• 한국산학기술학회논문지
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• 제16권12호
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• pp.8479-8486
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• 2015

본 연구는 Brain CT검사 시 영상에서 발생하는 선속경화현상의 원인과 감소방법을 알아보기 위하여 선속경화현상에 영향을 미치는 관전압, 관전류, 단면두께, 갠트리 각도, 기준선에 변화를 주었다. 사용한 장비로는 Somatom Sensation 16장비로 Bone opaque head phantom을 이용 영상영향인자에 변화를 주어 스캔하였고 획득한 영상 데이터를 이용하여, CT값 분석을 이용한 정량적 분석과 CT영상평가표를 이용한 정성적 평가를 시행하였다. 정량적 분석결과 관전압은 140kVp일 때 $31.56{\pm}2.89HU$로 측정되었고, 관전류의 경우 150mA에서 $-3.87{\pm}0.12HU$, 절편두께는 3mm에서 $2.29{\pm}0.78HU$로 측정되었으며 갠트리 각도에서 IOML이 $13.31{\pm}1.03HU$로 선속경화현상이 가장 적었다. 정성적 분석결과 대부분의 평가자들이 140kVp, 150mA, 3mm, IOML 또는 OML에서 스캔한 영상을 선속경화현상이 적게 발생한 영상으로 평가하였으며 모든 조건에서 변화 인자와 비교 시 통계학적으로 유의한 차이가 있었다.(P<0.05) 따라서, 임상적용 시 허용선량한도 범위 내에서 관전압은 높여주고 관전류는 영상 화질 저하에 영향을 미치지 않는 범위 내에서 낮게 설정하며, 절편두께는 해상도 저하를 고려하여 얇은 절편두께를 사용하고, 갠트리 각도는 IOML 또는 OML을 이용한다면 선속경화현상에 의해 발생되어지는 인공물을 최소화시켜 영상 판독자와 환자에게 보다 정확한 양질의 영상을 제공할 수 있을 것으로 사료된다.

• 한국압력기기공학회 논문집
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• 제16권2호
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• pp.10-17
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• 2020

Securing the integrity of steam generator tubes is an essential requirement for safe operation of nuclear power plants. Therefore, tubes that do not satisfy integrity requirements are no longer usable and must be repaired according to the related requirements. In general, the repair criterion is that the damage depth is more than 40% of the tube wall thickness. However, the plugging limit can be changed and be applied, provided a technical proof is given that integrity can be secured against specific degradation at a specific plants and that approval can be obtained from a regulatory agency. A typical example is alternative repair criteria for defects within the tube sheet or tube support plates. In this paper, a background of establishing the plugging limit for steam generator tubes and changes in maintenance criteria are reviewed as examples.

• Journal of Welding and Joining
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• 제21권7호
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• pp.34-41
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• 2003

Weld quality monitoring and seam tracking along the butt-joint lengthwise to the tube axis are studied. The material of tube is 60kg/$\textrm{mm}^2$ grade steel sheet, and the longitudinal butt-joint is shaped by 2 roll bending machine. The tube with a thickness of 1.5mm, diameter of 105.4mm and length of 2000mm is successfully obtained by the $CO_2$ laser welding system equipped with a seam tracker and plasma sensor. Experimental results show that the developed welding system can be used for the precision seam tracking and the real-time monitoring of weld quality, and the laser welded tube can be used for car body md component after tubular hydroforming.

• International Journal of Precision Engineering and Manufacturing
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• 제6권3호
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• pp.19-23
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• 2005

To minimize the weld defect in manufacturing of the welded tube by using $CO_2$ laser, the monitoring of the welding quality and the seam tracking along the butt-joint lengthwise to the tube axis are studied. The longitudinal butt-joint is shaped from $60kgf/mm^2$ grade steel sheet by 2 roll bending method, and welded by the $CO_2$ laser welding system equipped with the seam tracker and plasma sensor. The laser welded tube has the thickness of 1.5mm, diameter of 105.4mm and length of 2000mm. The precise positioning of the laser beam on the butt-joint to be assembled is obtained within $200{\mu}m$ by the laser vision sensor. The artificial defects in the butt-joint are well observed by the signal of plasma intensity measured from the plasma sensor of UV wavelength range within 400nm. The developed $CO_2$ laser tube welding system has the function of the precision seam tracking and the real-time monitoring of the welding quality. In conclusion, the laser welded tube can be used for manufacturing of automobile chassis and components after hydro-forming.

• 소성∙가공
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• 제14권6호
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• pp.514-519
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• 2005

A tube hydroformability testing system was designed and fabricated enabling to apply the forming condition along arbitrarily pre-programmed internal pressure-axial feed path. The free-bulging and T-forming tests were carried out on the extruded aluminum (A6063) tube specimens with 40.6 mm outer diameter and 2.25 mm thickness. Nine different combinations of internal pressure and axial feed, yielding different strain paths from one another, were taken into consideration in order to induce bursting at various deformation modes. Major and minor strains were automatically measured from deformed grids around the fracture using a stereo-vision-based surface strain measurement system, named ASIAS. The forming limit diagram of the A6063 tube material was successfully obtained. Most of the data points acquired from free bulging and T-forming tests appeared in the range of negative minor strain on the FLD and are mostly located near the strain paths calculated from explicit finite element simulations. The forming limit obtained from tests after pre-tension was considerably lower than that from tests without pre-tension, which showed the strain path-dependency of the forming limit as well known in the sheet forming fold.

• 한국정밀공학회지
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• 제18권7호
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• pp.179-185
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• 2001

Porthole die extrusion is profitable to manufacture long tube with hollow section. The material through portholes is gathered within chamber and welded under high pressure. This weldability which classifies the quality of tube product is affected by several variables and die shape. But, porthole die extrusion has been executed on the experience of experts due to the complicated die assembly and complexity of metal flow. Analytic approaches that are useful in profitable die design and in the improvement of productivity are inevitably demanded. Therefore, the objective of this study is respectively to analyze the behavior of metal flow and to determine welding pressure of hot extrusion product according to the various billet temperature, bearing length and tube thickness by FE analysis and its results are compared with tube expanding tests.

• 한국강구조학회 논문집
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• 제21권3호
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• pp.311-320
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• 2009

본 연구에서는 기존 각형 CFT기둥 실험체와 탄소섬유쉬트로 추가구속된 각형 CFT기둥 실험체의 단조압축거동 및 압축내력평가에 관한 실험을 수행하였다. 실험변수는 탄소섬유쉬트 보강겹수와 폭-두께비이며, 실험변수에 따라 총 9개의 실험체를 제작하여 단조압축실험을 수행하였다. 실험을 통하여 기존 CFT 실험체와 탄소섬유쉬트로 구속된 CFT 실험체의 파괴거동, 하중-축변위 곡선, 최대내력, 변형성능을 비교한다. 끝으로 탄소섬유쉬트의 추가구속은 기둥의 국부좌굴을 지연시켰으며 이로 인해 실험체의 최대내력이 상승한 것으로 나타났다.

• Journal of Welding and Joining
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• 제27권3호
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• pp.44-51
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• 2009

In this study, welding distortion analysis is performed for various design of tube shape structures which are assembled with aluminum sheet metal. Aluminum 5052 plates of 1mm thickness are used to analyze. An efficient keyhole model, as a welding heat source, is used for the prediction of full penetration weld size and shape which is required for the thermal analysis. The thermal and mechanical material properties are considered as temperature dependent functions, due to the high temperature variations during the welding. The numerical model is calculated by using a commercial software and evaluated with the experiments. The calculation results could make a comparative study in the view of distortion for the various size and shape of structure.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2009년 추계학술발표대회
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• pp.41-41
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• 2009

To evaluate the applicability of dissimilar joining between Mg and Al alloys in automobile manufacturing process, solid state joining processes such as magnetic pulse welding(MPW), friction stir welding(FSW) and friction spot joining(FSJ) were attempted successfully. MPW process has been concentrated mainly on round section tube to tube and tube to bar welds. AZ31 Mg alloy has been successfully welded to pure Al A1070 as well as to Al alloy A3003. While, for friction stir welding of dissimilar sheet joints, AZ31B/A6061 with the thickness of 2mm were used and a square butt joint with a good quality was obtained at the conditions of 0.8mm/sec of travel speed and tool rotation speed of 850rpm. The maximum tensile strength of 179 MPa, which was about 80 % of the Mg base metal tensile strength, has been obtained. Finally, friction spot joining was attempted to make a dissimilar lap joint between AZ31(0.8mm) and A6061(1mm), while the joint exhibited the same level of tensile shear strength as that of similar Mg joint.

• 소성∙가공
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• 제28권3호
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• pp.135-144
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• 2019

Electromagnetic impulse welding (EMIW) is a type of solid state welding using the Lorentz force generated by interaction between the magnetic field of the coil and the current induced in the workpiece. Although many experimental studies have been investigated on the expansion and compression welding of tube using the EMIW process, studies on the EMIW process of lap joint between flat sheets are uncommon. Since the magnetic field enveloped inside the tube can be controlled with ease, the electromagnetic technique has been widely used for tube welding. Conversely, it is difficult to control the magnetic field in the flat sheet welding so as to obtain the required welding velocity. The current study analyzed the effects of coil shape on the impulse velocity for suitable flat one-turn coil for the EMIW of the flat sheets. The finite element (FE) multi-physics simulation involving magnetic and structural field of EMIW were conducted with the commercial software LS-DYNA to evaluate the several shape variables, viz., influence of various widths, thicknesses, gaps and standoff distances of the flat one-turn coil on the impulse velocity. To obtain maximum impulse velocity, the flat one-turn coil was designed based on the FE simulation results. The experiments were performed using an aluminum alloy 1050 sheets of 1.0mm thickness using the designed flat one-turn coil. Through the microscopic interfacial analysis of the welded specimens, the interfacial connectivity was observed to have no defects. In addition, the single lap joint tests were performed to evaluate the welding strength, and a fracture occurred in the base material. As a result, a flat one-turn coil was successfully designed to guarantee welding with bond strength equal to or greater than the base material strength.