• 한국표면공학회지
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• 제41권6호
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• pp.255-263
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• 2008

Generally, deposition mechanism of diamond particle is mainly embedding effect in the kinetic spray process. Accordingly, in spite of high cost, helium gas was employed as process gas to get high diamond fraction in the composite coating. In this study, the deposition behavior of bronze/diamond by kinetic spray process was compared using different process gas (helium and nitrogen). Bare (mean size of $5{\mu}m$, $20{\mu}m$) and nickel coated diamond (mean size of $26{\mu}m$) were deposited on Al 6061-T6 substrate with fixed process temperature and pressure. For comparison with experimental results, plastic deformation behavior of nickel layer was simulated by finite element analysis (using ABAQUS/Explicit 6.7-2). The size, broken ratio, and fraction of diamond in the composite coating were analyzed through scanning electron microscopy and image analysis method. The uniform distribution and deposition efficiency of diamond particles in the coating layer could be achieved by tailoring the physical properties of the feedstock.

• 천문학회보
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• 제39권2호
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• pp.103-103
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• 2014

Manufacturing of lens and mirror using Diamond Turning Machine (DTM) offers distinct advantages including short fabrication time and low cost as compared to grinding or polishing process. However, the DTM process can leave mid-frequency error in the optical surface which generates an undesirable diffraction effect and stray light. The mid-frequency error is expected to be eliminated by mechanical polishing after the DTM process, but polishing of soft surface of ductile aluminum is extremely difficult because the polishing process inevitably degrades the surface form accuracy. In order to increase its surface hardness, we performed electroless nickel plating on the surface of diamond-turned aluminum (Al-6061T6) off-axis mirrors, which was followed by the 6-hour-long baking process at $200^{\circ}C$ for improving its hardness. Then we polished the nickel plated off-axis mirrors to remove the mid-frequency error and measured polished mirror surfaces using the optical surface profilometer (NT 2000, Wyko Inc.). Finally, we ascertained that the mid-frequency error on the mirror surface was successfully removed. During the whole processes of nickel plating and polishing, we monitored the form accuracy using the ultra-high accurate 3-D profilometer (UA3P, Panasonic Corp.) to maintain it within the allowable tolerance range (< tens of nm). The polished off-axis mirror was optically tested using a visible laser source and a pinhole, and the airy pattern obtained from the polished mirror was compared with the unpolished case to check the influence of mid-frequency error on optical images.

• Journal of Astronomy and Space Sciences
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• 제29권3호
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• pp.321-328
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• 2012

We have designed a 30 cm cryogenic space infrared telescope for astronomical observation. The telescope is designed to observe in the wavelength range of 0.5~2.1 ${\mu}m$, when it is cooled down to 77 K. The result of the preliminary design of the support structure and support method of the mirror of a 30 cm cryogenic space infrared telescope is shown in this paper. As a Cassegrain prescription, the optical system of a 30 cm cryogenic space infrared telescope has a focal ratio of f/3.1 with a 300 mm primary mirror (M-1) and 113 mm secondary mirror (M-2). The material of the whole structure including mirrors is aluminum alloy (Al6061-T6). Flexures that can withstand random vibration were designed, and it was validated through opto-mechanical analysis that both primary and secondary mirrors, which are assembled in the support structure, meet the requirement of root mean square wavefront error < ${\lambda}/8$ for all gravity direction. Additionally, when the M-1 and flexures are assembled by bolts, the effect of thermal stress occurring from a stainless steel bolt when cooled and bolt torque on the M-1 was analyzed.

• 한국자동차공학회논문집
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• 제24권4호
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• pp.425-431
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• 2016

The usage of Friction Stir Welding(FSW) technology has been increasing in order to reduce the weight in automobile industries. Previous studies that investigated on the FSW have focused on the aluminum alloy. In this study, Al6061-T6 alloy plates having 5 mm of thickness were welded under nine different conditions from three tool rotation speeds: 900, 1000 and 1100 rpm, and three feed rates: 270, 300 and 330 mm/min. Specimen size of Micro Shear Punch(MSP) test was $10{\times}10{\times}0.5mm$. The mechanical properties were evaluated by MSP test and Analysis of Variance (ANOVA). The specimens were classified by advancing side(AS), retreating side(RS), and center(C) of width of tool shoulder. The optimal welding condition of FSW based on micro strengh was obtained when the tool rotation speed was 1100 rpm and the feed rate was 300 mm/min. The maximum load measured AS, RS, and C in the weldment was measured 554.7 N, 642.9 N, and 579.2 N, respectively.

• Composites Research
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• 제19권4호
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• pp.23-30
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• 2006

극저온 추진제 탱크를 개발하는 과정에서 복합재와 알루미늄 라이너를 접합하기 위한 접착제의 선택은 탱크의 안전성과도 직결된 매우 중요한 문제이다. 따라서 적합한 극저온용 접착제를 선택하기 위해 3종류의 접착필름이 선정되었으며 극저온용으로 개발된 탄소섬유/에폭시와 라이너 재료로 사용되는 알루미늄으로 구성된 양면 겹치기 조인트 시편을 제작하였다. 제작된 시편을 극저온 환경챔버를 사용하여 상온과 $-150^{\circ}C$에서 인장실험을 수행하여 각 접착제의 접착강도를 비교하였으며 파손 특성을 분석하였다. 또한 양면 겹치기 조인트 시편의 각 구성재료의 온도에 따른 기계적 물성변화를 측정하였으며 이를 이용하여 ABAQUS를 통한 유한요소해석을 수행하여 양면 겹치기 조인트 시편의 인장시험결과를 분석하였다.