• Proceedings of the Computational Structural Engineering Institute Conference
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• 2007.04a
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• pp.309-314
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• 2007

Optimal layer sequencing of a multi-layered acoustical foam is solved to maximize its sound transmission loss. A foam consisting of air and poroelastic layers can be optimized when a limited amount of a poroelastic material is allowed. By formulating the sound transmission loss maximization problem as a one dimensional topology optimization problem, optimal layer sequencing and thickness were systematically found for several frequencies. For optimization, the transmission losses of air and poroelastic layers were calculated by the transfer matrix derived from Biot's theory. By interpolating five intrinsic parameters among several poroelastic material parameters, dear air-poroelastic layer distributions were obtained; no filtering or post-processing was necessary. The optimized foam layouts by the proposed method were shown to differ depending on the frequency of interest.

• Proceedings of the Korea Concrete Institute Conference
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• 2005.05b
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• pp.269-272
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• 2005

Epoxy resins are gradually becoming some of the most important and versatile polymers in modem civil engineering. Because epoxy resins have some unigue properties, such as toughness, versatility of viscosity and curing conditions, good handling characteristics, high adhesive strength, inertness, low shrinkage compared to most other thermo-setting resins and concrete, and resistance to chemicals, they have found many applications in construction castings, repair materials, road or bridge deck pavements, coatings, and as structural or non structural adhesives. In this applications, epoxy resins are widely used for polymer concretes, grouting materials, injection glues, and sealants. In this paper, characteristics of deformation of repair material after repaired have been investigated by viscosity of repair material and the width of crack. It is believed that flexural strength of epoxy resin with low viscosity is high because tensile strength is high and elongation at break is low, fracture energy is low.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1999.05a
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• pp.649-652
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• 1999

The (Ba, Sr)TiO$_3$(BST) thin films were fabricated on Pt/Ti/SiO$_2$/Si substrate by RF sputtering technique. The structural properties of the BST thin films were investigated with substrate temperature by XRD, SEM, EDS and AES depth profils. Increasing the substrate temperature, barium multi titanate phases were decreased. The BST thin film had a structure of perovskite type, and had peaks of (100), (200) at the substrate temperature of 50$0^{\circ}C$. When the BST thin films were deposited at the substrate temperature of 50$0^{\circ}C$, the composition ratio of Ba/sr was 52/48.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.16 no.9
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• pp.753-758
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• 2003

Ti films were deposited onto 100${\times}$100 mm alumina substrates using dc magnetron sputtering under the following conditions; substrate temperature of R.T～400 $^{\circ}C$, annealing temperature of 100～400 $^{\circ}C$, and sputtering gas pressure of 4${\times}$10$^{-3}$ Torr～4${\times}$10$^{-2}$ Torr. And the films were examined by X-ray diffraction analysis (XRD), scanning electron microscopy(SEM) and 4-point measurement system. The best electrical and structural properties was obtained by substrate temperature of ～200 $^{\circ}C$, target-substrate distance of ～14 cm and sputtering pressure of ～1${\times}$10$^{-2}$ Torr. Also at that condition the most excellent adhesion was observed.

• Korean Chemical Engineering Research
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• v.46 no.1
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• pp.7-14
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• 2008

Carbon nanotubes are considered as the most ideal nano filler in the field of composites with their excellent electrical, mechanical, and thermal properties. Therefore carbon nanotubes composites are increasingly utilized in conductive materials, structural material with high strength and low weight and multifunctional material. This review article describes recent research trend of carbon nanotubes synthesis, modification, various properties of the carbon nanotubes composites and their application. Furthermore the future development direction for the commercialization of carbon nanotubes composites is proposed.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2003.10a
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• pp.195-201
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• 2003

A fibered element for the material and geometric nonlinear analysis of three-dimensional reinforced and prestressed concrete frame is presented. The fibered frame element is idealized as an assemblage of concrete and reinforcing steel fibers in order to account for varied material properties within the cross section of the frame element through elastic, cracking and ultimated stages of materials. Prestressing tendon is modeled as an assemblage of multilinear prestressing steel segments each of which spans a frame element. The contribution of each prestressing steel is added directly to the fibered frame element. Numerical results from the ultimate analysis of three-dimensional PSC box girder are compared with those obtained from other investigator. The validity and the capability of the present nonlinear analysis model is well demonstrated.

• Smart Structures and Systems
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• v.20 no.5
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• pp.583-593
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• 2017

This research deals with the nonlocal temperature-dependent dynamic buckling analysis of embedded sandwich micro plates reinforced by functionally graded carbon nanotubes (FG-CNTs). The material properties of structure are assumed viscoelastic based on Kelvin-Voigt model. The effective material properties of structure are considered based on mixture rule. The elastic medium is simulated by orthotropic visco-Pasternak medium. The motion equations are derived applying Sinusoidal shear deformation theory (SSDT) in which the size effects are considered using Eringen's nonlocal theory. The differential quadrature (DQ) method in conjunction with the Bolotin's methods is applied for calculating resonance frequency and dynamic instability region (DIR) of structure. The effects of different parameters such as volume percent of CNTs, distribution type of CNTs, temperature, nonlocal parameter and structural damping on the dynamic instability of visco-system are shown. The results are compared with other published works in the literature. Results indicate that the CNTs have an important role in dynamic stability of structure and FGX distribution type is the better choice.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2002.04a
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• pp.335-342
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• 2002

A continuum-based design sensitivity analysis (DSA) method fur non-shape problems is developed for geometrically nonlinear elastic structures. The non-shape problem is characterized by the design variables that are not associated with the domain of system like sizing, material property, loading, and so on. Total Lagrangian formulation with the Green-Lagrange strain and the second Piola-Kirchhoff stress is employed to describe the geometrically nonlinear structures. The spatial domain is discretized using the 4-node isoparametric plane stress/strain elements. The resulting nonlinear system is solved using the Newton-Raphson iterative method. To take advantage of the derived analytical sensitivity In topology optimization, a fast and efficient design sensitivity analysis method, adjoint variable method, is employed and the material property of each element is selected as non-shape design variable. Combining the design sensitivity analysis method and a gradient-based design optimization algorithm, an automated design optimization method is developed. The comparison of the analytical sensitivity with the finite difference results shows excellent agreement. Also application to the topology design optimization problem suggests a very good insight for the layout design.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.23 no.6
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• pp.683-691
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• 2010

In this paper, using an adjoint variable method, we develop a design sensitivity analysis(DSA) method applicable to heat conduction problems in steady state. Also, a topology design optimization method is developed using the developed DSA method. Design sensitivity expressions with respect to the thermal conductivity are derived. Since the already factorized system matrix is utilized to obtain the adjoint solution, the cost for the sensitivity computation is trivial. For the topology design optimization, the design variables are parameterized into normalized bulk material densities. The objective function and constraint are the thermal compliance of structures and allowable material volume respectively. Through several numerical examples, the developed DSA method is verified to yield very accurate sensitivity results compared with finite difference ones, requiring less than 0.25% of CPU time for the finite differencing. Also, the topology optimization yields physical meaningful results.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.23 no.6
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• pp.627-633
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• 2010

This paper presents a method for identifying the parameter set of inelastic constitutive equations, which is based on an Evolutionary Algorithm. The advantage of the method is that appropriate parameters can be identified even when the measured data are subject to considerable errors and the model equations are inaccurate. The design of experiments suited for the parameter identification of a material model by Chaboche under the uniaxial loading and stationary temperature conditions was first considered. Then the parameter set of the model was identified by the proposed method from a set of experimental data. In comparison to those by other methods, the resultant stress-strain curves by the proposed method correlated better to the actual material behaviors.