• 한국구조물진단유지관리공학회 논문집
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• 제10권1호
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• pp.205-215
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• 2006

본 연구는 3차원 쉘요소를 이용한 유한요소해석을 통해 다이아프램으로 보강된 곡선 강박스거더교의 거동을 분석하였다. 매개변수연구를 통해 기존의 제안식과 비교함으로써 모델링의 타당성을 검증하였고, 뒤틀림 응력에 크게 영향을 미치는 인자는 중심내각, 지간길이, 다이아프램간격임을 확인하였다. 또한, 다이아프램의 간격, 개구율, 형상을 변수로 하여 해석한 결과에서는 지간이 30m, 곡률 반경이 40m인 해석모델에 대한 적정 다이아프램간격은 5m인 것으로 나타났다. 다이아프램의 형상 효과에 대해서는 라멘식 다이아프램의 경우가 개구율 0.4~0.6의 범위에서 개구부가 없는 충복판식 다이아프램보다 휨과 뒤틀림의 응력비가 낮아 거동에 유리한 것으로 나타났으며, 충복판식 다이아프램과 X형 트러스 방식의 다이아프램 비교에서는 동일한 강성을 가지더라도 충복판식 다이아프램이 뒤틀림응력을 보다 효과적으로 제어하였다.

• 마이크로전자및패키징학회지
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• 제25권2호
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• pp.31-34
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• 2018

차세대 유연 광전소자 적용을 위한 금속-산화물 샌드위치 구조인 ZnO/Al/ZnO 박막의 유연투명전극 기초연구를 수행하였다. 모든 증착은 유연성을 가지는 PET 기판 상에서 이루어졌으며, 상 하부 ZnO층의 두께가 광 투과도에 미치는 영향을 확인하기 위하여 Al 층의 두께는 모두 8 nm로 고정시킨 채 상부 ZnO 층의 두께는 5-70 nm, 하부 ZnO 층의 두께는 2.5-20 nm까지 변화를 주었다. 가시광선영역(380 nm-770 nm) 파장대를 가지는 광원의 투과도에 대하여 측정한 결과, 상부 ZnO 층의 두께가 30 nm이며 하부 ZnO 층의 경우 2.5 nm 일 때 가장 높은 투과도를 보였다. 400 nm 파장기준 투과도 62%, 면저항 $19{\Omega}/{\Box}$, 그리고 곡률반경 5 mm 조건에서의 휨 테스트 후 면저항과 투과도의 변화가 발생하지 않는 ZnO/Al/ZnO 유연투명전극 결과를 보고한다.

• 한국방재학회:학술대회논문집
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• 한국방재학회 2007년도 정기총회 및 학술발표대회
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• pp.297-302
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• 2007

최근에 빠른 발전을 이루고 있기는 하나, 하중 저항 계수나 미관효과 면에서 박스 거더를 고속도로 분야에 폭넓게 사용하고 있는 실정이다. 최근의 박스 거더 설계를 기반으로 살펴보면 뒤틀림 하중은 그다지 고려되지 않았다. 특히 직선교에서는 뒤틀림 하중의 효과가 작지만 곡선에서는 어떻게 작용하는지 조차 알려진 것이 없었다. 그러한 이유에서 이 연구는 뒤틀림 거동에 미치는 주요한 변수들에 대해 다루었다. 그리고 유한요소법을 사용하는 Dabrowski formula를 바탕으로 하여 다양한 변수의 교량에 대해 연구하였다. 이 연구에서는 다음과 같은 변수들이 사용된다. : 지간장, 곡률반경, 단면높이, 단면폭, 그리고 내부단면각(internal section angle) 연구된 결과로부터 적당한 초기 기하형상에 대한 변수들을 구할 수 있을 것이다.

• 한국항공우주학회지
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• 제41권8호
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• pp.665-672
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• 2013

적층된 복합재 구조물의 강도와 강성 저하를 발생시키는 중요원인 중의 하나는 복합재 층 사이에 발생하는 층간 분리이다. 적용되는 대부분의 복합재 구조물은 어느 정도 곡률을 가지고 있다. 만약 굽은 복합재 구조물이 굽힘 하중을 받게 되면 평평하게 되려는 현상 때문에 두께 방향의 수직응력이 발생하게 되며, 최대 응력이 발생되는 곳에서 층간 분리가 발생한다. 본 논문에서는 굽은 복합적층 보의 반경방향 응력을 결정하는 방법을 설명하고, 층간 분리 응력에 미치는 적층 순서의 영향을 검토하였다. 그리고 층간분리 응력의 크기와 위치를 이론적인 해와 유한요소 방법을 이용하여 해석하고 비교하였다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제44회 동계 정기학술대회 초록집
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• pp.314-314
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• 2013

Recently, flexibility is one of the hottest issues in the field of electronic devices. For flexible displays or solar cells, a development of transparent conductive electrodes (TCEs) with flexibility, bendability and foldability is an essential element. Hundreds of nanometers indium-tin-oxide (ITO) films have been widely used and commercialized as a transparent electrode, but their brittleness make them difficulty to apply flexible electronics. Many researchers have been studying for flexible TCEs such as a few layers of graphene sheets, carbon nanotube networks, conductive polymer films and combinations among them. Although gained flexibility, their transmittance and resistivity have not reached those of commercialized ITO films. Metal grids electrode cannot act as TCEs only, but they can be used to lower the resistance of TCEs with few losses of transmittance. However, the possibility of device shortage will be rise at the devices with metal grids because a surface flatness of TCEs may be deteriorated when metal grids are introduced using conventional methods. In our research, we have developed hybrid TCEs, which combined tens of nanometers ITO film and metal grids which are embedded in flexible substrate. They show $13{\Omega}$/${\Box}f$ sheet resistance with 94% of transmittance. Moreover, the sheet resistance was maintained up to 1 mm of bending radius. Also, we have verified that flexible organic light emitting diodes and organic solar cells with the TCEs showed similar performances compared to commercial ITO (on glass substrate) devices.

• 한국정밀공학회지
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• 제15권2호
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• pp.124-133
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• 1998

This paper describes a research work of developing a computer-aided design of blanking and piercing for irregular-shaped sheet metal products. An approach to the development of compact and practical CAB system is based on the knowledge-based rules. Knowledge for the CAD system is formulated from plasticity theories, experimental results and the empirical knowledge of field experts. The system has been written in AutoLISP on the AutoCAD with a personal computer. Based on knowledge-based rules, the system, STRT-DES, is designed by considering several factors, such as complexities of blank geometry and punch profile, availability of press equipment and standard parts, utilization ratio which minimizes the scrap in a single or a pairwise operation, bridge width, grain orientation and design requirements which maximize the strength of the part when subsequent bending is involved. This system checks a forming feasibility with both internal and external features, a dimension of blanked hole, and a corner and a fillet radius for irregualrly shaped sheet metal products. Therefore this system can carry out a die design for each process which is obtained from results of an automated blank layout drawing with a best utilization ratio for irregular shape of product that was successful in production feasibility check module and those of an automated strip layout drawing and generate part drawings and the assembly drawing of die set in graphic forms.

• 한국전기전자재료학회논문지
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• 제25권6호
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• pp.451-455
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• 2012

To compare an electrical and optical characteristics of indium tin oxide (ITO) and carbon nanotube (CNT) electrode on flexible and reflective display, we fabricate two charged particle-type display panels under the same panel condition of which the width of ribs is 10 ${\mu}m$, the cell size is $300{\mu}m{\times}300{\mu}m$, the q/m value of the white particles is -4.3 ${\mu}C/g$ and that for the black is +1.3 ${\mu}C/g$, and the cell gap is 75 ${\mu}m$, 125 ${\mu}m$, and 175 ${\mu}m$. We use plastic substrates coated with ITO and CNT electrode. To evaluate optical property, we measure a response time of particles using a laser and a photodiode. Threshold and driving voltages of CNT electrode according to the sheet resistance of 300, 600, 1,000 (ohm/sq) are compared with ITO electrode of 10 (ohm/sq). A response time of the CNT panel is similar to that of ITO panel, but the threshold and driving voltages of CNT panel are higher than that of ITO panel, inducing a large bombardment of the particles and shortening the lifetime of the panel. High difference of a threshold and a driving voltage of CNT panel will induce an particle clumping, resulting degradation of the panel. A bending radius of the fabricated CNT panel is 18 ${\mu}m$.

• 한국정밀공학회지
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• 제33권11호
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• pp.911-918
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• 2016

A conical roll-shaping process was proposed for fabrication of a metallic spiral blade applied to a small-scale wind turbine system. A spiral blade has continuously different curvatures, with a range of 100 to 350 mm radius. To fabricate this complex shape, we developed a conical roll-shaping process having two main conical rollers for feeding a blank sheet, and two cylindrical side rollers for control of local bending. For clear understanding of the process parameters, numerical analyses were conducted using a commercial code, Pam-Stamp. This study optimized the effects of process parameters, such as gap and angle between the main rollers and side rollers, and also the movement of side rollers. In order to increase the forming efficiency, a central rotation point was also calculated by the analytical approach. This developed rolling process can thus be utilized in a sheet metal forming process for obtaining spirally curved sheet metal shapes.

• 한국정밀공학회지
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• 제15권3호
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• pp.18-23
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• 1998

This paper describes a research work of developing a computer-aided design of blanking and piercing for irregular-shaped sheet metal products. An approach to the CAD system is based on the knowledge-based rules. Knowledge for the CAD system is formulated from plasticity theories, experimental results and the empirical knowledge of field experts. The system has been written in AutoLISP on the AutoCAD with a personal computer and is composed of four main modules, which are input and shape treatment, flat pattern layout, production feasibility check, and strip layout module. Based on knowledge-based rules, the system is designed by considering several factors, such as radius and angle of bend. material and thickness of product, complexities of blank geometry and punch profile, and availability of press. This system is capable of unfolding a formed sheet metal part to give flat pattern and automatically account for the adjustment of bend allowances to match tooling requirements by checking the dimensions and relationships of parts of the folded product. Also this system can carry out a process planning which is obtained from results of irregular shape of product that was successful in production feasibility check module according to flat pattern layout and generate strip layout drawing in graphic forms. The developed system provides its efficiency for flat pattern layout, and strip layout for the irregularly shaped sheet metal products.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2011년도 제40회 동계학술대회 초록집
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• pp.491-491
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• 2011

Transparent and flexible electronic devices that are light-weight, unbreakable, low power consumption, optically transparent, and mechanical flexible possibly have great potential in new applications of digital gadgets. Potential applications include transparent displays, heads-up display, sensor, and artificial skin. Recent reports on transparent and flexible field-effect transistors (tf-FETs) have focused on improving mechanical properties, optical transmittance, and performances. Most of tf-FET devices were fabricated with transparent oxide semiconductors which mechanical flexibility is limited. And, there have been no reports of transparent and flexible all-organic tf-FETs fabricated with organic semiconductor channel, gate dielectric, gate electrode, source/drain electrode, and encapsulation for sensor applications. We present the first demonstration of transparent, flexible all-organic sensor based on multifunctional organic FETs with organic semiconductor channel, gate dielectric, and electrodes having a capability of sensing infrared (IR) radiation and mechanical strain. The key component of our device design is to integrate the poly(vinylidene fluoride-triflouroethylene) (P(VDF-TrFE) co-polymer directly into transparent and flexible OFETs as a multi-functional dielectric layer, which has both piezoelectric and pyroelectric properties. The P(VDF-TrFE) co-polumer gate dielectric has a high sensitivity to the wavelength regime over 800 nm. In particular, wavelength variations of P(VDF-TrFE) molecules coincide with wavelength range of IR radiation from human body (7000 nm ~14000 nm) so that the devices are highly sensitive with IR radiation of human body. Devices were examined by measuring IR light response at different powers. After that, we continued to measure IR response under various bending radius. AC (alternating current) gate biasing method was used to separate the response of direct pyroelectric gate dielectric and other electrical parameters such as mobility, capacitance, and contact resistance. Experiment results demonstrate that the tf-OTFT with high sensitivity to IR radiation can be applied for IR sensors.