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Unformatted text preview: train hardening
ferrite and cementite temperature. Thus, matrix some steels.
contributes signiﬁcantly to the strength of the composite.
Pearlite forms by the decomposition of austenite.
percent reduction in area
The change in area
14.4 PRACTICAL COMPOSITE SYSTEMS (%RA)
divided by the original area (expressed in percent) of a
So far composites have been classiﬁed as unidirectional ﬁber composites, continuous and
discontinuous ﬁber composites, laminates,has been three-dimensional woven-fabric
tensile specimen that two- and fractured.
composites, particle-reinforced composites, and so on. These classiﬁcations are based
peritectic reaction The transformation, during cooling,
on the architecture and characteristics of the reinforcing phase. Composites are also
of a by their matrix types, including metal-matrix, polymer-matrix,
frequently classiﬁed solid and a liquid phase isothermally and reversibly
ceramic-matrix, and carbon-carbon composites. Some important commercial composites
into a solid having a different composition from either
in each of these classes are described below.
the initial liquid or solid phase.
peritectoid reaction The transformation, during
14.4.1 Metal-Matrix Composites
cooling, of two solid phases plasma spray of and reversibly
Metal-matrix composites (MMCs) are fabricated by isothermally the matrix material
over properly laid ﬁbers, liquidhaving a different composition from hot pressinto a solid inﬁltration methods, physical vapor deposition, either of
ing, squeeze casting, and other methods. These methods are discussed in Chapter 16.
the initial solids.
MMCs have good high-temperature capability, good transverse properties, and reasonably high compressive and shear strength, inmolecule inof a combination of good
permanent dipole A part because which the spatial
strength and toughness of the metal matrix and good interface bonding. Common MMC
center of positive charge is always different from that of
systems include boron ﬁbers in an aluminum matrix, SiC ﬁbers or whiskers in an aluminum matrix,the negative charge. and carbon ﬁbers in magnesium, copper, or
SiC in a titanium matrix,
aluminum matrices. Applications include piston heads for automotive engines, relates the
The materials property that connecting
rods in engine crankshafts, gas turbine blades, radar domes, and electronic packages.
magnetic MMCs are B, in Table 14.4–1.
Typical properties of some inductiongivento the magnetic ﬁeld strength H.
permittivity See dielectric constant.
14.4.2 Polymer-Matrix Composites
Petch-Hall equation Equation that provides the
Polymer-matrix composites (PMCs) are the workhorse of the and the yield stress.
relationship between the grain size composites industry. They
can have excellent room-temperature properties at a comparatively low cost. They have
been in use for The yield stressTwo of the best known early uses in the 1950s are in
about four decades. increases with decreasing grain size
body panels for the Chevy Corvette Petch-Hall equation. The matrix cons...
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