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The fatigue behaviors of metals containing small defects or inclusions are so complicated that the prediction of the influence of defects or inclusions is very difficult. However, recent advances in fracture mechanics have led to quantitative treatment of this problem. In this paper, first, the characteristics of the effects of small defects and inclusions are discussed by reviewing the existing literature, which mostly reports the defect and inclusion problems qualitatively. Next, it is revealed that the clue to solving the problems quantitatively is the concept that defects and inclusions are virtually equivalent to cracks from the viewpoint of fatigue strength. A method of evaluating the fatigue limits of metals containing small defects based on this concept is introduced. Finally, it is shown that the method is useful in predicting the lower limit of fatigue strength of high-strength steels containing nonmetallic inclusions which cause a distinct decrease in fatigue strength and a large scatter of fatigue strength.
Yukitaka MURAKAMI (Sun,) studied this question.