Method for Assessing Applicability of an Artificial Flaw as a Small Initial Crack for Fatigue Limit Evaluation and Its Application to a Drill Hole and an FIB Processed Sharp Notch in Annealed 0.45% Carbon Steel

Abstract In this study, we propose a method for assessing the applicability of an artificial flaw as a small initial crack for fatigue limit evaluation. The proposed method is applied to drill holes and sharp notches introduced using a focused ion beam (FIB) technique in annealed 0.45% carbon steel. It is found that under rotating bending fatigue, an FIB notch can be used as a small initial crack for fatigue limit evaluation, whereas a drill hole cannot, for √area of ∼50 μm. Here, √area is the square root of the area obtained by projecting the defect onto a plane perpendicular to the load axial direction. The results indicate that an FIB notch can be used as a small initial crack for fatigue limit evaluation in a greater number of materials than those in which a drill hole can be used.