section of 1 in.×1 in. weighing about 4 lb/ft. To suspend the same weight from a modern high-strength polymer fiber would require a fiber with a cross section of 0.3 in.×0.3 in. weighing about 1 oz/ft. We experience the results of these advances every day, for example, in household appliances that are lighter and more efficient, in eyeglasses that are more comfortable, and in automobiles and airplanes that use less fuel and go faster.
The efficiency with which heat energy is converted to mechanical or electrical energy in engines and power plants is another engineering measure important to society. This efficiency depends directly on the temperature at which the device can operate well; thus materials that are strong at high temperatures are desired. Superalloys can now operate at temperatures of over 2000°F, and advanced ceramics may push engine operating temperatures to 2500°F (Figure 1.2). The maximum theoretical efficiency of such engines is about 80 percent, whereas the efficiency of conventional engines is limited to about 60 percent. The ultimate result is more efficient production of energy