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Nishiyama, Nariaki; Nakajima, Toru; Goto, Akira*; Hakoiwa, Hiroaki; Nagata, Mitsuhiro; Shimada, Koji; Niwa, Masakazu
Earth and Space Science (Internet), 11(6), p.e2023EA003360_1 - e2023EA003360_15, 2024/06
Times Cited Count：0 Percentile：0.00(Astronomy & Astrophysics)Earthquakes with magnitudes of 6-7 have been reported even in various active tectonic settings where fault deformation topography have not been detected. Therefore, delineating concealed active faults generating such earthquakes is necessary to reduce earthquake damage; however, few studies exist to provide its clues regarding such faults. The 1984 Western Nagano Earthquake in Japan was a main shock with a magnitude of Mj 6.8 and a depth of 2 km at the source. Solid bedrocks are well-exposed in the earthquake source region; however, no surface rupture have been identified, and the active fault is known to be concealed. In this study, we collected data on striations observed in fractures by geological survey around the source area of the 1984 Western Nagano Earthquake. Using the collected data, the multiple inverse method was used to estimate the stresses that affected the striation formation. Consequently, stresses similar to acting faults in this area were detected in minor faults around the known concealed active fault. This suggests that the minor faults might be part of the damage zone that has been developed around the concealed active fault. Some minor faults were recognized in Quaternary volcanic rocks, confirming that they experienced displacements recently. This study indicates the possibility of detecting concealed active faults in the bedrock by geological survey.
Motooka, Takafumi; Kiuchi, Kiyoshi
Corrosion, 58(6), p.535 - 540, 2002/06
Times Cited Count：5 Percentile：39.25(Materials Science, Multidisciplinary)The fatigue crack growth of a commercial grade zirconium has been studied in boiling nitric acid and in air at room temperature under tensile load control. The fatigue crack growth rate in air is strongly dependent on the crystallographic texture. It is interpreted based on the crystal anisotropy on mechanical strength in the hexagonal closed pack structure of zirconium. The fatigue crack growth rate in nitric acid is about four times higher than that in air. Texture is found to have an effect on the fracture path in nitric acid. Microfractography of the fracture surfaces shows that the corrosion fatigue growth has a characteristic mechanism. The fracture surface consists of a mixture of grains: some broken by pseudo-cleavage as seen in stress corrosion cracking, and the others broken by fatigue with striation as seen in air. In the low crack growth rate regime pseudo-cleavage is dominant, whereas in the high crack growth rate regime the main fracture mode is ductile fracture.
Motooka, Takafumi; Kiuchi, Kiyoshi
Materials Transactions, 43(5), p.1220 - 1224, 2002/05
Times Cited Count：2 Percentile：23.42(Materials Science, Multidisciplinary)Refractory materials such as zirconium, niobium and titanium alloys with excellent corrosion resistance in boiling nitric acid have been selected for use as structural materials of spent fuel reprocessing equipment. The fatigue crack growth rates of these materials were investigated by load control tests as a function of the stress intensity factor range in boiling 3N nitric acid and in air at room temperature. The fracture surfaces were observed by SEM. The fatigue crack growth rates of zirconium and niobium were enhanced in boiling nitric acid compared with those in air at room temperature. Acceleration effect due to corrosion fatigue was not observed in the crack growth of Ti-5Ta alloy. The fracture surfaces of Ti-5Ta alloy showed the ductile striation in both environments. On the other hand, the fracture surfaces of niobium represented the fatigue striation in air and the brittle striation due to corrosion in nitric acid. The fracture surfaces of zirconium in nitric acid showed brittle fracture and the ductile fracture related to stress corrosion cracking.
Motooka, Takafumi; Kiuchi, Kiyoshi
Proceedings of the 2nd International Conference on Environment Sensitive Cracking and Corrosion Damage (ESCCD 2001), p.374 - 378, 2001/11
Refractory metals such as Zr, Nb and Ti alloys with the excellent corrosion resistance in boiling nitric acid have been selected for structural materials of spent fuel reprocessing equipment. On this study, the fatigue crack growth rate of these materials was investigated by load control tests as a function of the stress intensity in boiling nitric acid and in air at room temperature. The fracture surface was observed by scanning electron microscopy. The crack growth rate of Zr and Nb was enhanced in boiling nitric acid compared with that in air at room temperature. Acceleration effect due to corrosion fatigue was not observed in the crack growth of Ti-5Ta alloy. The fracture surfaces of Ti-5Ta alloy showed the ductile striation in both environments. On the other hand, the fracture surfaces of Nb showed the ductile striation in air and brittle striation in nitric acid. The anodic dissolution was interpreted to the acceleration factor on corrosion fatigue of Nb. The fracture surfaces of Zr in nitric acid showed both brittle and ductile fracture with fluted pattern due to SCC.
Suzuki, Satoshi; Ezato, Koichiro; Sato, Kazuyoshi; Nakamura, Kazuyuki; Akiba, Masato
Fusion Engineering and Design, 49-50, p.343 - 348, 2000/11
Times Cited Count：5 Percentile：37.10(Nuclear Science & Technology)no abstracts in English
