2. Composites
• Composites are the engineered materials which can
satisfy the requirements of modern technology as they
have several advantageous features such as
High specific strength (ratio of tensile strength to density)
High specific modulus (ratio of modulus of elasticity to
density)
High strength to weight ratio (low density high tensile strength)
High tensile strength at elevated temperatures
High toughness
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3. Composites
Definition:
• Composites are combinations of Two or more
chemically distinct materials which when combined
have improved properties over the individual materials.
• One of the material is called the reinforcing phase, is in
the form of fibers, sheets, or particles, and is
embedded in the other material called the matrix
phase.
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4. Composites could be natural or synthetic.
• Wood is a good example of a natural composite,
combination of cellulose fiber and lignin.
– The cellulose fiber provides strength and the lignin is the
"glue" that bonds and stabilizes the fiber.
• Bamboo is a very efficient wood composite structure.
The components are cellulose and lignin, as in all other
wood, however bamboo is hollow.
– This results in a very light yet stiff structure.
• The combination of mud and straw forms a composite
that is stronger than either the mud or the straw by
itself
Composites
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5. • The composite brick consisting of pieces of straw
embedded in a block of mud on drying exhibits
both compressive and tensile strength and hence
makes a good building material
• Another e.g. of a composite is concrete consisting
of aggregate (small stones or gravel) bound by
cement
– Concrete has good strength under compression and
its strength under tension can be improved by
embedding metal rods making it reinforced concrete.
Composites
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6. 6
• Typically, reinforcing materials are strong with low densities
while the matrix is usually a ductile or tough material.
• If the composite is designed and fabricated correctly, it
combines the strength of the reinforcement with the toughness
of the matrix to achieve a combination of desirable properties
not available in any single conventional material.
Reinforcement: fibers
Glass fibre
Carbon,
Metallic rods
Matrix materials
Polymers
Metals
Ceramics
Components of composite materials
Composites
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CLASSIFICATION OF COMPOSITES
May be classified on the basis of reinforcement and the
strengthening mechanism into three main types which include
1. Particle reinforced composites
2. Fibre reinforced composites
• Continuous fibers, unidirectionally aligned
• Discontinuous fibers, unidirectionally aligned
• Discontinuous fibers, randomly aligned
3. Structural composites
Composites
11. Large particle composites(Particle Reinforced composites)
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Consist of a high volume fraction of large sized
hard particles embedded in a relatively soft matrix.
The matrix and reinforcing particle share the load.
Large particle composites may involve metals,
polymers (plastics) and ceramics as matrices.
12. Examples:
Large particle composites
Concrete (cement with sand or gravel):cement is matrix, sand is
particulate,
Some polymers with added fillers
Carbon black reinforced rubber is an example of polymer
reinforced by particulate composites.
Carbon black is added to rubber in a range of 15-30% by weight
to improve the tensile strength, toughness and abrasion
resistance of rubber used for manufacturing tyres
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13. Large particle composites
• Cermets are metal matrix composites containing ceramic
particles
• A typical e.g. of cermet is the cermet carbide made of
extremely hard & refractory particles of ceramics such as WC
or TiC embeded in a matrix of ductile metal such as cobalt or
nickel
– These composites find use as cutting tools for hardened steel
Desired Characteristics
• Particles should be evenly distributed
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15. Dispersion strengthened composites
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• Contain extremely small sized particles in the range of
10-100 nm
• Dispersed in the matrix at low concentration which
increase the particle matrix interactions at the atomic
level thereby enhancing the strength of the matrix
against deformation.
16. Dispersion strengthened composites
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• The small particles hinder the migration of dislocations
within the matrix thereby restricting the plastic
deformation and increasing the tensile strength and
hardness of the matrix
17. Dispersion strengthened composites
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• Most of these composites involve metal matrix
composites
• Metal matrix composites of high strength can be
improved by dispersing small particles of metal or metal
oxides
e.g. Thoria (3%) dispersed in nickel (TD Nickel)
Al2O3 reinforced Al- sintered aluminum powder (SAP)
• TD Nickel retains its strenth at high temperatures and ni
doesn’t soften because of the dispersed microscopic
thoria (ThO2) particles
