Very High Cycle Fatigue

The traditional subdivision of the Wöhler curve into the three regions of Fig.  1.10 , at least for ferrous alloys or, better, for BCC crystal lattice materials has been recently extended to include a new region beyond some 107 or 108 cycles. It is the region of the so called Very-High-Cycle-FatigueVery-high cycle fatigue (VHCF) or VHCF. The more demanding request for life from many technological applications has been the driving force to explore, also for BCC materials, the field of 108 or even 109 cycles. The pressure to know how these materials perform in the VHCF region, whether or not they really have a definite fatigue limit, has unveiled a new as well unexpected behavior that still remains argument of vigorous discussion among researchers. It is a fact that vast majority of the data so far collected since Wöhler first tests with fatigue specimens, are confined within 107–108 cycles.