Page 247 - 04. Subyek Engineering Materials - Manufacturing, Engineering and Technology SI 6th Edition - Serope Kalpakjian, Stephen Schmid (2009)

Chapter 9 Composite Materials: Structure, General Properties, and Applications
Double coating of polyurethane

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lacquer with nonskid finish
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Section A-A
FIGURE 9.8 Cross section of a composite sailboard, an example of advanced materials
construction. Source: K. Easterling, Tomorrou/’s Materials, 2nd ed., Institute of Metals, 1990.

consisting of carbon and glass fibers, epoxy-resin matrices, high-temperature poly-
imides, and other advanced materials. The structure of the Lear Fan 2100 passenger
aircraft is almost totally made of graphite-epoxy reinforced plastic. Boron fiber-
reinforced composites are used in military aircraft, golf-club shafts, tennis rackets,
fishing rods, and sailboards (Fig. 9.8). Another example is the development of a
small, all-composite ship (twin-hull catamaran design) for the U.S. Navy capable of
speeds of 50 knots (93 km/h). More recent developments include (a) reinforcing
bars (rebar) for concrete, replacing steel bars and thus lowering the costs involved
due to their corrosion, and (b) rollers for papermaking and similar industries, with
lower deflections as compared to traditional steel rollers.

EXAMPLE 9.2 Composite Military Helmets and Body Armor
Personal protective equipment in the form of body There are two main types of body armor: soft
armor and composite helmets have become wide- armor, which relies upon many layers of woven,
spread for military and police applications. Body high-strength fibers and is designed mainly to defeat
armor depends on high-strength woven fibers to pre- handguns; and hard armor, which uses a metal,
vent the penetration of projectiles. To stop a bullet, ceramic, or polymer plate in addition to the woven
a composite material first must deform or flatten it; fiber and is intended to provide protection against
this process occurs when the bullet’s tip comes into rifle rounds and shrapnel. A schematic of body
contact with as many individual fibers of the com- armor is shown in Fig. 9.9.
posite as possible without the fibers being pushed A number of fiber meshes have been used in body
aside. The momentum associated with projectiles is armor applications. Different suppliers employ
felt, of course, by the user of the armor, but success- different combinations of fiber meshes and may
ful designs will contain bullets and shrapnel and pre- include additional layers to provide protection against
vent serious and fatal injuries. blunt trauma. Historically, the first fiber used for