| When stress amplitude was large, the best resistivity against fatigue crack growth was found in the pearlitic specimen due to high strength of the pearlitic matrix, while, when stress amplitude was small, it was found in the ferrite-pearlitic specimen due to high K_th of the specimen. The growth rate of fatigue crack increased with decreasing the cyclic frequency, while it was hardly affected by the wave form. The relation between the constant C and the exponent m in the Paris equation could be described by C = (1.1 ×10^(-4)㎜/cycle)/(20.1 Mpa√m)＾m for all specimens tested. Graphite nodules were found to act as the notches for crack initiation and to serve as the crack blunting points resisting against the fatigue crack growth. |
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