• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2005년도 추계학술대회 논문집
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• pp.685-688
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• 2005

In the micro electrochemical machining (MECM) using ultra short pulses, the machining rate is closely related to the tool electrode area. The machining rate varies according to the machining depth or the immersion depth. When using insulated tool electrodes, those depths do not matter. In addition, micro structures with high machining depth can be fabricated because the machining characteristics do not vary with the machining depth. Another advantage of insulated electrodes is prevention of taper shape. Micro structures with high machining depth or high aspect ratio were fabricated using insulated tool electrodes.

• 반도체디스플레이기술학회지
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• 제20권3호
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• pp.167-171
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• 2021

The core-shell InGaN/GaN Multi Quantum Well-Nanowires (MQW-NWs) that were selectively grown on oxide templates with perfectly circular hole patterns were highly crystalline and were shaped as high-aspect-ratio pyramids with semi-polar facets, indicating hexagonal symmetry. The formation of the InGaN active layer was characterized at its various locations for two types of the substrates, one containing defect-free MQW-NWs with GQDs and the other containing MQW-NWs with defects by using HRTEM. The TEM of the defect-free NW showed a typical diode behavior, much larger than that of the NW with defects, resulting in stronger EL from the former device, which holds promise for the realization of high-performance nonpolar core-shell InGaN/GaN MQW-NW substrates. These results suggest that well-defined nonpolar InGaN/GaN MQW-NWs can be utilized for the realization of high-performance LEDs.

• 한국항공우주학회지
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• 제43권5호
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• pp.396-404
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• 2015

무인기의 날개는 고고도 장기체류에 적합하도록 가로세로비가 크며, 비행 중 구조 대변형이 발생한다. 비행 중 날개 구조의 실시간 변형 상태 파악을 위해 변위-변형률 관계를 이용하여 비행체의 구조 건전성 및 관련 하중 상태 평가, 이상 진동 현상 발견 및 조종성 향상과 같은 영역에서 활용할 수 있다. 본 논문에서는 비행 중 변형이 발생하는 날개 구조물을 외팔보로 가정하여 구조 대변형을 보다 간편하게 예측하기 위한 변형률 기반의 비선형성을 고려한 변위 예측 알고리즘을 작성하였다. 변위 예측식은 외팔보의 다양한 끝단 변위 조건에서 이루어진 구조 실험과 유한요소 해석 결과의 비교를 통하여 검증하였다. 변형률은 스트레인 게이지로부터 취득한 값을 사용하였으며, 변형률을 이용하여 예측된 변위는 레이저 변위 센서로 측정한 변위와 잘 일치하였다.

• 센서학회지
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• 제13권6호
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• pp.430-435
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• 2004

The resolution of the accelerometer, fabricated with MEMS technology is mainly affected by mechanical and electrical noise. To reduce mechanical noise, we have to increase mass of the structure part and quality factor related with the degree of vacuum packaging. On the other hand, to increase mass of the structure part, the thickness of the structure must be increased and ICP-RIE is used to fabricate the high aspect ratio structure. At this time, footing effect make the sensitivity of the accelerometer decreasing. This paper presents a hybrid SOG(Silicon On Glass) Process to fabricate a lateral silicon accelerometer with differential capacitance sensing scheme which has been designed and simulated. Using hybrid SOG Process, we could make it a real to increase the structural thickness and to prevent the footing effect by deposition of metal layer at the bottom of the structure. Moreover, we bonded glass wafer to structure wafer anodically, so we could realize the vacuum packaging at wafer level. Through this way, we could have an idea of controlling of quality factor.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2003년도 춘계학술대회논문집
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• pp.452-457
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• 2003

As a fundamental study on developing elements with micro shape, micro mold parts machining and experiment of injection molding using it were performed. The ultra precision micro machining system with high functionality was fabricated, and utilized in the machining of micro parts. By using this machining system and micro end-mill tool, a micro circle column structure of high aspect ratio, diameter 60 $\mu\textrm{m}$, height 500 $\mu\textrm{m}$, was fabricated. And a micro lens molds were fabricated by using ball end-mill tool of 300 $\mu\textrm{m}$ diameter and diamond fly-cut tool of 150 $\mu\textrm{m}$ radius. A micro injection molding machine, which is clamping force 1.75 ton, injection capacity 2.8cc, was fabricated for injection molding experiment using micro molds. The injection molding experiment was performed by using the injection molding machine, micro cylinder structures and lens molds. This paper introduces these micro machining system and injection molding machine and demonstrates examples of injection molding using fabricated molds.

• 한국항해학회지
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• 제20권1호
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• pp.47-58
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• 1996

The use of high tensile steel plates is increasing in the fabrication of ship and offshore structures. The main portion of ship structure is usually composed of stiffened plates. In these structures, plate buckling is one of the most important design criteria and buckling load may usually be obtained as an eigenvalue solution of the governing equations for the plate. To use the high tensile steel plate effectively, its thickness may become thin so that the occurrence of buckling is inevitable and design allowing plate buckling may be necessary. When the panel elastic buckling is allowed, it is necessary to get precise understandings about the post-buckling behaviour of thin plates. It is well known that a thin flat plate undergoes secondary buckling after initial buckling took place and the deflection of the initial buckling mode was developed. From this point of view, this paper discusses the post-buckling behaviour of thin plates under thrust including the secondary buckling phenomenon. Series of elastic large deflection analyses were performed on rectangular plates with aspect ratio 3.6 using the analytical method and the FEM.

• 국제초고층학회논문집
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• 제10권3호
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• pp.193-201
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• 2021

Cheongna City Tower is a 448-meter-high rise observatory tower with 8.7:1 aspect ratio located at central lake park in Incheon Cheongna international city. The tower is a crystal shaped image and it turns invisible when the façade is activated. The tower was planned to be hexagonal 30-story building with two basements which are composed of mega frame structure using mega column and mega brace. In order to minimize the wind effect, the blow-through area was installed so that the wind can pass through. This observatory tower is an unprecedented project since the whole building is covered by façade for invisibility effect.

• 접착 및 계면
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• 제23권2호
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• pp.39-43
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• 2022

디스플레이, 태양전지와 같이 전기를 빛으로, 또는 빛을 전기로 변환시켜주는 광전자소자는 효율 향상을 위하여 빛의 거동 제어가 매우 중요하다. 즉, OLED의 경우 내부 빛 제어를 통해 더 많은 빛이 외부로 나갈 수 있도록 유도해 줄 때 발광효율을 향상시킬 수 있으며, 외부 빛 제어를 통해 광흡수층에서의 광경로를 증대시킬 경우 태양전지의 에너지 변환효율을 증가시킬 수 있다. 본 연구에서는 이러한 광거동 제어가 가능한 구조로서 주름구조에 대한 연구를 진행하였으며 응력 해소 시간을 제어하여 구조의 주기와 높이를 독립적으로 제어하고자 하였다. 주기와 높이의 변화가 광거동에 어떠한 영향을 미치는지 살펴보기 위하여 일정한 주기에서 높이 변화 및 유사한 높이에서 주기 변화에 따른 자외선/가시광선 분광분석(UV/Vis spectroscopy)을 실시하였으며 구조의 종횡비가 클수록 직진광의 비율이 낮고 분산광의 비율이 높음을 확인하였다. 이를 통해 광경로 변화 및 광경로 증가를 위하여 큰 종횡비의 주름구조가 요구됨을 확인할 수 있었다.

• 한국정밀공학회지
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• 제16권9호
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• pp.41-47
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• 1999

The scale of dendritic structure of a cast preform plays a key role in determining the mechanical properties of cast/forged products. In this study, casting experiments are carried out to reduce dendrite arm spacing (DAS) to smaller than 20 ${\mu}$m by increasing cooling rate of the mold and then to spheriodize dendritic structures by addition of alloying elements such as Zr and Ti-B. From the casting experiments, appropriate casting conditions for producing the cast preform of a motorcycle connecting rod are obtained. To obtain fine microstructures of the cast preform, mold temperature must set to be low whilst cooling rate being high. When cooling rate is 10 $^{\circ}C$/s, the size of DAS is 17.4 ${\mu}$m. And the degree of spheriodization of a grain in the cast preform is described by aspect ratio, which is defined as the ratio of major and minor radii of an elliptical grain. When 0.5% Zr and 0.24 % Ti+B are added to the molten aluminum alloy, the best aspect-ratio 0.75 is obtained. After forging the cast preform of a motorcycle connecting rod, the microstructure and mechanical properties of the cast preform are compared with those of the cast/forged product. Cast/forged products are superior in microstructure and in mechanical properties such as ultimate strength, elongation, and hardness.

• Structural Engineering and Mechanics
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• 제83권2호
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• pp.245-257
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• 2022

As the main lateral load resisting system in high-rise reinforced concrete structures, the mechanical performance of shear wall has a significant impact on the structure, especially for high-rise buildings. Steel corrosion has been recognized as an important factor affecting the mechanical performance and durability of the reinforced concrete structures. To investigate the effect on the seismic behaviour of corroded reinforced concrete shear wall induced by corrosion, analytical investigations and simulations were done to observe the effect of corrosion on the ultimate seismic capacity and drift capacity of shear walls. To ensure the accuracy of the simulation software, several validations were made using both non-corroded and corroded reinforced concrete shear walls based on some test results in previous literature. Thereafter, a parametric study, including 200 FE models, was done to study the influence of some critical parameters on corroded structural shear walls with boundary element. These parameters include corrosion levels, axial force ratio, aspect ratio, and concrete compressive strength. The results obtained would then be used to propose equations to predict the seismic resistance and drift capacity of shear walls with various corrosion levels.