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Study on the Performance of Laser Welded Joint of Aluminum Alloys for Car Body
Kutsuna, M.,Kitamura, S.,Shibata, K.,Sakamoto, H.,Tsushima, K. The Korean Welding and Joining Society 2002 International journal of Korean welding society Vol.2 No.2
Considering the fuel consumption of car, a light structure of aluminum alloys is desired fer car body nowadays. However, fusion welding of aluminum alloys has some problems of reduction of joint efficiency, porosity formation and hot cracking. In the present work, investigation to improve the joint performance of laser welded joint has been carried out by addition of Cu, Ni, and Zr to A6NO 1 alloy welds. Aluminum alloy plate of 2.Omm in thickness with filler metal bar was welded by twin beam Nd: YAG laser facility (total power: 5kW). The filler metals were prepared by changing the chemical compositions for adding the elements into the weld metal. Thirteen filler metal bars were prepared and pre-placed into the base metal before welding. Ar gas shielding with a flow rate of 10 1/min was used. The defocusing distance is kept at 0 mm. At travel speeds off 3 to 9 and at laser power of 5kW (front beam 2kW rear beam 3kW), full penetration welds were obtained, whereas at travel speeds of 12 to 18 m/min and same power, partial penetration was observed. The joint efficiency of laser-welded joint was improved by the addition of Cu, Ni, and Zr due to the solid solution hardening, grain refining and precipitation hardening. The type of hardening has been further considered by metallurgical examination.
Goto, M.,Iwamura, T.,Han, S.Z.,Kim, S.,Yamamoto, T.,Lim, S.H.,Ahn, J-H.,Kitamura, J.,Lee, J. Elsevier 2019 International journal of fatigue Vol.123 No.-
<P><B>Abstract</B></P> <P>Fatigue tests were conducted on round bar specimens of a solution-treated and air-cooled Cu-Ni-Si alloy with high solute concentrations of 6% Ni and 1.5% Si. This alloy was strengthened by disc-shaped Ni<SUB>2</SUB>Si precipitates, a few tens of nanometers in diameter, formed during air cooling. The results were compared with those of a conventional solution-treated Cu-Ni-Si alloy cooled by water quenching. The correlation between the tensile and fatigue strengths of the two alloys differed completely from the general tendency that enhanced tensile strength brings an increase in fatigue strength. Indeed, the fatigue strength of the air-cooled Cu-Ni-Si alloy was 1.1 times higher than that of the water-quenched alloy, while the tensile strength was only 75% that of the water-quenched alloy. Moreover, the electrical conductivity of the air-cooled specimens in International Annealed Copper Standard (IACS) percentage points was 1.7 times higher than that of the water-quenched specimens. The physical background for the superior fatigue strength of the air-cooled Cu-Ni-Si alloy, including the role of microstructure, is discussed.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Air cooling (AC) instead of water quenching (WQ) was applied after SHT. </LI> <LI> Fatigue strength of AC specimen was 1.1 times greater than WQ one. </LI> <LI> Electrical conductivity of AC specimen was 1.7 times greater than WQ one. </LI> <LI> Superior characteristics of AC specimen was discussed based on microstructure. </LI> </UL> </P>
Goto, M.,Yamamoto, T.,Han, S.Z.,Lim, S.H.,Kim, S.,Iwamura, T.,Kitamura, J.,Ahn, J.-H.,Yakushiji, T.,Lee, J. Elsevier 2019 Materials science & engineering. properties, micro Vol.747 No.-
<P><B>Abstract</B></P> <P>The effect of microstructure on the fatigue strength of age-hardened Cu–6Ni–1.5Si alloy was investigated in this study. The aging was conducted at 500 °C for 0.5 h for the precipitation of disk-shaped δ-Ni<SUB>2</SUB>Si precipitates (continuous precipitates) and 3 h for the discontinuous precipitation of fiber-shaped, stable δ-Ni<SUB>2</SUB>Si precipitates to strengthen the Cu matrix. The tensile strength of 0.5 h-aged specimens was about 1.3 times greater than that of the 3 h-aged counterparts, but with inferior electrical conductivity. Despite the considerable difference in tensile strength, no notable difference in fatigue strength was observed between 0.5 h- and 3 h-aged specimens. The 3 h-aged specimens had superior electrical conductivity without sacrificing fatigue strength of the 0.5 h-aged specimens. The physical background of high-cycle fatigue strength in Cu–6Ni–1.5Si alloys with continuous precipitates and discontinuous precipitates is discussed considering the microstructure-sensitive behavior of fatigue cracks.</P>
Goto, M.,Yamamoto, T.,Han, S.Z.,Kim, S.,Ahn, J-H.,Kitamura, J.,Iwamura, T.,Lee, J. Elsevier 2017 Engineering fracture mechanics Vol.182 No.-
<P>For low-cycle fatigued, ultrafine grained copper, processed by equal channel angular pressing, a unique crack growth direction, either inclined at 45 degrees or perpendicular to the loading direction, was observed around the circumference of round bar specimens. In addition, the perpendicular cracks showed a 45 degrees deflected crack face toward the center of the specimens. To clarify the growth behavior of such inclined and deflected cracks, the role of the deformation mode at the crack-tip areas was discussed in terms of the surface damage caused by cyclic stressing and the mixed-mode deformation at the crack tips. The preexistent shear-bands/shear-cracks around the crack tips and the in-plane shear-mode deformation at the crack tips assisted the formation of shallow inclined- and deep deflected-cracks. To quantitatively estimate the severity of mechanical damage at the crack tips, the comparative stress intensity factor range under combined mode I, II and III conditions were calculated. The crack growth rate along the growth direction at the surface and bottom for inclined and deflected surface-cracks was discussed in terms of the comparative stress intensity factor range. (c) 2017 Elsevier Ltd. All rights reserved.</P>
takaki Hatae,H. Yoshida,M. Nakatsuka,O. Naito,S. Kitamura,T. Hamano,T. Sakuma 한국물리학회 2006 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.49 No.III
Phase conjugate mirror based on stimulated Brillouin scattering (SBS) is a fundamentally new and promising technology, and it is applicable to plasma diagnostics in order to improve the measurement performance. A review is presented about the applications of SBS phase conjugation to Thomson scattering diagnostics in JT-60U and ITER. Proposed applications using the phase conjugate mirror to plasma diagnostics, namely double-pass and multipass Thomson scattering methods, were described. Improvement of diagnostic laser system for Thomson scattering employing the phase conjugate mirror are also described.I
A SURVEY OF T TAURI STARS WITH AKARI
Takita, S.,Kataza, H.,Kitamura, Y.,Ueno, M.,Oyabu, S.,Ishihara, D.,Ita, Y. The Korean Astronomical Society 2012 天文學論叢 Vol.27 No.4
We have carried out a survey of T Tauri stars (TTSs) in a 1,800-square-degrees region toward the Taurus-Auriga star forming region with the AKARI Mid-Infrared All-Sky Survey. By combination of AKARI, 2MASS, and UCAC surveys, we created new criteria to chose TTS candidates. We also considered Asymptotic Giant Branch stars and galaxies, which have similar infrared colors, to separate TTSs from these sources. On the basis of our criteria, we find 27 new TTS candidates. To verify our criteria, we performed follow-up observations for them and confirmed that 23 are TTSs.