• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2006년도 추계 학술발표회 논문집
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• pp.569-572
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• 2006

TSA(thaumasite sulfate attack) is one of the important and prevailing phenomena to damage concrete structures by sulfate attack. In the present study, the thaumasite ($CaSiO_3{\cdot}CaSO_3{\cdot}CaSO_4{\cdot}15H_2O$) has been observed by the authors and other researchers in concrete samples in laboratory or field. Microstructural and mechanical observations clearly confirm that the thaumasite formation is greatly associated with sulfate attack indicating mass loss, expansion and spalling in the sample. This study summarizes the results of observation carried out by the authors and researchers on TSA which thaumasite formation has been identified.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제49권11호
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• pp.635-639
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• 2000

In this paper, a new idea about ultra-clean aligning and mounting method of FED spacers was introduced. The glass-to -glass electrostatic bonding process was employed in order to bond the micro-structures of spacers to black matrix area formed on an FED anode substrate. It is possible to get adhesive-free bonding interface and well-aligned spacer array on an FED anode substrate with a ${\pm}5{\mu}m$ accuracy. Finally, I inch-sized FED panel was demonstrated to make sure of its applicability to FED panel fabrication.

• Steel and Composite Structures
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• 제17권2호
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• pp.159-172
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• 2014

A finite element model with the consideration of damage initiation and evolution has been developed for the analysis of the dynamic response of a composite sandwich panel subject to low velocity impact. Typical damage modes including fiber breakage, matrix crushing and cracking, delamination and core crushing are considered in this model. Strain-based Hashin failure criteria with stiffness degradation mechanism are used in predicting the initiation and evolution of intra-laminar damage modes by self-developed VUMAT subroutine. Zero-thickness cohesive elements are adopted along the interface regions between the facesheets and the foam core to simulate the initiation and propagation of delamination. A crushable foam core model with volumetric hardening rule is used to simulate the mechanical behavior of foam core material at the plastic state. The time history curves of contact force and the core collapse area are obtained. They all show a good correlation with the experimental data.

• Structural Engineering and Mechanics
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• 제30권4호
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• pp.467-480
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• 2008

An aggregation multigrid method (AMM) is a leading iterative solver in solid mechanics. Recently, AMM is applied for solving Schur Complement system in the FE analysis of shell structures. In this work, an extended application of AMM for solving Schur Complement system in the FE analysis of continuum elements is presented. Further, the performance of the proposed AMM in multiple load cases, which is a challenging problem for an iterative solver, is studied. The proposed method is developed by combining the substructuring and the multigrid methods. The substructuring method avoids factorizing the full-size matrix of an original system and the multigrid method gives near-optimal convergence. This method is demonstrated for the FE analysis of several elastostatic problems. The numerical results show better performance by the proposed method as compared to the preconditioned conjugate gradient method. The smaller computational cost for the iterative procedure of the proposed method gives a good alternative to a direct solver in large systems with multiple load cases.

• Steel and Composite Structures
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• 제7권4호
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• pp.263-278
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• 2007

A finite element implementation of the modified compression field theory (MCFT) using a tangential formulation is presented in this work. Previous work reported on implementations of MCFT has concentrated mainly on secant formulations. This work describes details of the implementation of a modular algorithmic structure of a reinforced concrete constitutive model in nonlinear finite element schemes that use a Jacobian matrix in the solution of the nonlinear system of algebraic equations. The implementation was verified and validated using experimental and analytical data reported in the literature. The developed algorithm, which converges accurately and quickly, can be easily implemented in any finite element code.

• Steel and Composite Structures
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• 제25권1호
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• pp.93-104
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• 2017

In the present work, the effect of hygrothermal aging on the glass fibre and epoxy matrix interface has been investigated by destructive and non-destructive techniques. The glass fiber reinforced polymer (GFRP) composite laminates were prepared using Vacuum Assisted Resin Infusion Molding (VARIM) technique and the specimens were immersed in simulated seawater, followed by quantitative measurement. Besides this, the tensile tests of GFRP specimens revealed a general decrease in the properties with increasing aging time. Also, exposed specimens were characterized by a non-destructive ultrasonic guided Lamb wave propagation technique. The experimental results demonstrate a correlation between the drop in ultrasonic voltage amplitude and fall in tensile strength with increasing time of immersion. Hence, the comparison of the transmitted guided wave signal of healthy vis-a-vis specimens subjected to different extents of hygrothermal aging facilitated performance evaluation of GFRP composites.

• 한국산학기술학회논문지
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• 제5권4호
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• pp.286-291
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• 2004

실무 현장에서 피로 파괴가 잘 일어나고 있는 상황이다. 그런데 그 하중도 불규칙적으로 일어나고 있어 예측이 불가능하여 언제 파괴가 일어나는지를 잘 알 수가 없는 상황이다. 본 연구에서는 그러한 불규칙적인 피로 하중을 시뮬레이션 하여 그 재료의 안정성과 수명 관계를 Ansys workbench 프로그램을 이용하여 이론적으로 해석하여 보았다. 이러한 결과들을 실제 구조물에서 응용하면 그 파손 방지 및 내구성을 예측하는데 활용이 크다고 본다.

• Transactions on Electrical and Electronic Materials
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• 제15권1호
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• pp.20-23
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• 2014

Dual phase steels have a microstructure comprising of a polygonal ferrite matrix together with dispersed islands of martensite. There are clear differences between the image quality (IQ) map of the dual phase and the corresponding ferritic/pearlitic structures, both in the as-heat treated and cold rolled conditions. Electron backscatter diffraction (EBSD) techniques were used to study the evolution substructure of steel due to plastic deformation. The martensite-ferrite and ferrite-pearlite interfaces were observed. The interface can be a source of mobile dislocations which the bands seem to originate from the martensite islands. In particular, the use of image quality is highlighted.

• 한국주조공학회지
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• 제2권2호
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• pp.10-17
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• 1982

This study has been carried out to determine the change of mechanical properties and microstructures by the heattreatment to relieve the residual stresses for gray cast irons. The results have been obtained from the experiment as follows; 1) The annealing above $600^{\circ}C$ for the stress relieving of gray cast iron decrease the tensile strength and hardness 2) The decrease reates of tensile strength and hardness of gray cast iron after annealing above $600^{\circ}C$ are increased with increasing the holding time. 3) The gray cast iron containing the elements of Mn, Cr has increased the heating temperature for the decrease of tensile strength and hardness. 4) The decrease of mechanical properties by annealing are assumed that the formation of ferrite takes placed from the decomposition of eutectoid cementite in the matrix.

• 산업공학
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• 제11권2호
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• pp.149-157
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• 1998

In this paper, various techniques considering the characteristics of computer memory management are suggested, which can be used in the implementation of simplex method. First, reduction technique of indirect addressing, redundant references of memory, and scatter/gather technique are implemented, and the effectiveness of the techniques is shown. Loop-unrolling technique, which exploits the arithmetic operation mechanism of computer, is also implemented. Second, a subroutine frequently called is written in low-level language, and the effectiveness is proved by experimental results. Third, row-column linked list and Gustavson's data structure are compared as the data structure for the large sparse matrix in LU form. Last, buffering technique and memory-mapped file which can be used in reading large data file are implemented and the effectiveness is shown.