• Computational Structural Engineering
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• v.9 no.4
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• pp.181-187
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• 1996

This paper concerns the singular thermal stresses at the interface corner between the elastic fiber and the viscoelastic matrix of a two-dimensional unidirectional laminate model induced during cooling from cure temperature down to room temperature. Time-domain boundary element method is employed to investigate the nature of residual thermal stresses at the interface. Numerical results show that very large stress gradients are present at the interface corner and such stress singularity might lead to local yielding or fiber-matrix debonding.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.26 no.1
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• pp.39-48
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• 2013

This paper develops a 2-D moving least squares(MLS) difference method for Stefan problem by extending the 1-D version of the conventional method. Unlike to 1-D interfacial modeling, the complex topology change in 2-D domain due to arbitrarily moving boundary is successfully modelled. The MLS derivative approximation that drives the kinetics of moving boundary is derived while the strong merit of MLS Difference Method that utilizes only nodal computation is effectively conserved. The governing equations are differentiated by an implicit scheme for achieving numerical stability and the moving boundary is updated by an explicit scheme for maximizing numerical efficiency. Numerical experiments prove that the MLS Difference Method shows very good accuracy and efficiency in solving complex 2-D Stefan problems.

• Proceeding of EDISON Challenge
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• 2014.03a
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• pp.505-507
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• 2014

본 연구에서는 제일원리 계산을 이용하여 $Si(100)/SiO_2$ 계면 내부에서 발생하는 point defect들의 거동에 대해 살펴보았다. Defect 계산에 앞서 안정한 $Si/SiO_2$ 계면을 찾아보았고 찾은 계면을 바탕으로 계면에서 point defect의 formation energy를 계산해 보았고 이를 통해 Si defect의 경우 Si층 쪽 보다는 $SiO_2$ 층에서, 그리고 계면 내부 보다는 계면 경계 근처에서 발생할 가능성이 높음을 보였다.

• Computational Structural Engineering
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• v.10 no.1
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• pp.129-134
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• 1997

Interfacial stress singularity in a unidirectional two-dimensional laminate model consisting of an elastic fiber and a viscoelastic matrix has been investigated using the time-domain boundary element method. First, the interfacial singular stresses between the fiber and the matrix of a unidirectional laminate subjected to a uniform transverse tensile strain have been investigated near the free surface, but without any defect or any edge crack. Such a stress singularity might lead to fiber-matrix debonding or interfacial edge cracks. Then, the overall stress intensity factor for the case of a small interfacial edge crack of length a has been computed.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2009.04a
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• pp.308-313
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• 2009

본 논문은 확장된 이동최소제곱 유한차분법을 이용하여 1차원 Stefan 문제를 해석할 수 있는 수치기법이 제시한다. 이동하는 경계의 자유로운 묘사를 위해 요소망이나 그리드 없이 절점만을 사용하는 이동최소제곱 유한차분법을 사용하였으며, 계면경계의 특이성을 모형화하기 위해 Taylor 다항식에 쐐기함수를 도입했다. 지배방정식은 안정성이 높은 음해법(implicit method)을 이용하여 차분하였다. 미분의 특이성을 갖는 이동경계를 포함한 반무한 융해문제의 수치해석을 통해 확장된 이동최소제곱 유한차분법이 높은 정확성과 효율성을 갖는 것을 보였다.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2013.05a
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• pp.7-7
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• 2013

계면은 하나의 성격(상(相, phase), 문화, 시대 등)이 다른 성격과 만나는 전선이라고 할 수 있다. 포괄적으로 말한다면 계면은 주어진 상황이 새로운 상황(현실)에 직면할 때 부딪히는 경험하는 경계 현상이라고 할 수 있는 것이다. 이러한 계면의 이슈는 소재들이 사용되는 환경과 불가분의 관계에 있기 때문에 재료공학의 주요 대상일 수밖에 없다. 하지만 소재의 종류가 매우 다양하고 노출되는 환경 역시 다양하기 때문에 계면 혹은 계면현상을 한마디로 설명하기는 매우 어렵다. 본 강연에서는 재료공학 연구부문에 종사하여 온 연구자가 나름대로 이해하여온 계면(계면현상 자체를 연구하는 연구자는 아니라는 의미)에 관한 지식을 실용적인 관점에서 설명하고 터득한 지식을 연구에 활용해 온 사례들에 관하여 소개하고자 한다. 계면을 움직이는 구동력, 재료연구를 통하여 관찰한 계면현상들, 계면현상의 관점에서 본 나노기술 등을 설명하고자 한다.

• Proceedings of the Optical Society of Korea Conference
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• 2003.07a
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• pp.242-243
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• 2003

최근 유전체와 유전체, 유전체와 금속 물질 경계면에서 일어나는 계면 현상에 대한 연구가 활발히 진행되고 있다. 본 연구에서는 유전체와 유전체 경계면에 형성된 소산파의 크기를 maxwell의 방정식을 이용하여 계산하고, 광학 trap을 이용한 광압 측정법을 사용하여 경계면에서 소산파의 크기를 실험적으로 측정하였다. 광압 측정 장치는 그림 1과 같다. (중략)

• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.11
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• pp.1355-1360
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• 2011

The interaction between the cell and the substrate is the most prominent feature affecting the migration of a crawling cell. This paper proposes a three-dimensional dynamic model using the diffuse interface description that reveals the effects of the interaction between a single crawling cell and the substrate during chemotactic migration. To illustrate the effects of interaction between the cell and the substrate, we consider the interfacial energy between the coexistent materials. Multiple mechanisms including the interface energy, chemotaxis effect, and diffusion, are addressed by employing a diffuse interface model.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.24 no.5
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• pp.577-588
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• 2011

This paper provides a novel extended Moving Least Squares(MLS) difference method for the potential problem with weak and strong discontinuities. The conventional MLS difference method is enhanced with jump functions such as step function, wedge function and scissors function to model discontinuities in the solution and the derivative fields. When discretizing the governing equations, additional unknowns are not yielded because the jump functions are decided from the known interface condition. The Poisson type PDE's are discretized by the difference equations constructed on nodes. The system of equations built up by assembling the difference equations are directly solved, which is very efficient. Numerical examples show the excellence of the proposed numerical method. The method is expected to be applied to various discontinuity related problems such as crack problem, moving boundary problem and interaction problems.

• Journal of the Korean Society for Nondestructive Testing
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• v.15 no.4
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• pp.540-548
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• 1996

In general residual stress is measured by X-ray diffraction method but in case of bonding residual thermal stress it is inadequate technique to examine the stress singularity. Therefore Two-dimensional elastic boundary element analyses were carried out to investigate the residual thermal stress and stress singularity of bonding interface in Al/Epoxy. This boundary element results were compared with the strain gauge measurements. The effects of different interface models, sub-element and adherend thickness are presented and discussed. On the basis of the obtained results, interface delamination causing by normal stress is expected and stress singularity is observed more intensively increasing with adherend thickness. It is concluded that the bonding strength of Al/Epoxy interface can be estimated correctly by taking into account the stress singularity at the edge of the interface.