Fatigue process zone at notches

Fatigue macrocrack initiation is considered to be a two-parameter process. It is governed by the local stress range and a certain linear parameter of the material, the process (prefracture) zone size, d*. The value of d* determines the fatigue stress concentration factor, Kf, and quantitative criterion, ai=d∗, for the micro- to macrocrack transition. The experimental and calculational methods for parameter d* estimation are analyzed. The value of Kf for the beam and CT specimens based on the authorʹs approach and calculated by the well-known equations of Neuber and Peterson are compared.