Composite material

•(or composites for short) are engineered materials made from two or more constituent materials with significantly different physical or chemical properties and which remain separate and distinct within the finished structure.

•Two types of constituent materials: - MATRIX and REINFORCEMENT

TYPES

The matrix material surrounds and supports the reinforcement materials by maintaining their relative positions. The reinforcements impart special physical (mechanical and electrical) properties to enhance the matrix properties.

Material properties – A COMBINATION OF THE TWO

Two Natural composites:

BONE and WOOD

Particle Reinforced Fibre Reinforced Structural

COMPOSITES

Large Dispersion Continuous Discontinuous laminates Sandwich

Particle Strengthened (Aligned) (short) panels

Aligned Randomly Oriented

Earliest examples

The most primitive composite materials comprised straw and mud in the form of bricks for building construction.

The ancient brick-making process can still be seen on Egyptian tomb paintings in the Metropolitan Museum of Art

Modern composites

• The most advanced examples are used on spacecraft in demanding environments.

• The most visible applications: roadways in the form of either steel and

portland cement concrete, Mastic asphalt and asphalt concrete.

• Engineered composite materials must be formed to shape.

• This involves placing the reinforcements while manipulating the matrix properties to achieve a melding event at or near the beginning of the component life cycle.

• Various methods used according to the end item design requirements.

• These methods are commonly named moulding or casting processes,with numerous variations

• The principle factors:

1. The natures of the chosen matrix and reinforcement materials.

2. Quantity of material to be produced. Large quantities to justify high capital expenditures for rapid and automated manufacturing technology.

Small production quantities with lower capital expenditures but higher labour costs at a correspondingly slower rate.

Mechanics• A polymer matrix material called a resin or

resin solution. • There are many different polymers available

depending upon the starting raw ingredients. Broad categories, each with numerous variations. The most common categories are known as polyester, vinyl ester, epoxy, phenolic, polyimide, polyamide, and others.

• The reinforcement materials: fibers & ground

minerals. • Fibers transformed into a textile material

such as a felt, fabric, knit or stitched construction.

• Advanced composite materials: a category comprising carbon fiber reinforcement and epoxy or polyimide matrix materials.

• These are the aerospace grade composites and typically involve laminate molding at high temperature and pressure to achieve high reinforcement volume fractions. These advanced composite materials feature high stiffness and/or strength to weight ratios.

• One component - a strong fibre such as fiberglass, quartz, kevlar, Dyneema or carbon fiber that gives the material its tensile strength

• another component (called a matrix)- a resin such as polyester, or epoxy that binds the fibres together, transferring load from broken fibers to unbroken ones and between fibers that are not oriented along lines of tension.

• The matrix chosen - flexible, prevents the fibers from buckling in compression.

• Some composites use an aggregate instead of, or in addition to, fibers.

• In terms of stress, fibers to resist tension, the matrix to resist shear, and all materials present serve to resist compression, including any aggregate.

• Composite materials - divided into two main categories:

1.Short fiber reinforced materials

2. continuous fiber reinforced materials

Continuous reinforced materials will often constitute a layered or laminated structure.

Shocks, impact, loadings 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.

Examples

• Fiber Reinforced Polymers or FRPs: – Classified by type of fiber:

• Wood (cellulose fibers in a lignin and hemicellulose matrix) • Carbon-fiber reinforced plastic or CFRP • Glass-fiber reinforced plastic or GFRP

– Classified by matrix: • Thermoplastic Composites

– short fiber thermoplastics – long fiber thermoplastics or long fiber reinforced thermoplastics – glass mat thermoplastics – continuous fiber reinforced thermoplastics

• Thermoset Composites • Reinforced carbon-carbon (carbon fiber in a graphite matrix)

• Metal matrix composites or MMC: – White cast iron – Hardmetal (carbide in metal matrix) – Metal-intermetallic laminate

• Ceramic matrix composites: – Bone (hydroxyapatite reinforced with collagen fibers) – Cermet (ceramic and metal) – Concrete

• Organic matrix/ceramic aggregate composites – Asphalt concrete – Mastic asphalt – Mastic roller hybrid – Dental composite – Syntactic foam – Mother of Pearl

• Chobham armour

• Engineered wood – Plywood – Oriented strand board – Wood plastic composite (recycled wood

fiber in polyethylene matrix) – Pykrete (sawdust in ice matrix)

• Plastic-impregnated or laminated paper or textiles – Arborite – Formica (plastic)

• Buckypaper Composites

Road design

• consists of two important technical aspects:

• geometrical road design

• structural road design

• Once these activities are completed, construction of the pavement can begin. First the native soil, known as the subgrade, is compacted. Weak soils may also be stabilized with additives such as portland cement and quicklime, or dug out and replaced with imported soils.

• Then a base course consisting of gravel or crushed stone is usually placed on the subgrade and compacted. On top of the base course is placed a surface course which typically consists of asphalt concrete or portland cement concrete. This surface course strengthens the pavement structure by spreading out the vehicle loads applied to the subgrade. It also provides a smooth and high-friction surface for vehicles to drive on.

• Modern roads, and indeed many ancient ones, such as those built by the Romans, feature a convex transverse profile known as superelevation or camber. This is designed to allow water to drain away from the road to its edges. Water is then carried away by gutters to drains placed at intervals. Some roads don't have gutters and water simply drains away to a naturally porous verge, or into ditches. Modern roads that carry motor traffic also employ camber in curves to aid traffic stability by allowing them to "bank into" the bend to some extent.

• On the side of the road there may be retroreflectors on pegs, rocks or crash barriers, white toward the direction of the traffic on that side of the road, and red toward the other direction. In the road surface there may be cat's eyes: retroreflectors that protrude slightly, but which can be driven over without damage.

• Road signs are often also made retroreflective or even illuminated in rare circumstances. For greater visibility of road signs at daytime, sometimes fluorescence is applied to get very bright colors.

All-weather road - an unpaved road that is constructed of material (particularly gravel) that does not create mud during rainfall.

Unpaved road - a road without a bound surface layer (such as asphalt concrete or portland cement concrete).

Types of unpaved roads include dirt roads and gravel roads. Unpaved roads are much cheaper to construct than paved roads, but may be more expensive to maintain especially when they have high traffic

volumes. The cost of operating a vehicle on an unpaved road is also much higher than on a paved road.

An unusual road at London Heathrow Airport, England. A British Airways Boeing 777-200 is being towed across a public road on its way

to the maintenance hangars.

Reinforced carbon-carbon

• Reinforced Carbon-Carbon (carbon-carbon or RCC) is a composite material consisting of carbon fiber reinforcement in a matrix of graphite, often with a silicon carbide coating to prevent oxidation. It was developed for the nose cones of intercontinental ballistic missiles, and is most widely known as the material for the nose cone and leading edges of the space shuttle.

• Carbon-carbon is well-suited to structural applications at high temperatures, or where thermal shock resistance and/or a low coefficient of thermal expansion is needed. While it is less brittle than many other ceramics, it lacks impact resistance; Space Shuttle Columbia was destroyed after one of its RCC panels was broken by the impact of a piece of foam insulation from the Space Shuttle External Tank. This was a catastrophic failure partly because original shuttle design requirements did not consider such a violent impact to be likely.

• The material is made in three stages:• First, material is laid up in its intended final shape, with

carbon filament and/or cloth surrounded by an organic binder such as plastic or pitch. Often, coke or some other fine carbon aggregate is added to the binder mixture.

• Second, the lay-up is heated, so that pyrolysis transforms the binder to relatively pure carbon. The binder loses volume in the process, so that voids form; the addition of aggregate reduces this problem, but does not eliminate it.

• Third, the voids are gradually filled by forcing a carbon-forming gas such as acetylene through the material at a high temperature, over the course of several days. This long heat treatment process also allows the carbon to form into larger graphite crystals, and is the major reason for the material's high cost, exceeding $100,000 per panel.

Metal matrix composite

• A metal matrix composite (MMC) is a type of 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 aluminum matrix to synthesize composites containing low density and high strength. However, carbon reacts with aluminum 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.

• Matrix• 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 aluminum, magnesium, or titanium, and provides a compliant support for the reinforcement. In high temperature applications, cobalt and cobalt-nickel alloy matricies are common.

• Reinforcement

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.

• 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.

• 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 dicontinuous 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. [1]

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 Aluminum 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 aluminum matrix insert for strengthening cast aluminum disc brake calipers [2], allowing them to weigh as much as 50% less while increasing stiffness.

• Toyota has since used metal matrix composites in the 2ZZ-GE engine block, and the Porsche Boxster and 911 use MMCs to reinforce the engine's cylinder sleeves. (Lotus uses the 2ZZ-GE in later Elise S2 versions). The 2ZZ-GE engine is actually designed and built by Yamaha, as were the Iron-block Toyota 4A-GE, etc. Prior, Honda had already used Aluminum MMC in its high-performance engine blocks such as the H22 and later the K20.

• 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 have used aluminium MMC compounds for their top of the range bicycle frames for several years.

• 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.

• 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.

• BUT, MMCs tend to be more expensive, the fiber-reinforced materials may be difficult to fabricate, and the available experience in use is limited.

Concrete.• Concrete is a construction material that consists, in its most

common form, of Portland cement, construction aggregate (generally gravel and sand) and water.

• Concrete does not solidify from drying after mixing and placement; the water reacts with the cement in a chemical process known as hydration. This water is absorbed by the cement, which hardens, bonding the other components together and eventually creating a stone-like material.

• Concrete is used more than any other man made material on the planet[1]. It is used to make pavements, building structures, foundations, motorways/roads, overpasses, parking structures, brick/block walls and footings for gates, fences and poles.

• As of 2005 about six billion cubic meters of concrete are made each year, which equals one cubic meter for every person on Earth. Concrete powers a US$35 billion industry which employs over two million workers in the United States alone. Over 55,000 miles of freeways and highways in America are made of this material. China currently consumes 40% of world cement production.

Composition

• The composition of concrete is determined initially during mixing and finally during placing of fresh concrete. The type of structure being built as well as the method of construction determine how the concrete is placed and therefore the composition of the concrete mix (the mix design).

• Cement• Main article: Portland cement• Portland cement is the most common type of cement in

general usage. It is a basic ingredient of concrete, mortar and plaster

• Water• Potable water can be used for

manufacturing concrete. The w/c ratio (mass ratio of water to cement) is the key factor that determines the strength of concrete. A lower w/c ratio will yield a concrete which is stronger, while a higher w/c ratio yields a concrete with a lower strength

Aggregates

• The water and cement paste hardens and develops strength over time. In order to ensure an economical and practical solution, both fine and coarse aggregates are utilised to make up the bulk of the concrete mixture. Sand, natural gravel and crushed stone are mainly used for this purpose. However, it is increasingly common for recycled aggregates (from construction, demolition and excavation waste) to be used as partial replacements of natural aggregates, whilst a number of manufactured aggregates, including air-cooled blast furnace slag and bottom ash are also permitted.

Admixtures

• Admixtures are materials in the form of powder or fluids that are added to the concrete to give it certain characteristics not obtainable with plain concrete mixes. In normal use, admixture dosages are less than 5% by mass of cement, and are added to the concrete at the time of batching / mixing. The most common types of admixtures are:

• Accelerators speed up the hydration (hardening) of the concrete.

• Retarders slow the hydration of concrete. • Air-entrainers add and distribute tiny air bubbles in the

concrete, which will reduce damage during freeze-thaw cycles.

• Plasticizers can be used to increase the workability of plastic or "fresh" concrete, allowing it be placed more easily, with less consolidating effort. Superplasticisers allow a properly designed concrete to flow in place even around congested reinforcing bars, see self consolidating concrete described below. Alternatively, they can be used to reduce the water content of a concrete (water reducers) while maintaining workability. This improves its strength and durability characteristics.

• Pigments can be used to change the colour of concrete, for aesthetics.

• Additions• Additions are very fine inorganic materials that usually have

pozzolanic or latent hydraulic properties. They are added at the concrete mixer to improve the properties of concrete. The term is not used when the materials are added at the factory as constituents of blended cements.

• Fly ash: A by product of coal fired elgenerating plants, it is used to partially replace Portland cement (by up to 60% by mass). The properties of fly ash depend on the type of coal burnt. In general, silicious fly ash is pozzolanic, while calcareous fly ash has latent hydraulic properties.

• Ground granulated blast furnace slag (ggbs): A by product of steel production, is used to partially replace Portland cement (by up to 80% by mass). It has latent hydraulic properties.

• Silica fume: A byproduct of the production of silicon and ferrosilicon alloys. Silica fume is similar to fly ash, but has a particle size 100 times smaller. This results in a higher surface to volume ratio and a much faster pozzolanic reaction. Silica fume is used to increase strength and durability of concrete, but generally requires the use of superplasticizers for workability

Characteristics

• During hydration and hardening, concrete needs to develop certain physical and chemical properties. Among other qualities, mechanical strength, low moisture permeability, and chemical and volumetric stability are necessary.

• Workability• Workability (or consistency, as it is known in Europe) is the ability of

a fresh (plastic) concrete mix to fill the form / mould properly with the desired work (vibration) and without reducing the concrete's quality. Workability depends on water content, chemical admixtures, aggregate (shape and size distribution), cementitious content and age (level of hydration)

• Curing• Because the cement requires time to fully hydrate before it acquires

strength and hardness, concrete must be cured once it has been placed. Curing is the process of keeping concrete under a specific environmental condition until hydration is relatively complete. Good curing is typically considered to use a moist environment which promotes hydration, since increased hydration lowers permeability and increases strength, resulting in a higher quality material. Allowing the concrete surface to dry out excessively can result in tensile stresses, which the still-hydrating interior cannot withstand, causing the concrete to crack.

• Strength• Concrete has relatively high compressive strength, but

significantly lower tensile strength (about 10% of the compressive strength). As a result, concrete always fails from tensile stresses — even when loaded in compression. The practical implication of this is that concrete elements subjected to tensile stresses must be reinforced. Concrete is most often constructed with the addition of steel or fiber reinforcement. The reinforcement can be by bars (rebar), mesh, or fibres, producing reinforced concrete. Concrete can also be prestressed (reducing tensile stress) using internal steel cables (tendons), allowing for beams or slabs with a longer span than is practical with reinforced concrete alone.

• Elasticity• The modulus of elasticity of concrete is a funcion of the modulus of

elasticity of the aggregates and the cement matrix and their relative proportions. The modulus of elasticity of concrete is relatively linear at low stress levels but becomes increasing non-linear as matrix cracking develops. The elastic modulus of the paste may be in the order of 10 GPa and aggregates about 45 to 85 GPa. The concrete composite is then in the range of 30 to 50 GPa.

• Expansion and shrinkage• Concrete has a very low coefficient of thermal expansion. However if

no provision is made for expansion very large forces can be created, causing cracks in parts of the structure not capable of withstanding the force or the repeated cycles of expansion and contraction.

• As concrete matures it continues to shrink, due to the ongoing reaction taking place in the material. Brickwork made of clay tends to expand for some time after manufacture of the bricks, and the relative shrinkage and expansion of concrete and brickwork require careful accommodation when the two forms of construction interface.

• Cracking• Concrete is placed while in a wet (or plastic) state, and therefore can be

manipulated and molded as needed. Hydration and hardening of concrete during the first three days is critical. Abnormally fast drying and shrinkage due to factors such as evaporation from wind during placement may lead to increased tensile stresses at a time when it has not yet gained significant strength, resulting in shrinkage cracks. The early strength of the concrete can be increased by keeping it damp for a longer period during the curing process. Minimizing stress prior to curing minimizes cracking. High early-strength concrete is designed to hydrate faster, often by increased use of cement, which increases shrinkage and cracking.

• Creep• Creep is the term used to describe the permanent movement or deformation of

a material in order to relieve stresses within the material. Concrete which is subjected to forces is prone to creep. Creep can sometimes reduce the amount of cracking that occurs in a concrete structure or element, but it also must be controlled. The amount of primary and secondary reinforcing in concrete structures contributes to a reduction in the amount of shrinkage, creep and cracking.

• Because it is a fluid, concrete can be pumped to where it is needed. Here a concrete transport truck is feeding concrete to a concrete pumper, which is pumping it to where a slab is being poured

Types of concrete• Regular concreteRegular concrete is the lay term describing concrete that is produced by

following the mixing instructions that are commonly published on packets of cement, typically using sand or other common material as the aggregate, and often mixed in improvised containers. This concrete can be produced to yield a varying strength from about 10 MPa to about 40 MPa, depending on the purpose, ranging from blinding to structural concrete respectively. Many types of pre-mixed concrete are available which include powdered cement mixed with an aggregate, needing only water.

• High-strength concrete• High-strength concrete is concrete with a compressive strength generally greater than

6,000 pounds/square inch (40 MPa). High-strength concrete is made by lowering the water-cement (w/c) ratio to 0.35 or lower. Often silica fume is added to prevent the formation of free calcium hydroxide crystals in the cement matrix, which might reduce the strength at the cement-aggregate bond.

• Low w/c ratios and the use of silica fume make concrete mixes significantly less workable, which is particularly likely to be a problem in high-strength concrete applications where dense rebar cages are likely to be used. To compensate for the reduced workability, superplasticizers are commonly added to high-strength mixtures. Aggregate must be selected carefully for high-strength mixes, as weaker aggregates may not be strong enough to resist the loads imposed on the concrete and cause failure to start in the aggregate rather than in the matrix or at a void, as normally occurs in regular concrete.

• In some applications of high-strength concrete the design criterion is the elastic modulus rather than the ultimate compressive strength.

• Self-compacting concretes• During the 1980s a number of countries including Japan, Sweden and France developed a

range of concretes that were self-compacting. These self-compacting concretes (SCCs) are characterised by their extreme fluidity, behaving more like a thick fluid that is self-leveling, as opposed to the traditional concrete that needs consolidating, normally by vibration or packing.

• Shotcrete• Shotcrete uses compressed air to shoot (cast) concrete

onto (or into) a frame or structure. Shotcrete is frequently used against vertical soil or rock surfaces, as it eliminates the need for formwork. It is sometimes used for rock support, especially in tunnelling. Today there are two application methods for shotcrete: the dry-mix and the wet-mix procedure. In dry-mix the dry mixture of cement and aggregates is filled into the machine and conveyed with compressed air through the hoses. The water needed for the hydration is added at the nozzle. In wet-mix, the mixes are prepared with all necessary water for hydration. The mixes are pumped through the hoses. At the nozzle compressed air is added for spraying. For both methods additives such as accelerators and fiber reinforcement may be used. [3]

• The term Gunite is occasionally used for shotcrete, but properly refers only to dry-mix shotcrete, and once was a proprietary name.

• Pervious concrete• With pervious or "no fines" concrete, carefully controlled amounts of water

and cementitious materials are used to create a paste that forms a thick coating around aggregate particles. A pervious concrete mixture contains little or no sand (fines), creating a substantial void content. Using sufficient paste to coat and bind the aggregate particles together creates a system of highly permeable, interconnected voids that drains quickly. Typically, between 15% and 25% voids are achieved in the hardened concrete, and flow rates for water through pervious concrete are typically around 480 in./hr (0.34 cm/s, which is 5 gal/ft²/ min or 200 L/m²/min), although they can be much higher. Both the low mortar content and high porosity also reduce strength compared to conventional concrete mixtures, but sufficient strength for many applications is readily achieved.

• Pervious concrete pavement is a unique and effective means to address important environmental issues and support sustainable growth. By capturing rainwater and allowing it to seep into the ground, porous concrete is instrumental in recharging groundwater, reducing stormwater runoff, and meeting US Environmental Protection Agency (EPA) stormwater regulations. The use of pervious concrete is among the Best Management Practices (BMPs) recommended by the EPA, and by other agencies and geotechnical engineers across the country, for the management of stormwater runoff on a regional and local basis. This pavement technology creates more efficient land use by eliminating the need for retention ponds, swales, and other stormwater management devices. In doing so, pervious concrete has the ability to lower overall project costs on a first-cost basis.

• Cellular concrete• Aerated concrete produced by the addition of an air entraining agent

to the concrete (or a lightweight aggregate like vermiculite ) is sometimes called Cellular concrete. See also aerated autoclaved concrete.

• Roller-compacted concrete• Roller-compacted concrete, sometimes called rollcrete, is a low-

cement-content stiff concrete placed using techniques borrowed from earthmoving and paving work. The concrete is placed on the surface to be covered, and is compacted in place using large heavy rollers typically used in earthwork. The concrete mix achieves a high density and cures over time into a strong monolithic block. [4] Roller-compacted concrete is typically used for concrete pavement, but has also been used to build concrete dams, as the low cement content causes less heat to be generated while curing than typical for conventionally placed massive concrete pours.

• Asphalt concrete• Strictly speaking, asphalt is a form of concrete as well, with

bituminous materials replacing Portland cement as the binder.

Cermet• Cermet is an abbreviation for "'ceramic" and "metal." 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.

• It is used in the manufacture of resistors (especially potentiometers), capacitors, and other electronic components which may experience high temperatures.

• Some types of cermet 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.

• One application of these materials is their use in vacuum tube coatings which are key to solar hot water systems.

• Cermets are also used in dentistry as a material for fillings and prostheses.

Bone

• Matrix• The matrix comprises the other major constituent of

bone. It has inorganic and organic parts. The inorganic is mainly crystalline mineral salts and calcium, which is present in the form of hydroxyapatite. The matrix is initially laid down as unmineralized osteoid (manufactured by osteoblasts). Mineralisation involves osteoblasts secreting vesicles containing alkaline phosphatase. This cleaves phosphate groups and acts as the foci for calcium and phosphate deposition. The vesicles then rupture and act as a centre for crystals to grow on.

• The organic part of matrix is mainly Type I collagen. This is made intracellularly as tropocollagen and then exported. It then associates into fibrils. Also making up the organic part of matrix include various growth factors, the functions of which are not fully known. Other factors present include GAGs, osteocalcin, osteonectin, bone sialo protein and Cell Attachment Factor.

Engineered wood• Engineered wood, also called composite

wood, includes a range of derivative wood products which are manufactured by binding together wood strands, particles, fibers, or veneers with adhesives to form composite materials. These products are engineered to precise design specifications which are tested to meet national or international standards.

Types

• Glued laminated timber • Veneer-based

– Plywood – Laminated veneer lumber (LVL) – Stamina wood

• Parallam • Parallel strand lumber • Particle-based

– Oriented strand board (OSB) – Waferboard – Particleboard (chipboard)

• Fiberboard – Insulation board – Homasote – Masonite – Medium-density fiberboard (MDF) – Hardboard

• Mineral-bonded particleboard and fiberboard – Cement board – Fiber cement siding – Gypsum board – Papercrete

• Strawboard • Wood-plastic composite

Plywood• Plywood was the first type of engineered wood to be invented. It is

made from thin sheets of wood veneer, called plies or veneers. These are stacked together with the direction of each ply's grain differing from its neighbors' by 90° (cross-banding). The plies are bonded under heat and pressure with strong adhesives, usually phenol formaldehyde resin, making plywood a type of composite material. A common reason for using plywood instead of plain wood is its resistance to cracking, shrinkage, twisting/warping, and its general high degree of strength.

• Types of plywood• . Softwood plywood is usually made either of Douglas fir or spruce,

pine, and fir, and is typically used for construction and industrial purposes. Decorative plywood is usually faced with hardwood, including red oak, birch, maple, lauan (Philippine mahogany) and a large number of other hardwoods.

• Plywood meant for indoor use generally uses the less expensive urea-formaldehyde glue which has limited water resistance, while outdoor and marine grade plywood are designed to withstand rot and use a water resistant phenol-formaldehyde glue to prevent delamination

• Plywood production• Plywood production requires a good log, called a peeler, which is

generally straighter and larger in diameter than one required for processing into dimensioned lumber by a sawmill. The log is peeled into sheets of veneer which are then cut to the desired dimensions, dried, patched and glued together to form the plywood panel. The panel can then be patched, resized, sanded or otherwise refinished, depending on the market it was intended for.

• History• Plywood has been made for thousands of years; the earliest known

occurrence of plywood was in ancient Egypt around 3500 BC when wooden articles were made from sawn veneers glued together crosswise. This was originally done due to a shortage of fine wood. Thin sheets of high quality wood were glued over a substrate of lower quality wood for cosmetic effect, with incidental structural benefits. This manner of inventing plywood has occurred repeatedly throughout history. Many of the great English furniture makers such as Sheridan used veneer as a raw material.

• Plywood is used in any application that needs high quality wooden sheet material. -means resistance to cracking, breaking, shrinkage, twisting and warping.

• Plywood is also used as an engineering material for stressed skin applications. -used in this fashion for marine and aviation application since the WW II era.

• Most notable is the British De Havilland Mosquito bomber which was primarily made out of wood. Plywood is currently used in stressed skin applications quite succesfully, as in this contemporary RJ.03 IBIS homebuilt aircraft project.

Formica (plastic)• Formica is a brand of composite materials

manufactured by the Formica Corporation based in Cincinnati, Ohio, United States. In common use, the term refers to the company's classic product, a heat resistant, wipe-clean, plastic laminate of paper or fabric with melamine resin.

• Formica was invented in 1912 by Daniel J. O'Conor and Herbert A. Faber, then working at Westinghouse. They originally conceived it as an electrical insulator as a substitute "for mica", hence the name they chose when they left Westinghouse to set up their own company in 1913.

• In its early years, Formica manufactured insulation along with other products such as phenolic composite gears, developing its classic range of surfacing laminates from the late 1920s. During World War II it manufactured plastic-impregnated wooden airplane propellers. Post-war, engineering uses declined, ceasing in 1970 in favour of decorative laminates.

• In the last quarter of the 20th century, after a management buyout from its then owners American Cyanamid, it diversified with products such as solid surfacing, metal laminates and flooring materials.

Buckypaper

• Buckypaper is a thin sheet made from nanotubes that are 250 times stronger than steel and 10 times lighter. It is being developed by Dr. Ben Wang with other professors and students from the Florida State University research group the Florida Advanced Center for Composite Technologies (FAC2T). The project has already attracted research funding from the Army Research Lab and Air Force Office of Scientific Research.

• The name "Buckypaper" derives from buckyballs and shows great promise as a building material for everything from aerospace vehicles, body armor and next-generation electronics and displays.

• Background• Buckypaper is made from carbon nanotubes —

amazingly strong fibers about 1/50,000th the diameter of a human hair that were first developed in the early 1990s. Buckypaper owes its name to Buckminsterfullerene, or Carbon 60 — a type of carbon molecule whose powerful atomic bonds make it twice as hard as a diamond. Sir Harold Kroto, now a professor and scientist with FSU's department of chemistry and biochemistry, and two other scientists shared the 1996 Nobel Prize in Chemistry for their discovery of Buckminsterfullerene, nicknamed "buckyballs" for the molecules' spherical shape. Their discovery has led to a revolution in the fields of chemistry and materials science — and directly contributed to the development of buckypaper.

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