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Composite Material Page | 1 Unit Second Composite Materials Prof. Shashank S. Bhamble Mechanical Engineering Department Shri Sant Gajanan Maharaj College of Engineering, Shegaon

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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.[1]

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

and strains/curvatures.

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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.[3]

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.[4]

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.

Examples Materials

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.

Vapor deposition

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

the matrix.

Applications Carbide drills are often made from a tough cobalt matrix with hard tungsten carbide

particles inside.

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 [1], allowing them

to weigh as much as 50% less while increasing stiffness. 3M has also used alumina

preforms for AMC pushrods. [2]

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

tungsten carbide.

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

against sunlight.


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.

Chemical properties

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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Thermal properties

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.

Other uses

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

square meter.

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.[citation needed]

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.

Composite materials

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

optical properties.

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

following factors:

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


Firewater systems

Cooling water systems

Drinking water systems

Waste water systems/Sewage systems

Gas 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

reusable mold.

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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.[1]

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.

A320 radome.

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:


Solar cells


Light-emitting diodes


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

electrical conduction.

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:

Yield strength

The stress at which material strain changes from elastic deformation to plastic

deformation, causing it to deform permanently.

Ultimate strength

The maximum stress a material can withstand when subjected to tension, compression

or shearing. It is the maximum stress on the stress-strain curve.

Breaking strength

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.

Ultimate failure

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

to oxidization.

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.