COMPOSITES - Materials for Civil and Construction Engineers - page 449

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11.1.3 Matrix Phase

Typically, the matrix used in most microscopic composites is polymer
(plastic) or metal. The matrix binds the dispersed materials (particles or
fibers) together, transfers loads to them, and protects them against environ-
mental attack and damage due to handling. Polymers have the advantages of
low cost, easy processibility, good chemical resistance, and low specific
gravity. The shortcomings of polymers are their low strength, low modulus,
low operating temperatures, and low resistance to prolonged exposure to
ultraviolet light and some solvents. On the other hand, metals have high
strength, high modulus, high toughness and impact resistance, relative in-
sensitivity to temperature changes, and high resistance to high temperatures
and other severe environmental conditions. However, metals have high den-
sity and high processing temperatures, due to their high melting points. Met-
als also may react with particles and fibers and they are vulnerable to attack
by corrosion (Agarwal and Broutman 1990). The metals most commonly
used as the matrix phase in composites are aluminum and titanium alloys.

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11.1.4 Fabrication

Fabrication of microscopic composites often combines the production of the
material during the fabrication of the composite. The composite is formed
by combining the matrix and dispersed material. Several methods have been
used to fabricate the composites. The selection of the fabrication process
typically is based on the chemical nature of the matrix and of the dispersed
phases and on the temperature required to form, melt, or cure the matrix.
Figure 11.4 illustrates fabrication of structural shape fiber-reinforced com-
posites by using the pultrusion process. Pultrusion is an automated process
for manufacturing fiber-reinforced composite materials into continuous,
constant-cross-section profiles.

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11.1.5 Civil Engineering Applications

Microscopic composites have been used in many civil and construction engi-
neering applications in the last several decades. In fact, composite materials

Pultrusion Process

Reinforcement Material

Finished
Product

Puller

Resin
Bath

Saw

Heated
Die

FIGURE 11.4 Pultrusion scheme used in fabricating structural shape
fiber-reinforced composites. Courtesy of Creative Pultrusions, Inc.