Author(s)

H. Nisitani & Y. Oda

Abstract

A study of fatigue crack growth laws in small and large cracks based on COD H. Nisitani, Y. Oda Faculty of Engineering, Kyushu University, 6-10-1 Hakozaki, Higashi-ku, Fukuoka, 812, Japan ABSTRACT Fatigue crack growth tests were carried out on an annealed 0.45%C steel. Crack opening displacement ranges (ACOD's) along a crack were measured in the neighborhood of the crack tip from the SEM photographs taken of positive metal replicas of surface cracks under the maximum and minimum loads. The physical background of the two representative crack growth laws: dl/dN — C\o™l for small cracks under high nominal stresses and dl/dN — CA/i™ for large cracks under low nominal stresses, which for- mally contradict each other, was discussed on the basis of the measured ACCWs. In small and large cracks having the same growth rate, the ge- ometries of measured ACOD's near the crack tips were also almost the same. Therefore, the ACOD distribution near the crack tip can be consid- e

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