α黄銅の疲労初期き裂の破面観察

概要

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In order to reveal the role of cross slip in fatigue crack nucleation and growth in the early stage of fatigue, a study on α-brass was made in succession to the preceding study on copper. As in the previous case, observations on the surfaces, Iongitudinal sections and fracture surfaces of the specimens fatigued at stress levels corresponding to fatigue lives 1.2×10^5〜8.0×10^6 cycles were made using optical and scanning electron microscopy. It was found that crack initiation and growth up to a few grain size occurred predominantly along the slip band. After this stage of growth, a crack route along the grain boundary was sometimes observed, especially in the specimens fatigued at high stress. Flat fracture surfaces accompanied with steps were observed just beneath the slip bands on the specimen surface. Transcrystalline fracture surfaces containing the crystallographic morphology such as parallel lamelae, however, were observed inside the specimen. Measurement of the angle between the facets suggested that the surfaces consisted of non-slip planes. Smooth surfaces containing clear and linear slip traces were found corresponding to the cracks growing along the grain boundaries just beneath the surface as well as inside the specimen, These results were not essentially different from those found in copper, and therefore, the mechanism of crack nucleation and growth in this material appeared not to be different from that in copper.
1977-06-15