• Proceedings of the Computational Structural Engineering Institute Conference
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• 2009.04a
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• pp.38-41
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• 2009

Debonding behavior of symmetric tilt bicrystal interfaces with <100> misorientation axis is investigated through molecular dynamics simulations. FCC single crystal copper is considered in each grain and the model is idealized as a grain boundary under mechanical loading. Embedded-Atom Method potential is chosen to calculate the interatomic forces between atoms. Constrained tensile deformations are applied to a variety of misorientation angles in order to estimate the effect of grain boundary angle on local peak stress. A new parameter of symmetric grain-boundary structure is introduced and refines the correlation between grain boundary angle and local peak stress.

• Journal of the Korean Ceramic Society
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• v.29 no.7
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• pp.539-543
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• 1992

The continuous growth method was developed for Mn-Zn Ferrite single crystals. It is a new process that the polycrystalline MnχZn1-χFe2O4 raw materials are supplied continuously from the powder feeding system to the crucible heated by R.F. induction and melted in the crucible, and after the single crystals seed is attached to crucible's hole, the crystals are pulled downward with rotation. Growing the crystals by using the growth method different from the conventional Bridgman or Floating Zone method, we defined the factors having effect on the crystal growing through the pre-experiments. They are temperature distribution in the crucible, melt velocity according to its height, wettability between the crucible's bottom and melt. Therefore, Mn-Zn Ferrite single crystals were to be grown by attaining the appropriate melt height in the crucible, powder feeding rate, temperature gradient between the crucible and interface, crystal growing speed, and this method was confirmed to have possibility for single crystal growing.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.14 no.2
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• pp.104-109
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• 2005

This article has been investigated the use of FFT for adhesive joints analysis between metal sheets. The method is based on the measurement of the reflection wave at the metal/adhesive interface. After describing briefly the physical aspects of the phenomenon, an index is defined to detect defective zone of the joint(both for the lack of adhesive and for insufficient adhesion): the influence of the experimental variables(variable stress...) on the measurement is discussed. By means of a control experiment it is shown that stress variation in adhesive joints are separate to be distinguished. In this paper, Nondestructive evaluation in adhesive joints are evaluated together with ultrasonic testing and finite element analysis.

• 한국신재생에너지학회:학술대회논문집
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• 2005.06a
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• pp.9-12
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• 2005

In this paper. we offer a new monitoring system that controls all of the windfar. it can also apply use general wind turbine systems and real meteorological tower. We propose a hierarchical releiable monitoring system connected by wireless communication channels between monitoring host computer and modular slave measuring subsystems. Our system has two hierarchical subsystems: slave measuring systems, and supervisory host computer. We design and implement that the slave measuring subsystems is placed in meteorological tower and wind turbines, and the supervisory host computer in safety zone, The micro-controller in slave measuring system is duplicated using cold-standby method for reliability. The host computer and slave system constructs a feedback system, with wireless communication channel between them. For monitoring and command function, the supervisory computer is implemented with a Personal Computer using graphic user interface. Consequently. we can get a reliable but economic system.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.06a
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• pp.337-340
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• 2005

The effect of residual stress on fatigue crack growth was investigated in terms of finite element analysis. Simulations were performed on a CT specimen in plane strain. An interface-cohesive element that accounts for damage accumulation due to fatigue along the notch direction has been used. Numerical results show that fatigue crack growth rate slows down when compressive residual stress field exists in front of the crack tip.

• Journal of Welding and Joining
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• v.8 no.1
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• pp.43-53
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• 1990

The transient temperature distribution in the continuous friction welding 304 stainless steel bars is investigated by experimental and analytical methods. It is calculated by F.D.M. (finite difference method). The heating pressure, the rotational speed and friction coefficient obtained from experiment are used to determine the heat input at the contacting surface. Thermal properties of the workpiece are the function of temperature. The calculated temperature is well coincided with the measured value. The grain size at weld interface is extremely small due to the severe plastic deformation at high temperature, and result of this refined zone reveals higher hardness value. Because the HAZ is very narror about 2-3 mm, welding defects do not occure.

• Proceedings of the Materials Research Society of Korea Conference
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• 2011.10a
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• pp.27.2-27.2
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• 2011

Polymer electronics is the one of the most promising way to realize the flexible electronics and many studies made remarkable progress to achieve the improvement in performance of polymer electronics comparable to current silicon-based technology. PBTTT is conjugated semiconducting polymer with highly ordered, chain-extended crystalline microstructures and shows high field effect mobilities above 0.1 $cm^2/Vs$. We studied PBTTTs FETs phase and explored methods to control channel interface in various device structures. Especially, in PBTTTs' unique nano-ribbon phase, we could obtain high mobilities of up to 0.4 $cm^2/Vs$, which was not reached before. Alignment of PBTTTs film was carried out using zone casting and anisotropy of mobilities in parallel and perpendicular to the polymer chain direction was investigated. Optical anisotropy in aligned nano-ribbon PBTTT FETs was also studied using a polarized optical absorption.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2004.10a
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• pp.860-864
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• 2004

This article discusses the use of pulse-echo ultrasonic testing for the stress analysis of adhesive bonds between metal sheets. The method is based on the measurement of the reflection wave at the metal/adhesive interface. After describing briefly the physical aspects of the phenomenon, an index is defined to detect defective zone of the joint(both for the lack of adhesive and for insufficient adhesion); the influence of the experimental variables(variables stress...) on the measurement is discussed. By means of a control experiment it is shown that Stress Variation in Adhesive Joints are separate to be distingguished. In this paper, Quantitative Nondestructive Evaluation in Adhesive Joints are together with Ultrasonic Testing and Finite Element Method.

• Journal of Ocean Engineering and Technology
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• v.6 no.2
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• pp.143-150
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• 1992

Numerical simulation is made of a stably stratified salt-water solution due to lateral heating in an equilateral trapezoidal enclosure using boundary-fitted coordinate in grid generation. Results show four types of the global fluid pattern depending on the buoyancy ratio in the enclosure, i.e., unicell flow pattern for the low buoyancy ratio, layered flow pattern for the increasing buoyancy ratio, layered flow pattern with stagnant zone for the relatively high buoyancy ratio and stagnant flow pattern for the much higher buoyancy ratio.

• Proceedings of the KIEE Conference
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• 1992.07b
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• pp.806-808
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• 1992

This paper describes a buried-island SOI MOSFET structure which can reduce the edge channel effect by improving the interface properties at the side wall of active island and by reducing the strength of electric field applied at the upper corner of the side wall from the gate. Also, the buried-island SOl structure can obtain the uniform thickness of SOl film. The buried-island structure can be achieved by Zone- Melting-Recrystallization of polysilicon and polishing. Both simulated and experimental results show that the buried-island SOl NMOSFET has less edge channel effect than the conventional SOl NMOSFET using LOCOS or mesa isolation technique.