Effects of Small Defects on Fatigue Properties of Materials, Mechanism of Ultralong Life Fatigue and Applications to Fatigue Design of Car Components

Effects of small defects, nonmetallic inclusions, and hydrogen trapped by inclusions on fatigue strength are overviewed. by the authors' group and Japanese industries are introduced. Other related problems such as the quality control of materials from viewpoint of the inclusion or defect rating by statistics of extreme and the effect of small defects on fatigue lives are also discussed. Finally, the mechanism of ultralong life fatigue in the regime of N > 10⁷ is discussed based on the particular morphology in the vicinity of the inclusion at fracture origin and it will be concluded that the hydrogen trapped by inclusions is a crucial factor which causes the elimination of conventional fatigue limit defined by N = 10⁷ and the ultralong life fatigue failure of high strength steels at N > 10⁷.