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Composites and Fillers 265

site of the arm to the living body. Artificial legs can be fashioned in glass/polyester and fi lled with

polyurethane foam adding strength to the thin-shelled glass/polyester shell. Artifi cial legs are also
made from carbon/epoxy composite materials. Some of these contain a strong interior core with a
soft, fl exible “skin.”
Carbon/epoxy “plates” are now used in bone surgery replacing the titanium plates that had previ-
ously been employed. Usually, a layer of connective tissue forms about the composite plate.
Rejection of composite materials typically does not occur, but as is the case of all biomaterials,
compatibility is a major criterion. Often, lack of biocompatibility has been found to be the result of
impurities (often additives) found in the materials. Removal of these impurities allows the use of
the purifi ed materials.
Carbon and carbon/glass composites are being used to make “advanced-material” fi shing rods,
bicycle frames, golf clubs, baseball bats, racquets, skis and ski poles, basketball backboards, and
so on. These come in one color—black—because the carbon fi bers are black. Even so, they can be
coated with about any color desired.
Composites are being employed in a number of automotive applications. These include racing car
bodies as well as “regular” automobiles. Most automobiles have the lower exterior panels composed
of rubbery, plastic blends, and/or composite materials. Corvettes have composite bodies that allow a
light-weight vehicle with decent fuel economy and they do not rust. Other parts such as drive shafts
and leaf springs in private cars and heavy trucks, antennas, and bumpers are being made from
composite materials.
Industrial storage vessels, pipes, reaction vessels, and pumps are now made from composite
materials. They offer needed resistance to corrosion, acids and bases, oils and gases, salt solutions,
and the necessary strength and ease of fabrication to allow their continued adoption as a major
industrial “building” material.
The Gulf War spot lighted the use of composite materials in the new-age aircraft. The bodies of

both the Stealth fighter and bomber are mainly carbon composites. The versatility is apparent when
one realizes that the Gossamer Albatross, the first plane to cross the English Channel with human

power, was largely composite materials, including a carbon/epoxy and aromatic nylon composite
body, propeller containing a carbon composite core, and so on.
The growth of composite materials in the aerospace industry is generally due to their outstanding
strength and resistance to weathering and friction and their light weight, allowing fuel reduction

savings. Its growth in commercial aircraft is seen in the increased use of fiber glass composite mate-
rial in succeeding families of Boeing aircraft from about 20 sq yards for the 707, to 200 sq yd for
the 727, to 300 sq yd for the 737, and more than 1,000 sq yd for the 747. This amount is increased in
the Boeing 767 and includes other structural applications of other space-age composites. Thus, the
Boeing 767 uses carbon/aromatic nylon/epoxy landing gear doors and wing-to-body fairings.
Until the late 1960s, almost all tactical aircraft were largely titanium. While titanium is rela-
tively light, it is costly and has demanding production requirements so that its use was limited to
moderate-temperature aircraft applications. Today, most tactical aircraft have a sizable component
that is polymeric, mainly composite. The Boeing F/A 18E/F and Lockheed F/A-22 have about 25%,
by weight, composite material. It is projected that future military aircraft will have more than 35%
composite materials.
Composites have displaced more conventional materials because they are lighter with greater
strength and stiffness, allowing them to carry a greater payload further. Composites are also rela-

tively insensitive to flaws. In comparison to metals, fatigue testing of composites shows that they
have a high resistance to cracking and fracture propagation. They are stable and are not subject to
corrosion. However, in the design process, particular care must be taken with respect to the metal-
composite interface because galvanic action of some metals will corrode when in contact with cer-
tain composites such as the carbon graphite/resin laminates.
The Stealth Bomber, more accurately known as the Northrop Grumman B-2 Spirit Stealth
Bomber, is cited as the largest composite structure produced with more than 30% of the weight being

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