• Journal of Advanced Marine Engineering and Technology
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• v.34 no.3
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• pp.369-375
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• 2010

The two-dimensional finite element formulation for the basic field equations governing electrochemical responses of ionic conducting polymer-metal composite(IPMC) actuators is proposed in the present study. Biaxial deformation of a platinum plated Nafion actuator having 4 electrodes is dominated by electro-osmosis of hydrated ions and self-diffusion of free water molecules. Some numerical studies for IPMC actuators with electric field are carried out in order to show the validity of the proposed formulation and electric field analysis for the initial condition of total charge distribution are conducted using commercial code ANSYS/Emag.

• Structural Engineering and Mechanics
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• v.61 no.3
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• pp.397-406
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• 2017

The use of fiber reinforced polymer (FRP) for torsional strengthening of reinforced concrete (RC) single cell box beams has been analyzed considerably by researchers worldwide. However, little attention has been paid to torsional strengthening of multicell box girders in terms of both experimental and numerical research. This paper reports the experimental work in an overall investigation for torsional strengthening of multicell box section RC girders with externally-bonded Carbon Fiber Reinforced Polymer CFRP strips. Numerical work was carried out using non-linear finite element modeling (FEM). Good agreement in terms of torque-twist behavior, steel and CFRP reinforcement responses, and crack patterns was achieved. The unique failure modes of all the specimens were modeled correctly as well.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.17 no.3
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• pp.101-107
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• 2008

A composite mechanics for discontinuous fiber reinforced polymer matrix composites(PMC) is analysed in order to predict fiber axial stresses. In continuum approach. frictional slip which usually takes place between fibers and polymers is accounted to derive PMC equations. The interfacial friction stress is treated by the product of the coefficient of friction and the compressive stress norma1 to the fiber/matrix interface. The residual stress and the Poisson's contraction implemented by the rule of mixture(ROM) are considered for the compressive stress normal to the fiber/matrix interface. In addition. the effects of fiber aspect ratio and fiber volume fraction on fiber axial stresses are evaluated using the derived equations. Results are illustrated numerically using the present equations with reasonable materials data. It is found that the fiber axial stress in the center region shows no great discrepancy for different fiber aspect ratios and fiber volume fractions while some discrepancies are shown in the fiber end region.

• Structural Engineering and Mechanics
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• v.63 no.5
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• pp.629-637
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• 2017

Continuous concrete beams are commonly used as structural members in the reinforced concrete constructions. The use of fiber reinforced polymer (FRP) bars provide attractive solutions for these structures particularly for gaining corrosion resistance. This paper presents experimental results of eight two-span continuous concrete beams; two of them reinforced with pure glass fiber reinforced polymer (GFRP) bars and six of them reinforced with combinations of GFRP and steel bars. The continuous beams were tested under monotonically applied loading condition. The experimental load-deflection behavior and failure mode of the continuous beams were examined. In addition, the continuous beams were analyzed with a numerical method to predict the load-deflection curves and to compare them with the experimental results. Results show that there is a good agreement between the experimental and the theoretical load-deflection curves of continuous beams reinforced with pure GFRP bars and combinations of GFRP and steel bars.

• Multiscale and Multiphysics Mechanics
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• v.1 no.1
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• pp.65-76
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• 2016

In this study, an influence of local variation of nanoparticulate volume fraction on the homogenized elastic properties is investigated. It is well known that interface effect is dependent on the radius and volume fraction of reinforced nanofillers. However, there is no study on the multiscale modeling and analysis of polymer nanocomposites including polydispersed nanoparticles with consideration of interphase zone, which is dependent on the volume fraction of corresponding nanoparticles. As results of numerical examples, it is confirmed that an influence of local variation of nanoparticulate volume fraction should be considered for non-dilute system such as cluster of nanoparticles. Therefore representative volume element analysis is conducted by considering local variation of nanoparticle volume fraction in order to analyze the practical size of cell including hundreds of nanoparticles. It is expected that this study could be extended to the multiparticulate nanocomposite systems including polydispersed nanoparticles.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.06a
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• pp.232-233
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• 2007

We manufactured Liquid Crystal Polymer (LCP) and (1-x)CaTiO3-xLaAlO3 (CT-LA) ceramic composites and investigated dielectric properties to use as embedded capacitor in printed circuit boards and replace LTCC substrate. The dielectric properties of these composites are varied with volume fraction of CT-LA and ratios of CT/LA. Dielectric constants are in the range of 3~15. In addition, we could get low TCC and High Q value that could not achieve in other ceramic-polymer composites. Especially, in composite with x=0.01 and 30 vol% CT-LA, the dieletric constant and Q-value are 10 and 200, respectively. And more TCC is $-28{\sim}300ppm/^{\circ}C$ in the temperature range of $-55{\sim}125^{\circ}C$. We think that this composites can be used high-Q substrate material like LTCC and embedded temperature compensation capacitor in printed circuit boards.

• Structural Engineering and Mechanics
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• v.59 no.1
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• pp.83-100
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• 2016

In this paper, the problem of interfacial stresses in steel beams strengthened with a fiber reinforced polymer plates is analyzed using linear elastic theory. The analysis is based on the deformation compatibility approach developed by Tounsi (2006) where both the shear and normal stresses are assumed to be invariant across the adhesive layer thickness. The analysis provides efficient calculations for both shear and normal interfacial stresses in steel beams strengthened with composite plates, and accounts for various effects of Poisson's ratio and Young's modulus of adhesive. Such interfacial stresses play a fundamental role in the mechanics of plated beams, because they can produce a sudden and premature failure. The analysis is based on equilibrium and deformations compatibility approach developed by Tounsi (2006). In the present theoretical analysis, the adherend shear deformations are taken into account by assuming a parabolic shear stress through the thickness of both the steel beam and bonded plate. The paper is concluded with a summary and recommendations for the design of the strengthened beam.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.11a
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• pp.156-156
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• 2009

전자기기의 Slim화에 따라 부품 일장용 Board 기판의 두께도 날로 감소해지고 있다. 이와는 정 반대로 기판의 층수는 더 늘어나고 있다. 이에 따라 기판의 구성요소인 절연재의 두께도 감소하고 있다. 전자기기는 각각의 Module이 저항을 가지는데 이를 matching하기 위해서 각 module이나 package가 가지는 저항값을 상호 비슷하게 맞춘다. 하지만, 기판의 절연재의 두께 감소는 이러한 저항값이 낮아지게 한다. 이렇게 낮아진 저항값을 높이기 위해서는 전도체의 폭을 줄여야 한다. 하지만, 이렇게 전도체의 폭을 줄이는 것은 기판 제작 비용의 상승 및 제작 물가에 이르게 할 수 있다. 이를 해결하기 위해서는 절연재의 유전율을 낮추는 것이 가장 효과적이다. 본 연구에서는 PCB 기판의 유전율을 낮추기 위해 Liquid Crystalline Polymer(LCP)에 PTFE powder를 넣어 기판 재료의 가능성을 조사하였다. 유전율은 PTFE의 첨가량이 증가함에 따라 감소하여 40wt% 첨가할 경우 유전율이 2.4 정도로 낮아졌다. 이에 반해 열팽창계수는 증가가 크지 않고 peel strength는 감소함을 알 수 있었다.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.23 no.6
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• pp.458-463
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• 2010

MLCC (multi-layer ceramic capacitor) is usually fabricated by lamination of predetermined number of single layers. Often, the state of MLCC before sintering is called the green state, whose strength comes from the adhesion between the dielectric material and the polymer binder. Therefore the lamination of a single layer before sintering can be easily deformed by environment due to the relatively lower strength. After the compression process, which helps single sheets cohereto with adjacent sheets, the MLCC green bar is preheated to resolve the probable internal stress. Unfortunately, unexpected deformation after preheating resulted in problems during cutting of the MLCC green bar. In this study, one of 2 primary hypotheses which were proposed to resolve the unexpected deformation after preheating was examined by quantitative experiment with GC/MS (gas chromatograpy/mass spectrometer). The proportion of deformation caused by DOP evaporation, which was primarily evaporated componet during preheating, to the total deformation of the MLCC green bar was found to be 53%.

• Structural Engineering and Mechanics
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• v.34 no.4
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• pp.525-539
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• 2010

Polymer matrix composites are widely used in many engineering applications as they can be customized to meet a desired performance while not only maintaining low cost but also reducing weight. Polymers can experience viscoelastic-viscoplastic response when subjected to external loadings. Various reinforcements and fillers are added to polymers which bring out more complexity in analyzing the timedependent response. This study formulates an integrated micromechanical model and finite element (FE) analysis for predicting effective viscoelastic-viscoplastic response of polymer based hybrid composites. The studied hybrid system consists of unidirectional short-fiber reinforcements and a matrix system which is composed of solid spherical particle fillers dispersed in a homogeneous polymer constituent. The goal is to predict effective performance of hybrid systems having different compositions and properties of the fiber, particle, and matrix constituents. A combined Schapery's viscoelastic integral model and Valanis's endochronic viscoplastic model is used for the polymer constituent. The particle and fiber constituents are assumed linear elastic. A previously developed micromechanical model of particle reinforced composite is first used to obtain effective mechanical properties of the matrix systems. The effective properties of the matrix are then integrated to a unit-cell model of short-fiber reinforced composites, which is generated using the FE. The effective properties of the matrix are implemented using a user material subroutine in the FE framework. Limited experimental data and analytical solutions available in the literatures are used for comparisons.