2 SMALL-CRACK EXTENSION FORCE CONCEPT APPLIED TO FATIGUE LIMIT OF BLUNT NOTCHED COMPONENTS

The fatigue limit of blunt notched components is analyzed here from an energetic point of view. A total crack extension force is estimated b y using both the local extension force, related with the surface strai n concentration phenomena, and the external extension force given by t he applied stress intensity factor. This concept is used to analyze th e fatigue limit and the occurrence of non-propagating cracks in notche d specimens of ferrite steel. The analyses show that the local crack e xtension force can only explain the occurrence of microstructurally sh ort non-propagating cracks, that is to say, it plays an important role in defining the microstructural threshold that defines the fatigue li mit of blunt notched components. (C) 1998 Elsevier Science Ltd. All ri ghts reserved.