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Material Science

Composite materials

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Composite Materials A composite material consists of two

independent and dissimilar materials

In which one material forms the matrix to bond together the other, reinforcing material

The matrix and the reinforcement are chosen so that their desirable mechanical properties complement each other, whilst their deficiencies are neutralised.

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Composite Materials• Composites include reinforced metals, polymers, ce

ramics and concretes• Reinforced concrete is composite, being steel rod in

a matrix of concrete• Many plastic components are composite materials, i

nvolving glass fibres and carbon fibres• Cermets, widely used for cutting tool tips, are ceram

ic particles in a metal matrix. • Wood is a natural composite consisting of tubes of c

ellulose bonded by a natural polymer called lignin.

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Glass fibres Glass, in the form of fibre, is considerably

stronger than when in the 'bulk' condition and can be used in engineering as a structural material

The high strength of glass fibres is due partly to the fact that they are free from scratches and other surface defects, and partly to the surface tension effects resulting from the high surface to volume ratio of the fine fibres

Four classes are considered: E‑glass(electrical grade) C‑glass(chemical grade) S‑glass(high‑strength grade) M‑glass(high‑modulus grade)

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E‑glass (electrical grade) It has good insulation properties and is

used for making glass reinforced printed circuit boards for the electronics industry.

It is not attacked by water or alkalis and has high strength

As well as electrical components it is the composition most widely used for general‑purpose mouldings

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C‑glass (chemical grade)

It is used for chemical plant equipment

It is low in aluminium oxide and calcium oxide and has good resistance to acid attack

It is also used for fibreglass surfacing mats, which must resist environmental attack

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S‑glass (high‑strength grade)

It is produced in continuous filaments for weaving into mats and fabrics for pressure vessels and boat hulls.

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M‑glass (high‑modulus grade)

It is an expensive material reserved for very high strength applications where exploitation of its special properties offsets its high cost.

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Carbon fibres These have higher elastic modulus and a lower

density than glass fibres and therefore, can be used to reinforce composite materials having a higher strength to weight ratio

Carbon fibres are produced by the pyrolysis of polyacrylonitrile filaments in an inert atmosphere

They may be classified as high‑strength fibres or high-modulus fibres

Its uses range widely over such diverse applications as fan blades for gas turbines, sports equipment, and racing‑car body panels

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Particle hardened materials These materials are commonly known as cermets

since they are metals hardened and strengthened by particles of ceramic materials uniformly distributed throughout the metallic matrix

The preformed compact of the powdered ingredients is then sintered

Cermets are widely used for cutting tools. For example, cemented carbides consist of particles of tungsten carbide or mixtures of tungsten and titanium carbides in a matrix of metallic cobalt.