50840364 Composite Materials
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Transcript of 50840364 Composite Materials
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Composite Materials Prof. Shashank S. Bhamble
Mechanical Engineering Department
Shri Sant Gajanan Maharaj College of Engineering, Shegaon
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Composite materials (or composites for short) are engineered materials made from
two or more constituent materials with significantly different physical or chemical properties
which remain separate and distinct on a macroscopic level within the finished structure.
The most primitive composite materials were straw and mud combined to form bricks
for building construction; the Biblical Book of Exodus speaks of the Israelites being
oppressed by Pharaoh, by being forced to make bricks without straw being provided. The
ancient brick-making process can still be seen on Egyptian tomb paintings in the
Metropolitan Museum of Art. The most advanced examples perform routinely on spacecraft
in demanding environments. The most visible applications pave our roadways in the form of
either steel and aggregate reinforced portland cement or asphalt concrete. Those composites
closest to our personal hygiene form our shower stalls and bath tubs made of fiberglass. Solid
surface, imitation granite and cultured marble sinks and counter tops are widely used to
enhance our living experiences.
Composites are made up of individual materials referred to as constituent materials.
There are two categories of constituent materials: matrix and reinforcement. At least one
portion of each type is required. The matrix material surrounds and supports the
reinforcement materials by maintaining their relative positions. The reinforcements impart
their special mechanical and physical properties to enhance the matrix properties. A
synergism produces material properties unavailable from the individual constituent materials,
while the wide variety of matrix and strengthening materials allows the designer of the
product or structure to choose an optimum combination.
Engineered composite materials must be formed to shape. The matrix material can be
introduced to the reinforcement before or after the reinforcement material is placed into the
mold cavity or onto the mold surface. The matrix material experiences a melding event, after
which the part shape is essentially set. Depending upon the nature of the matrix material, this
melding event can occur in various ways such as chemical polymerization or solidification
from the melted state.
A variety of molding methods can be used according to the end-item design
requirements. The principal factors impacting the methodology are the natures of the chosen
matrix and reinforcement materials. Another important factor is the gross quantity of material
to be produced. Large quantities can be used to justify high capital expenditures for rapid and
automated manufacturing technology. Small production quantities are accommodated with
lower capital expenditures but higher labor and tooling costs at a correspondingly slower rate.
Most commercially produced composites use a polymer matrix material often called a
resin solution. There are many different polymers available depending upon the starting raw
ingredients. There are several broad categories, each with numerous variations. The most
common are known as polyester, vinyl ester, epoxy, phenolic, polyimide, polyamide,
polypropylene, PEEK, and others. The reinforcement materials are often fibers but also
commonly ground minerals. The various methods described below have been developed to
reduce the resin content of the final product, or the fibre content is increased. As a rule of
thumb, lay up results in a product containing 60% resin and 40% fibre, whereas vacuum
infusion gives a final product with 40% resin and 60% fibre content. The strength of the
product is greatly dependent on this ratio.
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Moulding methods In general, the reinforcing and matrix materials are combined, compacted and
processed to undergo a melding event. After the melding event, the part shape is essentially
set, although it can deform under certain process conditions. For a thermoset polymeric
matrix material, the melding event is a curing reaction that is initiated by the application of
additional heat or chemical reactivity such as an organic peroxide. For a thermoplastic
polymeric matrix material, the melding event is a solidification from the melted state. For a
metal matrix material such as titanium foil, the melding event is a fusing at high pressure and
a temperature near the melt point.
For many molding methods, it is convenient to refer to one mold piece as a "lower"
mold and another mold piece as an "upper" mold. Lower and upper refer to the different faces
of the molded panel, not the mold's configuration in space. In this convention, there is always
a lower mold, and sometimes an upper mold. Part construction begins by applying materials
to the lower mold. Lower mold and upper mold are more generalized descriptors than more
common and specific terms such as male side, female side, a-side, b-side, tool side, bowl, hat,
mandrel, etc. Continuous manufacturing processes use a different nomenclature.
The molded product is often referred to as a panel. For certain geometries and
material combinations, it can be referred to as a casting. For certain continuous processes, it
can be referred to as a profile. Applied with a pressure roller, a spray device or manually.
This process is generally done at ambient temperature and atmospheric pressure. Two
variations of open moulding are Hand Layup and Spray-up.
Vacuum bag moulding A process using a two-sided mould set that shapes both surfaces of the panel. On the
lower side is a rigid mould and on the upper side is a flexible membrane or vacuum bag. The
flexible membrane can be a reusable silicone material or an extruded polymer film. Then,
vacuum is applied to the mould cavity. This process can be performed at either ambient or
elevated temperature with ambient atmospheric pressure acting upon the vacuum bag. Most
economical way is using a venturi vacuum and air compressor or a vacuum pump.
Pressure bag moulding This process is related to vacuum bag moulding in exactly the same way as it sounds.
A solid female mould is used along with a flexible male mould. The reinforcement is placed
inside the female mould with just enough resin to allow the fabric to stick in place. A
measured amount of resin is then liberally brushed indiscriminately into the mould and the
mould is then clamped to a machine that contains the male flexible mould. The flexible male
membrane is then inflated with heated compressed air or possibly steam. The female mould
can also be heated. Excess resin is forced out along with trapped air. This process is
extensively used in the production of composite helmets due to the lower cost of unskilled
labor. Cycle times for a helmet bag moulding machine vary from 20 to 45 minutes, but the
finished shells require no further curing if the moulds are heated.
Autoclave moulding A process using a two-sided mold set that forms both surfaces of the panel. On the
lower side is a rigid mold and on the upper side is a flexible membrane made from silicone or
an extruded polymer film such as nylon. Reinforcement materials can be placed manually or
robotically. They include continuous fiber forms fashioned into textile constructions. Most
often, they are pre-impregnated with the resin in the form of prepreg fabrics or unidirectional
tapes. In some instances, a resin film is placed upon the lower mold and dry reinforcement is
placed above. The upper mold is installed and vacuum is applied to the mold cavity. The
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assembly is placed into an autoclave. This process is generally performed at both elevated
pressure and elevated temperature. The use of elevated pressure facilitates a high fiber
volume fraction and low void content for maximum structural efficiency.
Resin transfer moulding (RTM) A process using a two-sided mold set that forms both surfaces of the panel. The lower
side is a rigid mold. The upper side can be a rigid or flexible mold. Flexible molds can be
made from composite materials, silicone or extruded polymer films such as nylon. The two
sides fit together to produce a mold cavity. The distinguishing feature of resin transfer
molding is that the reinforcement materials are placed into this cavity and the mold set is
closed prior to the introduction of matrix material. Resin transfer molding includes numerous
varieties which differ in the mechanics of how the resin is introduced to the reinforcement in
the mold cavity. These variations include everything from vacuum infusion (for resin
infusion see also Boat building) to vacuum assisted resin transfer moulding. This process can
be performed at either ambient or elevated temperature.
Other Other types of molding include press molding, transfer molding, pultrusion molding,
filament winding, casting, centrifugal casting and continuous casting. There are also forming
capabilities including CNC filament winding, vacuum infusion, wet lay-up, compression
molding, and thermoplastic molding, to name a few. The use of curing ovens and paint
booths is also needed for some projects.
Tooling Some types of tooling materials used in the manufacturing of composites structures
include invar, steel, aluminum, reinforced silicone rubber, nickel, and carbon fiber. Selection
of the tooling material is typically based on, but not limited to, the coefficient of thermal
expansion, expected number of cycles, end item tolerance, desired or required surface
condition, method of cure, glass transition temperature of the material being molded, molding
method, matrix, cost and a variety of other considerations.
Mechanics The physical properties of composite materials are generally not isotropic
(independent of direction of applied force) in nature, but rather are typically orthotropic
(different depending on the direction of the applied force or load). For instance, the stiffness
of a composite panel will often depend upon the orientation of the applied forces and/or
moments. Panel stiffness is also dependent on the design of the panel. For instance, the fiber
reinforcement and matrix used, the method of panel build, thermoset versus thermoplastic,
type of weave, and orientation of fiber axis to the primary force.
In contrast, isotropic materials (for example, aluminium or steel), in standard wrought
forms, typically have the same stiffness regardless of the directional orientation of the applied
forces and/or moments.
The relationship between forces/moments and strains/curvatures for an isotropic
material can be described with the following material properties: Young's Modulus, the Shear
Modulus and the Poisson's ratio, in relatively simple mathematical relationships. For the
anisotropic material, it requires the mathematics of a second order tensor and up to 21
material property constants. For the special case of orthogonal isotropy, there are three
different material property constants for each of Young's Modulus, Shear Modulus and
Poisson's ratio—a total of 9 constants to describe the relationship between forces/moments
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Resins Typically, most common composite materials, including fiberglass, carbon fiber, and
Kevlar, include at least two parts, the substrate and the resin.
Polyester resin, tends to have yellowish tint, and is suitable for most backyard
projects. Its weaknesses are that it is UV sensitive and can tend to degrade over time, and
thus generally is also coated to help preserve it. It is often used in the making of surfboards
and for marine applications. Its hardener is a MEKP, and is mixed at 14 drops per oz. MEKP
is composed of methyl ethyl ketone peroxide, a catalyst. When MEKP is mixed with the
resin, the resulting chemical reaction causes heat to build up and cure or harden the resin.
Vinylester resin, tends to have a purplish to bluish to greenish tint. This resin has
lower viscosity than polyester resin, and is more transparent. This resin is often billed as
being fuel resistant, but will melt in contact with gasoline. This resin tends to be more
resistant over time to degradation than polyester resin, and is more flexible. It uses the same
hardener as polyester resin (at the same mix ratio) and the cost is approximately the same.
Epoxy resin is almost totally transparent when cured. In the aerospace industry, epoxy
is used as a structural matrix material or as a structural glue.
Shape memory polymer (SMP) resins have varying visual characteristics depending
on their formulation. These resins may be epoxy-based, which can be used for auto body and
outdoor equipment repairs; cyanate-ester-based, which are used in space applications; and
acrylate-based, which can be used in very cold temperature applications, such as for sensors
that indicate whether perishable goods have warmed above a certain maximum
These resins are unique in that their shape can be repeatedly changed by
heating above their glass transition temperature (Tg). When heated, they become flexible and
elastic, allowing for easy configuration. Once they are cooled, they will maintain their new
shape. The resins will return to their original shapes when they are reheated above their Tg.
The advantage of shape memory polymer resins is that they can be shaped and reshaped
repeatedly without losing their material properties, and these resins can be used in fabricating
shape memory composites.
Categories of fiber-reinforced composite materials Fiber-reinforced composite materials can be divided into two main categories
normally referred to as short fiber-reinforced materials and continuous fiber-reinforced
materials. Continuous reinforced materials will often constitute a layered or laminated
structure. The woven and continuous fiber styles are typically available in a variety of forms,
being pre-impregnated with the given matrix (resin), dry, uni-directional tapes of various
widths, plain weave, harness satins, braided, and stitched.
The short and long fibers are typically employed in compression molding and sheet
molding operations. These come in the form of flakes, chips, and random mate (which can
also be made from a continuous fiber laid in random fashion until the desired thickness of the
ply / laminate is achieved).
Failure Shock, impact, or repeated cyclic stresses can cause the laminate to separate at the
interface between two layers, a condition known as delamination. Individual fibers can
separate from the matrix e.g. fiber pull-out.
Composites can fail on the microscopic or macroscopic scale. Compression failures
can occur at both the macro scale or at each individual reinforcing fiber in compression
buckling. Tension failures can be net section failures of the part or degradation of the
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composite at a microscopic scale where one or more of the layers in the composite fail in
tension of the matrix or failure the bond between the matrix and fibers.
Some composites are brittle and have little reserve strength beyond the initial onset of
failure while others may have large deformations and have reserve energy absorbing capacity
past the onset of damage. The variations in fibers and matrices that are available and the
mixtures that can be made with blends leave a very broad range of properties that can be
designed into a composite structure. The best known failure of a brittle ceramic matrix
composite occurred when the carbon-carbon composite tile on the leading edge of the wing of
the Space Shuttle Columbia fractured when impacted during take-off. It led to catastrophic
break-up of the vehicle when it re-entered the earth's atmosphere on February 1, 2003.
Compared to metals, composites have relatively poor bearing strength.
To aid in predicting and preventing failures, composites are tested before and after
construction. Pre-construction testing uses computer aided engineering tools such as NEi
Software Nastran FEA (finite element analysis) for ply-by-ply analysis of curved surfaces
and predicting wrinkling, crimping and dimpling of composites. Materials may be tested after
construction through several nondestructive methods including ultrasonics, thermography,
shearography and X-ray radiography.
Fiber-reinforced polymers or FRPs include wood (comprising cellulose fibers in a
lignin and hemicellulose matrix), carbon-fiber reinforced plastic or CFRP, and glass-
reinforced plastic or GRP. If classified by matrix then there are thermoplastic composites,
short fiber thermoplastics, long fiber thermoplastics or long fiber-reinforced thermoplastics.
There are numerous thermoset composites, but advanced systems usually incorporate aramid
fibre and carbon fibre in an epoxy resin matrix.
Shape memory polymer composites are high-performance composites, formulated
using fiber or fabric reinforcement and shape memory polymer resin as the matrix. Since a
shape memory polymer resin is used as the matrix, these composites have the ability to be
easily manipulated into various configurations when they are heated above their activation
temperatures and will exhibit high strength and stiffness at lower temperatures. They can also
be reheated and reshaped repeatedly without losing their material properties. These
composites are ideal for applications such as lightweight, rigid, deployable structures; rapid
manufacturing; and dynamic reinforcement.
Composites can also use metal fibres reinforcing other metals, as in metal matrix
composites or MMC. Magnesium is often used in MMCs because it has similar mechanical
properties as epoxy. The benefit of magnesium is that it does not degrade in outer space.
Ceramic matrix composites include bone (hydroxyapatite reinforced with collagen fibers),
Cermet (ceramic and metal) and concrete. Ceramic matrix composites are built primarily for
toughness, not for strength. Organic matrix/ceramic aggregate composites include asphalt
concrete, mastic asphalt, mastic roller hybrid, dental composite, syntactic foam and mother of
pearl. Chobham armour is a special composite used in military applications.
Additionally, thermoplastic composite materials can be formulated with specific metal
powders resulting in materials with a density range from 2 g/cm³ to 11 g/cm³ (same density as
lead). These materials can be used in place of traditional materials such as aluminum,
stainless steel, brass, bronze, copper, lead, and even tungsten in weighting, balancing,
vibration dampening, and radiation shielding applications. High density composites are an
economically viable option when certain materials are deemed hazardous and are banned
(such as lead) or when secondary operations costs (such as machining, finishing, or coating)
are a factor.
Engineered wood includes a wide variety of different products such as plywood,
oriented strand board, wood plastic composite (recycled wood fiber in polyethylene matrix),
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Pykrete (sawdust in ice matrix), Plastic-impregnated or laminated paper or textiles, Arborite,
Formica (plastic) and Micarta. Other engineered laminate composites, such as Mallite, use a
central core of end grain balsa wood, bonded to surface skins of light alloy or GRP. These
generate low-weight, high rigidity materials.
Products Composite materials have gained popularity (despite their generally high cost) in
high-performance products that need to be lightweight, yet strong enough to take harsh
loading conditions such as aerospace components (tails, wings, fuselages, propellers), boat
and scull hulls, bicycle frames and racing car bodies. Other uses include fishing rods, storage
tanks, and baseball bats. The new Boeing 787 structure including the wings and fuselage is
composed largely of composites.
Carbon composite is a key material in today's launch vehicles and spacecraft. It is
widely used in solar panel substrates, antenna reflectors and yokes of spacecraft. It is also
used in payload adapters, inter-stage structures and heat shields of launch vehicles.
In 2007 an all-composite military High Mobility Multi-purpose Wheeled Vehicle
(HMMWV or Hummvee) was introduced by TPI Composites Inc and Armor Holdings Inc,
the first all-composite military vehicle. By using composites the vehicle is lighter, allowing
higher payloads. In 2008 carbon fiber and DuPont Kevlar (five times stronger than steel)
were combined with enhanced thermoset resins to make military transit cases by ECS
Composites creating 30-percent lighter cases with high strength.
METAL MATRIX COMPOSITE A metal matrix composite (MMC) is composite material with at least two
constituent parts, one being a metal. The other material may be a different metal or another
material, such as a ceramic or organic compound. When at least three materials are present, it
is called a hybrid composite. An MMC is complementary to a cermet.
Composition MMCs are made by dispersing a reinforcing material into a metal matrix. The
reinforcement surface can be coated to prevent a chemical reaction with the matrix. For
example, carbon fibers are commonly used in aluminium matrix to synthesize composites
showing low density and high strength. However, carbon reacts with aluminium to generate a
brittle and water-soluble compound Al4C3 on the surface of the fiber. To prevent this
reaction, the carbon fibers are coated with nickel or titanium boride.
The matrix is the monolithic material into which the reinforcement is embedded, and
is completely continuous. This means that there is a path through the matrix to any point in
the material, unlike two materials sandwiched together. In structural applications, the matrix
is usually a lighter metal such as aluminium, magnesium, or titanium, and provides a
compliant support for the reinforcement. In high temperature applications, cobalt and cobalt-
nickel alloy matrices are common.
The reinforcement material is embedded into the matrix. The reinforcement does not
always serve a purely structural task (reinforcing the compound), but is also used to change
physical properties such as wear resistance, friction coefficient, or thermal conductivity. The
reinforcement can be either continuous, or discontinuous. Discontinuous MMCs can be
isotropic, and can be worked with standard metalworking techniques, such as extrusion,
forging or rolling. In addition, they may be machined using conventional techniques, but
commonly would need the use of polycrystaline diamond tooling (PCD).
Continuous reinforcement uses monofilament wires or fibers such as carbon fiber or
silicon carbide. Because the fibers are embedded into the matrix in a certain direction, the
result is an anisotropic structure in which the alignment of the material affects its strength.
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One of the first MMCs used boron filament as reinforcement. Discontinuous reinforcement
uses "whiskers", short fibers, or particles. The most common reinforcing materials in this
category are alumina and silicon carbide.
Manufacturing and forming methods MMC manufacturing can be broken into three types: solid, liquid, and vapor.
Solid state methods
Powder blending and consolidation (powder metallurgy): Powdered metal and
discontinuous reinforcement are mixed and then bonded through a process of
compaction, degassing, and thermo-mechanical treatment (possibly via hot isostatic
pressing (HIP) or extrusion).
Foil diffusion bonding: Layers of metal foil are sandwiched with long fibers, and then
pressed through to form a matrix.
Liquid state methods
Electroplating / Electroforming: A solution containing metal ions loaded with
reinforcing particles is co-deposited forming a composite material.
Stir casting: Discontinuous reinforcement is stirred into molten metal, which is
allowed to solidify.
Squeeze casting: Molten metal is injected into a form with fibers preplaced inside it.
Spray deposition: Molten metal is sprayed onto a continuous fiber substrate.
Reactive processing: A chemical reaction occurs, with one of the reactants forming
the matrix and the other the reinforcement.
Physical vapor deposition: The fiber is passed through a thick cloud of vaporized
metal, coating it.
In situ fabrication technique
Controlled unidirectional solidification of a eutectic alloy can result in a two-phase
microstructure with one of the phases, present in lamellar or fiber form, distributed in
Applications Carbide drills are often made from a tough cobalt matrix with hard tungsten carbide
Some tank armors may be made from metal matrix composites, probably steel
reinforced with boron nitride. Boron nitride is a good reinforcement for steel because
it is very stiff and it does not dissolve in molten steel.
Some automotive disc brakes use MMCs. Early Lotus Elise models used aluminium
MMC rotors, but they have less than optimal heat properties and Lotus has since
switched back to cast-iron. Modern high-performance sport cars, such as those built
by Porsche, use rotors made of carbon fiber within a silicon carbide matrix because of
its high specific heat and thermal conductivity. 3M sells a preformed aluminium
matrix insert for strengthening cast aluminum disc brake calipers , allowing them
to weigh as much as 50% less while increasing stiffness. 3M has also used alumina
preforms for AMC pushrods. 
Ford offers a Metal Matrix Composite (MMC) driveshaft upgrade. The MMC
driveshaft is made of an aluminum boron carbide matrix, allowing the critical speed
of the driveshaft to be raised by reducing inertia. The MMC driveshaft has become a
common modification for racers, allowing the top speed to be increased far beyond
the safe operating speeds of a standard aluminum driveshaft.
Honda has used aluminium metal matrix composite cylinder liners in some of their
engines, including the B21A1, H22A and H23A, F20C and F22C, and the C32B used
in the NSX. Toyota has since used metal matrix composites in the Yamaha designed
2ZZ-GE engine which is used in the later Lotus Lotus Elise S2 versions as well as
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Toyota car models. Porsche also uses MMCs to reinforce the engine's cylinder sleeves
in the Boxster and 911.
The F-16 Fighting Falcon uses monofilament silicon carbide fibres in a titanium
matrix for a structural component of the jet's landing gear.
Specialized Bicycles has used aluminum MMC compounds for its top of the range
bicycle frames for several years. Griffen Bicycles also makes boron carbide-
aluminum MMC bike frames, and Univega briefly did so as well.
Some equipment in particle accelerators such as Radio Frequency Quadrupoles
(RFQs) or electron targets use copper MMC compounds such as Glidcop to retain the
material properties of copper at high temperatures and radiation levels.
MMCs are nearly always more expensive than the more conventional materials they are
replacing. As a result, they are found where improved properties and performance can justify
the added cost. Today these applications are found most often in aircraft components, space
systems and high-end or "boutique" sports equipment. The scope of applications will
certainly increase as manufacturing costs are reduced.
In comparison with conventional polymer matrix composites, MMCs are resistant to fire, can
operate in wider range of temperatures, do not absorb moisture, have better electrical and
thermal conductivity, are resistant to radiation, and do not display outgassing. On the other
hand, MMCs tend to be more expensive, the fiber-reinforced materials may be difficult to
fabricate, and the available experience in use is limited.
CERMET A cermet is a composite material composed of ceramic (cer) and metallic (met)
materials. A cermet is ideally designed to have the optimal properties of both a ceramic, such
as high temperature resistance and hardness, and those of a metal, such as the ability to
undergo plastic deformation. The metal is used as a binder for an oxide, boride, carbide, or
alumina. Generally, the metallic elements used are nickel, molybdenum, and cobalt.
Depending on the physical structure of the material, cermets can also be metal matrix
composites, but cermets are usually less than 20% metal by volume.
Cermets are used in the manufacture of resistors (especially potentiometers),
capacitors, and other electronic components which may experience high temperatures.
Cermets are being used instead of tungsten carbide in saws and other brazed tools due to their
superior wear and corrosion properties. Titanium nitride (TiN or TiCN), titanium carbide
(TiC) and similar can be brazed like tungsten carbide if properly prepared however they
require special handling during grinding.
More complex materials, known as Cermet 2 or Cermet II, are being utilized since
they give considerably longer life in cutting tools while both brazing and grinding like
Some types of cermets are also being considered for use as spacecraft shielding as
they resist the high velocity impacts of micrometeoroids and orbital debris much more
effectively than more traditional spacecraft materials such as aluminum and other metals.
Applications Ceramic-to-metal joints and seals
Cermets were first used extensively in ceramic-to-metal joint applications.
Construction of vacuum tubes was one of the first critical systems, with the electronics
industry employing and developing such seals. German scientists recognized that vacuum
tubes with improved performance and reliability could be produced by substituting ceramics
for glass. Ceramic tubes can be outgassed at higher temperatures. Because of the high-
temperature seal, ceramic tubes withstand higher temperatures than glass tubes. Ceramic
tubes are also mechanically stronger and less sensitive to thermal shock than glass tubes.
Today, cermet vacuum tube coatings have proved to be key to solar hot water systems.
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Ceramic-to-metal mechanical seals have also been used. Traditionally they have been used in
fuel cells and other devices that convert chemical, nuclear, or thermionic energy to electricity.
The ceramic-to-metal seal is required to isolate the electrical sections of turbine-driven
generators designed to operate in corrosive liquid-metal vapors.
Bioceramics Bioceramics play an extensive role in biomedical materials. The development of these
materials and diversity of manufacturing techniques has broadened the applications that can
be used in the human body. They can be in the form of thin layers on metallic implants,
composites with a polymer component, or even just porous networks. These materials work
well within the human body for several reasons. They are inert, and because they are
resorbable and active, the materials can remain in the body unchanged. They can also
dissolve and actively take part in physiological processes, for example, when hydroxylapatite,
a material chemically similar to bone structure, can integrate and help bone grow into it.
Common materials used for bioceramics include alumina, zirconia, calcium phosphate, glass
ceramics, and pyrolytic carbons.
One important use of bioceramics is in hip replacement surgery. A hip joint
essentially is a multiaxial ball and socket. The materials used for the replacement hip joints
were usually metals such as titanium with the hip socket usually lined with plastic. The
multiaxial ball was tough metal ball but was eventually replaced with a longer lasting ceramic
ball. This reduced the roughening associated with the metal wall against the plastic lining of
the artificial hip socket. The use of ceramic implants extended the life of the hip replacement
Cermets are also used in dentistry as a material for fillings and prostheses.
Cermets in transportation Ceramic parts have been used in conjunction with metal parts as friction materials for
brakes and clutches.
Other applications The United States Army and British Army have had extensive research in the
development of cermets. These include the development of lightweight ceramic projectile
proof armor for soldiers and also Chobham armor.
Cermets are also used in machining on cutting tools.
A cermet of depleted fissiable material (e.g. uranium, plutonium) and sodalite has
been researched for its benefits in the storage of nuclear waste. Similar composites have also
been researched for use as a fuel source.
Kevlar is the registered trademark for a light, strong para-aramid synthetic fiber,
related to other aramids such as Nomex and Technora. Developed at DuPont in 1965 by
Stephanie Kwolek, It was first commercially used in the early 1970s as a replacement for
steel in racing tires. Typically it is spun into ropes or fabric sheets that can be used as such or
as an ingredient in composite material components.
Currently, Kevlar has many applications, ranging from bicycle tires and racing sails to
body armor because of its high tensile strength-to-weight ratio—famously: "...5 times
stronger than steel on an equal weight basis..."
A similar fiber called Twaron with roughly the same chemical structure was
introduced by Akzo in 1978, and now manufactured by Teijin.
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When Kevlar is spun, the resulting fiber has great tensile strength (ca. 3 620 MPa),
and a relative density of 1.44. When used as a woven material, it is suitable for mooring lines
and other underwater applications.
There are three grades of Kevlar: (i) Kevlar, (ii) Kevlar 29, and (iii) Kevlar 49.
Typically, Kevlar is used as reinforcement in tires and rubber mechanical goods. Kevlar 29's
industrial applications are as cables, in asbestos replacement, brake linings, and body armor.
Kevlar 49 has a higher strength, and is used in plastic reinforcement for boat hulls, airplanes,
and bicycles. The ultraviolet light component of sunlight degrades and decomposes Kevlar, a
problem known as UV degradation, and so it is rarely used outdoors without protection
Kevlar is synthesised in solution from the monomers 1,4-phenylene-diamine (para-
phenylenediamine) and terephthaloyl chloride in a condensation reaction yielding
hydrochloric acid as a byproduct. The result has liquid-crystalline behaviour, and mechanical
drawing orients the polymer chains in the fiber's direction. Hexamethylphosphoramide
(HMPA) was the polymerization solvent first used, but toxicology tests demonstrated it
provoked tumors in the noses of rats, so DuPont replaced it by a N-methyl-pyrrolidone and
calcium chloride as the solvent. As this process was patented by Akzo (see above) in the
production of Twaron, a patent war ensued.
Kevlar (poly paraphenylene terephthalamide) production is expensive because of the
difficulties arising from using concentrated sulfuric acid, needed to keep the water-insoluble
polymer in solution during its synthesis and spinning.
Fibers of Kevlar consist of long molecular chains produced from PPTA (poly-
paraphenylene terephthalamide). There are many inter-chain bonds making the material
extremely strong. Kevlar derives part of its high strength from inter-molecular hydrogen
bonds formed between the carbonyl groups and protons on neighboring polymer chains and
the partial pi stacking of the benzenoid aromatic stacking interactions between stacked
strands. These interactions have a greater influence on Kevlar than the van der Waals
interactions and chain length that typically influence the properties of other synthetic
polymers and fibers such as Dyneema. The presence of salts and certain other impurities,
especially calcium, could interfere with the strand interactions and caution is used to avoid
inclusion in its production. Kevlar's structure consists of relatively rigid molecules which
tend to form mostly planar sheet-like structures rather like silk protein.
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For a polymer, Kevlar has very good resistance to high temperatures, and maintains
its strength and resilience down to cryogenic temperatures (-196°C); indeed, it is slightly
stronger at low temperatures.
At higher temperatures the tensile strength is immediately reduced by about 10-20%,
and after some hours the strength progressively reduces further. For example at 160°C about
10% reduction in strength occurs after 500 hours. At 260°C 50% strength reduction occurs
after 70 hours. At 450°C Kevlar sublimates.
Kevlar is well-known as a component of modern personal armor such as combat
helmets, Ballistic face masks and Ballistic vests. The PASGT helmet and vest used by United
States military forces since the early 1980s both have Kevlar as a key component, as do their
replacements. Other military uses include bulletproof facemasks used by sentries. Civilian
applications include Kevlar reinforced clothing for motorcycle riders to protect against
abrasion injuries and also Emergency Service's protection gear if it involves high heat (e.g.,
tackling a fire), and Kevlar body armor such as vests for police officers, security, and SWAT.
It is used as an inner lining for some bicycle tires to prevent punctures, and due to its
excellent heat resistance, is used for fire poi wicks. It is used for motorcycle safety clothing,
especially in the areas featuring padding such as shoulders and elbows. It was also used as
speed control patches for certain Soap Shoes models. In Kyudo or Japanese archery, it may
be used as an alternative to more expensive hemp for bow strings. It is one of the main
materials used for paraglider suspension lines.
Audio equipment It has also been found to have useful acoustic properties for loudspeaker cones,
specifically for bass and midrange drive units.
Drumheads Kevlar is sometimes used as a material in high tension drum heads usually used on
marching snare drums. It allows for an extremely high amount of tension, resulting in a
cleaner sound. There is usually some sort of resin poured onto the kevlar to make the head
airtight, and a nylon top layer to provide a flat striking surface. This is one of the primary
types of marching snare drum heads. Remo's "Falam Slam" Patch is made with kevlar and is
used to reinforce bass drum heads where the beater strikes.
Woodwind reeds Kevlar is used in the woodwind reeds of Fibracell. The material of these reeds is a
composite of aerospace materials designed to duplicate the way nature constructs cane reed.
Very stiff but sound absorbing Kevlar fibers are suspended in a lightweight resin formulation.
Rope and cable The fiber is used in woven rope and in cable, where the fibers are kept parallel within
a polyethylene sleeve. Known as "Parafil", the cables have been used in small suspension
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bridges such as the bridge at Aberfeldy in Scotland. They have also been used to stabilise
cracking concrete cooling towers by circumferential application followed by tensioning to
close the cracks.
Electricity generation Kevlar was used by scientists at Georgia Institute of Technology as a base textile for
an experiment in electricity-producing clothing. This was done by weaving zinc oxide
nanowires into the fabric. If successful, the new fabric would generate about 80 milliwatts per
Fiber Optic Cable Kevlar is widely used as a protective outer sheath for optical fiber cable, as its
strength protects the cable from damage and kinking.
Building construction A retractable roof of over 60,000 square feet (5,575 square metres) of Kevlar was a
key part of the design of Montreal's Olympic stadium for the 1976 Summer Olympics. It was
spectacularly unsuccessful, as it was completed ten years late and replaced just ten years later
in May 1998 after a series of problems.
Brakes The chopped fiber has been used as a replacement for asbestos in brake pads. Dust
produced from asbestos brakes is toxic, while aramids are a benign substitute.
Expansion joints and hoses Kevlar can be found as a reinforcing layer in rubber bellows expansion joints and rubber
hoses, for use in high temperature applications, and for its high strength. It is also found as a
braid layer used on the outside of hose assemblies, to add protection against sharp objects.
Aramid fibers are widely used for reinforcing composite materials, often in
combination with carbon fiber and glass fiber. The matrix for high performance composites is
usually epoxy resin. Typical applications include monocoque bodies for F1 racing cars,
helicopter rotor blades, tennis, table tennis, badminton and squash rackets, kayaks, cricket
bats, and field hockey, ice hockey and lacrosse sticks.
Solid The solid state of matter is one of the three main states that matter is found in. The
solid state is characterized by structural rigidity and resistance to changes of shape or volume.
Unlike a liquid, a solid object does not flow to take on the shape of its container, nor does it
expand to fill the entire volume available to it like a gas does. The atoms in a solid are tightly
bound to each other, either in a regular geometric lattice, or in a less ordered structure.
The branch of physics that deals with solids is called solid-state physics, and is the main
branch of condensed matter physics (which also includes liquids). Materials science is
primarily concerned with the physical and chemical properties of solids. Solid-state chemistry
is especially concerned with the synthesis of novel materials, as well as the science of
identification and chemical composition.
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Microscopic description Solid materials are formed from densely-packed atoms, with intense interaction forces
between them. These interactions are responsible for the mechanical (e.g. hardness and
elasticity), thermal, electrical, magnetic and optical properties of solids. Depending on the
material involved and the conditions in which it was formed, the atoms may be arranged in a
regular, geometric pattern (crystalline solids, which include metals and ordinary water ice) or
irregularly (an amorphous solid such as common window glass).
The forces between the atoms in a solid can take a variety of forms. For example, in a
crystal of sodium chloride (common salt), the crystal is made up of ionic sodium and
chlorine, and held together with ionic bonds. In others, the atoms share electrons and form
covalent bonds. In metals, electrons are shared in metallic bonding. Other solids, particularly
including most organic compounds, are held together with van der Waals forces resulting
from the polarisation of the electronic charge cloud on each molecule. The differences
between the types of solid result from the differences between their bonding.
Crystal and glass In crystalline solids, the atoms or molecules that compose the solid are packed closely
together. These constituent elements have fixed positions in space relative to each other. This
accounts for the solid's structural rigidity. In mineralogy and crystallography, a crystal
structure is a unique arrangement of atoms in a crystal. A specific symmetry or crystal
structure is composed of a Bravais lattice which is typically represented by a single unit cell.
The unit cell is periodically repeated in three dimensions on a lattice. The spacings between
unit cells in various directions are called lattice parameters. The symmetry properties of the
crystal are embodied in its space group. A crystal's structure and symmetry play a role in
determining many of its physical properties, such as cleavage, electronic band structure, and
Glasses do not exhibit the long-range order exhibited by crystalline substances.
Strongly supercooled liquids behave partly as liquids, partly as glasses, depending on the
time scale of observation (see glass transition).
Much work has been done to elucidate the primary microstructural features of glass
forming substances (e.g. silicates) on both small (microscopic) and large (macroscopic)
scales. One emerging school of thought is that a glass is simply the "limiting case" of a
polycrystalline solid at small crystal size. Within this framework, domains, exhibiting various
degrees of short-range order, become the building blocks of both metals and alloys, as well as
glasses and ceramics. The microstructural defects of both within and between these domains
provide the natural sites for atomic diffusion and the occurrence of viscous flow and plastic
deformation in solids.
Classes of solids Metals
The study of metallic elements and their alloys makes up a significant portion of the
fields of solid-state chemistry, physics, materials science and engineering. Generally
speaking, metals have delocalized electrons and an electronic band structure containing
partially filled bands. The resulting large number of free electrons (often referred to as a "sea
of electrons") gives metals their high values of electrical and thermal conductivity. The free
electrons also prevent transmission of visible light, making metals opaque, shiny and
When considering the electronic band structure and binding energy of a metal, it is
necessary to take into account the positive potential caused by the specific arrangement of the
ion cores, which is periodic in crystals. The most important consequence of the periodic
potential is the formation of a small band gap at the boundary of the Brillouin zone.
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Mathematically, the potential of the ion cores can be treated by various models, the simplest
being the nearly free electron model.
Mechanical properties of metals include their ductility, which is largely due to their
inherent capacity for plastic deformation. Thus, elasticity in metals can be described by
Hooke's Law for restoring forces, where the stress is linearly proportional to the strain.
Larger forces in excess of the elastic limit may cause a permanent (irreversible) deformation
of the object. This is what is known in the literature as plastic deformation -- or plasticity.
This irreversible change in atomic arrangement may occur as a result of either (or both) of the
The action of an applied force (or work)
A change in temperature (or heat).
In the former case, the applied force may be tensile (pulling) force, compressive
(pushing) force, shear, bending or torsion (twisting) forces. In the latter case, the most
significant factor which is determined by the temperature is the mobility of the structural
defects such as grain boundaries, point vacancies, line and screw dislocations, stacking faults
and twins in both crystalline and non-crystalline solids. The movement or displacement of
such mobile defects is thermally activated, and thus limited by the rate of atomic diffusion.
Viscous flow near grain boundaries, for example, can give rise to internal slip, creep,
fatigue in metals. It can also contribute to significant changes in the microstructure like grain
growth and localized densification due to the elimination of intergranular porosity. Screw
dislocations may slip in the direction of any lattice plane containing the dislocation, while the
principal driving force for "dislocation climb" is the movement or diffusion of vacancies
through a crystal lattice.
Polymers Other than metals, polymers and ceramics are also an important part of materials
science. Polymers are the raw materials (the resins) used to make what we commonly call
plastics. Plastics are the final product, created after one or more polymers or additives have
been added to a resin during processing, which is then shaped into a final form. Polymers
which have been around, and which are in current widespread use, include carbon-based
polyethylene, polypropylene, polyvinyl chloride, polystyrene, nylons, polyesters, acrylics,
polyurethane, and polycarbonates, and silicium-based silicones. Plastics are generally
classified as "commodity", "speciality" and "engineering" plastics.
Ceramics A ceramic material may be defined as any inorganic polycrystalline solid or mineral.
Mechanically speaking, ceramic materials are brittle, hard, strong in compression, weak in
shearing and tension. Brittle materials may exhibit significant tensile strength by supporting a
static load. Toughness indicates how much energy a material can absorb before mechanical
failure, while fracture toughness (denoted KIc ) describes the ability of a material with
inherent microstructural flaws to resist fracture via crack growth and propagation. If a
material has a large value of fracture toughness, the basic principles of fracture mechanics
suggest that it will most likely undergo ductile fracture. Brittle fracture is very characteristic
of most ceramic and glass-ceramic materials which typically exhibit low (and inconsistent)
values of KIc.
Ceramic solids are chemically inert (or stable), and often are capable of withstanding
chemical erosion that occurs in an acidic or caustic environment. Ceramics generally can
withstand high temperatures ranging from 1,000 °C to 1,600 °C (1,800 °F to 3,000 °F).
Exceptions include non-oxide inorganic materials, such as nitrides, borides and carbides.
Ceramic engineering is the science and technology of creating solid-state devices from
inorganic, non-metallic materials. This is done either by the action of heat, or, at lower
temperatures, using precipitation reactions from high-purity chemical solutions. The term
includes the purification of raw materials, the study and production of the chemical
compounds concerned, their formation into components, and the study of their structure,
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composition and properties. Ceramic materials may have a crystalline or partly crystalline
structure, with long-range order on a molecular scale.
Glass ceramics may have an amorphous or glassy structure, with limited or short-
range molecular order. They are typically formed from a molten mass that solidifies on
cooling, or formed and matured by the action of heat. Glass by definition is not a ceramic
because, although it may be identical in chemical composition (e.g. glassy SiO2 vs.
crystalline quartz) it is an amorphous solid.
Traditional ceramic raw materials include clay minerals such as kaolinite, more recent
materials include aluminium oxide (alumina). The modern ceramic materials, which are
classified as advanced ceramics, include silicon carbide and tungsten carbide. Both are valued
for their abrasion resistance, and hence find use in such applications as the wear plates of
crushing equipment in mining operations. Advanced ceramics are also used in the medicine,
electrical and electronics industries.
Most ceramic materials, such as alumina and its compounds, are formed from fine
powders, yielding a fine grained polycrystalline microstructure which is filled with scattering
centers comparable to the wavelength of visible light. Thus, they are generally opaque
materials, as opposed to transparent materials. Recent nanoscale (e.g. sol-gel) technology has,
however, made possible the production of polycrystalline transparent ceramics such as
transparent alumina and alumina compounds for such applications as high-power lasers.
Composites Composite materials are structured materials composed of two or more macroscopic
phases. While there is considerable interest in composites with one or more non-ceramic
constituents, the greatest attention is on composites in which all constituents are ceramic.
These typically comprise two ceramic constituents: a continuous matrix, and a dispersed
phase of ceramic particles, whiskers, or short (chopped) or continuous ceramic fibers.
The challenge, as in wet chemical processing, is to obtain a uniform distribution of the
dispersed particle or fiber phase. Applications range from structural elements such as steel-
reinforced concrete, to the thermally insulative tiles used to protect the surface of NASA
Space Shuttles from the heat of re-entry into the Earth's atmosphere. Domestic examples can
be seen in the "plastic" casings of television sets, cell-phones and so on. These plastic casings
are usually a composite made up of a thermoplastic matrix such as acrylonitrile butadiene
styrene (ABS) in which calcium carbonate chalk, talc, glass fibers or carbon fibers have been
added for strength, bulk, or electro-static dispersion. These additions may be referred to as
reinforcing fibers, or dispersants, depending on their purpose.
Biomaterials Most natural (or biological) materials are complex composites whose mechanical
properties are often outstanding, considering the weak constituents from which they are
assembled. These complex structures, which have risen from hundreds of million years of
evolution, are inspiring materials scientists in the design of novel materials. Their defining
characteristics include structural hierarchy, multifunctionality and self-healing capability.
Self-organization is also a fundamental feature of many biological materials and the manner
by which the structures are assembled from the molecular level up.
The basic building blocks often begin with the 20 amino acids, and proceed to
polypeptides, polysaccharides, and polypeptides–saccharides. These compose the basic
proteins, which are the primary constituents of ‘soft tissues’ and are also present in most
biominerals. There are over 1000 proteins, including collagen, chitin, keratin, and elastin. The
‘hard’ phases of biomaterials are primarily strengthened by minerals, which nucleate and
grow in a biomediated environment that determines the size, shape and distribution of
individual crystals. The most important mineral phases hydroxyapatite, silica, and aragonite.
Thus, the principal mechanical characteristics and structures of biological ceramics,
polymer composites, elastomers, and cellular materials are being investigated. Molecular
self-assembly is found widely in biological organisms and provides the basis of a wide
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variety of biological structures. For example, the crystallization of inorganic materials in
nature generally occurs at ambient temperature and pressure. Yet the vital organisms through
which these inorganic materials form are able to create extremely precise and complex
structures. Understanding the process in which living organisms control the growth of
inorganic materials could lead to significant advances in materials science, opening the door
to novel synthesis techniques for nanoscale composite materials.
One system which has been under intense scientific scrutiny by several major research
groups is the microstructure of the mother-of-pearl (or nacre) portion of the abalone shell.
This natural material exhibits the highest mechanical strength and fracture toughness of any
non-metallic substance known. Electron microscopy has revealed neatly stacked (or ordered)
mineral tiles separated by thin organic sheets along with a macrostructure of larger periodic
growth bands which collectively form what scientists are currently referring to as a
hierarchical composite structure. (The term hierarchy simply implies that there is a range of
structural features which exist over a wide range of length scales). Early work showed that
the overall nacre composite consists of only 5 wt.% organic material. Yet the work necessary
to fracture the body was increased by up to 3000 times over inorganic CaCO3 crystals as a
result of the intricate hierarchy of structural organization.
Self-assembly is also emerging as a new strategy in chemical synthesis,
nanotechnology and biotechnology. Technical ceramics are in a very dynamic stage of
development because of the increasingly diverse nature of ceramic needs and opportunities.
This introduces an increasing need for improved properties, greater uniformity,
reproducibility and reliability. This is coupled with the need for larger scale, more efficient
production. All of these demands can benefit from further development in both basic science
and the engineering aspects of the field.
Semiconductors Semiconductors are materials that have an electrical resistivity (and conductivity)
between that of metallic conductors and non-metallic insulators. They can be found in the
periodic table moving diagonally downward right from boron. They separate the electrical
conductors (or metals, to the left) from the insulators (to the right).
Devices made from semiconductor materials are the foundation of modern
electronics, including radio, computers, telephones, etc. Semiconductor devices include the
transistor, solar cells, diodes and integrated circuits. Solar photovoltaic panels are large
semiconductor devices that directly convert light energy into electrical energy.
In a metallic conductor, current is carried by the flow of a "sea of electrons". In
semiconductors, current can be carried either by the flow of electrons or by the flow of
positively charged "holes" in the electronic band structure of the material. Silicon is used to
create most semiconductors. Other semiconductor materials of commercial interest include
germanium (Ge) and gallium arsenide (GaAs).
GLASS-REINFORCED PLASTIC Glass-reinforced plastic is a material made of a plastic reinforced by fine fibers
made of glass, also called GFK for Glass Fiber Komposit.
Like carbon fiber reinforced plastic, the composited material is commonly referred to
by the name of its reinforcing fibers (fiberglass). The plastic is thermosetting, most often
polyester or vinylester, but other plastics, like epoxy and thermoplastics are also used.
Production The manufacturing process for GRP fiber glass uses large furnaces to gradually melt
the sand/chemical mix to liquid form, then extrude it through bundles of very small orifices
(typically 17-25 micrometres in diameter for E-Glass, 9 micrometres for S-Glass). These
filaments are then 'sized' with a chemical solution. The individual filaments are now bundled
together in large numbers to provide a 'roving'. The diameter of the filaments, as well as the
number of filaments in the roving determine its 'weight'. This is typically expressed in yield-
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yards per pound (how many yards of fiber in one pound of material, thus a smaller number
means a heavier roving, example of standard yields are 225yield, 450yield, 675yield) or in
tex-grams per km (how many grams 1 km of roving weighs, this is inverted from yield, thus a
smaller number means a lighter roving, examples of standard tex are 750tex, 1100tex,
2200tex). These rovings are then either used directly in a composite application such as
pultrusion, filament wounding (pipe), gun roving (automated gun chops the glass into small
lengths and drops it into a jet of resin, projected onto the surface of a mold), or used in an
intermediary step, to manufacture fabrics such as chopped strand mat (CSM) (made of
randomly oriented small cut lengths of fiber all bonded together), woven fabrics, knit fabrics
or uni-directional fabrics.
Sizing A sort of coating, or primer, which both helps protect the glass filaments for
processing/manipulation as well as ensure proper bonding to the resin matrix, thus allowing
for transfer of shear loads from the glass fibers (which would buckle) to the thermoset plastic
(which is quite good at handling shear loads), without this 'bonding', the fibers can 'slip' in the
matrix and localised failure will ensue.
Properties An individual structural glass fiber is both stiff and strong in tension and
compression—that is, along its axis. Although it might be assumed that the fiber is weak in
compression, it is actually only the long aspect ratio of the fiber which makes it seem so; i.e.,
because a typical fiber is long and narrow, it buckles easily. On the other hand, the glass fiber
is unstiff and unstrong in shear—that is, across its axis. Therefore if a collection of fibers can
be arranged permanently in a preferred direction within a material, and if the fibers can be
prevented from buckling in compression, then that material will become preferentially strong
in that direction.
Furthermore, by laying multiple layers of fiber on top of one another, with each layer
oriented in various preferred directions, the stiffness and strength properties of the overall
material can be controlled in an efficient manner. In the case of glass-reinforced plastic, it is
the plastic matrix which permanently constrains the structural glass fibers to directions
chosen by the designer. With chopped strand mat, this directionality is essentially an entire
two dimensional plane; with woven fabrics or unidirectional layers, directionality of stiffness
and strength can be more precisely controlled within the plane.
A glass-reinforced plastic component is typically of a thin "shell" construction,
sometimes filled on the inside with structural foam, as in the case of surfboards. The
component may be of nearly arbitrary shape, limited only by the complexity and tolerances of
the mold used for manufacturing the shell.
Applications GRP is an immensely versatile material which combines lightweight with inherent
strength to provide a weather resistant finish, with a variety of surface texture and an
unlimited colour range available.
GRP was developed in the UK during the Second World War as a replacement for the
molded plywood used in aircraft radomes (GRP being transparent to microwaves). Its first
main civilian application was for building of boats, where it gained acceptance in the 1950s.
Its use has broadened to the automotive and sport equipment sectors as well as model aircraft,
although its use there is now partly being taken over by carbon fiber which weighs less per
given volume and is stronger both by volume and by weight. GRP uses also include hot tubs,
pipes for drinking water and sewers, office plant display containers and flat roof systems.
Advanced manufacturing techniques such as pre-pregs and fiber rovings extend the
applications and the tensile strength possible with fiber-reinforced plastics.
GRP is also used in the telecommunications industry for shrouding the visual
appearance of antennas, due to its RF permeability and low signal attenuation properties. It
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may also be used to shroud the visual appearance of other equipment where no signal
permeability is required, such as equipment cabinets and steel support structures, due to the
ease with which it can be molded, manufactured and painted to custom designs, to blend in
with existing structures or brickwork. Other uses include sheet form made electrical
insulators and other structural components commonly found in the power industries.
Storage tanks Storage tanks can be made of GRP with capacities up to about 300 tonnes. The
smaller tanks can be made with chopped strand mat cast over a thermoplastic inner tank
which acts as a preform during construction. Much more reliable tanks are made using woven
mat or filament wound fibre with the fibre orientation at right angles to the hoop stress
imposed in the side wall by the contents. They tend to be used for chemical storage because
the plastic liner (often polypropylene) is resistant to a wide range of strong chemicals. GRP
tanks are also used for septic tanks.
House building Glass reinforced plastics are also used in the house building market for the production
of roofing laminate, door surrounds, over-door canopies, window canopies and dormers,
chimneys, coping systems, heads with keystones and sills. The use of GRP for these
applications provides for a much faster installation and due to the reduced weight manual
handling issues are reduced. With the advent of high volume manufacturing processes it is
possible to construct GRP brick effect panels which can be used in the construction of
composite housing. These panels can be constructed with the appropriate insulation which
reduces heat loss.
Piping GRP and GRE pipe systems can be used for a variety of applications, above and under the
Cooling water systems
Drinking water systems
Waste water systems/Sewage systems
Construction methods Fiberglass hand lay-up operation
Resin is mixed with a catalyst (e.g. butanox LA) or hardener if working with epoxy,
otherwise it will not cure (harden) for days/ weeks. Next, the mold is wetted out with the
mixture. The sheets of fiberglass are placed over the mold and rolled down into the mold
using steel rollers. The material must be securely attached to the mold, air must not be
trapped in between the fiberglass and the mold. Additional resin is applied and possibly
additional sheets of fiberglass. Rollers are used to make sure the resin is between all the
layers, the glass is wetted throughout the entire thickness of the laminate, and any air pockets
are removed. The work must be done quickly enough to complete the job before the resin
starts to cure. Various curing times can be achieved by altering the amount of catalyst
Fiberglass spray lay-up operation The fiberglass spray lay-up process is similar to the hand lay-up process but the
difference comes from the application of the fiber and resin material to the mold. Spray-up is
an open-molding composites fabrication process where resin and reinforcements are sprayed
onto a mold. The resin and glass may be applied separately or simultaneously "chopped" in a
combined stream from a chopper gun. Workers roll out the spray-up to compact the laminate.
Wood, foam or other core material may then be added, and a secondary spray-up layer
imbeds the core between the laminates. The part is then cured, cooled and removed from the
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Pultrusion operation in this case fiberglass. Fibers (the glass material) are pulled from spools through a
device that coats them with a resin. They are then typically heat treated and cut to length.
Pultrusions can be made in a variety of shapes or cross-sections such as a W or S cross-
section. The word pultrusion describes the method of moving the fibers through the
machinery. It is pulled through using either a hand over hand method or a continuous roller
method. This is opposed to an extrusion which would push the material through dies.
Chopped strand mat Chopped strand mat or CSM is a form of reinforcement used in glass-reinforced
plastic. It consists of glass-fibers laid randomly across each other and held together by a
It is typically processed using the hand lay-up technique, where sheets of material are
placed in a mold and brushed with resin. Because the binder dissolves in resin, the material
easily conforms to different shapes when wetted out. After the resin cures, the hardened
product can be taken from the mold and finished.Using chopped strand mat gives a glass-
reinforced plastic with isotropic in-plane material properties.
Examples of GRP use Sailplanes, kit cars, sports cars, microcars, karts, bodyshells, boats, kayaks, flat roofs,
lorries, wind turbine blades.
Pods, domes and architectural features where a light weight is necessary.
Bodies for automobiles, such as the Chevrolet Corvette and Studebaker Avanti.
FRP tanks and vessels: FRP is used extensively to manufacture chemical equipments
and tanks and vessels. BS4994 is a British standard related to this application.
UHF-broadcasting antennas are often mounted inside a glass-reinforced plastic
cylinder on the pinnacle of a broadcasting tower
Thinkpads from Lenovo/IBM
Pultrusion is a continuous process of manufacturing of composite materials with
constant cross-section whereby reinforced fibers are pulled through a resin, possibly
followed by a separate preforming system, and into a heated die, where the resin
undergoes polymerization. Many resin types may be used in pultrusion including
polyester, polyurethane, vinylester and epoxy.
But the technology isn't limited to thermosetting resins. More recently, pultrusion has
also been successfully used with thermoplastic matrices such as polybutylene
terephthalate (PBT) either by powder impregnation of the glass fiber or by
surrounding it with sheet material of the thermoplastic matrix which is then molten
Extrinsic semiconductor An extrinsic semiconductor is a semiconductor that has been doped, that is, into
which a doping agent has been introduced, giving it different electrical properties than the
intrinsic (pure) semiconductor.
Doping involves adding dopant atoms to an intrinsic semiconductor, which changes
the electron and hole carrier concentrations of the semiconductor at thermal equilibrium.
Dominant carrier concentrations in an extrinsic semiconductor classify it as either an n-type
or p-type semiconductor. The electrical properties of extrinsic semiconductors make them
essential components of many electronic devices.
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The two types of extrinsic semiconductor
N-type semiconductors P-type semiconductors
Band structure of an n-type semiconductor. Dark circles in the conduction band are
electrons and light circles in the valence band are holes. The image shows that the electrons
are the majority charge carrier.
Extrinsic semiconductors with a larger electron concentration than hole concentration
are known as n-type semiconductors. The phrase 'n-type' comes from the negative charge of
the electron. In n-type semiconductors, electrons are the majority carriers and holes are the
minority carriers. N-type semiconductors are created by doping an intrinsic semiconductor
with donor impurities. In an n-type semiconductor, the Fermi energy level is greater than the
that of the intrinsic semiconductor and lies closer to the conduction band than the valence
As opposed to n-type semiconductors, p-type semiconductors have a larger hole
concentration than electron concentration. The phrase 'p-type' refers to the positive charge of
the hole. In p-type semiconductors, holes are the majority carriers and electrons are the
minority carriers. P-type semiconductors are created by doping an intrinsic semiconductor
with acceptor impurities. P-type semiconductors have Fermi energy levels below the intrinsic
Fermi energy level. The Fermi energy level lies closer to the valence band than the
conduction band in a p-type semiconductor.
Utilization of extrinsic semiconductors Extrinsic semiconductors are components of many common electrical devices. A
semiconductor diode (devices that allow current flow in only one direction) consists of p-type
and n-type semiconductors placed in junction with one another. Currently, most
semiconductor diodes use doped silicon or germanium.
Transistors (devices that enable current switching) also make use of extrinsic
semiconductors. Bipolar junction transistors (BJT) are one type of transistor. The most
common BJTs are NPN and PNP type. NPN transistors have two layers of n-type
semiconductors sandwiching a p-type semiconductor. PNP transistors have two layers of p-
type semiconductors sandwiching an n-type semiconductor.
Field-effect transistors (FET) are another type of transistor implementing extrinsic
semiconductors. As opposed to BJTs, they are unipolar and considered either N-channel or P-
channel. FETs are broken into two families, junction gate FET (JFET) and insulated gate FET
Other devices implementing the extrinsic semiconductor:
Intrinsic semiconductor An intrinsic semiconductor, also called an undoped semiconductor or i-type
semiconductor, is a pure semiconductor without any significant dopant species present. The
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number of charge carriers is therefore determined by the properties of the material itself
instead of the amount of impurities. In intrinsic semiconductors the number of excited
electrons and the number of holes are equal: n = p.
The conductivity of intrinsic semiconductors can be due to crystal defects or to
thermal excitation. In an intrinsic semiconductor the number of electrons in the conduction
band is equal to the number of holes in the valence band. An example is Hg0.8Cd0.2Te at room
An indirect gap intrinsic semiconductor is one where the maximum energy of the
valence band occurs at a different k (k-space wave vector) than the minimum energy of the
conduction band. Examples include silicon and germanium. A direct gap intrinsic
semiconductor is one where the maximum energy of the valence band occurs at the same k as
the minimum energy of the conduction band. Examples include gallium arsenide.
A silicon crystal is different from an insulator because at any temperature above
absolute zero temperature, there is a finite probability that an electron in the lattice will be
knocked loose from its position, leaving behind an electron deficiency called a "hole".
If a voltage is applied, then both the electron and the hole can contribute to a small
current flow. The conductivity of a semiconductor can be modeled in terms of the band
theory of solids. The band model of a semiconductor suggests that at ordinary temperatures
there is a finite possibility that electrons can reach the conduction band and contribute to
The term intrinsic here distinguishes between the properties of pure "intrinsic" silicon
and the dramatically different properties of doped n-type or p-type semiconductors.
Electrons and Holes: In an intrinsic semiconductor such as silicon at temperatures
above absolute zero, there will be some electrons which are excited across the band gap into
the conduction band and which can produce current. When the electron in pure silicon
crosses the gap, it leaves behind an electron vacancy or "hole" in the regular silicon lattice.
Under the influence of an external voltage, both the electron and the hole can move across the
material. In an n-type semiconductor, the dopant contributes extra electrons, dramatically
increasing the conductivity. In a p-type semiconductor, the dopant produces extra vacancies
or holes, which likewise increase the conductivity. It is however the behavior of the p-n
junction which is the key to the enormous variety of solid-state electronic devices.
Tensile strength Tensile strength (σUTS or SU ) is indicated by the maxima of a stress-strain curve
and, in general, indicates when necking will occur. As it is an intensive property, its value
does not depend on the size of the test specimen. It is, however, dependent on the preparation
of the specimen and the temperature of the test environment and material.
Tensile strength, along with elastic modulus and corrosion resistance, is an important
parameter of engineering materials used in structures and mechanical devices. It is specified
for materials such as alloys, composite materials, ceramics, plastics and wood.
Explanation There are three definitions of tensile strength:
The stress at which material strain changes from elastic deformation to plastic
deformation, causing it to deform permanently.
The maximum stress a material can withstand when subjected to tension, compression
or shearing. It is the maximum stress on the stress-strain curve.
The stress coordinate on the stress-strain curve at the point of rupture.
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Testing Typically, the testing involves taking a small sample with a fixed cross-section area,
and then pulling it with a controlled, gradually increasing force until the sample changes
shape or breaks.
When testing metals, indentation hardness correlates linearly with tensile strength.
This important relation permits economically important nondestructive testing of bulk metal
deliveries with lightweight, even portable equipment, such as hand-held Rockwell hardness
Flexural strength Flexural strength, also known as modulus of rupture, bend strength, or fracture
strength, a mechanical parameter for brittle material, is defined as a material's ability to resist
deformation under load. The transverse bending test is most frequently employed, in which a
rod specimen having either a circular or rectangular across section is bent until fracture using
a three point flexural test technique. The flexural strength represents the highest stress
experienced within the material at its moment of rupture. It is measured in terms of stress.
In mechanical engineering, ultimate failure describes the breaking of a material. In
general there are two types or failure: fracture and buckling. Fracture of a material
occurs when either an internal or external crack elongates the width or length of the
material. In ultimate failure this will result in one or more breaks in the material.
Buckling occurs when compressive loads are applied to the material and instead of
cracking the material bows. This is undesirable because most tools that are designed
to be straight will be inadequate if curved. If the buckling continues the material will
create tension on the inner side of the material and compression on the outer part, thus
fracturing the material.
In engineering there are multiple types of failure based upon the application of the
material. In many machine applications any change in the part due to yielding will
result in the machine piece needing to be replaced. Although this deformation or
weakening of the material is not the technical definition of ultimate failure, the piece
has failed. In most technical applications pieces are rarely allowed to reach their
ultimate failure or breakage point, instead for safety factors they are removed at the
first signs of significant wear.
There are two different types of fracture: brittle and ductile. Each of these types of
failure occur based on the material's ductility. Brittle failure occurs with little to no
plastic deformation before fracture. An example of this would be stretching a clay pot
or rod, when it is stretched it will not neck or elongate merely break into two ore more
pieces. While applying a tensile stress to a ductile material, instead of immediately
breaking the material will instead elongate. The material will begin by elongating
uniformly until it reaches the yield (engineering) point, then the material will begin to
neck. When necking occurs the material will begin to stretch more in the middle and
the radius will decrease. Once this begins the material has entered a stage called
plastic deformation. Once the material has reached its ultimate tensile strength it will
elongate more easily until it reaches ultimate failure and breaks.
There are numerous methods to improve the strength of a material and therefore
increase its ultimate failure point. Cold working a material is done by plastically
deforming a material below its recrystallization temperature. This is most commonly
seen by manufacturers hammering a material at room temperature. Hot working is any
plastic deformation that is done above the recrystallization temperature. Cold working
remains less effective because it is done below the recrystallization factor, but also
remains more accurate. Because of thermal expansion and contraction of a material
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when heated hot working adds additional strength but also adds a rougher surface due
Heat treatment of a material is when the material is heated to extreme temperatures
and quenching the material in water to cool it quickly. By heating the material to these
very high temperatures the materials atomic structure is capable of being altered into a
stronger material. This will also hopefully remove any cracks or deformations that
will weaken a material. These cracks will weaken a material because they focus the
stress or strain of a material to a particular point.
Toughness Toughness, in materials science and metallurgy, is the resistance to fracture of a
material when stressed. It is defined as the amount of energy per volume that a material can
absorb before rupturing.
Toughness tests Tests can be done by using a pendulum and some basic physics to measure how much
energy it will hold when released from a particular height. By having a sample at the bottom
of its swing a measure of toughness can be found, as in the Charpy and Izod impact tests.
Toughness and strength Strength and toughness are related. A material may be strong and tough if it ruptures
under high forces, exhibiting high strains; on the other hand, brittle materials may be strong
but with limited strain values, so that they are not tough. Generally speaking, strength
indicates how much force the material can support, while toughness indicates how much
energy a material can absorb before rupture.