• Computational Structural Engineering : An International Journal
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• v.1 no.1
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• pp.21-29
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• 2001

The general topology optimization can be considered as optimal material distribution. Such an approach can be unstable, unless composite materials are introduced. In this research, a nodal volume fraction method is used to obtain the optimum topology of continuum structures. This method is conducted from a composite material model composed of isotropic matter and spherical void. Because the appearance of the chessboard patterns makes the interpretation of the optimal material layout very difficult, this method contains a chessboard prevention strategy. In this research, several topology optimization problems are presented to demonstrate the validity of the present method and the recursive quadratic programming algorithm is used to solve the topology optimization problems.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2006.04a
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• pp.365-372
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• 2006

A new meshfree formulation is developed for material discontinuity problems. A local interfacial jump function which is defined as hyperplane function is embedded in the meshless approximation and the approximation accurately models functions with jumps in the displacement and the derivative fields. Diffuse derivative technique copes with difficulty due to complexity of derivative computation of meshfree approximation. Collocation method with diffuse derivative accelerates computing speed for numerical solution. By solving inclusion and composite material problems, the robustness and effectiveness of the method are verified.

• Journal of the Korean Society for Railway
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• v.9 no.6 s.37
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• pp.635-643
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• 2006

In this paper, a theorectical approach is studied to predict structural performances and weight-reduction rates of hybrid bodyshells in case that the materials of roof structures are substituted. To determine other light-weight materials to be substituted for the original roof materials, bending and twisting deformations are considered under constant stiffness and strength conditions, which derive some new weight-reduction indices from a structural performance point of view. The indices derived to estimate the weight-reduction can be utilized as a good criterion at the conceptual design for material substitution of the roofs.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.14 no.5
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• pp.397-404
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• 2001

This study describes the effect of γ-ray irradiation on the properties of insulation materials for low voltage cables in a nuclear power plant. The radiation effects were characterized by measuring OIT, FTIR, electrical properties of the irradiated specimens. As a result, they showed the decrease of OIT and the increase of chemical structural defects with the increase of γ-ray amount. Also, the electrical properties such as dielectrical constant, tan $\delta$ and current were changed by aging. These changes may come from the increase of chemical structural defects by $\delta$-ray irradiation.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.384-384
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• 2012

PRAM switching device by using current pulse modulation was investigated to verify its possibility for 3D architecture. In this work, two phase change materials connected in series having a different crystallization temperature are used. Its structural for different phase change material was evaluated by electrical resistance. We confirmed that Germanium-Antimony-Tellurium (GST) alloy and Germanium- Copper-Tellurium (GCT) alloy material were selected according to crystallization temperature, ${\sim}180^{\circ}C$ for switching and ${\sim}240^{\circ}C$ for memory devices, respectively. From this research, it is expected that phase change switching device could have advantages of process in terms of material similarity and structural simplification.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2001.10a
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• pp.59-66
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• 2001

The post-peak analysis of concrete structures is carried out using a nine-node Reissner-Mindlin(RM) shell element which is formulated by using degenerated solid concepts. In order to avoid element deficiencies inherited in the standard RM shell element, assumed strains are adopted in the present shell element. A microscopic material model is adopted to represent the inelastic characteristic of concrete material. In particular, a concrete softening model is introduced to this material model. The arc-length control method is used to trace the post-peak behaviour of concrete structures. From the numerical test of the single-edge-notched beam, the present shell element shows a reasonable agreement with experimental data.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2007.04a
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• pp.557-562
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• 2007

In order to analyze the PSC box-girder bridge by the cantilever construction method, three dimensional analysis method using the PSC shell clement is suggested. The time dependent material functions are based on the ACI and CEB code. The time dependent concrete material properties considered are changes in strength, elastic modulus, creep and shrinkage. For the prestressing tendon, relaxation effects are considered. Anchorage and friction loses during tendon installations are also included. The ACI and CEB material models for creep and elastic modulus are also included.

• Structural Engineering and Mechanics
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• v.4 no.6
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• pp.679-702
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• 1996

The finite element method is employed in conjunction with micromechanical modelling in order to assess the performance of ceramic thermal barrier coatings applied to structural components. The study comprises the conditions of the deposition of the coating by plasma spraying as well as the thermal cycling of the coated component, and it addresses particularly turbine blades. They are exposed to high temperature changes strongly influencing the behaviour of the core material and inducing damage in the ceramic material by intense straining. A concept of failure analysis is discussed starting from distributed microcracking in the ceramic material, progressing to the formation of macroscopic crack patterns and examining their potential for propagation across the coating. The theory is in good agreement with experimental observations, and may therefore be utilized in proposing improvements for a delayed initiation of failure, thus increasing the lifetime of components with ceramic thermal barrier coatings.

• Proceedings of the KSR Conference
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• 2005.11a
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• pp.1071-1082
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• 2005

In this paper is studied a theoretical approach to predict structural performances and weight reduction rates of a carbody with shell type sections in case that its materials have to be substituted. For the material substitution design of a carbody, bending, axial and twisting deformations are considered under constant stiffness and strength conditions, which utilizes some new indices derived from a structural point of view. The developed indices to measure the weight reduction by the material substitution give good guidelines on conceptual design of carbodies.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 1997.04a
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• pp.11-18
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• 1997

Mechanical properties of a composite mixed by components with known material properties are numerically predicted at various volume fractions rather than investigated through experiments. The properties, elastic modulus and Poisson's ratio, are estimated by minimizing the error between the static displacements computed from a model for the composite and those computed from a model of homogeneous and isotropic material. A finite element model for a composite is proposed to distribute different types of material components easily into the model depending on the volume fraction. Mechanical properties of a composite filled with solid mircospheres are predicted numerically through a sample study and the estimated results are compared with experimental results and some theories.