PBnJ

1 Overview Introduction This Chapter provides an overview of the notions used in this Thesis, starting with the derivation of stress vs. number of cycles (S/N) curve models for short cracks, since the work of these years is relying on the stress-life approach. Then, an overview of crack propagation models is given, in fact power law type crack propagation equations are integrated to recharacterize the concept of S/N curve for long cracks. Subsequently, the effect of notches in the stress-life formulation is treated mostly by means of the theory of the critical distances. Besides providing a variety of fatigue S/N curve models, a brief overview of damage accumulation rules for fatigue prediction deriving from variable amplitude loading is given. The Chapter concludes with a brief overview of the regulatory aspects of fatigue tolerance evaluation for rotorcrafts. 1.1 The SN curve The advent