高張力鋼を用いた安定延性き裂の発生ならびに伝ぱ過程の観察

概要

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In structural steels, the growth of stable fibrous crack from the tip of a pre-existing notch can be observed except at very low temperature. In the present paper, fracture toughness tests have been carried out by the use of high tensile strength steels, KD32 and HT 80, and the behaviors of initiation and growth of stable fibrous crack have been studied by the observation of microstructure in longitudinal section of the notched specimen deformed and by the scanning electron fractographs. In the high tensile strength steel, initiation and growth of fibrous crack occur due to coalescence of micro-voids which are nucleated from micro-inclusions in the vicinity of the tip of pre-existing crack, and this coalescence occurs as soon as the micro-voids are formed. The inclination angle of stretched zone is smaller than 45 degrees. The mutual relation between the width of stretched zone and the displacement at loading point in three point notched bend test can be observed, and this relation is independent of the kind of steel and testing temperature. The equivalent plastic-strain distributions in the vicinity of the tip of fibrous crack are independent of the length of fibrous crack and the singularity of the strain ' distribution is nearly equal to the results obtained by Hutchinson's analysis.
社団法人日本船舶海洋工学会の論文