In flight, aerospace components are in a state of constant cyclic stress. The term “flying fatigue machines” is commonly used by those in the industry for a good reason. The dynamic forces planes and helicopters experience during service, while hopefully well below the yield strength of the material, require attention to potential fatigue-related issues during the design stage. The tiniest crack can be propagated by fatigue into a major failure. There are several ways to reduce the risk of fatigue failure, including modifying component geometry to reduce stress concentrations or by surface treatment. In modifying part geometry, it is important to keep in mind that these components are required to be as lightweight as possible. Strengthening the material is another valid option to combat fatigue without increasing part weight. Structural components in planes are often held together with rivets or bolts, requiring holes to be drilled or punched before the fasteners can be applied. These holes act as concentrators to any stresses that are developed in service. Figure 1 shows a classic example of stress concentrations around a hole in a plate which is loaded axially. Notice the tension at the 3 o’clock and 9 o’clock positions, and the compression in the 12 o’clock and 6 o’clock positions from the vertical load. In service, these stresses will cycle the edges of any hole through tension and compression, and any micro-cracks or defects around the edges of the holes will eventually lead to crack propagation and failure.