A numerical study on the thermal expansion coefficients of fiber

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Metals are strong and tough. They can be plastically deformed and strengthened
by a wide variety of methods. Metal matrix composite construction is used
primarily to increase the strength of low density metals such as aluminum alloys,
copper, titanium alloys and magnesium alloys. Another reason for constructing
MMCs is to increase the wear resistance and higher temperature performance. The
matrix material can be reinforced with continuous fibers and wires or by short fibers,
whiskers or particles. The complex nature of these materials and their manufacture
limits their use to high performance applications, in industries such as, automotive,
aerospace, and power. Some of the commonly used reinforcing materials are
boron/tungsten, titanium, alumina, graphite and silicon carbide.
Particle or discontinuously reinforced MMCs have become very important
because they are less expensive than continuous fiber reinforced composites and they
have relatively isotropic properties compared to fiber reinforced composites. Use of
nanometer-sized fullerenes (a form of carbon having a large molecule consist of an
empty cage of sixty or more carbon atoms, C 60 is the most common) as a reinforcement
has also been tried.
2.2.1.3 Ceramic Matrix Materials
Generally, ceramics consist of one or more metals combined with a nonmetal
such as oxygen, carbon or nitrogen. They have strong covalent and ionic bonds.
Ceramic materials in general have a very attractive package of properties such as
high strength and high stiffness at very high temperatures, chemical inertness, and
low density. This attractive package is defaced by one deadly defect; lack of
toughness. They are extremely susceptible to thermal shock and are easily damaged
during fabrication and/or service. It is therefore understandable that an overriding
consideration in ceramic matrix composites is to toughen the ceramics by incorporating
fibers in them and thus exploit the attractive high-temperature strength and
environmental resistance of ceramic materials without risking a catastrophic failure.
There are certain basic differences between CMCs and other composites. The general
philosophy in nonceramic matrix composites is to have the fiber bear a greater