• Journal of Korea Foundry Society
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• v.18 no.6
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• pp.578-585
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• 1998

A multi-purpose code MAGMA was employed for mold design and process control in producing Al wheel by lowpressure die casting. Three-dimensional solid modeling was followed by mesh generation of casting and molds(top, bottom and side). The simulation of stability of casting cycle time, mold filling simulation with pressure variation from P1 to P2, solidification simulation by solidification time and feeding criteria, and temperature distribution of molds during processes were studied in this research. The thermal stability of molds was attained after 5 cycles when molds were preheated at $400^{\circ}C$. The pressure increase from P1 to P2 for mold filling was evaluated as slightly higher, and 6 seconds were taken for the mold filling. The cycle time was believed to be designed properly judged from the solidification time of casting and open/close time of molds.

• Advanced Composite Materials
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• v.16 no.3
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• pp.195-206
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• 2007

Carbon nanofiber (CNF)/unsaturated polyester resin (UPR) was prepared by a solvent evaporation method, and the temperature dependency of electrical conductivity was investigated. The CNF/UPR composites had quite a low percolation threshold due to CNF having a larger aspect ratio and being well dispersed in the UPR matrix. The positive temperature coefficient (PTC) was found in the CNF/UPR composites and it showed stronger effect around the percolation threshold. The electrical resistance of the CNF/UPR composites decreased and had lower temperature dependency with increasing numbers of thermal cycles.

• Electrical & Electronic Materials
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• v.8 no.1
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• pp.21-26
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• 1995

Highly sensitive and mechanically stable gas sensors have been fabricated using the microfabrication and micromaching techniques. The sensing material used to detect the offensive trimethylarnine ((CH$_{3}$)$_{3}$N) gas is 6 wt% $Al_{2}$O$_{3}$-doped, 1000.angs.-thick ZnO deposited by r. f. magnetron sputtering. The optimum operating temperature of the sensor is 350.deg.C and the corresponding heater power is about 85mW. Excellent thermal insulation is achieved by the use of a double-layer structure of 0.2.mu.m -thick silicon nitride and 1.4.mu.m-thick phosphosilicate glass(PSG) prepared by low pressure chemical vapor deposition(LPCVD) and atmospheric pressure chemical vapor deposition(APCVD), respectively. The sensors are mechanically stable enough to endure at least 43, 200 heat cycles between room temperature and 350.deg. C.

• Solar Energy
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• v.17 no.3
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• pp.23-33
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• 1997

The theory on phase change temperature control and nucleation of PCM was suggested in this research. The crystallization model of PCM was established. And H2O-NaCl mixtures were selected as cold storage materials for agricultural products and thermo-physical properies of the PCM were analyzed with experimental processes including freeze-thaw cycles.

• ETRI Journal
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• v.20 no.2
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• pp.241-249
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• 1998

The structure and electrical characteristics of metal-ferroelectric-semiconductor FET(MFSFET) for a single transistor memory are presented. The MFSFET was comprised of polysilicon islands as source/drain electrodes and $BaMgF_4$ film as a gate dielectric. The polysilicon source and drain were built-up prior to the formation of the ferroelectric film to suppress a degradation of the film due to high thermal cycles. From the MFS capacitor, the remnant polarization and coercive field were measured to be about $0.6{\mu}C/cm^2$ and 100 kV/cm, respectively. The fabricated MFSFETs also showed good hysteretic I-V curves, while the current levels disperse probably due to film cracking or bad adhesion between the film and the Al electrode.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.10a
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• pp.73-76
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• 2000

Traction motors that is one of the rotating machines for urban transit EMU have been subjected to increased demand for higher operating temperature, more demanding duty cycles, higher starting current, frequent voltage transients and severe environmental exposure. With the advent of PWM drives using power IGBTs in addition to the thermal considerations, it is important to take into account the impact of the dielectric stress upon the winding insulation system life. In analyzing the life of the stator winding, which is the heart of the motor, the majority of all winding failures are usually caused by a combination of various stresses acting on the insulation materials and system. In this paper, to evaluate the expected life of traction motor for urban transit E.M.U. it is proposed a new test method of complex accelerating degradation.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.11 no.3
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• pp.110-116
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• 2002

Here are shown on stress and vibration evaluations and application of piping system in petrochemical plant with and actual example. While stress evaluation by thermal growth has no argument on the calculated results, vibrational evaluations have some different results in accordance with the evaluation methods. In case of the static stress evaluation the ASME B3l.3 code defines 7000 cycles of fatigue lift: in operating the piping system with a design condition. However, the method of vibrational evaluation on piping systems in petrochemical plants has not been established clearly, yet. In this stuffy, it is purposed to present the requirement of a vibrational evaluation method for petrochemical plant piping system, with an actual application.

• Journal of Advanced Marine Engineering and Technology
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• v.6 no.2
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• pp.51-68
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• 1982

A method of calculation of temperature distribution during welding was studied and compared with the existing formulas and experimental results. In contrast to the existing formulas which are founded on the suppositions that the heat source is a point and that the dimensions of welded pieces are infinite, we tried to make the distribution of calorific density of heat source approach reality more closely, so we considered it as a normal distribution of Gauss, and we presented the formulas for calculation of temperature during welding. We also used the principle of superposition for the temperature calculations of finite welded pieces. We compared the formulas presented in this paper with the existing formulas by calculations for the welding of various materials, and considerable differences around the heat source were convinced. The thermal cycles of various points were traced through the welding experiments for the mild steel, and they were compared with the results of calculations.

• Journal of Welding and Joining
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• v.8 no.3
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• pp.53-59
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• 1990

Temperature distribution of thick plate during welding was investigated. Applied weldng process was shielded metal arc welding which was known as one of the most utilized processes in fabrication fields. Heating and cooling cycles were recorded by imploying high fidelity recorded and K-type thermocouple of 0.3mm in diameter. Both analytical and numerical calculations were preformed so as to verify the thermal cycle measurement. Results showed that the temperature of a welded points at given time could be predicted by the theoretical calculations. It was considered that methods could be applied to real structural components with slight modification.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.7 no.3
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• pp.68-78
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• 1998

Welding structure contains residual stress due to thermal-plastic strain during welding process, and its magnitude and distribution depend on welding conditions. Cracks initiate from various defects of the weldment, propagate and lead to final fracture, The crack initiation and propagation processes are affected by the magnitude and distribution. Therefore, the magnitude and distribution of weldment residual stress should be considered for safety design and service of welding structures. Also it is very important that more accurate assessment method of fatigue crack growth must take into account the redistributing the residual stress quantitively. because the residual stress in weldment has characteristics of its redistribution with loading magnitude, number of cycles and fatigue crack propagation. In this study fatigue crack behavior of STS-304 weldment was investigated during crack propagation into tensile residual stress region or compressive residual stress region. Crack growth rates were predicted and compared with experimental results.