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RISS 인기검색어
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- 저자 : 최동혁 ( Dong Hyeok Choi ) (검색결과 30 건)
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MIAB용접에서 코일에 의한 자속밀도 분포의 수치적 해석에 관한 연구
최동혁(Dong-Hyeok Choi),김재웅(Jae-Woong Kim) Korean Society for Precision Engineering 2001 한국정밀공학회지 Vol.18 No.12
The MIAB welding uses a rotating arc as its heat source and is known as an efficient method for pipe butt welding. The arc is rotated around the weld line by the electro-magnetic force resulting from the interaction of arc current and magnetic field. The electro-magnetic force is affected by magnetic flux density, arc current, and arc length. Especially, the magnetic flux density is an important factor on arc rotation and weld quality. This paper presents a 2D finite element model for the analysis of magnetic flux density in the actual welding conditions. The magnetic flux density is mainly dependent on gap between two pipes, the position of coil from gap center, exciting current, and relative permeability. Thus, the relations between magnetic flux density and main factors were investigated through experiment and analysis. Experiments were performed for the steel pipes(48.1mm O.D and 2.0mm thickness). The analysis results of magnetic flux density reveal that it increases with increasing exciting current, increasing relative permeability, decreasing distance from gap center to coil, and decreasing gap size. It is considered that the results of this study can be used as important data on the design of coil system and MIAB welding system.
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PLD를 이용한 HoMn1 - xFexO₃ 박막 제조 및 후방 산란형 뫼스바우어 분광 연구
최동혁(Dong Hyeok Choi),심인보(In-Bo Shim),김철성(Chul Sung Kim) 한국자기학회 2007 한국자기학회지 Vol.17 No.1
Pulsed laser deposition(PLD) 박막 증착법을 이용하여 hexagonal HoMn1 − xFexO₃(x = 0.0, 0.05) 물질을 박막으로 Pt/Ti/SiO₂/Si 기판 위에 증착하였다. 또한 x-ray diffraction(XRD), atomic force microscopy(AFM), scanning electron microscope(SEM), 및 x-ray photoelectron spectroscopy(XPS)를 통하여 박막의 결정학적 및 미세 구조를 분석하였고, conversion electron Mössbauer spectroscopy(CEMS)를 이용하여 자기적 특성에 관해 연구하였다. 결정구조는 hexagonal 구조로써 space group이 P6₃㎝로 분석되었고, single crystal과는 달리 (110) 방향으로 우선 배향성을 가지고 증착되었다. HoMn0.95Fe0.05O₃ 박막의 경우 single crystal과 비교했을 때 hexagonal unit cell의 c₀ 축은 일정하나 a₀ 축은 다소 감소함으로 분석되었다. 이는 박막 증착에 사용된 Pt/Ti/SiO₂/Si 기판과의 lattice mismatch 때문으로 해석된다. Fe가 미량 치환된 HoMn0.95Fe0.05O₃ 박막을 상온에서 CEMS 측정을 수행한 결과, HoMn0.95⁵⁷Fe0.05O₃ 분말의 경우 magnetic TN이 72 K 부근이므로, 상온에서 doublet absorption spectrum이 관측되었고, 전기사중극자 분열값(quadrupole splitting; ∆EQ)이 1.62±0.01 ㎜/s로 비교적 큰 값을 가짐을 확인하였다. The hexagonal HoMn1 − xFexO₃ (x = 0.00, 0.05) thin films were prepared using pulsed laser deposition (PLD) method on Pt/Ti/SiO₂/Si substrate. The microstructure and magnetic properties have been studied by x-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscope (SEM), x-ray photoelectron spectroscopy (XPS), and conversion electron Mössbauer spectroscopy (CEMS). From the analysis of the x-ray diffraction patterns, the crystal structure for all films was found to be a hexagonal (P6₃㎝), which was preferentially grown along (110) direction. The lattice constant c₀ of the film with x = 0.05 was close to that of single crystal, whereas lattice constant a₀ with respect to single crystal shows a slight decrease. This difference of lattice parameters between film and single crystal was caused by the lattice mismatch between the film and Pt/Ti/SiO₂/Si substrate. Conversion electron Mössbauer spectrum of HoMn0.95Fe0.05O₃ thin film shows an asymmetry doublet absorption ratio at room temperature, which is due to the oriented direction of crystallographic domains. This is corresponding with analysis of x-ray diffraction. The quadrupole splitting (∆EQ) at room temperature is found to be 1.62 ± 0.01 mm/s. This large ∆EQ was caused by asymmetry environment surrounding Fe ion.
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불안정성 전자간 골절의 인공관절 치환술에서 골절된 대전자의 고정 방법
최동혁 ( Dong Hyeok Choi ),허주영 ( Ju Yeong Heo ),장영재 ( Young Jae Jang ),정영률 ( Young Yool Chung ) 대한골절학회 2014 대한골절학회지 Vol.27 No.1
Purpose: We classified fractures of the greater trochanter (GT) and evaluated fracture fragment stability according to GT type. Materials and Methods: A total of 43 patients with an unstable intertrochanteric fracture treated between January 2007 and July 2009 with bipolar hemiarthroplasty were included in this study. GT fractures were classified as type A, B, C, or D and fixed using either cerclage wiring alone, cerclage wiring and non-absorbable suture or a greater trochanteric reattachment (GTR) plate. Results: Type A fractures were fixed using cerclage wiring with non-absorbable suture in two cases, cerclage wiring in six cases and GTR plate in seven cases. Failure occurred in three cases of type A fractures treated with cerclage wiring alone. A total of 11 type B fractures were fixed with cerclage wiring (7), cerclage wiring and non-absorbable suture (3) and GTR plate (1). There was no failure of type B fractures. Type C fractures were fixed using cerclage wiring with non-absorbable suture in one case and GTR plate in three. There was no fixation in three cases. Of 10 type D fractures, six were treated with cerclage wiring and one with GTR plate. Fixation was not performed in three patients. There was no failure in type C and D type fractures. Conclusion: Fracture fragment stability differed according to fracture types. Cerclage wiring alone was insufficient to fix type A fractures, so type A fracture required a stronger fixation method.
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