and repair procedures for reinforced plastic are covered
in chapter 14 of this TRAMAN.
COMPOSITE MATERIAL
Composites are materials consisting of a com-
bination of high-strength stiff fibers embedded in a
common matrix (binder) material; for example, graphite
fibers and epoxy resin. Composite structures are made
of a number of fiber and epoxy resin laminates. These
laminates can number from 2 to greater than 50, and are
generally bonded to a substructure such as aluminum or
nonmetallic honeycomb. The much stiffer fibers of
graphite, boron, and Kevlar® epoxies have given com-
posite materials structural properties superior to the
metal alloys they have replaced.
The use of composites is not new. Fiber glass, for
example, has been used for some time in various aircraft
components. However, the term advanced composites
applies to graphite, boron, and Kevlar®, which have
fibers of superior strength and stiffness. The use of these
advanced composite materials does represent a new
application for naval aircraft.
Composite materials are replacing and supple-
menting metallic materials in various aircraft structural
components. The first materials were used with
laminated fiber glass radomes and helicopter rotor
blades. In recent years, the replacement of metallic
materials with more advanced composite materials has
rapidly accelerated. This has become particularly
evident with the advent of the F/A-18, AV-8B, SH-60B,
and CH-53E aircraft; and it is anticipated that composite
materials will continue to comprise much of the
structure in future aircraft. As a result, there is a growing
requirement to train you in the use of advanced
composite materials.
There are numerous combinations of composite
materials being studied in laboratories and a number of
types currently used in the production of aircraft
components. Examples of composite materials are as
follows: graphite/epoxy, Kevlar®/epoxy, boron poly-
amide, graphite polyamide, boron-coated boron
aluminum, coated boron titanium, boron graphite epoxy
hybrid, and boron/epoxy. The trend is toward minimum
use of boron/epoxy because of the cost when compared
to current generation of graphite/epoxy composites.
Composites are attractive structural materials
because they provide a high strength/weight ratio and
offer design flexibility. In contrast to traditional
materials of construction, the properties of these
materials can be adjusted to more efficiently match the
Figure 1-32.—Sandwich construction.
requirements of specific applications. However, these
materials are highly susceptible to impact damage, and
the extent of the damage is difficult to determine
visually. Nondestructive inspection (NDI) is required to
analyze the extent of damage and the effectiveness of
repairs. In addition, repair differs from traditional
metallic repair techniques. A more detailed explanation
of advanced composites and their inspection and repair
procedures are covered in chapter 14 of this TRAMAN.
SANDWICH CONSTRUCTION
From the standpoint of function, sandwich parts in
naval aircraft can be divided into two broad classes: (1)
radomes and (2) structural. The first class, radomes, is
a reinforced plastic sandwich construction designed
primarily to permit accurate and dependable functioning
of the radar equipment. This type of construction was
discussed in the preceding section under “Reinforced
Plastics.”
The second class, referred to as structural sandwich,
normally has either metal or reinforced plastic facings
on cores of aluminum or balsa wood. This material is
found in a variety of places such as wing surfaces, decks,
bulkheads, stabilizer surfaces, ailerons, trim tabs, access
doors, and bomb bay doors. Figure 1-32 shows one type
of sandwich construction using a honeycomb-like
aluminum alloy core, sandwiched between aluminum
alloy sheets, called “facings.” The facings are bonded to
the lightweight aluminum core with a suitable adhesive
so as to develop a strength far greater than that of the
components themselves when used alone.
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