Fiberglass is simply a composite consisting
of glass fibers, either continuous or discontinuous, contained within a polymer
matrix; this type of composite is produced in the largest quantities. The
composition of the glass that is most commonly drawn into fibers (sometimes
referred to as E-glass) . fiber diameters normally range between 3 and
20 _m. Glass is popular as a fiber reinforcement material for several reasons:
1. It
is easily drawn into high-strength fibers from the molten state.
2. It
is readily available and may be fabricated into a glass-reinforced plastic
economically using a wide variety of composite-manufacturing techniques.
3. As
a fiber, it is relatively strong, and when embedded in a plastic matrix, it
produces a composite having a very high specific strength.
4. When
coupled with the various plastics, it possesses a chemical inertness that
renders the composite useful in a variety of corrosive environments.
The surface characteristics of glass fibers
are extremely important because even minute surface flaws can deleteriously
affect the tensile properties. Surface flaws are easily introduced by rubbing
or abrading the surface with another hard material. Also, glass surfaces that
have been exposed to the normal atmosphere for even short time periods
generally have a weakened surface layer that interferes with bonding to the
matrix. Newly drawn fibers are normally coated during drawing with a ‘‘size,’’
a thin layer of a substance that protects the fiber surface from damage and
undesirable environmental interactions. This size is ordinarily removed prior
to composite fabrication and replaced with a ‘‘coupling agent’’ or finish that
promotes a better bond between the fiber and matrix.
There are several limitations to this group
of materials. In spite of having high strengths, they are not very stiff and do
not display the rigidity that is necessary for some applications (e.g., as
structural members for airplanes and bridges).
Most fiberglass materials are limited to
service temperatures below 200C (400F); at higher temperatures, most polymers
begin to flow or to deteriorate. Service temperatures may be extended to
approximately 300C (575F) by using high-purity fused silica for the fibers and
high-temperature polymers such as the polyimide resins. Many fiberglass
applications are familiar: automotive and marine bodies, plastic pipes, storage
containers, and industrial floorings. The transportation industries are
utilizing increasing amounts of glass fiber-reinforced plastics in an effort to
decrease
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