• Transactions of the Korean Society of Machine Tool Engineers
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• v.17 no.1
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• pp.98-105
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• 2008

In this paper, the system for monitoring process of aluminum laser welding was developed using the light signal emitted from the plasma which comes from interaction between material and laser. Photodiode for monitoring system was selected based on the spectrum analysis of light from plasma and keyhole. Behavior of plasma and keyhole was analyzed through the sensor signals. Value of sensor signal represented the light intensity and fluctuation of signal indicated the stability of plasma and keyhole. For the relation between welding condition and sensor signals, the input power and weld geometry greatly effected on the average of each sensor signals. Using the feature values of signals, estimation model for tensile strength of weld was formulated with neural network algorithm. Performance of this model was verified through coefficient of determination and average error rate.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.17 no.1
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• pp.65-70
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• 2008

The shape and the material of a reflective sheet affect the amount and the range of retroreflection on incident angle of light, significantly. In this study, the method to determine the shape and the material of the reflective sheet is introduced for the maximum retroreflection. Since the microprism shape with an equilateral triangle base has been used widely, the shape optimization of the microprism shape is carried out. The path of the light within the prism is geometrically calculated to find the relationship between incoming and outgoing light to and from a microprism. The optimal shape of a microprism found by the simulation has almost same figure with the one being used in industry for the maximum retroreflection. It is also found that the refraction index of the reflective sheet is another parameter to control for maximum retroreflection and the range of retroreflection.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.20 no.5
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• pp.523-527
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• 2011

Polycarbonate (PC) polymer is an engineering plastic which has large tensile strength and impact resistance and is wildly used as functional parts like micro mold. Direct machining of PC materials produces lots of burrs and rough surface due to large ductility and weak heat resistance and hence it is very difficult to machine PC materials using cutting tool to make micro-parts. In this study, elliptical vibration cutting (EVC) or 2-dimensional vibration cutting was performed to minimize the size of micro V-grooves on PC material. From the experimental results, it was observed that as the cutting depth and pattern size become smaller, the better machining quality was obtained, which is attributed to the positive effect of EVC that is dependent on the ratio of vibration amplitude to cutting depth. As the height of V-groove becomes less than $1.8{\mu}m$, however, the machining quality becomes lower as the pattern size decreases.

• Computational Structural Engineering
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• v.7 no.1
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• pp.125-134
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• 1994

Response variability of reinforced concrete frame subjected to material property randomness has been evaluated with the aid of the finite element method. The spatial variation of Young's modulus is assumed to be a two-dimensional homogeneous stochastic process. Young's Modulus of concrete material has been investigated based on the uiaxial strength of concrete cylinder. Direct Monte Carlo simulation method is used to investigate the response of reinforced concrete frame due to the variation of Young's modulus with the Neumann expansion method and the pertubation method. The results by three analytic methods are compared with those by deterministic finite element analysis. These stochastic technique may be an efficient tool for evaluating the structural safety and reliability of reinforced concrete structures.

• Journal of Power System Engineering
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• v.13 no.5
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• pp.82-88
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• 2009

The purpose of this paper is to provide technical background, techniques and actual diesel engine signature analysis evaluation result. Engine signature analysis(ESA) is a process for monitoring the material condition of diesel engine using external sensors, eliminating the need to periodically disassemble the engine. ESA is also used to balanced the engine. Engine balancing is the process of tuning the engine so that all cylinders carry equal load. ESA is a useful tool to non-intrusively determine the operability and performance and assessment of the material condition of internal component of a diesel engine.

• Journal of the Korean Society for Precision Engineering
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• v.19 no.3
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• pp.80-87
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• 2002

Tungsten carbide microshaft is used as micro-punch, electrode of MEDM (micro-electro-discharge machining), and micro-tool because it has high hardness and high rigidity. In this study, the tungsten carbide microshaft was fabricated using electrochemical machining. Concentration of material removal at the sharp edge and metal corrosion layer affect the shape of the microshaft. Control of microshaft shape was possib1e through conditioning the machining voltage and electrolyte concentration. By applying periodic voltage, material removal rate increased and surface roughness improved. The fabricated microshaft in $H_2 SO_4$ electrolyte maintained sharper end edge and better surface finish than those fabricated by other electrolytes.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1998.03a
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• pp.28-31
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• 1998

Wrinkling is one of the major defects in sheet metal products and may be also attributable to the wear of the tool. The initiation and growth of the wrinkles are influenced by many factors such as stress state, mechanical properites of the sheet material, geometry of the body, and contact condition. It is difficult to analyze the wrinkling initiation and growth considering the factors because the effects of the factors are very complex and the wrinkling behavior may show wide variation for small deviation of the factors. In this study, the bifurcation theory is introduced for the finite element analysis of wrinkling initiation and growth, All the above mentioned factors are conveniently considered by finite element method. The finite element formulation is based on the incremental deformation theory and elastic-plastic material modeling. The finite element analysis is carried out using the continuum-based resultant shell elements considering the planar anisotropy of the sheet metal. The proposed method is verified by employing to column buckling problem. And then, the initiation and growth of wrinkling in deep drawing of cylindrical cup are analyzed.

• Proceedings of the Korea Concrete Institute Conference
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• 2000.04a
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• pp.553-558
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• 2000

In this study, a numerical simulation that can effectively predict the interfacial fracture behavior in repaired structures is developed using the axial deformation link elements. In repaired structures, concrete and interface are considered as quais-brittle materials, and steel plate as a repair material and reinforcement are modeled as elasto-plastic materials. The behavior of repaired reinforced concrete structures under flexural loading conditions is numerically simulated, and compaired with experimental results. The strengthening effect according to the length and thickness of the repair material is studied and rip-off, debonding and rupture failure mechanism of interface between substrate and repair materials are detected. It is shown that the interface properties affect on the mechanical behavior of repaired structures. Therefore, the developed numerical method using axial deformation link elements can be used for determining the strengthening effects and failure mechanism of repaired structures.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.20 no.3
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• pp.197-201
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• 2007

The accelerated aging test equipment which is possible to apply voltage and temperature at the same time, is fabricated to predict lifetime of high capacity thyristor in short time. The variations of the forward/reverse breakdown voltage and the leakage current are investigated as an aging diagnostic tool. Lifetimes of the devices which are predicted from the reverse breakdown voltage with an accelerated aging time, have shown 3-15 years.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.04b
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• pp.83-84
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• 2009

This paper presents a step-down converter IC for automotive applications. This device was designed for a 40V/1A high-power output for voltage reference of automotive IC. It provides 250kHz PWM(pulse width modulation) and PFM(pulse frequency modulation) according to load conditions. This device was simulated Spectre of IC Design Tool And fabricated Dong-bu Hitec 0.35um BD350BA process.