in the natural fibre as a substitute for glass, motivated
by potential advantages of weight saving, lower raw material price, and 'thermal recycling' or the
ecological advantages of using resources which are renewable. On the other hand natural fibres
have their shortcomings, and these have to be solved in order to be competitive with glass.
Natural fibres have lower durability and lower strength than glass fibres. However, recently
developed fibre treatments have improved these properties considerably. To understand how
fibres should be treated, a closer look into the fibre is required.
NATURAL FIBRES IN COMPOSITES
The vegetable world is full of examples where cells or groups of cells are 'designed' for
strength and stiffness. A sparing use of resources has resulted in optimisation of the cell
functions. Cellulose is a natural polymer with high strength and stiffness per weight, and it is the
building material of long fibrous cells. These cells can be found in the stem, the leaves or the
seeds of plants. Hereunder a few successful results of evolution are described.
Bast fibres (flax, hemp, jute, kenaf, ramie (china grass))
In general, the bast consists of a wood core surrounded by a stem. Within the stem there
are a number of fibre bundles, each containing individual fibre cells or filaments. The filaments
are made of cellulose and hemicellulose, bonded together by a matrix, which can be lignin or
pectin. The pectin surrounds the bundle thus holding them on to the stem. The pectin is removed
during the retting process. This enables separation of the bundles from the rest of the stem
(scutching).

8. After fibre bundles are impregnated with a resin during the processing of a composite, the
weakest part in the material is the lignin between the individual cells. Especially in the case of
flax, a much stronger composite is obtained if the bundles are pre-treated in a way that the cells
are separated, by removing the lignin between the cells. Boiling in alkali is one of the methods to
separate the individual cells.
Flax delivers strong and stiff fibres and it can be grown in temperate climates. The fibres
can be spun to fine yarns for textile (linen). Other bast fibres are grown in warmer climates. The
most common is jute, which is cheap, and has a reasonable strength and resistance to rot. Jute is
mainly used for packaging (sacks and bales).
As far as composite applications are concerned, flax and hemp are two fibres that have
replaced glass in a number of components, especially in the German automotive industries.
Leaf fibres (sisal, abaca (banana), palm)
In general the leaf fibres are coarser than the bast fibres. Applications are ropes, and
coarse textiles. Within the total production of leaf fibres, sisal is the most important. It is
obtained from the agave plant. The stiffness is relatively high and it is often applied as binder
twines.
As far as composites is concerned, sisal is often applied with flax in hybrid mats, to
provide good permeability when the mat has to be impregnated with a resin. In some interior
applications sisal is prefered because of its low level of smell compared to fibres like flax.
Especially manufacturing processes at increased temperatures (NMT) fibres like flax can cause
smell.
Seed fibres (cotton, coir, kapok)
Cotton is the most common seed fibre and is used for textile all over the world. Other seed fibres
are applied in less demanding applications such as stuffing of upholstery. Coir is an exception to
this. Coir is the fibre of the coconut husk, it is a thick and coarse but durable fibre. Applications
are ropes, matting and brushes.

9. With the rise of composite materials there is a renewed interest for natural fibres. Their
moderate mechanical properties restrain the fibres from using them in high-tech applications, but
for many reasons they can compete with glass fibres. Advantages and disadvantages determine
the choice:
Advantages of natural fibres:
 Low specific weight, which results in a higher specific strength and stiffness than glass.
This is a benefit especially in parts designed for bending stiffness.
 It is a renewable resource, the production requires little energy, CO2 is used while oxygen
is given back to the environment.
 Producible with low investment at low cost, which makes the material an interesting
product for low-wage countries.
 Friendly processing, no wear of tooling, no skin irritation
 Thermal recycling is possible, where glass causes problems in combustion furnaces.
 Good thermal and acoustic insulating properties
ADVANTAGES AND DRAWBACKS OF COMPOSITES OVER MONOLITHIC
MATERIALS
Metal-matrix composites are either in use or prototyping for the Space Shuttle,
commercial airliners, electronic substrates, bicycles, automobiles, golf clubs, and a variety of
other applications. While the vast majority are aluminum matrix composites, a growing number
of applications require the matrix properties of superalloys, titanium, copper, magnesium, or
iron.
Like all composites, aluminum-matrix composites are not a single material but a family
of materials whose stiffness, strength, density, and thermal and electrical properties can be
tailored. The matrix alloy, the reinforcement material, the volume and shape of the
reinforcement, the location of the reinforcement, and the fabrication method can all be varied to
achieve required properties. Regardless of the variations, however, aluminum composites offer
the advantage of low cost over most other MMCs. In addition, they offer excellent thermal

10. conductivity, high shear strength, excellent abrasion resistance, high-temperature operation,
nonflammability, minimal attack by fuels and solvents, and the ability to be formed and treated
on conventional equipment.
Aluminum MMCs are produced by casting, powder metallurgy, in situ development of
reinforcements, and foil-and-fiber pressing techniques. Consistently high-quality products are
now available in large quantities, with major producers scaling up production and reducing
prices. They are applied in brake rotors, pistons, and other automotive components, as well as
golf clubs, bicycles, machinery components, electronic substrates, extruded angles and channels,
and a wide variety of other structural and electronic applications.
Super alloy composites reinforced with tungsten alloy fibers are being developed for
components in jet turbine engines that operate temperatures above 1,830 °F.
Graphite/copper composites have tailorable properties, are useful to high temperatures in
air, and provide excellent mechanical characteristics, as well as high electrical and thermal
conductivity. They offer easier processing as compared with titanium, and lower density
compared with steel. Ductile superconductors have been fabricated with a matrix of copper and
superconducting filaments of niobium-titanium. Copper reinforced with tungsten particles or
aluminum oxide particles is used in heat sinks and electronic packaging.
Titanium reinforced with silicon carbide fibers is under development as skin material for
the National Aerospace Plane. Stainless steels, tool steels, and Inconel are among the matrix
materials reinforced with titanium carbide particles and fabricated into draw-rings and other
high-temperature, corrosion-resistant components.
Compared to monolithic metals, MMCs have:
 Higher strength-to-density ratios
 Higher stiffness-to-density ratios
 Better fatigue resistance
 Better elevated temperature properties
o -- Higher strength

11. o -- Lower creep rate
 Lower coefficients of thermal expansion
 Better wear resistance
The advantages of MMCs over polymer matrix composites are:
 Higher temperature capability
 Fire resistance
 Higher transverse stiffness and strength
 No moisture absorption
 Higher electrical and thermal conductivities
 Better radiation resistance
 No outgassing
 Fabricability of whisker and particulate-reinforced MMCs with conventional
metalworking equipment.
Some of the disadvantages of MMCs compared to monolithic metals and polymer matrix
composites are:
 Higher cost of some material systems
 Relatively immature technology
 Complex fabrication methods for fiber-reinforced systems (except for casting)
 Limited service experience
Numerous combinations of matrices and reinforcements have been tried since work on MMC
began in the late 1950s. However, MMC technology is still in the early stages of development,
and other important systems undoubtedly will emerge.
Reinforcements: MMC reinforcements can be divided into five major categories: continuous
fibers, discontinuous fibers, whiskers, particulates, and wires. With the exception of wires, which
are metals, reinforcements generally are ceramics.

12. Key continuous fibers include boron, graphite (carbon), alumina, and silicon carbide.
Boron fibers are made by chemical vapor deposition (CVD) of this material on a tungsten core.
Carbon cores have also been used. These relatively thick monofilaments are available in 4.0, 5.6,
and 8.0-mil diameters. To retard reactions that can take place between boron and metals at high
temperature, fiber coatings of materials such as silicon carbide or boron carbide are sometimes
used.
Silicon carbide monofilaments are also made by a CVD process, using a tungsten or
carbon core. A Japanese multifilament yarn, designated as silicon carbide by its manufacturer, is
also commercially available. This material, however, made by pyrolysis of organometallic
precursor fibers, is far from pure silicon carbide and its properties differ significantly from those
of monofilament silicon carbide.
Continuous alumina fibers are available from several suppliers. Chemical compositions
and properties of the various fibers are significantly different. Graphite fibers are made from two
precursor materials, polyacrilonitrile (PAN) and petroleum pitch. Efforts to make graphite fibers
from coal-based pitch are under way. Graphite fibers with a wide range of strengths and moduli
are available.
The leading discontinuous fiber reinforcements at this time are alumina and alumina-
silica. Both originally were developed as insulating materials. The major whisker material is
silicon carbide. The leading U.S. commercial product is made by pyrolysis of rice hulls. Silicon
carbide and boron carbide, the key particulate reinforcements, are obtained from the commercial
abrasives industry. Silicon carbide particulates are also produced as a by-product of the process
used to make whiskers of this material.
A number of metal wires including tungsten, beryllium, titanium, and molybdenum have
been used to reinforce metal matrices. Currently, the most important wire reinforcements are
tungsten wire in superalloys and superconducting materials incorporating niobium-titanium and
niobium-tin in a copper matrix. The reinforcements cited above are the most important at this
time. Many others have been tried over the last few decades, and still others undoubtedly will be
developed in the future.

13. Matrix materials and key composites: Numerous metals have been used as matrices. The most
important have been aluminum, titanium, magnesium, and copper alloys and superalloys.
MECHANICAL PROPERTIES AND APPLICATIONS OF COMPOSITES
Composites are one of the most widely used materials because of their adaptability to
different situations and the relative ease of combination with other materials to serve specific
purposes and exhibit desirable properties. In surface transportation, reinforced plastics are the
kind of composites used because of their huge size. They provide ample scope and receptiveness
to design changes, materials and processes. The strength-weight ratiois higher than other
materials. Their stiffness and cost effectiveness offered, apart from easy availability of raw
materials, makethem the obvious choice for applications insurface transportation. In heavy
transport vehicles, the composites are used in processing of component parts with cost-
effectiveness. Good
Reproductivity and resilience handling by semi-skilled workers are the basic
requirements of a good composite material. While the costs of achieving advanced composites
may not justify the savings obtained interms of weight vis-a-vis vehicle production, carbon fibers
reinforced epoxies have been used in racing cars and recently for the safety of cars. Polyester
resin with suitable fillers and reinforcements were the first applications of composites in road
transportation. The choice was dictated by properties like low cost, ease in designing and
production of functional parts etc. Using a variety of reinforcements, polyester has continued to
be used in improving the system and other applications. Most of the thermoplastics are combined
with reinforcing fibers in various proportions. Several methods are used to produce vehicle parts
from thermo plastics.
Selection of the material is made from the final nature of the component, the volume
required, apart from cost-effectiveness and mechanical strength. Components that need
conventional paint finishing are generally made with thermosetting resins, while thermoplastics
are used to build parts that are moulded and can be pigmented. Press moulded reinforced
polyester possess the capability to produce large parts in considerable volume with cost-
effectiveness. In manufacturing of automobile parts, glass and sisal fibers usually find the
maximum use. Sisal costs very less and this alone has prompted extensive research to come up

14. with applications in which sisal is the dominant reinforcing material infilled polyester resin, in
parts where specific mechanical properties are required and appearance is not very important.
Heater housings, which find uses for sisal, are produced by compression moulding. Since a
variety of glass fibers are available, it is used as reinforcement for a large range of parts of
different types. Rovings, non-woven matsare the commonly used low cost versions. Woven cloth
is applied in special cases, where particular properties are required as cloth is not known to be
amenable to large quantity production methods. Since the automobile industry is replete with
models, options and changes in trends, the material selection and combinations offered by the
materials is also wide-ranging. Along with a measure of conservation, the choice is alsodictated
by the demands of the competitive market for new and alternate materials. A reinforced-plastic
composite is likely to costmore than sheet steel, when considered on the basis of cost and
performance. In such a case, other qualities must necessarily justify the high expenditure.
Mechanical properties of the parts, which affect the thickness and weight, must offer enough
savings to render them more effective than steel. It however shows a higher machining waste
than reinforced plastics. The fabrication costs of reinforced plastics is controlled by the devices
and tooling used for producing them. In turn, it is dependent on the basis of the quantity of
components needed. Some complicated parts of light commercial vehicles, which need casting,
may be compression moulded from composites of the sheet or bulk variety. State-of-art
technologies of moulding, tooling and fabricating have thrown open possibilities of increased
manufacturing of vehicles that use reinforced polyesters. Materials used in automotive body
parts show high tensile strength and flexural moduli. The material is not ductile and hence will
not yield and the failure is accounted only in terms of fracture. These properties and thickness,
determine the maximum bending moment which is several times higher than the pointof fracture
for steel sheets. Reinforced plastics can be given the metal finish, although the cost of achieving
this continues to be prohibitive. They are restricted in their use in car components. While the
defects in painted sheet metal parts are easily overlooked, the fiber pattern texture is
obvious,though the surface-roughness measurements report that it is smoother. In commercial
vehicles, appearance is also important as is the functional aspect. Since a commercial vehicle is
more a capital investment, it is the returns from such investment that are considered. The rate of
return depends on initial cost, durability and maintenance costs. Reinforced plastic is a boon in
the sense that it uses shorter lead times and tooling cost is considerably cheaper. Commitments to

15. launch a new model are kept easily, since the time between production and introduction can be
co-ordinate perfectly. Studies have shown that composite panels may be used as the complete
outer skin of the body to give a unique look. Sheet moulding compounds of resins are most
suited for this purpose. Inner and outer reinforcing is done by panel assembled by adhesive
bonding and riveting.
CHARACTERISTICS OF FIBER
Composites have high stiffness, strength, and toughness, often comparable with structural
metal alloys. Further, they usually provide these properties at substantially less weight than
metals: their “specific” strength and modulus per unit weight is near five times that of steel or
aluminum. This means the overall structure may be lighter, and in weight-critical devices such as
airplanes or spacecraft this weight savings might be a compelling advantage.
• Composites can be made anisotropic, i.e. have different properties in different
directions, and this can be used to design a more efficient structure. In many structures the
stresses are also different in different directions; for instance in closed-end pressure vessels –
such as a rocket motor case – the circumferential stresses are twice the axial stresses. Using
composites,such a vessel can be made twice as strong in the circumferential direction as in the
axial.
•Many structures experience fatigueloading, in which the internal stresses vary with time.
Axles on rolling stock are examples; here the stresses vary sinusoidally from tension to
compression as the axle turns. These fatigue stresses can eventually lead to failure, even when
the maximum stress is much less than the failure strength of the material as measured in a static
tension test. Composites of then have excellent fatigue resistance in comparison with metal
alloys, and often show evidence of accumulating fatigue damage, so that the damage can be
detected and the part replaced before a catastrophic failure occurs.
•Materials can exhibit damping, in which a certain fraction of the mechanical strain
energy deposited in the material by a loading cycle is dissipated as heat. This can be
advantageous, for instance in controlling mechanically-induced vibrations. Composites generally
offer relatively high levels of damping, and furthermore the damping can often be tailored to
desired levels by suitable formulation and processing.

16. • Composites can be excellent in applications involving sliding friction, with tribological
(“wear”) properties approaching those of lubricated steel.
• Composites do not rust as do many ferrous alloys, and resistance to this common form
of environmental degradation may offer better life-cycle cost even if the original
structure is initially more costly.
• Many structural parts are assembled from a number of subassemblies, and the
assembly process adds cost and complexity to the design. Composites offer a lot of flexibility in
processing and property control,and this often leads to possibilities for part reduction and simpler
manufacture.
FIBER-REINFORCED COMPOSITE
A fiber-reinforced composite (FRC) is a composite building material that consists of three
components: (i) the fibers as the discontinuous or dispersed phase, (ii) the matrix as the
continuous phase, and (iii) the fine interphase region, also known as the interface.[1][2]
This is a
type of advanced composite group, which makes use of rice husk, rice hull, and plastic as
ingredients. This technology involves a method of refining, blending, and compounding natural
fibers from cellulosic waste streams to form a high-strength fiber composite material in a
polymer matrix. The designated waste or base raw materials used in this instance are those of
waste thermoplastics and various categories of cellulosic waste including rice husk and saw dust.
FRC is high-performance fiber composite achieved and made possible by cross-linking cellulosic
fiber molecules with resins in the FRC material matrix through a proprietary molecular re-
engineering process, yielding a product of exceptional structural properties.
Through this feat of molecular re-engineering selected physical and structural properties of wood
are successfully cloned and vested in the FRC product, in addition to other critical attributes to
yield performance properties superior to contemporary wood.
This material, unlike other composites, can be recycled up to 20 times, allowing scrap FRC to be
reused again and again.

17. The failure mechanisms in FRC materials include delamination, intralaminar matrix cracking,
longitudinal matrix splitting, fiber/matrix debonding, fiber pull-out, and fiber fracture.

18. UNIT II
MANUFACTURING OF COMPOSITES
HAND LAY-UP TECHNIQUE
Hand lay-up technique is the simplest method of composite processing. The
infrastructural requirement for this method is also minimal. The processing steps are quite
simple. First of all, a release gel is sprayed on the mold surface to avoid the sticking of polymer
to the surface. Thin plastic sheets are used at the top and bottom of the mold plate to get good
surface finish of the product. Reinforcement in the form of woven mats or chopped strand mats
are cut as per the mold size and placed at the surface of mold after perspex sheet. Then
thermosetting polymer in liquid form is mixed thoroughly in suitable proportion with a
prescribed hardner (curing agent) and poured onto the surface of mat already placed in the mold.
The polymer is uniformly spread with the help of brush. Second layer of mat is then placed on
the polymer surface and a roller is moved with a mild pressure on the mat-polymer layer to
remove any air trapped as well as the excess polymer present. The process is repeated for each
layer of polymer and mat, till the required layers are stacked. After placing the plastic sheet,
release gel is sprayed on the inner surface of the top mold plate which is then kept on the stacked
layers and the pressure is applied. After curing either at room temperature or at some specific
temperature, mold is opened and the developed composite part is taken out and further
processed. The schematic of hand lay-up is shown in figure 1. The time of curing depends on
type of polymer used for composite processing. For example, for epoxy based system, normal
curing time at room temperatur is 24-48 hours. This method is mainly suitable for thermosetting
polymer based composites. Capital and infrastructural reuirement is less as compared to other
methods. Production rate is less and high volume fraction of reinforcement is difficult to achieve
in the processed composites. Hand lay-up method finds application in many areas like aircraft
components, automotive parts, boat hulls, diase board, deck etc.

19. SPRAY LAY-UP
The spray lay-up technique can be said to be an extension of the hand lay-up method. In
this technique, a spray gun is used to spray pressurized resin and reinforcement which is in the
form of chopped fibers. Generally, glass roving is used as a reinforcement which passes through
spray gun where it is chopped with a chopper gun. Matrix material and reinforcement may be
sprayed simultaneously or separately one after one. Spray release gel is applied on to the mold
surface to facilitate the easy removal of component from the mold. A roller is rolled over the
sprayed material to remove air trapped into the lay-ups. After spraying fiber and resin to required
thickness, curing of the product is done either at room temperature or at elevated temperature.
After curing, mold is opened and the developed composite part is taken out and further processed
further. The time ofcuring depends on type of polymer used for composite processing. The
schematic of the spray lay-up process is shown in figure. Spray lay-up method is used for lower
load carrying parts like small boats, bath tubs, fairing of trucks etc. This method provides high
volume fraction of reinforcement in composites and virtually, there is no part size limitation in
this technique. Generally, the materials used to develop composites through spray lay-up method
are given in table.

20. FILAMENT WINDING
Filament winding is a fabrication technique mainly used for manufacturing open
(cylinders) or closed end structures (pressure vessels or tanks). The process involves winding
filaments under tension over a rotating mandrel. The mandrel rotates around the spindle (Axis 1
or X: Spindle) while a delivery eye on a carriage (Axis 2 or Y: Horizontal) traverses horizontally
in line with the axis of the rotating mandrel, laying down fibers in the desired pattern or angle.
The most common filaments are glass or carbon and are impregnated in a bath with resin as they
are wound onto the mandrel. Once the mandrel is completely covered to the desired thickness,
the resin is cured. Depending on the resin system and its cure characteristics, often the rotating
mandrel is placed in an oven or placed under radiant heaters until the part is cured. Once the
resin has cured, the mandrel is removed or extracted, leaving the hollow final product. For some
products such as gas bottles the 'mandrel' is a permanent part of the finished product forming a
liner to prevent gas leakage or as a barrier to protect the composite from the fluid to be stored.
Filament winding is well suited to automation, and there are many applications, such as
pipe and small pressure vessel that are wound and cured without any human intervention. The
controlled variables for winding are fiber type, resin content, wind angle, tow or bandwidth and
thickness of the fiber bundle. The angle at which the fiber has an effect on the properties of the

21. final product. A high angle "hoop" will provide circumferential strength, while lower angle
patterns (polar or helical) will provide greater longitudinal / axial tensile strength.
Products currently being produced using this technique range from pipes, golf clubs,
Reverse Osmosis Membrane Housings, oars, bicycle forks, bicycle rims, power and transmission
poles, pressure vessels to missile casings, aircraft fuselages and lamp posts and yacht masts.
PULTRUSION
Pultrusion is a continuous process for manufacture of composite materials with constant
cross-section. The term is a portmanteau word, combining "pull" and "extrusion". As opposed to
extrusion, which pushes the material, pultrusion works by pulling the material.

22. 1 - Continuous roll of reinforced fibers/woven fiber mat
2 - Tension roller
3 - Resin Impregnator
4 - Resin soaked fiber
5 - Die and heat source
6 - Pull mechanism
7 - Finished hardened fiber reinforced polymer
RESIN TRANSFER PROCESS
RTM is a vacuum-assisted, resin transfer process with a flexible solid counter tool for the
B-side surface compression. This process yields increased laminate compression, a high glass-to-
resin ratio, and outstanding strength-to-weight characteristics. RTM parts have two finished
surfaces.
Reinforcement mat or woven roving is placed in the mold, which is then closed and
clamped. Catalyzed, low-viscosity resin is pumped in under pressure, displacing the air and
venting it at the edges, until the mold is filled. Molds for this low-pressure system are usually
made from composite or nickel shell-faced composite construction.
Suitable for medium volume production of larger components, resin transfer molding is
usually considered an intermediate process between the relatively slow spray-up with lower
tooling costs and the faster compression molding methods with higher tooling costs.
 Recommended for products with high strength-to-weight requirements
 Best suited for mid-volume production rates, in the range of 200 to 10,000 parts per year*
 Gel coats may be used to provide a high-quality, durable finish
 Tooling can be made from many different materials - polyester, nickel shell, aluminum or
even mild steel. The volume and life of program and tooling budget will help determine
what is best

23. * Volume recommendations are averages and provided only as a general guideline. Actual
volume efficiencies are a more complex matter requiring detailed statistics about the part to be
manufactured.
VACUUM BAG MOLDING
Vacuum bag molding, a refinement of hand lay-up, uses a vacuum to eliminate entrapped air and
excess resin. After the lay-up is fabricated on either a male or female mold from precut plies of
glass mat or fabric and resin, a nonadhering film of polyvinyl alcohol or nylon is placed over the
lay-up and sealed at the mold flange. A vacuum is drawn on the bag formed by the film while the
composite is cured at room or elevated temperatures. Compared to hand lay-up, the vacuum
method provides higher reinforcement concentrations, better adhesion between layers, and more
control over resin/glass ratios. Advanced composite parts utilize this method with
preimpregnated fabrics rather than wet lay-up materials and require oven or autoclave cures.

24. INJECTION MOULDING
Injection moulding (injection molding in the USA) is a manufacturing process for
producing parts by injecting material into a mould. Injection moulding can be performed with a
host of materials, including metals, (for which the process is called diecasting), glasses,
elastomers, confections, and most commonly thermoplastic and thermosetting polymers.
Material for the part is fed into a heated barrel, mixed, and forced into a mould cavity, where it
cools and hardens to the configuration of the cavity.[1]:240
After a product is designed, usually by
an industrial designer or an engineer, moulds are made by a mouldmaker (or toolmaker) from
metal, usually either steel or aluminum, and precision-machined to form the features of the
desired part. Injection moulding is widely used for manufacturing a variety of parts, from the
smallest components to entire body panels of cars. Advances in 3D printing technology, using
photopolymers which do not melt during the injection moulding of some lower temperature
thermoplastics, can be used for some simple injection moulds.
Parts to be injection moulded must be very carefully designed to facilitate the moulding process;
the material used for the part, the desired shape and features of the part, the material of the
mould, and the properties of the moulding machine must all be taken into account. The
versatility of injection moulding is facilitated by this breadth of design considerations and
possibilities.

25. HOT PRESSING
Hot pressing is a high-pressure, low-strain-rate powder metallurgy process for forming of a
powder or powder compact at a temperature high enough to induce sintering and creep
processes. This is achieved by the simultaneous application of heat and pressure.
Hot pressing is mainly used to fabricate hard and brittle materials. One large use is in the
consolidation of diamond-metal composite cutting tools and technical ceramics. The
densification works through particle rearrangement and plastic flow at the particle contacts. The
loose powder or the pre-compacted part is in most of the cases filled to a graphite mould that
allows induction or resistance heating up to temperatures of typically 2,400 °C (4,350 °F).
Pressures of up to 50 MPa (7,300 psi) can be applied.other great use is in the pressing of
different types of polymers.

26. REACTION BONDING PROCESS
Reactive bonding describes a wafer bonding procedure using highly reactive nanoscale
multilayer systems as an intermediate layer between the bonding substrates. The multilayer
system consists of two alternating different thin metallic films. The self-propagating exothermic
reaction within the multilayer system contributes the local heat to bond the solder films. Based
on the limited temperature the substrate material is exposed, temperature-sensitive components
and materials with different CTEs, i.e. metals, polymers and ceramics, can be used without
thermal damage.

27. UNIT III
INTRODUCTION, LAMINA CONSTITUTIVE EQUATIONS
Lamina Constitutive Equations: Lamina Assumptions
An approximate elasticity theory solution is given for the stress-strain relations
of a cracked composite lamina. These relations are written in the familiar form of two-
dimensional compliances appropriate for use with laminated plate theory, and include the effects
of non-mechanical strains. It is shown explicitly that the cracked lamina com pliances depend
upon the overall laminate construction in which the lamina is contained.
Macroscopic Viewpoint. Generalized Hooke’s Law
Macroscopic Viewpoint.
The macroscopic scale is the length scale on which objects or phenomena are large
enough to be visible practically with the naked eye, without magnifying devices.
When applied to physical phenomena and bodies, the macroscopic scale describes things
as a person can directly perceive them, without the aid of magnifying devices. This is in contrast
to observations (microscopy) or theories (microphysics, statistical physics) of objects of
geometric lengths smaller than perhaps some hundreds of micrometers.
A macroscopic view of a ball is just that: a ball. A microscopic view could reveal a thick
round skin seemingly composed entirely of puckered cracks and fissures (as viewed through a
microscope) or, further down in scale, a collection of molecules in a roughly spherical shape.
Classical mechanics may describe the interactions of the above-mentioned ball. It can be
considered a mainly macroscopic theory. On the much smaller scale of atoms and molecules,
classical mechanics may not apply, and the interactions of particles is then described by quantum
mechanics. As another example, near the absolute minimum of temperature, the Bose–Einstein
condensate exhibits elementary quantum effects on macroscopic scale.

28. The term "megascopic" is a synonym. No word exists that specifically refers to features
commonly portrayed at reduced scales for better understanding, such as geographic areas or
astronomical objects. "Macroscopic" may also refer to a "larger view", namely a view available
only from a large perspective. A macroscopic position could be considered the "big picture".
Generalized Hooke’s Law

29. REDUCTION TO HOMOGENEOUS ORTHOTROPIC LAMINA
Some natural parabolic deformations of convex curves in the plane are those in which
each point moves in a direction normal to the curve with speed equal to a power of the curvature:
That is, given a convex curve which is the image of an embedding x0 : S1 ! R2, the deformation
is obtained by solving the equation (1.1) @x @t = �1___n with _ 6= 0, and initial condition
x(p; 0) = x0(p). This produces a family of curves t = x(S1; t). Here _ is the curvature, and n is the
outward-pointing unit normal vector. These equations are particularly natural in that they are
isotropic (equivariant under rotations in the plane) and homogeneous (equivariant under dilation
of space, if time is also scaled accordingly).The main aim of this paper is to provide a complete
description of the behavior of embedded convex curves moving by equations. In certain cases
this description has already been provided: If _ = 1 then Equation is the curve-shortening ow, for
which the following holds:
Theorem 1.1. Let _ = 1 and let 0 be a smooth convex embedded closed curve given by an
embedding x0 : S1 ! R2. Then there exists a unique solution x : S1 _ [0; T )! R2 of the curve-
shortening ow (1.1) with initial data x0, and t = x(S1; t) converges to a point p 2 R2 as t ! T . The
rescaled curves (t �p)= p 2(T �t) converge to the unit circle about the origin as t ! T .This
result was _rst proved by Gage and Hamilton ([11], [12], [15]). The assumption of smooth initial
data can be relaxed to allow any curve 0 which is the boundary of a bounded open convex
region, in which case the curves t approach 0 in Hausdor_ distance as t ! 0 [2, Theorem II2.8].
Furthermore, Grayson [14] proved that the assumption of convexity of the initial curve can be
removed, and the result holds for arbitrary smooth embedded initial curves. More recent proofs
ofGrayson's theorem have been given by Hamilton [16] and by Huisken [17]. Similar results for
anisotropic analogues of this ow appear in Oaks [18] and Chou and Zhu[10]. Another case which
is well understood is that with _ = 1=3. In this case the results reect a surprising a invariance
property of the equation:
Theorem 1.2. Let _ = 13. If 0 = x0(S1) is a smooth convex closed curve given by an embedding
x0 : S1 ! R2, then there exists a unique solution x : S1_[0; T ) ! R2 of (1.1) with initial data x0,
and t = x(S1; t) converges to a point p 2 R2 as t ! Twhile (t �p)=(4(T �t)=3)3=4 converges to
an ellipse of enclosed area _ centred at the origin. The regularity assumptions on the initial curve
can be relaxed to allow boundaries of open bounded convex regions. This result was _rst proved
in [19] and [2] (see also [5, x9]). Results for non-convex curves appear in [7]. If _ > 1, then the

30. results are similar to those in Theorem 1.1, except for somedi_erences in the regularity of
solutions
Theorem 1.3. Let _ > 1 and let 0 be the boundary of an open bounded convex set in R2. Then
there exists a solution x : S1 _ [0; T )! R2 of Equation (1.1) with x(S1; t) converging to 0 in
Hausdor_ distance as t ! 0. This solution is unique up to time-independent reparametrisation,
C2+1=(_�1) for positive times, and C1 for times close to T . The curves t = x(S1; t) converge to
a point p 2 R2 as t ! T while (t�p)=((1+_)(T �t))1=(1+_) converges smoothly to the unit circle
about the origin. If 0 is smooth and strictly convex, then the solution is smooth and strictly
convex for all t.
ORTHOTROPIC STIFFNESS MATRIX (QIJ)
Consider the stress strain curve _ = f(_) of a linear elastic material subjected to uni-axial
stress loading conditions.
This further reduces the number of material constants to 21. The most general anisotropic
linear elastic material therefore has 21 material constants. We can write the stress-strain relations
for a linear elastic material exploiting these symmetries
Anisotropy refers to the directional dependence of material properties (mechanical or
otherwise). It plays an important role in Aerospace Materials due to the wide use of engineered
composites.
The different types of material anisotropy are determined by the existence of symmetries
in the internal structure of the material. The more the internal symmetries, the simpler the
structure of the sti_ness tensor. Each type of symmetry results in the invariance of the stiffness
tensor to a specifc symmetry transformations
Transversely isotropic
The physical properties are symmetric about an axis that is normal to a plane of isotropy
(xy-plane in the _gure). Three mutually orthogonal planes of reection symmetry and axial
symmetry with respect to z-axis.
Cubic
Three mutually orthogonal planes of reection symmetry plus 90_ rotation symmetry with
respect to those planes. a = b = c; a= b= c = 90 Number of independent coe_cients: 3 Symmetry
transformations: reections and 90_ rotations about all three orthogonal planes

31. Independent coe_cients for linear elastic isotropic materials.
For a linearly elastic, homogeneous, isotropic material, the constitutive laws involve three
parameters: Young's modulus, E, Poisson's ratio, and the shear modulus, G.
1. Write and explain the relation between stress and strain for this kind of material.
2. What is the physical meaning of the coe_cients E, _ and G.
3. Are these three coe_cients independent of each other? If not, derive the expressions that relate
them. Indicate also the relationship with the Lame's constants.
4. Explain why the Poisson's ratio is constrained to the range _ 2 (1; 1=2). Hint: use the concept
of bulk modulus. Solution: In a homogeneous material the properties are the same at each point.
Isotropic means that the physical properties are identical in all directions. Linear elastic makes
reference to the relationship between strain and stress
DEFINITION OF STRESS AND MOMENT RESULTANTS
Normal stress is defined as the force per unit area acting perpendicular to the surface of
the area. The corresponding strain is defined as the elongation (or stretch) per unit length of
material in the direction of the applied force. For isotropic materials, the relationship between
slress and ser~ne! is independent of the direction of force, thus only one elastic constant
(Young's modulus) is required to describe the stress-strain relationship for a uniaxially applied
force. For a nonisotrspic material, at least two elastic constants are needed to describe the stress-
strain behavior of the material.
The previous section dealt with an extremely simple type of stress state, uniaxial. In
general, plates will experience stresses in more than one direction within the plane. This is
referred to as plane s&ess. In addition, Poisson's ratio now becomes important. Poisson's ratio is
the ratio of the strain perpendicular to a given loading direction.

32. MECHANICS OF LAMINATED COMPOSITES
Assumptions
The following assumptions are made for the remainder of this paper:
(1) The laminate thickness is very small compared to its other dimensions.
(2) The lamina (layers) of the laminate are perfectly bonded.
(3) Lines perpendicular to the surface of the laminate remain straight and
perpendicular to the surface after deformation.
(4) The laminae and laminate are linear elastic.
(5) The through-the-thickness stresses and strains are negligible. These assumptions
are good ones as long as the laminate is not damaged anid undergoes small deflections.
The directions for all of the stress and moment resultants are shown in figure 8 for clarity.
The double-headed arrow indicates torque in a direction determined by the right-hand-rule (i.e.,
point the thumb of your right hand in the direction of the double-headed arrows and the direction
of rotation of the torque is in the direction that your four fingers are pointing). Note that Mx and
My will cause the plate to bend and Mxy will cause the plate to twist.
For symmetric laminates (laminates that are configured such that the geometric midplme is a
mirror image of the ply configurations above and below the midplane), the geometric midplane
is also the neutral plane of the plate, and the [B] matrix will have all elements equal to zero (as
will be shown later). However, if the laminate is unsymmetric, i.e., if the plies near the bottom of
the plate are much stiffer in the x-direction, then the geometric midplane will not be the neutral
plane of the plate; and the neutral plane will be closer to the bottom of the plate for x-direction
beading in figure. This is accounted for in the constitutive equations, since the [B] matrix will
have some nonzero elements (as will be shown later), implying that a bending strain (plate
curvature) will cause a midplane strain as depicted in figure 10. Likewise, a midplane strain will

33. cause a bending moment. A method to find the neutral axis of the plate will be discussed in a
later section about stresses within the plies of a laminate.
STRAIN DISPLACEMENT RELATIONS.
The strain was introduced in Book I: §4. The concepts examined there are now extended
to the case of strains which vary continuously throughout a material. Consider a line element of
length xemanating from position ),(yxand lying in the x- direction, denoted by AB. After
deformation the line element occupies BA, having undergone a translation, extension and
rotation.
The particle that was originally at xhas undergone a displacement ),(yxux and the other
end of the line element has undergone a displacement ),(yxxux. By the definition of (small)
normal strain,
This partial derivative is a displacement gradient, a measure of how rapid the
displacement changes through the material, and is the strain at),(yx. Physically, it represents
the(approximate) unit change in length of a line element
The strains give information about the deformation of material particles but, since they do
not encompass translations and rotations, they do not give information about the precise location
in space of particles. To determine this, one must specify three displacement components (in
two-dimensional problems). Mathematically, this is equivalent to saying that one cannot
uniquely determine the displacements from the strain-displacement relations.
BASIC ASSUMPTIONS OF LAMINATED ANISOTROPIC PLATES
Using the basic assumptions of thin-plate theory, including nonlinear terms in
the von Karman sense, the governing equations of a laminated anisotropic plate are formulated.
In particular, the type of plate under discussion consists of n layers of orthotropic sheets bonded
together. Each layer has arbitrary thickness, elastic properties, and orientation of orthotropic axes
with respect to the plate axes. The governing equations are obtained by integrating the equations
of nonlinear elasticity. Inertia terms and thermal stresses are included. Closed-form solutions to
the linearized equations are obtained for bending, flexural vibration, and buckling of special, but

34. important, classes of laminates for which coupling between bending and stretching is
unavoidable.
LAMINATE CONSTITUTIVE EQUATIONS
INTRODUCTION
• Equations of Motion
• Symmetric of Stresses
• Tensorial and Engineering Strains
• Symmetry of Constitutive Equations
THREE-DIMENSIONAL CONSTITUTIVEEQUATIONS
• General Anisotropic Materials
• Orthotropic Materials
• Transversely IsotropicMaterials
• Isotropic Materials
RELATION BETWEEN MATHEMATICAL & ENGINEERING
CONSTANTS
• Isotropic Materials
• Orthotropic Materials
CONSTITUTIVE EQUATIONS FOR AN ORTHOTROPICLAMINA
• Plane Strain Condition
• Plane Stress Condition
CONSTITUTIVE EQUATIONS FOR AN ARBITRARILY ORIENTED
LAMINA
• CoordinateTransformation
• Stress Transformation

35. • Strain Transformation
• Stiffness and Compliance Matrix Transformation
ENGINEERING CONSTANTS OF ALAMINATE
• Lamina
• Laminate
Restrictions on Elastic Constants of Orthotropic Materials
From Energy Principles, Lempriere showed that the Strain Energy is Positive if the
Stiffness and Compliance Matrices are Positive Definite.Mathematical Argument (a) If only one
stress is applied at a time, then the work done is positive if and only when the corresponding
direct strain is positive. That is when Sii > 0 Therefore: E1, E2 , E3, G12 , G23, and G13 > 0
All organic composites absorbs moisture. The absorption depends on the relative
humidity to which it is exposed and its moisture content. For a given RH, temperature, and
atmospheric pressure composite will have a saturation value. This is moisture content that the
material will reach, if it is exposed for a very long time. This is a fixed value for a material. The
moisture content is expressed as percent change in weight of the material. Like thermal
expansion, increase in moisture would also expands the material.
The orthotropic materials have two coefficients of moisture expansion, one along the
fiber and the other across the fiber.
COUPLING INTERACTIONS, BALANCED LAMINATES
A ceramic is an inorganic, nonmetallic solid material comprising metal, nonmetal or
metalloid atoms primarily held in ionic and covalent bonds. The crystallinity of ceramic
materials ranges from highly oriented to semi-crystalline, and often completely amorphous (e.g.,
glasses). Varying crystallinity and electron consumption in the ionic and covalent bonds cause
most ceramic materials to be good thermal and electrical insulators and extensively researched in
ceramic engineering. Nevertheless, with such a large range of possible options for the

36. composition/structure of a ceramic (e.g. nearly all of the elements, nearly all types of bonding,
and all levels of crystallinity), the breadth of the subject is vast, and identifiable attributes (e.g.
hardness, toughness, electrical conductivity, etc.) are hard to specify for the group as a whole.
However, generalities such as high melting temperature, high hardness, poor conductivity, high
moduli of elasticity, chemical resistance and low ductility are the norm,[1]
with known exceptions
to each of these rules (e.g. piezoelectric ceramics, glass transition temperature, superconductive
ceramics, etc.). Many composites, such as fiberglass and carbon fiber, while containing ceramic
materials, are not considered to be part of the ceramic family.
In behavioral psychology, reinforcement is a consequence that will strengthen an
organism's future behavior whenever that behavior is preceded by a specific antecedent stimulus.
This strengthening effect may be measured as a higher frequency of behavior (e.g., pulling a
lever more frequently), longer duration (e.g., pulling a lever for longer periods of time), greater
magnitude (e.g., pulling a lever with greater force), or shorter latency (e.g., pulling a lever more
quickly following the antecedent stimulus). Although in many cases a reinforcing stimulus is a
rewarding stimulus which is "valued" or "liked" by the individual (e.g., money received from a
slot machine, the taste of the treat, the euphoria produced by an addictive drug), this is not a
requirement. Indeed, reinforcement does not even require an individual to consciously perceive
an effect elicited by the stimulus.[1]
Furthermore, stimuli that are "rewarding" or "liked" are not
always reinforcing: if an individual eats at a fast food restaurant (response) and likes the taste of
the food (stimulus), but believes it is bad for their health, they may not eat it again and thus it
was not reinforcing in that condition. Thus, reinforcement occurs only if there is an observable
strengthening in behavior.
A particle is a minute fragment or quantity of matter. In the physical sciences, the word
is used to describe a small localized object to which can be ascribed several physical or chemical
properties such as volume or mass; subatomic particles such as protons or neutrons; and other
elementary particles. The word is rather general in meaning, and is refined as needed by various
scientific fields. Something that is composed of particles may be referred to as being particulate.
However, the term particulate is most frequently used to refer to pollutants in the Earth's
atmosphere, which are a suspension of unconnected particles, rather than a connected particle
aggregation.

37. SYMMETRIC LAMINATES, ANGLE PLY LAMINATES
Metal-matrix composites are either in use or prototyping for the Space Shuttle,
commercial airliners, electronic substrates, bicycles, automobiles, golf clubs, and a variety of
other applications. While the vast majority are aluminum matrix composites, a growing number
of applications require the matrix properties of superalloys, titanium, copper, magnesium, or
iron.
Like all composites, aluminum-matrix composites are not a single material but a family
of materials whose stiffness, strength, density, and thermal and electrical properties can be
tailored. The matrix alloy, the reinforcement material, the volume and shape of the
reinforcement, the location of the reinforcement, and the fabrication method can all be varied to
achieve required properties. Regardless of the variations, however, aluminum composites offer
the advantage of low cost over most other MMCs. In addition, they offer excellent thermal
conductivity, high shear strength, excellent abrasion resistance, high-temperature operation,
nonflammability, minimal attack by fuels and solvents, and the ability to be formed and treated
on conventional equipment.
Aluminum MMCs are produced by casting, powder metallurgy, in situ development of
reinforcements, and foil-and-fiber pressing techniques. Consistently high-quality products are
now available in large quantities, with major producers scaling up production and reducing
prices. They are applied in brake rotors, pistons, and other automotive components, as well as
golf clubs, bicycles, machinery components, electronic substrates, extruded angles and channels,
and a wide variety of other structural and electronic applications.
Superalloy composites reinforced with tungsten alloy fibers are being developed for
components in jet turbine engines that operate temperatures above 1,830 °F.
Graphite/copper composites have tailorable properties, are useful to high temperatures in
air, and provide excellent mechanical characteristics, as well as high electrical and thermal
conductivity. They offer easier processing as compared with titanium, and lower density
compared with steel. Ductile superconductors have been fabricated with a matrix of copper and

38. superconducting filaments of niobium-titanium. Copper reinforced with tungsten particles or
aluminum oxide particles is used in heat sinks and electronic packaging.
Titanium reinforced with silicon carbide fibers is under development as skin material for the
National Aerospace Plane. Stainless steels, tool steels, and Inconel are among the matrix
materials reinforced with titanium carbide particles and fabricated into draw-rings and other
high-temperature, corrosion-resistant components.
Compared to monolithic metals, MMCs have:
 Higher strength-to-density ratios
 Higher stiffness-to-density ratios
 Better fatigue resistance
 Better elevated temperature properties
o -- Higher strength
o -- Lower creep rate
 Lower coefficients of thermal expansion
 Better wear resistance
The advantages of MMCs over polymer matrix composites are:
 Higher temperature capability
 Fire resistance
 Higher transverse stiffness and strength
 No moisture absorption
 Higher electrical and thermal conductivities
 Better radiation resistance
 No outgassing
 Fabricability of whisker and particulate-reinforced MMCs with conventional
metalworking equipment.
Some of the disadvantages of MMCs compared to monolithic metals and polymer matrix
composites are:

39.  Higher cost of some material systems
 Relatively immature technology
 Complex fabrication methods for fiber-reinforced systems (except for casting)
 Limited service experience
Numerous combinations of matrices and reinforcements have been tried since work on MMC
began in the late 1950s. However, MMC technology is still in the early stages of development,
and other important systems undoubtedly will emerge.
MMC reinforcements can be divided into five major categories: continuous fibers,
discontinuous fibers, whiskers, particulates, and wires. With the exception of wires, which are
metals, reinforcements generally are ceramics.
Key continuous fibers include boron, graphite (carbon), alumina, and silicon carbide. Boron
fibers are made by chemical vapor deposition (CVD) of this material on a tungsten core. Carbon
cores have also been used. These relatively thick monofilaments are available in 4.0, 5.6, and
8.0-mil diameters. To retard reactions that can take place between boron and metals at high
temperature, fiber coatings of materials such as silicon carbide or boron carbide are sometimes
used.
Silicon carbide monofilaments are also made by a CVD process, using a tungsten or carbon core.
A Japanese multifilament yarn, designated as silicon carbide by its manufacturer, is also
commercially available. This material, however, made by pyrolysis of organometallic precursor
fibers, is far from pure silicon carbide and its properties differ significantly from those of
monofilament silicon carbide.
Continuous alumina fibers are available from several suppliers. Chemical compositions
and properties of the various fibers are significantly different. Graphite fibers are made from two
precursor materials, polyacrilonitrile (PAN) and petroleum pitch. Efforts to make graphite fibers
from coal-based pitch are under way. Graphite fibers with a wide range of strengths and moduli
are available.

40. The leading discontinuous fiber reinforcements at this time are alumina and alumina-
silica. Both originally were developed as insulating materials. The major whisker material is
silicon carbide. The leading U.S. commercial product is made by pyrolysis of rice hulls. Silicon
carbide and boron carbide, the key particulate reinforcements, are obtained from the commercial
abrasives industry. Silicon carbide particulates are also produced as a by-product of the process
used to make whiskers of this material.
CROSS PLY LAMINATES
Composites are one of the most widely used materials because of their adaptability to
different situations and the relative ease of combination with other materials to serve specific
purposes and exhibit desirable properties. In surface transportation, reinforced plastics are the
kind of composites used because of their huge size. They provide ample scope and receptiveness
to design changes, materials and processes. The strength-weight ratiois higher than other
materials. Their stiffness and cost effectiveness offered, apart from easy availability of raw
materials, makethem the obvious choice for applications insurface transportation. In heavy
transport vehicles, the composites are used in processing of component parts with cost-
effectiveness. Good
Reproductivity and resilience handling by semi-skilled workers are the basic
requirements of a good composite material. While the costs of achieving advanced composites
may not justify the savings obtained interms of weight vis-a-vis vehicle production, carbon fibers
reinforced epoxies have been used in racing cars and recently for the safety of cars. Polyester
resin with suitable fillers and reinforcements were the first applications of composites in road
transportation. The choice was dictated by properties like low cost, ease in designing and
production of functional parts etc. Using a variety of reinforcements, polyester has continued to
be used in improving the system and other applications. Most of the thermoplastics are combined
with reinforcing fibers in various proportions. Several methods are used to produce vehicle parts
from thermo plastics.

41. Selection of the material is made from the final nature of the component, the volume
required, apart from cost-effectiveness and mechanical strength. Components that need
conventional paint finishing are generally made with thermosetting resins, while thermoplastics
are used to build parts that are moulded and can be pigmented. Press moulded reinforced
polyester possess the capability to produce large parts in considerable volume with cost-
effectiveness. In manufacturing of automobile parts, glass and sisal fibers usually find the
maximum use. Sisal costs very less and this alone has prompted extensive research to come up
with applications in which sisal is the dominant reinforcing material infilled polyester resin, in
parts where specific mechanical properties are required and appearance is not very important.
Heater housings, which find uses for sisal, are produced by compression moulding. Since a
variety of glass fibers are available, it is used as reinforcement for a large range of parts of
different types. Rovings, non-woven matsare the commonly used low cost versions. Woven cloth
is applied in special cases, where particular properties are required as cloth is not known to be
amenable to large quantity production methods. Since the automobile industry is replete with
models, options and changes in trends, the material selection and combinations offered by the
materials is also wide-ranging. Along with a measure of conservation, the choice is alsodictated
by the demands of the competitive market for new and alternate materials. A reinforced-plastic
composite is likely to costmore than sheet steel, when considered on the basis of cost and
performance. In such a case, other qualities must necessarily justify the high expenditure.
Mechanical properties of the parts, which affect the thickness and weight, must offer enough
savings to render them more effective than steel. It however shows a higher machining waste
than reinforced plastics. The fabrication costs of reinforced plastics is controlled by the devices
and tooling used for producing them. In turn, it is dependent on the basis of the quantity of
components needed. Some complicated parts of light commercial vehicles, which need casting,
may be compression moulded from composites of the sheet or bulk variety. State-of-art
technologies of moulding, tooling and fabricating have thrown open possibilities of increased
manufacturing of vehicles that use reinforced polyesters. Materials used in automotive body
parts show high tensile strength and flexural moduli. The material is not ductile and hence will
not yield and the failure is accounted only in terms of fracture. These properties and thickness,
determine the maximum bending moment which is several times higher than the pointof fracture
for steel sheets. Reinforced plastics can be given the metal finish, although the cost of achieving

42. this continues to be prohibitive. They are restricted in their use in car components. While the
defects in painted sheet metal parts are easily overlooked, the fiber pattern texture is
obvious,though the surface-roughness measurements report that it is smoother. In commercial
vehicles, appearance is also important as is the functional aspect. Since a commercial vehicle is
more a capital investment, it is the returns from such investment that are considered. The rate of
return depends on initial cost, durability and maintenance costs. Reinforced plastic is a boon in
the sense that it uses shorter lead times and tooling cost is considerably cheaper. Commitments to
launch a new model are kept easily, since the time between production and introduction can be
co-ordinate perfectly. Studies have shown that composite panels may be used as the complete
outer skin of the body to give a unique look. Sheet moulding compounds of resins are most
suited for this purpose. Inner and outer reinforcing is done by panel assembled by adhesive
bonding and riveting.
EVALUATION OF LAMINA PROPERTIES FROM LAMINATE TESTS
Filament winding is a fabrication technique mainly used for manufacturing open (cylinders) or
closed end structures (pressure vessels or tanks). The process involves winding filaments under
tension over a rotating mandrel. The mandrel rotates around the spindle (Axis 1 or X: Spindle)
while a delivery eye on a carriage (Axis 2 or Y: Horizontal) traverses horizontally in line with
the axis of the rotating mandrel, laying down fibers in the desired pattern or angle. The most
common filaments are glass or carbon and are impregnated in a bath with resin as they are
wound onto the mandrel. Once the mandrel is completely covered to the desired thickness, the
resin is cured. Depending on the resin system and its cure characteristics, often the rotating
mandrel is placed in an oven or placed under radiant heaters until the part is cured. Once the
resin has cured, the mandrel is removed or extracted, leaving the hollow final product. For some
products such as gas bottles the 'mandrel' is a permanent part of the finished product forming a
liner to prevent gas leakage or as a barrier to protect the composite from the fluid to be stored.
Filament winding is well suited to automation, and there are many applications, such as pipe and
small pressure vessel that are wound and cured without any human intervention. The controlled
variables for winding are fiber type, resin content, wind angle, tow or bandwidth and thickness of

43. the fiber bundle. The angle at which the fiber has an effect on the properties of the final product.
A high angle "hoop" will provide circumferential strength, while lower angle patterns (polar or
helical) will provide greater longitudinal / axial tensile strength.
Products currently being produced using this technique range from pipes, golf clubs, Reverse
Osmosis Membrane Housings, oars, bicycle forks, bicycle rims, power and transmission poles,
pressure vessels to missile casings, aircraft fuselages and lamp posts and yacht masts.
DETERMINATION OF LAMINA STRESSES WITHIN LAMINATES
Reinforcement mat or woven roving is placed in the mold, which is then closed and
clamped. Catalyzed, low-viscosity resin is pumped in under pressure, displacing the air and
venting it at the edges, until the mold is filled. Molds for this low-pressure system are usually
made from composite or nickel shell-faced composite construction.
Suitable for medium volume production of larger components, resin transfer molding is usually
considered an intermediate process between the relatively slow spray-up with lower tooling costs
and the faster compression molding methods with higher tooling costs.
 Recommended for products with high strength-to-weight requirements
 Best suited for mid-volume production rates, in the range of 200 to 10,000 parts per year*
 Gel coats may be used to provide a high-quality, durable finish
 Tooling can be made from many different materials - polyester, nickel shell, aluminum or
even mild steel. The volume and life of program and tooling budget will help determine
what is best
* Volume recommendations are averages and provided only as a general guideline. Actual
volume efficiencies are a more complex matter requiring detailed statistics about the part to be
manufactured.

44. UNIT IV LAMINA STRENGTH ANALYSIS AND ANALYSIS OF LAMINATED FLAT
PLATES
INTRODUCTION - MAXIMUM STRESS AND STRAIN CRITERIA.
A fiber-reinforced composite (FRC) is a high-performance composite material made up
of three components - the fibers as the discontinuous or dispersed phase, the matrix acts as the
continuous phase, and the fine interphase region or the interface.
The matrix is basically a homogeneous and monolithic material in which a fiber system of a
composite is embedded. It is completely continuous. The matrix provides a medium for binding
and holding reinforcements together into a solid. It offers protection to the reinforcements from
environmental damage, serves to transfer load, and provides finish, texture, color, durability and
functionality.
Ceramic matrix composites (CMCs) are a subgroup of composite materials. They consist
of ceramic fibers embedded in a ceramic matrix, thus forming a ceramic fiber reinforced ceramic
(CFRC) material. The matrix and fibers can consist of any ceramic material. CMC materials
were designed to overcome the major disadvantages such as low fracture toughness, brittleness,
and limited thermal shock resistance, faced by the traditional technical ceramics.
VON-MISSES YIELD CRITERION FOR ISOTROPIC MATERIALS
Metal matrix composites (MMCs) are composite materials that contain at least two
constituent parts – a metal and another material or a different metal. The metal matrix is
reinforced with the other material to improve strength and wear. Where three or more constituent
parts are present, it is called a hybrid composite. In structural applications, the matrix is usually
composed of a lighter metal such as magnesium, titanium, or aluminum. In high temperature
applications, cobalt and cobalt-nickel alloy matrices are common. Typical MMC's manufacturing
is basically divided into three types: solid, liquid, and vapor. Continuous carbon, silicon carbide,
or ceramic fibers are some of the materials that can be embedded in a metallic matrix material.
MMCs are fire resistant, operate in a wide range of temperatures, do not absorb moisture, and
possess better electrical and thermal conductivity. They have also found applications to be

45. resistant to radiation damage, and to not suffer from outgassing. Most metals and alloys make
good matrices for composite applications.
GENERALIZED HILL’S CRITERION FOR ANISOTROPIC MATERIALS
A particle is a minute fragment or quantity of matter. In the physical sciences, the word
is used to describe a small localized object to which can be ascribed several physical or chemical
properties such as volume or mass; subatomic particles such as protons or neutrons; and other
elementary particles. The word is rather general in meaning, and is refined as needed by various
scientific fields. Something that is composed of particles may be referred to as being particulate.
However, the term particulate is most frequently used to refer to pollutants in the Earth's
atmosphere, which are a suspension of unconnected particles, rather than a connected particle
aggregation.
The inorganic fibers are constituted mainly by inorganic chemicals, based on natural
elements such as carbon, silicon and boron, that, in general, after receiving treatment at elevated
temperatures are transformed into fibers.
Inorganic fibers, also sometimes dubbed high performance fibers or super-fibers, have
characteristics and properties that differ from other non-natural fibers and therefore rarely find
applications in the field of conventional textiles.
Effectively, these fibers have general characteristics as high thermal and mechanical
resistance, which makes them especially in engineering solutions applied in many cases in
combination with other materials – composites.
In these applications, they compete normally with conventional materials, replacing them
often due to their ease of processing, thermal resistance, resistance to chemical agents and
especially due to the excellent weight/mechanical properties correlation.
In general, the inorganic fibers are difficult to process by conventional textile techniques,
such as weaving or knitting, due to the fact that easily break in flexure (weak), presenting low

46. elongation at break and possess high coefficients of friction with metals , forcing many times to
its surface lubrication.
TSAI-HILL’S FAILURE CRITERION FOR COMPOSITES
Ceramic matrix composites (CMCs) are a subgroup of composite materials as well as a
subgroup of technical ceramics. They consist of ceramic fibres embedded in a ceramic matrix,
thus forming a ceramic fibre reinforced ceramic (CFRC) material. The matrix and fibres can
consist of any ceramic material, whereby carbon and carbon fibres can also be considered a
ceramic material.
Ceramic fibres in CMCs can have a polycrystalline structure, as in conventional
ceramics. They can also be amorphous or have inhomogeneous chemical composition, which
develops upon pyrolysis of organic precursors. The high process temperatures required for
making CMCs preclude the use of organic, metallic or glass fibres. Only fibres stable at
temperatures above 1000 °C can be used, such as fibres of alumina, mullite, SiC, zirconia or
carbon. Amorphous SiC fibres have an elongation capability above 2% – much larger than in
conventional ceramic materials (0.05 to 0.10%).[1]
The reason for this property of SiC fibres is
that most of them contain additional elements like oxygen, titanium and/or aluminium yielding a
tensile strength above 3 GPa. These enhanced elastic properties are required for various three-
dimensional fibre arrangements (see example in figure) in textile fabrication, where a small
bending radius is essential.
The use of composite materials dates from centuries ago, and it all started with natural
fibres. In ancient Egypt some 3 000 years ago, clay was reinforced by straw to build walls. Later
on, the natural fibre lost much of its interest. Other more durable construction materials like
metals were introduced. During the sixties, the rise of composite materials began when glass
fibres in combination with tough rigid resins could be produced on large scale. During the last
decade there has been a renewed interest in the natural fibre as a substitute for glass, motivated
by potential advantages of weight saving, lower raw material price, and 'thermal recycling' or the
ecological advantages of using resources which are renewable. On the other hand natural fibres
have their shortcomings, and these have to be solved in order to be competitive with glass.

47. Natural fibres have lower durability and lower strength than glass fibres. However, recently
developed fibre treatments have improved these properties considerably. To understand how
fibres should be treated, a closer look into the fibre is required.
TENSOR POLYNOMIAL (TSAI-WU) FAILURE CRITERION.
In general, the bast consists of a wood core surrounded by a stem. Within the stem there
are a number of fibre bundles, each containing individual fibre cells or filaments. The filaments
are made of cellulose and hemicellulose, bonded together by a matrix, which can be lignin or
pectin. The pectin surrounds the bundle thus holding them on to the stem. The pectin is removed
during the retting process. This enables separation of the bundles from the rest of the stem
(scutching).
After fibre bundles are impregnated with a resin during the processing of a composite, the
weakest part in the material is the lignin between the individual cells. Especially in the case of
flax, a much stronger composite is obtained if the bundles are pre-treated in a way that the cells
are separated, by removing the lignin between the cells. Boiling in alkali is one of the methods to
separate the individual cells.
Flax delivers strong and stiff fibres and it can be grown in temperate climates. The fibres can be
spun to fine yarns for textile (linen). Other bast fibres are grown in warmer climates. The most
common is jute, which is cheap, and has a reasonable strength and resistance to rot. Jute is
mainly used for packaging (sacks and bales).
As far as composite applications are concerned, flax and hemp are two fibres that have replaced
glass in a number of components, especially in the German automotive industries.
In general the leaf fibres are coarser than the bast fibres. Applications are ropes, and coarse
textiles. Within the total production of leaf fibres, sisal is the most important. It is obtained from
the agave plant. The stiffness is relatively high and it is often applied as binder twines.
As far as composites is concerned, sisal is often applied with flax in hybrid mats, to provide good
permeability when the mat has to be impregnated with a resin. In some interior applications sisal

48. is prefered because of its low level of smell compared to fibres like flax. Especially
manufacturing processes at increased temperatures (NMT) fibres like flax can cause smell.
Cotton is the most common seed fibre and is used for textile all over the world. Other seed fibres
are applied in less demanding applications such as stuffing of upholstery. Coir is an exception to
this. Coir is the fibre of the coconut husk, it is a thick and coarse but durable fibre. Applications
are ropes, matting and brushes.
With the rise of composite materials there is a renewed interest for natural fibres. Their moderate
mechanical properties restrain the fibres from using them in high-tech applications, but for many
reasons they can compete with glass fibres. Advantages and disadvantages determine the choice:
PREDICTION OF LAMINATE FAILURE
Metal-matrix composites are either in use or prototyping for the Space Shuttle, commercial
airliners, electronic substrates, bicycles, automobiles, golf clubs, and a variety of other
applications. While the vast majority are aluminum matrix composites, a growing number of
applications require the matrix properties of superalloys, titanium, copper, magnesium, or iron.
Like all composites, aluminum-matrix composites are not a single material but a family of
materials whose stiffness, strength, density, and thermal and electrical properties can be tailored.
The matrix alloy, the reinforcement material, the volume and shape of the reinforcement, the
location of the reinforcement, and the fabrication method can all be varied to achieve required
properties. Regardless of the variations, however, aluminum composites offer the advantage of
low cost over most other MMCs. In addition, they offer excellent thermal conductivity, high
shear strength, excellent abrasion resistance, high-temperature operation, nonflammability,
minimal attack by fuels and solvents, and the ability to be formed and treated on conventional
equipment.
Aluminum MMCs are produced by casting, powder metallurgy, in situ development of
reinforcements, and foil-and-fiber pressing techniques. Consistently high-quality products are
now available in large quantities, with major producers scaling up production and reducing

49. prices. They are applied in brake rotors, pistons, and other automotive components, as well as
golf clubs, bicycles, machinery components, electronic substrates, extruded angles and channels,
and a wide variety of other structural and electronic applications.
Superalloy composites reinforced with tungsten alloy fibers are being developed for components
in jet turbine engines that operate temperatures above 1,830 °F.
Graphite/copper composites have tailorable properties, are useful to high temperatures in air, and
provide excellent mechanical characteristics, as well as high electrical and thermal conductivity.
They offer easier processing as compared with titanium, and lower density compared with steel.
Ductile superconductors have been fabricated with a matrix of copper and superconducting
filaments of niobium-titanium. Copper reinforced with tungsten particles or aluminum oxide
particles is used in heat sinks and electronic packaging.
Titanium reinforced with silicon carbide fibers is under development as skin material for the
National Aerospace Plane. Stainless steels, tool steels, and Inconel are among the matrix
materials reinforced with titanium carbide particles and fabricated into draw-rings and other
high-temperature, corrosion-resistant components.
EQUILIBRIUM EQUATIONS OF MOTION.
MMC reinforcements can be divided into five major categories: continuous fibers, discontinuous
fibers, whiskers, particulates, and wires. With the exception of wires, which are metals,
reinforcements generally are ceramics.
Key continuous fibers include boron, graphite (carbon), alumina, and silicon carbide. Boron
fibers are made by chemical vapor deposition (CVD) of this material on a tungsten core. Carbon
cores have also been used. These relatively thick monofilaments are available in 4.0, 5.6, and
8.0-mil diameters. To retard reactions that can take place between boron and metals at high
temperature, fiber coatings of materials such as silicon carbide or boron carbide are sometimes
used.

50. Silicon carbide monofilaments are also made by a CVD process, using a tungsten or carbon core.
A Japanese multifilament yarn, designated as silicon carbide by its manufacturer, is also
commercially available. This material, however, made by pyrolysis of organometallic precursor
fibers, is far from pure silicon carbide and its properties differ significantly from those of
monofilament silicon carbide.
Continuous alumina fibers are available from several suppliers. Chemical compositions and
properties of the various fibers are significantly different. Graphite fibers are made from two
precursor materials, polyacrilonitrile (PAN) and petroleum pitch. Efforts to make graphite fibers
from coal-based pitch are under way. Graphite fibers with a wide range of strengths and moduli
are available.
The leading discontinuous fiber reinforcements at this time are alumina and alumina-silica. Both
originally were developed as insulating materials. The major whisker material is silicon carbide.
The leading U.S. commercial product is made by pyrolysis of rice hulls. Silicon carbide and
boron carbide, the key particulate reinforcements, are obtained from the commercial abrasives
industry. Silicon carbide particulates are also produced as a by-product of the process used to
make whiskers of this material.
A number of metal wires including tungsten, beryllium, titanium, and molybdenum have been
used to reinforce metal matrices. Currently, the most important wire reinforcements are tungsten
wire in superalloys and superconducting materials incorporating niobium-titanium and niobium-
tin in a copper matrix. The reinforcements cited above are the most important at this time. Many
others have been tried over the last few decades, and still others undoubtedly will be developed
in the future.
ENERGY FORMULATIONS.
Composites are one of the most widely used materials because of their adaptability to different
situations and the relative ease of combination with other materials to serve specific purposes
and exhibit desirable properties. In surface transportation, reinforced plastics are the kind of

51. composites used because of their huge size. They provide ample scope and receptiveness to
design changes, materials and processes. The strength-weight ratiois higher than other materials.
Their stiffness and cost effectiveness offered, apart from easy availability of raw materials,
makethem the obvious choice for applications insurface transportation. In heavy transport
vehicles, the composites are used in processing of component parts with cost-effectiveness. Good
Reproductivity and resilience handling by semi-skilled workers are the basic requirements of a
good composite material. While the costs of achieving advanced composites may not justify the
savings obtained interms of weight vis-a-vis vehicle production, carbon fibers reinforced epoxies
have been used in racing cars and recently for the safety of cars. Polyester resin with suitable
fillers and reinforcements were the first applications of composites in road transportation. The
choice was dictated by properties like low cost, ease in designing and production of functional
parts etc. Using a variety of reinforcements, polyester has continued to be used in improving the
system and other applications. Most of the thermoplastics are combined with reinforcing fibers in
various proportions. Several methods are used to produce vehicle parts from thermo plastics.
Selection of the material is made from the final nature of the component, the volume
required, apart from cost-effectiveness and mechanical strength. Components that need
conventional paint finishing are generally made with thermosetting resins, while thermoplastics
are used to build parts that are moulded and can be pigmented. Press moulded reinforced
polyester possess the capability to produce large parts in considerable volume with cost-
effectiveness. In manufacturing of automobile parts, glass and sisal fibers usually find the
maximum use. Sisal costs very less and this alone has prompted extensive research to come up
with applications in which sisal is the dominant reinforcing material infilled polyester resin, in
parts where specific mechanical properties are required and appearance is not very important.
Heater housings, which find uses for sisal, are produced by compression moulding. Since a
variety of glass fibers are available, it is used as reinforcement for a large range of parts of
different types. Rovings, non-woven matsare the commonly used low cost versions. Woven cloth
is applied in special cases, where particular properties are required as cloth is not known to be
amenable to large quantity production methods. Since the automobile industry is replete with
models, options and changes in trends, the material selection and combinations offered by the
materials is also wide-ranging. Along with a measure of conservation, the choice is alsodictated

52. by the demands of the competitive market for new and alternate materials. A reinforced-plastic
composite is likely to costmore than sheet steel, when considered on the basis of cost and
performance. In such a case, other qualities must necessarily justify the high expenditure.
Mechanical properties of the parts, which affect the thickness and weight, must offer enough
savings to render them more effective than steel. It however shows a higher machining waste
than reinforced plastics. The fabrication costs of reinforced plastics is controlled by the devices
and tooling used for producing them. In turn, it is dependent on the basis of the quantity of
components needed. Some complicated parts of light commercial vehicles, which need casting,
may be compression moulded from composites of the sheet or bulk variety. State-of-art
technologies of moulding, tooling and fabricating have thrown open possibilities of increased
manufacturing of vehicles that use reinforced polyesters. Materials used in automotive body
parts show high tensile strength and flexural moduli. The material is not ductile and hence will
not yield and the failure is accounted only in terms of fracture. These properties and thickness,
determine the maximum bending moment which is several times higher than the pointof fracture
for steel sheets. Reinforced plastics can be given the metal finish, although the cost of achieving
this continues to be prohibitive. They are restricted in their use in car components. While the
defects in painted sheet metal parts are easily overlooked, the fiber pattern texture is
obvious,though the surface-roughness measurements report that it is smoother. In commercial
vehicles, appearance is also important as is the functional aspect. Since a commercial vehicle is
more a capital investment, it is the returns from such investment that are considered. The rate of
return depends on initial cost, durability and maintenance costs. Reinforced plastic is a boon in
the sense that it uses shorter lead times and tooling cost is considerably cheaper. Commitments to
launch a new model are kept easily, since the time between production and introduction can be
co-ordinate perfectly. Studies have shown that composite panels may be used as the complete
outer skin of the body to give a unique look. Sheet moulding compounds of resins are most
suited for this purpose. Inner and outer reinforcing is done by panel assembled by adhesive
bonding and riveting.

53. STATIC BENDING ANALYSIS
Composites have high stiffness, strength, and toughness, often comparable with structural metal
alloys. Further, they usually provide these properties at substantially less weight than metals:
their “specific” strength and modulus per unit weight is near five times that of steel or aluminum.
This means the overall structure may be lighter, and in weight-critical devices such as airplanes
or spacecraft this weight savings might be a compelling advantage.
• Composites can be made anisotropic, i.e. have different properties in different
directions, and this can be used to design a more efficient structure. In many structures the
stresses are also different in different directions; for instance in closed-end pressure vessels –
such as a rocket motor case – the circumferential stresses are twice the axial stresses. Using
composites,such a vessel can be made twice as strong in the circumferential direction as in the
axial.
•Many structures experience fatigueloading, in which the internal stresses vary with time.
Axles on rolling stock are examples; here the stresses vary sinusoidally from tension to
compression as the axle turns. These fatigue stresses can eventually lead to failure, even when
the maximum stress is much less than the failure strength of the material as measured in a static
tension test. Composites of then have excellent fatigue resistance in comparison with metal
alloys, and often show evidence of accumulating fatigue damage, so that the damage can be
detected and the part replaced before a catastrophic failure occurs.
•Materials can exhibit damping, in which a certain fraction of the mechanical strain
energy deposited in the material by a loading cycle is dissipated as heat. This can be
advantageous, for instance in controlling mechanically-induced vibrations. Composites generally
offer relatively high levels of damping, and furthermore the damping can often be tailored to
desired levels by suitable formulation and processing.
• Composites can be excellent in applications involving sliding friction, with tribological
(“wear”) properties approaching those of lubricated steel.
• Composites do not rust as do many ferrous alloys, and resistance to this common form
of environmental degradation may offer better life-cycle cost even if the original
structure is initially more costly.
• Many structural parts are assembled from a number of subassemblies, and the