• 한국정밀공학회지
• /
• 제23권4호
• /
• pp.153-161
• /
• 2006

Micro-forming is a suited technology to manufacture very small metallic parts(several $mm{\sim}{\mu}m$). Micro-forming of $Zr_{62}Cu_{17}Ni_{13}Al_8$ bulk metallic glass(BMG) as a candidate material for this developing process are feasible at a relatively low stress in the supercooled liquid state without any crystallization during hot deformation. In this study, micro- formability of a representative bulk metallic glass, $Zr_{62}Cu_{17}Ni_{13}Al_8$. was investigated for micro-forging of U-shape pattern. Micro-formability was estimated by comparing $R_f$ values ($=A_f/A_g$), where $A_g$ is cross-sectional area of U groove, and $A_f$ the filled area by material. Micro-forging process was simulated and analyzed by applying finite element method. FEM simulation results showed reasonable agreement with the experimental results when the material properties and simulation conditions such as top die speed, remeshing criteria and boundary conditions were tightly controlled. The micro-formability of $Zr_{62}Cu_{17}Ni_{13}Al_8$ was increased with increasing load and time in the temperature range of the supercooled liquid state. Also, FEM simulation using a commercial software, DEFORM was confirmed to be applicable for the optimization of micro-forming process.

• 한국정밀공학회:학술대회논문집
• /
• 한국정밀공학회 2005년도 추계학술대회 논문집
• /
• pp.589-592
• /
• 2005

Micro-forming is a suited technology to manufacture very small metallic parts(several $mm{\sim}{\mu}m$). Micro-forming of $Zr_{62}Cu_{17}Ni_{13}Al_8$ bulk metallic glass(BMG) as a candidate material for this developing process are feasible at a relatively low stress in the supercooled liquid state without any crystallization during hot deformation. In this study, micro-formability of a representative bulk metallic glass, $Zr_{62}Cu_{17}Ni_{13}Al_8$, was investigated for micro-forging of U-shape pattern. Micro-formability was estimated by comparing $R_f$ values $(=A_f/A_g)$, where Ag is cross-sectional area of U groove, and $A_f$ the filled area by material. Microforging process was simulated and analyzed by applying finite element method. FEM simulation results should reasonable agreement with the experimental results when the material properties and simulation conditions such as top die speed, remeshing criteria and boundary conditions tightly controlled. The micro-formability of $Zr_{62}Cu_{17}Ni_{13}Al_8$ was increased with increasing load and time in the temperature range of the supercooled liquid state. Also, FEM Simulation using DEFORM was confirmed to be applicable for the micro-forming process simulation.

• 환경생물
• /
• 제33권4호
• /
• pp.375-382
• /
• 2015

We discovered three soil ciliates of the class Colpodea-Colpoda henneguyi Fabre-Domergue, 1889; C. lucida Greeff, 1888; and Bursaria truncatella $M{\ddot{u}}ller$, 1773 from Obong-ri, Ayajin-ri and Elwang-ri (Korea), respectively. Colpoda henneguyi had the following features: often wider preorally than postorally, size in vivo $60-80{\mu}m{\times}50-70{\mu}m$; extrusomes indistinct in vivo, cylindroid approximately $1{\mu}m$ long; notches caused by deep diagonal groove; yellowish globules on the cortex of the cell; 10-12 postoral kineties; silverline system aspera-type. Colpoda lucida exhibited the following features: broadly reniform, size in vivo $70-90{\mu}m{\times}50-70{\mu}m$; conspicuous extrusomes, $3.5-5{\mu}m$ long in vivo, cylindroid to fusiform; 13-16 postoral kineties; silverline system cucullus-type. Bursaria truncatella had the following features: bursiform, size in vivo $300-470{\mu}m{\times}120-260{\mu}m$; macronucleus coiled with highly variable shapes, $600-1100{\mu}m{\times}30-40{\mu}m$ long in vivo; micronuclei 16-25 in number, approximately $4{\mu}m$ in diameter; extrusomes cylindroid, $3-4{\mu}m$ long in vivo. This is the first report of colpodean ciliates from Korea, and we describe these species based on observations of live and impregnated (protargol and silver nitrate impregnation) specimens.

• Steel and Composite Structures
• /
• 제34권3호
• /
• pp.347-359
• /
• 2020

The objective of this study is to experimentally scrutinize the axial performance of built-up concrete filled steel tube (CFT) columns composed of steel plates. In this case, the main parameters cross section types, compressive strength of filled concrete, and the effect of welding lines. Welded built-up steel box columns are fabricated by connecting two pieces of cold-formed U-shaped or four pieces of L-shaped thin steel plates with continuous penetration groove welding line located at mid-depth of stub column section. Furthermore, traditional square steel box sections with no welding lines are investigated for the comparison of axial behavior between the generic and build-up cross sections. Accordingly, 20 stub columns with thickness and height of 2 and 300 mm have been manufactured. As a result, welding lines in built-up specimens act as stiffeners because have higher strength and thickness in comparison to the plates. Subsequently, by increasing the welding lines, the load bearing capacity of stub columns has been increased in comparison to the traditional series. Furthermore, for specimens with the same confinement steel tubes and concrete core, increment of B/t ratio has reduced the ductility and axial strength.

• 한국자동차공학회논문집
• /
• 제6권5호
• /
• pp.199-210
• /
• 1998

The skill that utilizes atomization of the liquid has been widely used in the field of industry and engineering. Though there are dozens of methods to make atomization, the pressure type injection nozzle is frequently used in washing of parts, pastourization and painting because it has relatively simple system. This study is to reveal the characteristics of atomizing formed by three different types of the pressure type injection nozzle. We measured velocity and diameter of droplet to compare and analyze characteristic of each nozzle. In case of velocity, atomization of hollow-cone nozzle is irregular than others and change of radial direction is especially large. Atomization of flat nozzle is nearly uniform. In case of diameter, atomization of hollow-cone nozzle is increased rapidly, as measurement point become more distant from the center of nozzle. Atomization of flat nozzle has the most fixed magnitude. Accordingly, full-cone nozzle can be used irrespective of the form of subject and hollow-cone nozzle is proper to the occasion to spray large and smooth subject. Also, flat nozzle is proper to the occasion to spray a part of subject and long groove.

• Journal of Chest Surgery
• /
• 제18권2호
• /
• pp.305-313
• /
• 1985

Surgical therapy for dissection of the aorta has had a high mortality. One contributing factor has been hemorrhage from the prosthesis and the suture lines. Recently, a new method of treatment with an intraluminal graft that requires no end-to-end anastomosis has been developed. Of the four patients with dissecting aneurysm of the aorta treated by inserting sutureless ringed intraluminal graft at the Department of Thoracic and Cardiovascular Surgery, S.N.U.H., three were DeBakey type I [one with associated aortic insufficiency] and the other was DeBakey type III. Suspected etiology of the dissection was Marfan`s syndrome in one and hypertension in the others. Total cardiopulmonary bypass was utilized in repairing dissecting aneurysms of the ascending aorta [type A] and simple aortic crossclamping was used for the patient with dissecting aneurysm of the descending aorta. The basic technique consists of inserting the whole ringed graft into the true lumen of the dissected aorta and circumferentially ligating the aorta against the groove in the rings. The proximal ring of the graft effectively stabilized the flail aortic valve in patient with aortic insufficiency associated with dissection of the ascending aorta. There were no hospital deaths and one patient with type III dissecting aneurysm developed postoperative paraparesis and renal insufficiency which was resolved. Follow-up has been from 1 month to 16 months with no evidence of prosthetic problems, such as erosion, migration, or thrombosis.

• 한국결정성장학회지
• /
• 제6권3호
• /
• pp.424-430
• /
• 1996

태양전지의 공정중 고온공정을 줄여줌으로서 최종 태양전지의 가격을 저가화할 수가 있다. 이 논문은 점액 상태의 인을 희석시켜서 접촉 홈에 확산공정을 마친 후, 그 기본 특성을 조사하였다. 점액상태점의 희석도와 스핀속도가 산화막의 두께에 영향을 미치는 것이 확인되었다. 희석도가 높을수록 산화막은 두꺼워지고 균일도는 낮아졌다. 희석도 60%의 인이 홈에서의 균일도와 깊이를 고려할 때 가장 적당한 것으로 사료된다.

• 한국정밀공학회지
• /
• 제17권9호
• /
• pp.145-150
• /
• 2000

Out-of-sphericity is degree of deformation of an air bearing sphere deviated from a perfect sphere. This paper investigates numerically the effect of out-of-sphericity error on the radial stiffness of an air bearing Three types of out-of-sphericity modes are considered. in this study the stiffness is calculated from pressure distribution at the bearing surface which is obtained by solving th Reynolds equation. in some cases large out-of-sphericity errors are found to improve the stiffnesses of air bearings. This implies that an air bearing of perfect hemispheres is not necessarily of the best performance. Thus much labor and cost in manufacturing air bearings can be saved, In addition the radial stiffness of an air bearing depends greatly on the application direction.

• 한국소성가공학회:학술대회논문집
• /
• 한국소성가공학회 2004년도 추계학술대회논문집
• /
• pp.40-43
• /
• 2004

Stamps for microcontact processing are fabricated by casting elastomer such as PDMS on a master with a negative of the desired pattern. After curing, the PDMS stamp is peeled away from the master and exposed to a solution of ink and then dried. Transfer of the ink from the PDMS stamp to the substrate occurs during a brief contact between stamp and substrate. Generally, negative-tone masters, which are used for making positive-tone PDMS stamps, are fabricated by using photolithographic technique. The shortcomings of photolithography are a relative high-cost process and require extensive processing time and heavy capital investment to build and maintain the fabrication facilities. The goal of this study is to fabricate a negative-tone master by using Nano-indenter based patterning technique. Various sizes of V-grooves and U-groove were fabricated by using the combination of nanoscratch and HF isotropic etching technique. An achieved negative-tone structure was used as a master in the PDMS replica molding process to fabricate a positive-tone PDMS stamp.

• 한국소성가공학회:학술대회논문집
• /
• 한국소성가공학회 2004년도 제3회 금형가공 심포지엄
• /
• pp.249-254
• /
• 2004

광의 효율적 사용을 위해 표면에 마이크로 그루브가 새겨진 고성능 광학 부품의 개발이 활발하고, 이들 부품의 다량 생산을 위한 초정밀 금형제조기술이 각광을 받고 있다. 최근의 초정밀 미세 기계가공의 경우 간단한 공정으로 이러한 마이크로 그루브 금형을 제작할 수 있다. 특히 조명각 변조용 렌티큘러 렌즈와 같이 실린더형 그루브 금형의 경우에는 기존의 Lithography, MEMS, LIGA 등 광 에너지를 이용한 다른 제조방법들에서는 가공하기 어려운 점이 있으나, 기계가공에서는 쉽게 제작가능한 장점이 있다. 본 연구에서는 이러한 미세기계가공기술의 장점을 활용하여 U 형 마이크로 그루브를 가진 Lenticular 렌즈용 금형을 가공하고자 하였다. 가공에는 3 축 구동의 초정밀 미세 복합가공기와 단결정 천연 다이아몬드공구가 사용되었고, 가공방식은 마이크로 세이핑 공정을 적용하였으며, 가공 금형 재료에는 Brass와 무전해 Nickel이 사용되었다. 실험을 통하여 금형가공시의 절삭력, 칩 형상, 가공표면 등의 분석이 수행되었으며 이를 기반으로 여러 가지 가공문제점을 해결하고, 최종적으로 양호한 렌티큘러렌즈용 금형을 가공하였다.