• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2004년도 추계학술발표대회 개요집
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• pp.254-256
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• 2004

The purpose of this study is to establish the control method of angular distortion at the weldment of the pressure hull penetration. In order to do it, comprehensive experiment and FEA were performed to evaluate the distortion behavior for the weldment of HY-100. Based on the results, a proper deposit sequence for the both sides X groove penetration weldment was established. In addition, a proper welding sequence was proposed by evaluation of bending restraint intensity with size and position of pressure hull penetration.

• 한국압력기기공학회 논문집
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• 제16권1호
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• pp.100-109
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• 2020

Pipelines subjected to ground movement would be easily exposed to large-scale deformation. Since such deformations may cause the pipeline failure, it is important to ensure the safety of pipelines in various operation conditions. However, crack in weld metal have been considered as one of the main causes that can deteriorate the structural integrity of the pipeline. For this reason, the structural integrity of the pipe containing the crack in the weld should be obtained. In order to assess cracked pipe, J-integral and crack-tip opening displacement(CTOD) have been applied widely as the elastic-plastic fracture mechanics parameters representing crack driving force. In this study, engineering solutions to calculate the J-integral and CTOD of pipes with a circumferential outer surface crack in the weld are proposed. For this purpose, 3-dimensional elastic-plastic finite element(FE) analyses have been performed considering the effect of overmatch and width of weld. The shape of the weld was simplified to I-groove, and axial displacement was employed as for loading condition. Based on FE results, the effects of crack size, material properties and width of weldment on J-integral and CTOD were investigated. Additionally, the J-integral and CTOD for I-groove were compared with those for V-groove to examine the effects of the weld shape, and a proportionality coefficient of J-integral and CTOD was calculated from the results of this paper.

• 한국산학기술학회논문지
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• 제12권12호
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• pp.5412-5419
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• 2011

산업의 발달에 따른 각종기기 장치들의 고속화, 소형화, 정밀화로 인해 고속 스핀들의 필요성은 점점 커지고 있다. 또한 공기동압베어링은 스테이지 모션에 대해서 무마찰 실현을 위해서 웨이퍼 생산용 광학 리소그래피 분야에도 적용된다. 공기동압베어링은 마찰에 의한 동력손실과 열 발생이 적어 고속회전에 유리하고 고정밀 회전이 가능하기 때문에 고속 고정밀 스핀들 시스템 및 하드 디스크 드라이브에 사용될 수 있다. 본 연구에서는 축 하중 지지를 위해 헤링본 홈 형상을 가지는 공기동압베어링의 성능에 대한 수치해석을 수행하였다. 또한 본 연구에서는 공기동압베어링을 제작하기 위해서 기존의 기계 가공방법과는 다른 비접촉식 초정밀 가공 방법인 마이크로 전기화학가공에 의한 방법으로 마이크로 그루브 가공을 수행하였고, 수치해석 프로그램을 이용하여 전극의 간극, 전해용액 농도, 가공시간 등 이론적인 수치를 시뮬레이션 하였다.

• Tribology and Lubricants
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• 제16권1호
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• pp.39-45
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• 2000

In this paper, the effects of shaft and bearing flexibilities are investigated for the accurate modeling of a shaft-bearing system supported by ball bearings. Generally, rolling bearings are modeled by simple rigid pin-joint in the mechanical design. However, they can no longer be modeled by ideal boundary conditions in the advanced applications because the rigid pin-joint model cannot satisfy the current trends of mechanical design decreasing mass and reducing volume. Consequently the flexible support model of ball bearing is investigated using the static analysis module developed by A .B. Jones and T. A. Harris. A simple two-bearing system, supported by two deep groove ball bearings and radially loaded on the shaft midway between the bearings, is utilized to validate the coupled model of shaft-bearing system. Numerical computations using the model indicate that the shaft span length, locating/floating bearing arrangements and applied bearing size are significant factors in determining the mechanical behaviors. The flexible support model of ball bearing can be escaped to over-estimate in the bearing fatigue life. The proposed simple design formulation obtained by numerical simulations can approximately predict a rate of bearing life reduction as a function of shaft span length/shaft diameter (L/d).

• 한국정보통신설비학회:학술대회논문집
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• 한국정보통신설비학회 2009년도 정보통신설비 학술대회
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• pp.54-58
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• 2009

In this paper, the ECT(eddy current testing) signal analysis of eddy current array probe for inspection of SG(steam generator) tube in NPP(nuclear power plant) using electromagnetic FEM(finite element method) was performed. To obtain the electromagnetic characteristics of probes, the governing equation was derived from Maxwell's equation, and the problem was solved by using the 3-dimensional FEM. The types of defects were FBH(flat bottomed hole) and OD groove, Spiral groove, natural defects(pitting, SCC, multiple SCC, wear). The depth of FBH defects were 20%, 40%, 60%, 80%, 100 of SG tube thickness, and it was assumed that the defects were located on the tube outside. And the operation frequency of 100kHz, 300kHz and 400kHz were used. Material of specimen was Inconel 600 which is usually used for SG tubes in NPP. The signal difference could be observed according to the variation of size and depth on FBH defects and operation frequencies. The results in this paper can be helpful when the ECT signals from EC array probe are evaluated and analyzed.

• 대한금속재료학회지
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• 제49권2호
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• pp.104-111
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• 2011

An ultrafine grained Mg-9Al-1Zn magnesium alloy with the mean grain size less than $1{\mu}m$ was produced by using high-ratio differential speed rolling. The processed alloy exhibited excellent superplasticity at relatively low temperatures. The micro-forming tests were carried out using a micro-forging apparatus with micro V-grooved shaped dies made of silicon and the micro-formability was evaluated by means of micro-formability index, $R_f$ ($=A_f/A_g$, $A_f$: formed and inflowed area into the V-groove, $A_g$: area of the V-groove). The $R_f$ value increased with temperature up to $280^{\circ}C$ and then decreased beyond $300^{\circ}C$. The decrease of the $R_f$ value at $300^{\circ}C$ was attributed to the accelerated grain coarsening. Increasing the micro-forging pressure increased the $R_f$ values. At a given die geometry, die filling ability decreased as the die position moved away from the die center to the end. FEM simulation predicted this behavior and a method of improving this problem was proposed.

• 한국에너지공학회:학술대회논문집
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• 한국에너지공학회 2004년도 춘계 학술발표회 논문집
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• pp.201-212
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• 2004

An experimental study of the absorption process of water vapor into a lithium bromide solution was performed. For the purpose of developing high performance absorption chiller/hater utilizing lithium bromide solution as working fluid, it is important to improve the performance of absorber with the larger heat transfer area of the four heat exchangers. The experimental apparatus was composed of a plate type absorber which could increase the heat exchange area per unit volume to investigate more detail characteristics instead of the conventional type, that is, horizontal tube bundle type. The size of plate absorbers were made for 0.4m$\times$0.6m and the design objective of a refrigeration capacity was 1RT. In this experiment, three kinds of plate absorbers namely flat plate, dimple plate and groove plate were used. The obtained results were less than the design objective values, that is, the refrigeration capacity was about 0.3 ～0.4RT and the overall heat transfer coefficient was 500～600 kcal/$m^2$h$^{\circ}C$ at the standard conditions.

• 한국안광학회지
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• 제12권3호
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• pp.55-58
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• 2007

티타늄과 그 합금은 경량성, 우수한 기계적 성질 그리고 우수한 내식성 때문에 주요한 안경테 소재로 사용되고 있다. 본 연구에서는 티타늄 합금 홈선에 대하여 안경테 브레이징용으로 사용되고 있는 고주파유도가열 장치를 이용한 열처리 시간의 변화에 따른 경도 및 미세조직의 변화에 대하여 조사하였다. ${\beta}-Ti$ 합금은 고주파유도가열처리 시간의 증가에 따라 경도값의 감소가 나타났으며, 이는 열처리 시간의 증가에 따른 결정립의 조대화 때문인 것으로 생각된다. Ti-325 합금의 고주파유도가열처리에서는 2초까지는 경도값이 감소하였으나, 3초에서는 급격히 증가하였다. 이는 2초까지는 결정립의 조대화에 의한 경도값의 감소가 일어나지만, 3초에서는 미세한 ${\alpha}+{\beta}$ 상의 층상조직이 발달하였기 때문으로 판단된다.

• Journal of Welding and Joining
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• 제16권5호
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• pp.119-133
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• 1998

To implement full automation in pipe welding, it si most important to develop special sensors and their related systems which act like human operator when detecting irregular groove conditions. In this study, an automatic pipe Gas Metal Arc Welding (GMAW) system was proposed to full control pipe welding procedure with intelligent sensor systems. A five-axes manipulator was proposed for welding torch to automatically access to exact welding position when pipe size and welding angle were given. Pool status and torch position were measured by using a weld-pool image monitoring and processing technique in root-pass welding for weld seam tracking and weld pool control. To overcome the intensive arc light, pool image was captured at the instance of short circuit of welding power loop. Captured image was processed to determine weld pool shape. For weld seam tracking, the relative distance of a torch position from the pool center was calculated in the extracted pool shape to move torch just onto the groove center. To control penetration of root pas, gap was calculated in the extracted pool image, and then weld conditions were controlled for obtaining appropriate penetration. welding speed was determined with a fuzzy logic, and welding current and voltage were determined from a data base to correspond to the gap. For automatic fill-pass welding, the function of human operator of real time weld seam control can be substituted by a sensor system. In this study, an arc sensor system was proposed based on a fuzzy control logic. Using the proposed automatic system, root-pass welding of pipe which had gap variation was assured to be appropriately controlled in welding conditions and in torch position by showing sound welding result and good seam tracking capability. Fill-pass welding by the proposed system also showed very successful result by tracking along the offset welding line without any control of human operator.

• 대한전자공학회논문지SD
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• 제48권3호
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• pp.18-24
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• 2011

본 논문에서는 double boss 구조의 저압용 압력 센서의 다이아프램 브리지 모서리에 홈을 형성함으로서 압력센서의 내압특성을 향상시킬 수 있음을 확인하였다. 저압용 실리콘 압력센서에서는 일반적으로 boss구조가 널리 사용되고 있으나 칩에서의 제한된 다이아프램의 사이즈와 두께로 인하여 좋은 감도를 얻을 수는 없다. 특히, double boss구조는 다이아프램의 브리지 모서리 응력이 크게 작용함에 따라서 크랙이 생겨 다이아프램의 파괴가 진행되어 센서의 감도는 우수하지만 동작영역의 범위가 줄어들어 신뢰성에 문제가 있다는 단점을 가진다. 기존 double boss구조 압력센서 다이아프램 브리지에 모서리 홈의 길이를 $0.5{\sim}10{\mu}m$로 변화시키며 ANSYS 시뮬레이션을 시행하여 다이아프램 브리지 모서리와 브리지의 가장자리 그리고 압저항 소자가 위치하는 곳의 최대응력을 확인하였다. 그 결과 브리지 모서리의 길이가 6${\mu}m$이상인 경우, 브리지 모서리에서 발생하는 응력은 압저항 소자에 작용하는 응력보다 적다.