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polymers of other polymers, metals, and also display isotropic
by random orientation to discontinuous ﬁbers. These compositesceramics and
propertiesalsoare less expensivecomposites. counterparts. Their properties, howand for bonding than their woven
ever, are inferior to those of woven composites because of the short ﬁber length and
aggregate composites Composites containing
inherent low ﬁber volume fraction.
reinforcements in the aggregate form such as sand and
14.3.6 Strengthening in Aggregate Composites
If, in contrast to a ﬁber, the reinforcing phase that precipitates a second direcaging A heat treatment has roughly equal dimensions in all
tions, the material is known as an aggregate composite. As shown in Figure 14.2–1, an
phase from a is concrete, which is a mixture of ﬁne aggregate in the form
example of such a composite supersaturated solid solution.
of sand and coarse aggregate in the formA material a matrix of cement (calcium
of gravel, in that lacks the
aluminosilicate). By mixing large and small particles, the volume fraction of reinforcelong-range order that particles can ﬁt into of a crystalline
ment can be increased because the smallis characteristicthe cavities among the large
solid. Amorphous materials are either rubbers or glasses.
particles. Typical total aggregate (ﬁne plus coarse) volume fractions in concrete are 0.60
to 0.75. The aggregate strengthens the composite in two ways. First, the inherent compresanisotropic Having properties that vary with direction.
sive strength of the aggregate is higher than that of the matrix. Second, the high volume
fraction of irregularly shaped process by which the surface of a
anodizing A aggregate particles provides strength in compression
through mechanical interlocking. As an added bonus, the aggregate is less expensive than
component is converted into a hard oxide by an
the cement, so high aggregate volume fractions reduce the composite cost. Similarly,
asphalt onelectrochemical action. aggregate and 10% tar, is a low cost material
the highway, which is about 90%
that serves its purpose.
antiferromagnetic A class of materials in which
Concrete is one of the most common structural materials. Its use, however, is someadjacent tensile strength is much equal strength point in
what limited, since itsmagnetic dipoles oflower than its compressive strength. A
opposite directions. These materials show weak response
to external magnetic ﬁelds.
Arrhenius equation Textbook Table of Contents form
| e-Text Main Menu | Any equation of the
C0 exp Q RT . This equation states that the
variable C increases exponentially as the temperature
artiﬁcial aging The precipitation of a second phase
from a supersaturated solid solution at a temperature
above room temperature.
atactic Conﬁguration of a vinyl polymer whose side
groups are randomly positioned during polymerization. v Two-dimensional fabric
(a) plain weave, and
(b) ﬁve-harness satin
weave. (Source: K. K.
Chawla, Composites Material Science and Engineering, 1987, Springer-Verlag,
New York. Reprinted with
permission of Springer-Verlag, New Yor...
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