• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.6A
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• pp.943-953
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• 2006

We investigated experimentally the static behavior of an orthotropic bridge deck which is made from glass fiber reinforced polymer (GFRP) and polyurethane foam. The bridge deck consists of many unit cells with rectangular holes which are filled with the foam to improve its structural behavior in its weak axis. It is found that although the elastic modulus of the foam compared to that of the GFRP is about the order of, the structural behaviors in the weak axis such as nominal strength, stiffness, etc. are greatly improved. Owing to the low mass density of the foam used in this study, the bridge deck is still light enough with the improved structural properties. Webs of the cells filled with the foam did not significantly contribute to the strength development of the deck. However, the propagation of a crack initiated in a cell is caught by the webs and limited to the inside of that cell only, which makes the load-displacement behavior of the foam-filled GFRP deck less brittle.

• Composites Research
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• v.15 no.6
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• pp.38-43
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• 2002

Rapid Prototyping(RP) technologies provide the ability to fabricate initial prototypes from various model materials. Stratasys' Fused Deposition Modeling(FDM) is a typical RP process that can fabricate prototypes out of plastic materials, and the parts made from FDM were often used as load-carrying elements. Because FDM deposits materials in about 300$\mu$m thin filament with designated orientation, parts made from FDM show anisotropic material properties. In this paper an analytic model was proposed to predict the tensile strength of FDM parts. Applying the Classical Lamination Theory, which was developed for laminated composite materials, a computer code was implemented. Tsai-Wu failure criterion was added to the code to predict the failure of the FDM parts. The tensile strengths predicted by the analytic model were compared with experimental data. The data and prediction agreed reasonably well to prove the validity of the model. In addition, a web-based advisory service(FDMAS) was developed to provide strength prediction and design rules for FDM parts.

• Journal of the Korea institute for structural maintenance and inspection
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• v.11 no.3
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• pp.123-131
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• 2007

The buckling behavior of a fiber reinforced plastic pipe was researched. When a cylindrical structure is made of isotropic material, it shows two dimensional buckled shape which has same deformed section along the longitudinal direction. But an anisotropic cylindrical structure shows three dimensional buckled shape which has different deformed section along the longitudinal direction. Because the modulus of elasticity is varied in a certain direction when ply angles are changed, the strength of a pipe are changed as ply angles are changed. In this study, the limitation of two dimensional and three dimensional buckling mode was investigated and the buckling strength of a laminated composite pipe was evaluated.

• Geotechnical Engineering
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• v.7 no.3
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• pp.33-42
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• 1991

Increasing demand of rational analysis of dynamic soil behavior subjected to repetitive loading has evolved soil dynamics which is essential for proper design and/or analysis of dynamically loaded soil structure. In this paper, the stress-strain behavior of weathered granite soil under cyclic loading is stud- ied by measuring the strength and the strain before and after application of at least 11, 000 cycles of repetitive load. Relationships are suggested for predicting results of soil dynamics from those of soil statics.

• Proceedings of the Materials Research Society of Korea Conference
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• 2003.03a
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• pp.228-228
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• 2003

고강성 탄소섬유는 높은 비강도 및 고 강성 특성 때문에 탄소-탄소 복합재료의 가장 우수한 강화재로 각광을 받고 있다. 이 섬유는 미세 결정립의 높은 이방성을 나타내며, 이러한 높은 흑연화 특성은 기계적, 전기적, 전기적 그리고 화학적 특성 등을 좋게한다. 이러한 모든 방면에서의 우수한 특성 때문에 항공우주 재료분야에 의심 없이 가장 우수한 재료로 고려되고 있다. 이렇게 가벼우면서 고온강도가 요구되는 재료로써 탄소재료가 이용되면서 rocket의 nozzle이나 nosecone으로의 응용에는 고온 산화가 중요한 연구주제로 대두되어 왔다. 탄소재료의 산화반응은 결정구조 인자 및 그 배열에 가장 큰 영향을 받는다고 알려져 있는데, 출발원료 및 제조 조건에 따라 그 구조 및 배열이 현격하게 달라진다. 탄소재료의 구조 해석은 주로 TEM과 XRD를 이용해 왔다. 많은 연구자들은 오래 전부터 탄소재료 연구에 TEM에서 얻은 상이 불확실하고 문제가 있다고 보고하였고, 최근 TEM 장치의 발달과 더불어 실제 구조를 얻기가 가능함을 보여주고 있다 그러나 TEM 시편은 여전히 작고 시편으로부터 얻는 정보는 불과 nm 수준이다. 따라서 일반적으로 TEM으로 얻은 정량적인 정보는 불과 특정한 점에서의 정보이기 때문에 여전히 논란의 소지가 많다. XRD는 탄소재료의 미세구조 해석을 위하여 가장 널리 이용되는 분석기기이다.

• Proceedings of the KIEE Conference
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• 1988.11a
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• pp.175-178
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• 1988

A film is fabricated by depositing several sliced organic ultra thin films on a slide glass. Both UV-absorbance and the capacitance of a multi - layered organic ultra thin film with (N-docosyl pyridinium)-TCNQ(1:2) complex have a desired value on the condition of well alignment in depositing several layers. Forethermore the conductivity of this film measured by the direction of either horizontal or vertical axis. respectively, is results in a quite different value.

• Electrical & Electronic Materials
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• v.5 no.4
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• pp.411-420
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• 1992

C$_{2+}$-Quinolium(TCNQ) 유기 초박막을 Langmuir-Blodgett 방법을 이용하여 유리기판 위에 누적하였다. 이의 최적 누적조건을 알아보기 위하여 .pi.-A isotherm특성을 온도, pH, 압축 속도, 분산량 등을 변화시키면서 조사하였다. 누적 과정은 전이비를 통하여 고체 기판에 누적되는 정도를 살펴볼 수 있었으며 누적된 박막은 다음과 같은 방법으로 확인하였다. 광학적인 방법으로 광흡수도, 전기적인 방법으로 전기 용량, 그리고 기계적인 방법으로 두께를 직접 측정하여 누적된 박막의 상태를 관찰하였다. 상온에서 이방성 전기 전도도를 측정하였는데 수평 방향으로 ~1 x $10^{-7}$S/cm, 수직 방향으로 ~1 x $10^{-14}$S/cm의 값을 얻었다.

• Transactions of Materials Processing
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• v.20 no.8
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• pp.595-600
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• 2011

This paper investigates the effect of strain rate on the anisotropic deformation behavior of advanced high strength steel sheets. Uniaxial tensile tests were carried out on TRIP590 and DP780 steel sheets at strain rates ranging from 0.001/sec to 100/sec to determine yield stresses and r-values at various loading angles from the reference rolling direction. R-values were determined by the digital image correlation technique. Hill48 and Yld2000-2d yield functions were tested for their capability to describe the plastic deformation anisotropy of the materials. Initial yield loci were constructed using the Yld2000-2d yield function, which adequately described the anisotropic behavior of the materials. The shape of the initial yield loci was found to change with different strain rate, and the anisotropic behavior decreased with increasing strain rate.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2004.05a
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• pp.116-116
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• 2004

편마비 환자의 보행운동 개선을 위한 보조기구로 족부보장구(Ankle Foot Orthosis, A.F.O.)가 활용되고 있다 족부보장구는 Fig. 1에 제시한 바와 같이 보행특성상 무수히 반복되는 충격과 굽힘하중을 받는다. 따라서 족부보장구용 재료는 피로특성이 우수한 탄소섬유 강화재(Carbon Fiber Reinforced Plastic, 이하 CFRP)를 주로 사용한다. 그러나 CFRP의 상용재인 프리프레그(prepreg)는 강한 이방성의 단방향 섬유이므로 섬유방향과 하중작용방향의 관계에 매우 민감하다.(중략)

• Journal of the Korean Chemical Society
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• v.17 no.4
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• pp.240-246
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• 1973

An analytic expression for the intensity of collision-induced light scattering obstained by introducing both short-range and long-range effects on the induced anisotropy. By taking argon as a specific example, it is shown that a narrow band at small frequency shifts is caused by long-range effects, while a broad band in the far wing of the spectrum is due to short-range effects. The overall intensity is a synthesis of these two bands and does not follow a simple exponential form. As temperature increases, the intensity at large frequency shifts increases makedly, while at small frequency shifts it changes little.