Material Science

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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,
  ceramics and concretes
• Reinforced concrete is composite, being steel rod
  in a matrix of concrete
• Many plastic components are composite materials,
  involving glass fibres and carbon fibres
• Cermets, widely used for cutting tool tips, are
  ceramic particles in a metal matrix.
• Wood is a natural composite consisting of tubes
  of cellulose 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.