CHAPTER 3 DESCRIBED various fracture mechanics test methods that can be used to measure the resistance force of structural materials regardless of the fracture toughness level. That is, test methods ranging from linear elastic, KIc test methods to fully plastic J-R or δU test methods were described. Furthermore, the relationships between K-J-δ were described so that the engineer can estimate the resistance force in terms of a Kc value for comparison with the driving force, KI, as described in Chapter 2. Thus, regardless of the inherent fracture toughness of a structural material or the service loading conditions, it is possible to use fracture mechanics to predict the fracture behavior of actual structures.