• Journal of Korean Society of Steel Construction
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• v.18 no.5
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• pp.525-534
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• 2006

Column-to-beam pinned connections can cause local moment to the web of a steel tube due to the distance of eccentricity between the row of bolts and the column flange, which possibility deteriorates the load capacity of column. In this study, a square hollow section tubular used finite element analysis of a square hollow section tubular column was carried out, and the column width and thickness, existence and non-existence of internal reinforcement, and existence and non-existence of compressive force were taken as variables to examine the load capacity deterioration of a square column caused by moment. To guarantee the reliability of the finite element results, some specimens were fabricated and tested. The yield line method was applied to suggest the strength formulas of the square tubular column to the beam pinned connections. Based on the study results, the column strength the moment of the square hollow section tubular column to the beam pined connections improved with the increase in the w to strength limitations, a no-reinforcement type of square hollow section tubular column was proposed, and if the limitation values were not satisfied, the reinforcement of the internal column was made mandatory. Therefore, the horizontal -reinforcement type considered the strength increase, and the fabrication of the square hollow section tubular column was ar column that considered its load capacity with the moment for the no-reinforcement and the horizontal-reinforcement types.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.47 no.1
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• pp.77-83
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• 2010

Radiation characteristics of $5{\times}4$ pin array patch antennas are compared to those of $5{\times}2$ pin array patch antennas for several substrate thicknesses using the computer simulation. Since the number of unit cells of a $5{\times}2$ pin array patch antenna is half of that of a $5{\times}4$ pin array patch antenna, the number of pins used in a $5{\times}2$ pin array patch antenna is half of that in a $5{\times}4$ pin array patch antenna and the patch width of a $5{\times}2$ pin array patch antenna is very small compared to that of a $5{\times}4$ pin array patch antenna. However, the radiation characteristics of a $5{\times}2$ pin array patch antenna are almost similar to those of a $5{\times}4$ pin array patch antenna.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.5
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• pp.1276-1293
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• 1993

A numerical and experimental flow visualization study of the louvered fin array, commonly used in a compact heat exchanger was performed. The flow structure which was obtained by using a finite difference method, was compared with an experimental result. The experimental flow visualization was performed by using a dye injection technique with 13:1 scale model. The effects of Reynolds number and fin geometries on flow structure and heat transfer were examined.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.464-464
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• 2013

그래핀 옥사이드(Graphene Oxide)는 그래핀과 마찬가지로 많은 분야로의 응용 가능성을 보이는 소자중 하나로 각광받고 있다. 그래핀 옥사이드가 가지는 유전체 특징은 전하 트랩층(charge trap layer)으로 사용을 가능하게 하고 또한 물에 녹는 수용성 특징은 스핀코터(spin coator)를 이용한 간단한 도포과정을 통하여 저비용으로 간단하게 소자를 제작 가능하게 한다. 이 연구에서 우리는 금속-절연체-반도체 구조를 가지는 메모리 소자를 제작하여 0.4 mg/ml의 농도로 DI에 용해된 그래핀 옥사이드가 플로팅게이트(floating gate)로써 사용되었을 때의 특성을 알아보기 위해 Boonton 720를 사용하여 C-V (hysteresis) 커브와 C-T(Capacitance-Time)를 측정하여 그래핀 옥사이드의 유무에 따른 메모리 윈도우 폭의 증가 및 저장된 정보가 손실되지 않고 얼마나 길게 유지 되는지를 살펴봄으로 플로팅게이트로써 그래핀 옥사이드의 특성을 살펴보았다. 먼저 터널링층으로 쓰이는 SiO2가 5 nm 증착된 P타입 Si기판위에 플로팅게이트로 쓰이는 그래핀 옥사이드층을 쉽게 쌓기 위하여 APTES 자기조립 단분자막 코팅을 한 후 그래핀 옥사이드를 3,000 rpm으로 40초간 스핀코팅을 하였다. 그 후 블로킹층으로 쓰이는 400 nm 두께의 폴리비닐페놀(PVP)를 3,000 rpm으로 40초간 스핀코팅을 하고 $130^{\circ}C$에서 열처리를 하였으며 $10^{-5}$ Torr의 압력에서 진공 열증착으로 알루미늄 게이트 전극을 증착했다.

• Composites Research
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• v.18 no.6
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• pp.9-18
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• 2005

With the wide applications of fiber-reinforced composite material in aero-structures and mechanical parts, the design of composite joints have become a very important research area because the joints are often the weakest areas in composite structures. This paper presents an analytical study of the stress distributions in mechanically single-fastened and multi-fastened composite laminates. The finite element models which treat the pin and hole contact problem using a contact stress analysis are described. A dimensionless stress concentration factor is used to compare the stress distributions in composite laminates quantitatively In the case of single-pin loaded composite laminate, the effects of stacking sequence, the ratio of a hole diameter and the width of a laminate (W/D ratio), the ratio of hole diameter and distance from edge to hole (E/D ratio), friction coefficient and clamping force are considered. In the case of multi-pin loaded composite laminate, the influence of the number of pins, pitch distance, number of rows, row spacing and hole pattern are considered. The results show that P/D ratio and E/D ratio affect more on stress distributions near the hole boundary than the other factors. In the case of multi-pin loaded composite laminate, the stress concentration in the double column case is better than the other cases of multi-pin loaded composite laminate.

• Proceedings of the Korea Water Resources Association Conference
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• 2010.05a
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• pp.1089-1093
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• 2010

최근 하천의 자연성 및 생태기능의 향상을 위해 매트류 호안공법의 적용이 증가하고 있다. 이러한 공법이 적용된 호안은 강수 및 하천수의 지속적인 유입으로 인해 앵커핀과 비탈면 간의 마찰력을 저하시킬 수 있다. 마찰력의 저하는 앵커핀의 고정능력을 저하시켜 매트가 들뜨는 현상을 발생시키고, 이로 말미암아 비탈면에 식재된 식생의 고사는 물론 비탈면의 슬라이딩 현상의 발생에 의해 비탈면 붕괴에 까지 이르게 하고 있다. 그러나 현재 호안매트와 함게 시공하는 앵커핀의 적용에 대한 구체적인 기준과 연구가 미흡한 실정이다. 본 연구에서는 매트류 호안제품을 비탈면에 고정시키는 목적으로 사용하고 있는 앵커핀에 대한 인발특성을 파악하고자 하였다. 인발실험에 사용된 앵커핀은 실제 하천호안에 적용되고 있는 상용제품으로 형태가 다른 4가지 type을 실험에 사용하였으며, 앵커핀의 관입깊이(170mm, 250mm) 별로 인발실험을 실시하였다. 실험에 사용된 인발장치는 인발부에 로드셀을 장착하여 앵커핀과 결합이 가능하도록 하였으며, 인발시 발생하는 계측 값을 컴퓨터를 통해 출력이 가능하도록 제작하였다. 실험결과 4가지 형태의 앵커핀에 대한 관입깊이별 형태별 인발특성을 파악할 수 있었으며, 비탈면 및 매트의 고정효과가 우수한 앵커핀의 형태에 대해서도 파악할 수 있었다. 관입깊이별 최대 인발력은 두 변위(170mm, 250mm) 모두 Type 4가 337N, 594N 으로 가장 큰 인발력을 가지는 것으로 측정되었으며, 변위에 의한 인발력의 증가는 Type 2가 138%로 가장 큰 폭의 증가 값을 보였다. 또한 토양과 앵커핀의 마찰력 향상을 위해 하부가 돌출된 형태로 제작된 Type 2와 Type 4가 상대적으로 실험 후반부에서 최대 인발력이 발생하고 인발지속시간이 길게 나타나는 것으로 볼 때, 인발저항은 앵커핀 하부의 돌출면적에 영향을 받는 것으로 판단된다.

• Clean Technology
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• v.28 no.4
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• pp.293-300
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• 2022

The remarkable mechanical, electrical, and thermal properties of graphene have recently sparked tremendous interest in various research fields. One of the most promising methods to produce large quantities of graphene dispersion is liquid-phase exfoliation (LPE) which utilizes ultrasonic waves or shear stresses to exfoliate bulk graphite into graphene flakes that are a few layers thick. Graphene dispersion produced via LPE can be transformed into graphene ink to further boost graphene's applications, but producing high-quality graphene more economically remains a challenge. To overcome this shortcoming, an advanced LPE process should be developed that uses relatively cheap natural graphite as a graphene source. In this study, a flow-LPE process was used to exfoliate natural graphite to produce graphene that was three times cheaper and seven times larger than synthetic graphite. The optimal exfoliation conditions in the flow-LPE process were determined in order to produce high-quality graphene flakes. In addition, the structural and electrical properties of the flakes were characterized. The electrical properties of the exfoliated graphene were investigated by carrying out an ink formulation process to prepare graphene ink suitable for inkjet printing, and fabricating a printed graphene pattern. By utilizing natural graphite, this study offers a potential protocol for graphene production, ink formulation, and printed graphene devices in a more industrial-comparable manner.

• Journal of the Institute of Electronics and Information Engineers
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• v.53 no.2
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• pp.117-122
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• 2016

Recently, the detection of pH with real-time and in vivo has been focal pointed in the environmental or medical fields. In this work, we developed the pH sensor using graphene sheet. Graphene has high biocompatibility. We fabricated flexible solution-gated field-effect transistors (SGFETs) on graphene sheet transferred on the polyethylene terephthalate (PET) substrate to detect pH in electrolyte solution. The gate length was $500{\mu}m$ and the gate width was 8 mm. We evaluated the current-voltage (I-V) transfer characteristics of graphene SGFETs in pH solution. The drain-source current ($I_{DS}$) and the gate-source voltage ($V_{GS}$) curves of graphene SGFETs were depended on pH value. The Dirac point of graphene SGFETs linearly shifted to the positive direction about 19.32 mV/pH depending on the pH value in electrolyte solution.

• Journal of Adhesion and Interface
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• v.23 no.3
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• pp.94-99
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• 2022

Ternary phased graphene/silica/EVOH nanocomposite coating materials were prepared via sol-gel process and solution blending process. From both SEM observations and XRD analysis, the exfoliated structure and dispersion state of graphene nanosheets and silica particles in the nanocomposites as well as the intercalated and exfoliated structure of the prepared graphene oxide were confirmed. The incorporation of GrO and silica at appropriate content resulted in remarkable improvement in oxygen barrier property of the ternary phased nanocompoiste-coated BOPP films, compared with that of binary(silica/EVOH) phased nanocomposite coating films, however, at excess amount of GrO and silica, very slight variation was observed due to incomplete exfoliation, dispersion of graphene tactoids, and formation of micro cracks in the silica clusters. In addition, the transparency of nanocomposite-coated film was investigated by measuring the light transmittance as a function of GrO contents, suggesting the possibility for the application of food packaging films.

• Composites Research
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• v.25 no.6
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• pp.186-190
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• 2012

With the wide application of fiber-reinforced composite material in aero-structures and mechanical parts, composite joint have become a very important research area because they are often the weakest sites in composite structures. In this paper, the failure strengths of the bolted joint and pin joint which have variable hole clearance were evaluated and compared. From the tests, the first failure loads of the bolted joint and pin joint with $880{\mu}m$ hole clearance have decreased by 24.2 % and 51.3 % compared to those of joints with $0{\mu}m$ hole clearance, respectively. Also, the failure index of the joints were calculated by the finite element method and compared with experimental results.