IN CHAPTER 2 we described various analytical relationships for determining stress-intensity factors in elastic bodies with different-shaped cracks. These stress-intensity factors are a function of load, crack size, and geometry, but not material properties. Ideally, a KI stress-intensity factor associated with a specific crack geometry can be used to model an actual crack in a real structure. Three of the most common geometries are the edge crack, surface crack, and through-thickness crack, as shown in Figure 3.1.