• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제48권4호
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• pp.221-225
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• 1999

This paper shows the parameters to affect the critical characteristic of YBaCuO superconducting bulk fabricated by MPMG (Melt Powdered Melt Growth)process. In order to investigate proper processing variables, the effect of the holding time at the melting temperature and that of the slow cooling time in $O_2\; ambient\; on\; the\; J_c$ were experimented. And then with the above obtained heat treatment conditions, the effects of addition of $Y_2BaCuO_5\; and\; Ag\; on\; the\; J_c$ were also investigated. A proper slow cooling time yields phase transformation from Tetragonal $(YBa_2Cu_3O_6)$ to Orthorhombic $(YBa_2Cu_3O_7)$ during an annealing time in $O_2$. Ag addition plays a role in increasing the $T_c\; and\; the J_c$, but the magnetization decreases. The $J_c$ and the magnetization increase with addition of Y211. $J_c$ of the sample added Ag 10wt% is superiorover 3000 G. Proper holding time, slow cooling time and amount of impurity addition are important parameters in fabricating the YBaCuO bulk by MPMG process with high $J_c$.

• Journal of Welding and Joining
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• 제31권1호
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• pp.43-50
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• 2013

The spot welds of Transformation Induced Plasticity (TRIP) steels are prone to interfacial failure and narrow welding current range. Hard microstructures in weld metal and heat affected zone arenormally considered as one of the main reason to accelerate the interfacial failure mode. There fore, detailed observation of weld microstructure for TRIP steels should be made to ensure better weld quality. However, it is difficult to characterize the microstructure, which has similar color, size, and shape using the optical or electron microscopy. The atomic force microscope (AFM) can help to analyze microstructure by using different energy levels for different surface roughness. In this study, the microstructures of resistance spot welds for AHSS are analyzed by using AFM with measuring the differences in average surface roughness. It has been possible to identify the different phases and their topographic characteristics and to study their morphology using atomic force microscopy in resistance spot weld TRIP steels. The systematic topographic study for each region of weldments confirmed the presence of different microstructures with height of 350nm for martensite, 250nm for bainite, and 150nm for ferrite, respectively.

• 한국재료학회지
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• 제4권3호
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• pp.364-375
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• 1994

공냉에 의한 중탄소 비조질강은 페라이트와 펄라이트의 미세구조를 갖는다. 기존의 조질강과 비교하여 이재료는 V, Nb, Ti을 첨가하여 강도는 거의 동등한 반면 인성에 있어서 조질강에 비해 취약하다. 본 연구에서는 직접 소입 저탄소 비조질강의 기계적 성질에 미치는 몰리브덴의 영향을 조사하였다. 몰리브덴 첨가 직접 소입 비조질강은 고강도와 고인성을 나타내었다. 몰리브덴은 변태 온도를 저하시켜 미세한 구조와 균일한 석출 구조를 효과적으로 생성시킨ㄷ. 본 실험의 결과로 0.15C+0.11V+0.035Nb+1.81Mo의 재료를 유냉시켜 121MPo의 강도와 127.5J의 인성을 얻었다.

• 공업화학
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• 제18권5호
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• pp.424-432
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• 2007

본 연구에서는 용암석상의 무기물인 퍼라이트의 팽창에 관한 전산 모사 및 실험을 실시하여 모델의 유효성을 검증하고자 하였다. 전산 모사는 등온 상태를 가정하여 실시하였고 초기 온도 및 수분 함량을 변화시켜 보았다. 초기 온도보다는 수분함량이 팽창에 더 큰 영향을 주었고 이는 퍼라이트의 점도 변화에 기인한 것으로 결론지을 수 있었다. 실험 결과와 비교를 위하여 시료의 충전 밀도를 측정하였고 이를 원석의 충전 밀도와 비교하여 내부 동공을 가지는 팽창 퍼라이트의 밀도를 계산하였다. 이의 결과를 전산 모사 결과와 비교하였으며 등온 상태의 전산 모사가 실험 결과와 큰 차이가 남을 알 수 있었다. 이러한 차이는 열의 일로의 변환과 이에 따른 파라미터 값의 변화가 있을 것으로 결론내릴 수 있었다.

• 한국세라믹학회지
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• 제36권12호
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• pp.1356-1363
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• 1999

출발원료의 상분을 제어와 가압소결 및 열처리에 의하여 자체강화 미세구조를 갖는 탄화규소 세라믹스를 제조하여 그 특성을 고찰하였다. 자체강화 탄화규소 세라믹스는 알파상과 베타상 탄화규소 분말을 혼합한 모든 원료조합으로부터 얻어졌으며, 이러한 미세구조는 열처리 동안 베타상 탄화규소 입자가 긴 막대상 입자 형태를 갖는 4H 상의 알파 탄화규소로 상변태하면서 형성되었다. 긴 막대상의 탄화규소 입자의 부피분율 및 장단축비는 베타상 탄화규소 분말의 함유량이 50%인 시편에서 가장 크게 나타났으며, 이로 인하여 이 시편은 제조된 시편 중에서 가장 높은 인성을 나타내었다.

• 한국태양에너지학회 논문집
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• 제33권1호
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• pp.73-78
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• 2013

Hexadecane and exfoliated graphite nanoplate (xGnP)composite was prepared as a shape-stabilized phase change material (SSPCM) in a vacuum to develope thermal energy storage. The Hexadecane as an organic phase change material (PCM) is very stable against phase separation of PCM and has a melting point at $18^{\circ}C$ that is under the thermally comfortable temperature range in buildings. The xGnP is a porous carbon nanotube material with high thermal conductivity. Scanning electron microscope (SEM) and Fourier transformation infrared spectrophotometer (FT-IR)were used to confirm the chemical and physical stability of Hexadecane/xGnP SSPCM. In addition, thermal properties were determined by Deferential scanning calorimeter(DSC) and Thermogravimetric analysis (TGA). The specific heat of Hexadecane/xGnPSSPCM was $10.0J/g{\cdot}K$ at $21.8^{\circ}C$. The melting temperature range of melting and freezing were found to be $16-25^{\circ}C$ and $17-12^{\circ}C$. At this time, the laten heats of melting and freezing were 96.4J/g and 94.8J/g. The Hexadecane was impregnated into xGnP as much about 48.8% of Hexadecane/xGnP SSPCM's mass fraction.

• 한국주조공학회지
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• 제33권4호
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• pp.171-180
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• 2013

The effects of alloying elements on the solidification characteristics, microstructure, thermal conductivity, and tensile strength of Al-Zn-Mg-Fe alloys were investigated for the development of high strength and high thermal conductivity aluminium alloy for die casting. The amounts of Zn and Mg in Al-Zn-Mg-Fe alloys had little effect on the liquidus/solidus temperature, the latent heat for solidification, the energy release for solidification and the fluidity of Al-Zn-Mg-Fe alloys. Thermo-physical modelling of Al-Zn-Mg-Fe alloys by the JMatPro program showed $MgZn_2$, AlCuMgZn and $Al_3Fe$ phases in the microstructure of the alloys. Increased amounts of Mg in Al-Zn-Mg-Fe alloys resulted in phase transformation, such as $MgZn_2{\Rightarrow}MgZn_2+AlCuMgZn{\Rightarrow}AlCuMgZn$ in the microstructure of the alloys. Increased amounts of Zn and Mg in Al-Zn-Mg-Fe alloys resulted in a gradual reduction of the thermal conductivity of the alloys. Increased amounts of Zn and Mg in Al-Zn-Mg-Fe alloys had little effect on the tensile strength of the alloys.

• 항공우주시스템공학회지
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• 제12권5호
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• pp.1-7
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• 2018

본 연구에서는 전자기-열 연동 모사를 기반으로 한 고주파 유도경화 해석방법을 제안하였다. 고주파 유도가열 해석 시 온도에 따른 재료의 물성치 변화 및 냉각 요소를 고려한 유한요소해석 및 이를 S45C 시편을 이용한 고주파 유도경화 실험결과와 비교하였다. S45C 시편을 마이크로 비커스를 사용하여 경도를 측정하여 경화깊이를 확인하였고 이를 유한요소해석 결과와 비교하였다. 고주파 유도가열 해석결과 온도는 S45C의 A2변태점인 $750^{\circ}C$도 이상 가열되었으며, 급랭 시 $200^{\circ}C$이하였다. 유한요소해석결과와 실험에 의한 경화깊이 차이는 0.2mm 수준인 것을 확인할 수 있었다.

• 건축역사연구
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• 제13권4호
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• pp.19-34
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• 2004

This study examines the dwellings of the Korean diaspora in Maritime Provinces of Russia, and Kazakhstan and Uzbekistan of Central Asia to find the gist of the residence transformed as Korean traditional residence culture to accept Russian foreign culture. Through the examination, transformation process of the dwellings of the Korean diaspora was found as follows: - 1st Period(1864-1937): The Korean diaspora who Immigrated to Maritime Provinces of Russia built traditional houses of Korean style and few of them lived in Russian style houses. - 2nd Period(1937-1955): The Koreans who immigrated to Central Asia from Maritime Provinces under compulsion built 'ground house' by digging the earth and installed gudeul which is a traditional Korean heating system and roofed with reed. - 3rd period(1955-1991): The Koreans built straight lined '-' shape houses with two or three rooms wherein most of them were installed with gudeul to heat the room. Around the 1940s as they economically got well, the Koreans started to build houses with Russian style with one or two rooms with gudeul or a separate building with gudeul. - 4th period(1991-present): Houses of the 3rd period are still used by being enlarged or remodeled with less use of gudeul which is well reflected on Ujeong-maul village in Russia Maritime Provinces. As can be found above, the dwellings of the Korean diaspora in Russia Maritime Provinces and Central Asia are on the process of being transformed into Russian style to adapt to Russian culture.

• 전기학회논문지
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• 제65권5호
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• pp.738-744
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• 2016

Current rating of a power cable can be calculated by the maximum allowable temperature in an insulating material considering the heat transfer from cable conductor. Therefore, it is very important to calculate the current rating using electrical equivalent circuit by calculated cable thermal circuit parameters but, it has not been fully investigated yet. In this paper, in order to determine the current rating of power cable, conventional calculation method has been reviewed considering the conductor resistance, loss factor of sheath, dielectric losses and thermal resistances based on the maximum allowable temperature of 345 kV $2500mm^2$ XLPE cable. To confirm the calculation result of the current rating, the conductor temperature should be examined whether it reaches the maximum allowable temperature by the thermal equivalent circuit of the cable. Then, utilizing EMTP (Electro-Magnetic Transient Program) which is a conventional program for electrical circuit, the thermal equivalent circuit was transformed to an electric equivalent circuit using an analogous relationship between thermal circuit and electrical circuit, and temperature condition including cable conductor, sheath, cable jacket could be calculated by the current rating of 345 kV $2500mm^2$ XLPE cable.