Engineering Fundamentals: An Introduction to Engineering, 4th ed.c

The optical signals generated in this manner can travel to distances as far as 100 km without

any need to amplify them again. Plastic fibers made of polymethylmethacrylate, polystyrene,

or polycarbonate are also used in fiber optics. These plastic fibers are, in general, cheaper and

more flexible than glass fibers. But when compared to glass fibers, plastic fibers require more

amplification of signals due to their greater optical losses. They are generally used in network-

ing computers in a building.

Composites

Because of their light weight and good strength, composite materials are increasingly becom-

ing the materials of choice for a number of products and aerospace applications. Today you will

find composite materials in military planes, helicopters, satellites, commercial planes, fast-food

restaurant tables and chairs, and many sporting goods. They are also commonly used to repair

bodies of automobiles. In comparison to conventional materials, such as metals, composite

materials can be lighter and stronger. For this reason, composite materials are used extensively

in aerospace applications.

Composites are created by combining two or more solid materials to make a new material

that has properties that are superior to those of the individual components. Composite materi-

als consist of two main ingredients: matrix material and fibers. Fibers are embedded in matrix

materials, such as aluminum or other metals, plastics, or ceramics. Glass, graphite, and

silicon carbide fibers are examples of fibers used in the construction of composite materials. The

strength of the fibers is increased when embedded in the matrix material, and the composite

material created in this manner is lighter and stronger. Moreover, once a crack starts in a single

material, due to either excessive loading or imperfections in the material, the crack will propa-

gate to the point of failure. In a composite material, on the other hand, if one or a few fibers fail,

it does not necessarily lead to failure of other fibers or the material as a whole. Furthermore, the

fibers in a composite material can be oriented either in a certain direction or many directions to

offer more strength in the direction of expected loads. Therefore, composite materials are

designed for specific load applications. For instance, if the expected load is uniaxial, meaning that

570 Chapter 17 Engineering Materials

Examples of fiber optic cables

made by Corning.

Source:Corning Cable Systems

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