• 한국해양공학회지
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• 제13권1호통권31호
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• pp.29-38
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• 1999

In this paper the forming simulation of circular bulge by using PAM-STAMP has been performed to estimate the sheet metal forning and the plastic deformation characteristic of circular bulge. The uniaxial tension tests adn bulge tests are carried out for studying the forming characteristics of materials, and also Moire experiment are carried out for measuring the radius of curvature of the bulge and the polar compressive thickness strain. In order to compare the simulation results with the experiment and Hills theory, the relationships between redius of curvature adn polar height of the bulge, between hydraulic pressure and polar height, and between polar compressive thickness strain and polar height, are used. According to this study, the results of simulation and Hills theory are good agreement to the experiment. So, the results of simulation by using PAM-STAMP and Hills theory will give engineers good information to assess the formagbility and plastic deformation characteristic of hydraulic circular bulge test.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 1997년도 춘계학술대회논문집
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• pp.175-178
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• 1997

A modified Mukerjee's model considering the microstructural evolution was developed to study the superplastic bulge forming process of Ti-6Al-4V alloy. Through the microstructual observation after deformation, it was found that the grain growth rate of uniaxially tested specimens was different from that of biaxially deformed specimens. From this result, bulge forming experiments with and without back pressure were performed to examine the grain growth behavior and to compare the results of biaxial test with those of triaxial test. Good agreement between the prediction by a modified Mukerjee's model and the experimental measurements was obtained for bulge profile and thickness distribution.

• 대한기계학회논문집
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• 제12권3호
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• pp.397-408
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• 1988

본 연구에서는 세가지 형상비의 연강판타원벌지 시험에 대하여 다이반경부분 의 형상과 수직이방성을 고려하여 해석고 이에 따른 실험과 비교검토하여 타원벌지시 험에서의 변형특성에 대해 논의하고자 한다. 또 불안정현상이 일어나는 압력을 예측 하여 실험에서 구한 파괴압력과 비교하여 타원벌지 시험에서의 파괴특성을 고찰하고자 한다.

• 대한기계학회논문집B
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• 제37권1호
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• pp.19-25
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• 2013

본 연구에서는 벌지 실험을 이용하여 티타늄 박막의 기계적 물성을 측정하였다. 벌지 실험은 외적 지지구조를 가지지 않는 박막 시편의 한 면에 일정한 압력을 가하여 박막의 변위를 측정, 압력과 변위의 관계를 이용하여 박막의 기계적 물성을 측정하는 실험이다. 스퍼터링을 이용해 증착된 티타늄 박막의 두께는 1.0, 1.5, $2.0{\mu}m$ 이고, 물성의 열처리 시간에 대한 영향을 알아보기 위해 증착된 시편은 $600^{\circ}C$에서 각각 150, 300, 600 초 동안 열처리 되었다. 박막의 탄성 계수, 잔류 응력, 항복 응력이 벌지 실험을 통해 측정되었고, 실험 결과 항복 응력은 열처리 시간에 의존하는 특성을 확인하였다. 또한 시편 두께가 감소할수록 강도가 증가하는 크기효과를 관찰하였다.

• 대한기계학회논문집A
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• 제27권9호
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• pp.1508-1516
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• 2003

In numerical analysis for hydroforming process, the stress calculation is effected by flow stress which is general obtained by stress-strain relationship from uni-axial tension test, so the result of the analysis, especially in tube hydroforming, has limitation of accuracy, tubes are made in roll-forming process and become work-hardened. Then roll forming process causes material properties between rolling direction and circumstantial direction of the tube to be different. So it is difficult to predict material behavior in the process condition of bi-axial stress state. In this study, the flow stress of the tube is determined by inverse engineering approach and bulge test that is widely used for formability test in the condition of bi-axial stress. And Hill's quadratic yield function and flow rule are used to consider the anisotropy of the tube in the roll forming process.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2006년도 춘계학술대회 논문집
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• pp.318-321
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• 2006

In this strudy, the free-bulge test and FE analysis have been used to define the fracture criteria based on the cockroft and Latham's criterion in warm hydroforming of Al 6061 tube. Full annealing and T6 treatment for heat treatment of Al 6061 tube ware used in this study. As-extruded, full annealed and T6-treated Al 6061 seamless tubes were prepared. To evaluate the hydroformability, uni-axial tensile test and bulge test were performed between room temperature and $200^{\circ}C$. And measured flow stress was used to simulate the warm hydroforming. A commercial FEM code, DEFORM-$2D^{TM}$, was used to calculate the damage value. A forming limit based ductile fracture criteria has been proposed by the results of experimental and FE analysis. The calculated values for fracture criteria will be efficient to predict the forming limit in hydroforming for real complex shaped part.

• 대한기계학회논문집
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• 제12권5호
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• pp.935-943
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• 1988

본 연구에서는 유압벌지시험기를 이용한 저속 벌지시험과 낙하해머(drop hammer)를 응용한 충격벌지시험기를 제작, 사용하여 충격벌지시험을 하여 저속변형과 충격변형에서 판재금속의 성형한계선도를 구하고 변형율속도가 판재의 불안정 및 성형 성에 미치는 영향을 조사하고 다이의 형상비(단축/장축)를 0.5, 0.75, 1.0 등으로 달 리하여 실험하므로써 변형경로에 따른 한계변형율의 변화를 관찰하고 아울러 기존의 성형한계이론과 비교, 검토하였다.

• 천문학회보
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• 제43권2호
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• pp.39.3-40
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• 2018

The presence of double red clump (RC) in the Milky Way bulge is widely accepted as evidence for a giant X-shaped structure originated from the bar instability. We suggested, however, a drastically different interpretation based on the multiple stellar populations phenomenon as is observed in globular clusters. Our discovery of a significant difference in CN-band between two RCs strengthens our scenario. On the other hand, recent Gaia survey provides trigonometric parallax distances for more than one billion stars in our Galaxy. These distance measurements would provide the important test as to the origin of the double RC in the Milky Way bulge. In this talk, we will present our preliminary results from Gaia DR2.

• 소성∙가공
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• 제16권6호
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• pp.426-431
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• 2007

Hydroformability and fracture criteria of FE analysis based on ductile fracture were investigated in warm hydroforming of A16061 tube. To evaluate the hydroformability, uni-axial tensile test and bulge test were performed at room temperature and $200^{\circ}C$. The measured flow stresses were used as input parameters for FE analysis. The damage values were calculated by FE analysis based on ductile fracture criteria at maximum radius of free bulged tubes. Damage values were compared of hexagonal shaped hydroformed parts. As a result, the formability by critical damage value for extruded tube is lower than that of full annealed tube up to 0.5.

• 소성∙가공
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• 제16권8호
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• pp.567-574
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• 2007

Double layered tube is assembled with an inner tube and an outer tube, similar in material or not, contacting closely and deforming simultaneously when subjected to external force. For the manufacturing of double layered tube, the hydroforming assembly technology has several advantages. Therefore in this study, hydroforming characteristics of double layered tube was investigated. The free bulge test was performed to produce formability diagrams of double layered tubes at various forming pressure and feeding amounts. The hexagonal shape hydroforming test was also performed to estimate the dimensional accuracies of double layered tube through the corner filling ratio and the gap between inner and outer tube. Besides experimental analyses, the analytical model that can predict internal pressure for the hydroforming of double-layered tube was proposed and experimentally validated.