| The behavior of crack nucleation and propagation during low cycle fatigue of ductile the cast irons with different nodule counts and similar nodule size have been compared. In spite of similar nodule size, the fatigue life of ductile cast iron with lower nodule count was longer than that with higher one. This fact shows that not only the nodule size but also the nodule count is the factor governing the fatigue life. Meanwhile, the crack nucleation density of the former was notably increased in the early stage of stress cycling, but the increasing rate was diminished greatly in the middle one. Therefore, difference in fatigue life of these specimens could not be explained with the crack nucleation behaviors only. The difference in fatigue life of these specimens can be explained by the easiness of crack coalescence which depends upon the nodule count. Consequently, the effect of the nodule count on the fatigue life was significant because of the importance of crack coalescence and propagation. |
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