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

it is applied in a single direction, then all the fibers are aligned in the direction of the expected

load. For applications expecting multidirection loads, the fibers are aligned in different directions

to make the material equally strong in various directions.

Depending upon what type of host matrix material is used in creating the composite mate-

rial, the composites may be classified into three classes: (1) polymer – matrix composites,

(2) metal – matrix composites, and (3) ceramic – matrix composites. We discussed the charac-

teristics of matrix materials earlier when we covered metals and plastics.

17.4 Some Common Fluid Materials

Fluidrefers to both liquids and gases. Air and water are among the most abundant fluids on

earth. They are important in sustaining life and are used in many engineering applications. We

will briefly discuss them next.

Air

We all need air and water to sustain life. Because air is readily available to us, it is also used in

engineering as a cooling and heating medium in food processing, in controlling thermal com-

fort in buildings, as a controlling medium to turn equipment on and off, and to drive power

tools. Compressed air in the tires of a car provides a cushioned medium to transfer the weight

of the car to the road. Understanding the properties of air and how it behaves is important in

many engineering applications, including understanding the lift and drag forces. Better under-

standing of how air behaves under certain conditions leads to the design of better planes and

automobiles. The earth’s atmosphere, which we refer to as air, is a mixture of approximately 78%

nitrogen, 21% oxygen, and less than 1% argon. Small amounts of other gases are present in

earth’s atmosphere, as shown in Table 17.5.

17.4 Some Common Fluid Materials 571

TABLE 17.5 The Composition of Dry Air

Gases Volume by Percent

Nitrogen (N 2 ) 78.084

Oxygen (O 2 ) 20.946

Argon (Ar) 0.934

Small amounts of other gases are

present in atmosphere including:

Neon (Ne) 0.0018

Helium (He) 0.000524

Methane (CH 4 ) 0.0002

Krypton (Kr) 0.000114

Hydrogen (H 2 ) 0.00005

Nitrous oxide (N 2 O) 0.00005

Xenon (Xe) 0.0000087

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