球状黒鉛鋳鉄の疲労挙動 : 第2報,高サイクル疲労に及ぼす微小欠陥の影響

To examine the effect of a small defect on the high cycle fatigue strength of spheroidal graphite ductile iron, rotating bending fatigue tests were performed. To simulate surface defects small artificial holes were introduced on specimen surface. A geometrical parameter, the square root of the projected area (√(area)) proposed by Murakami, was applied to estimate quantitatively the effect of the defect. From the relationship between the fatigue limit and √(area), critical values of √(area) were about 50μm and 100μm for the ferritic and the pearlitic material, respectively. The length of the nonpropagating crack observed at the fatigue limit was about twice as large as the size of spheroidal graphite. The concept an equivalent half-ellipse in calculating √(area) gave a reasonable prediction of the fatigue strength of plain specimens. agreement with the experimental results.