単一過大荷重下における疲労き裂進展挙動の動的直接観察

概要

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Fatigue crack growth tests under single overloads were carried out on a 3% silicon iron in a scanning electron microscope (SEM), using the specially designed servo-hydraulic fatigue loading system. Fatigue crack growth behavior under single overloads is discussed based on direct, real time observation and microscopic quantitative analysis of the principal shear strain distribution near the crack tip. It was found that the fatigue crack tip was remarkably blunted by an overload, and two fatigue cracks reinitiated along the preferred slip directions (±55°) at the root of the blunted crack tip within 300 load cycles after the overload and grew simultaneously, which resulted in the retardation of the crack growth rate. When one of the branched cracks arrested and the other grew by itself, the recovery of the crack growth rate was observed and followed by another retardation. The second retardation was due to the frequent branching and deflection of the main crack, the mechanism of which was identical to that of the delayed retardation observed in Hi-Lo two-step loading tests. The measured principal shear strain distribution represented that the preferred slips occurred actively at not only the main crack tip but also the branched crack tips. Such decentralization of the crack driving force was observed during the period of retarded fatigue crack growth.
一般社団法人日本機械学会の論文
1997-09-25