• 소성∙가공
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• 제32권6호
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• pp.303-310
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• 2023

Electrohydraulic forming(EHF), one of the high-speed forming method, can supplement the weak point of previous forming process such as deep-drawing and electromagnetic forming. Indeed, EHF is time-consuming process during installing wire before experiment that hard to apply to industry. In this research, applying wireless electrode, the formability of SUS430 sheet was compared through EHF experiments using wire-installed electrode and the other, wireless. Although the power was a little lacking, the advantages of the experiment using wireless electrode could be confirmed with checking the optimal location of electrodes where the plasma is generated and comparing free-bulging height depending on former and later condition of electrodes with performing several single and multistage experiments for same voltage, 6 kV.

• 한국해양공학회지
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• 제16권6호
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• pp.49-54
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• 2002

The Finite Element Method is applied to the determination of the deformed bulge profile and strain distribution during upset forming of cylindrical billets. From the results of simulation, the bulging along the z-axis becomes more severe with increasing eight reduction, and with increasing friction at the die-material interface. The present method can be used for the simple prediction of the deformed shape and strain distribution in upset forging of cylindrical billets with dissimilar fictional conditions at the die-material interfaces.

• Journal of Mechanical Science and Technology
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• 제14권6호
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• pp.633-644
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• 2000

Recently, in proportion to the increase of earthquake occurrence-frequency and its strength in the countries within the circum-pan Pacific earthquake belt, a concept of earthquake-proof design for huge structures containing liquid has been growing up. This study deals with the refinement of classical numerical approaches for the free vibration analysis of separated structure and liquid motions. According to the liquid-structure interaction, LNG-storage tanks exhibit two distinguished eigenmodes, the sloshing mode and the bulging mode. For the sloshing -mode analysis, we refine the classical rigid-tank model by reflecting the container flexibility. While, for the bulging-mode analysis, we refine the classical uncoupled structural vibration system by taking the liquid free-surface fluctuation into consideration. We first construct the refined dynamic models for both problems, and present the refined numerical procedures. Furthermore, in order for the efficient treatment of large-scale matrices, we employ the Lanczos iteration scheme and the frontal-solver for our test FEM program. With the developed program we carry out numerical experiments illustrating the theoretical results.

• 대한기계학회논문집A
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• 제38권8호
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• pp.899-904
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• 2014

자유벌징에 있어서 성형 높이를 최대화하기 위하여 블랭크의 두께 분포를 최적화 하였으며, 등가정하중을 이용한 구조최적화법을 사용하였다. 두께형상은 부드러운 곡선으로 나타내기 위하여 베지어곡선을 사용하였고 제어점의 위치가 설계변수이며, 최대 변형률을 일정 값으로 제한하였다. 사용된 소재는 인코넬 718 이며 최적화된 두께분포로 가공된 블랭크를 이용한 자유벌징 시험을 수행하여 평판형 블랭크를 사용한 결과보다 22% 더 높은 성형 높이를 얻었다. 최적화결과에서 예측된 변형형상, 정점에서의 변형 경향, 두께분포가 실험에서 얻은 결과와 유사하여 최적화 과정의 유효성을 입증하였고, 최적화 결과가 실제 구현될 수 있음을 검증하였다.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2007년도 춘계학술대회 논문집
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• pp.306-309
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• 2007

In this study, hydroforming characteristic of the double-layered tube was investigated in the hydroforming process. The double-layered tube can be made outer surface on the stainless steel by only one processing. The free bulging test was performed to analysis optimized pressure and axial feeding amount of the double layered tubes. And the experimental results between stainless/carbon and carbon/carbon double-layered tube were compared with the forming data. Moreover analysis model that can be hydroformability and predictable forming pressure of double-layered tube was presented.

• 소성∙가공
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• 제21권7호
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• pp.441-446
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• 2012

A sequential coupled field analysis of electromagnetic free bulging was performed by using FEM. A 2D axi-symmetric electromagnetic model based on the magnetic vector potential is proposed for the calculation of magnetic field and Lorentz's forces. The Newmark integration method is used to calculate the transient dynamic plastic deformation of sheet during free bulging. In the finite element model, the effect of sheet deformation on the electromagnetic field analysis is taken into consideration. In order to confirm the sequential electromagnetic-mechanical coupling analysis, an experiment with an electromagnetic forming apparatus was conducted. The results showed that the final bulge height of the sheet predicted from the proposed method is in good agreement with experimentally measured height.

• 한국소음진동공학회논문집
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• 제13권10호
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• pp.751-759
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• 2003

The theoretical method is developed to investigate the vibration characteristics of the sloshing and bulging mode for the circular cylindrical storage tank with an annular plate on free surface. The cylindrical tank is filled with an inviscid and incompressible liquid. The liquid domain is limited by a rigid cylindrical surface and a rigid flat bottom. As the effect of free surface waves Is taken into account in the analysis, the bulging and sloshing modes are studied. The solution for the velocity potential of liquid movement is assumed as a suitable harmonic function that satisfies Laplace equation and the relevant boundary conditions. The Rayleigh-Ritz method is used to derive the frequency equation of the cylindrical tank. The effect of Inner-to-outer radius ratio and thickness of annular plate and liquid volume on vibration characteristics of storage tank is studied. The finite element analysis is performed to demonstrate the validity of present theoretical method.

• 대한조선학회논문집
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• 제40권6호
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• pp.88-95
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• 2003

Liquid storage rectangular tank structures are used in many fields of airplane and marine engineering. Fatigue damages are sometimes observed in these tanks which seem to be caused by resonance. Therefore it is essentially important to estimate vibration characteristics of tank structures. Many Investigators studied the vibration of cylindrical and rectangular tank structures containing still fluid. In general, the eigenbehavior of interior liquid is characterized by the sloshing mode while that of the structure by the bulging mode. However, the structure deformation to the sloshing mode and the liquid free-surface fluctuation to the bulging mode have been neglected in the classical added-mass computation. in the present paper, we study the vibration characteristics with sloshing mode effect.

• Structural Engineering and Mechanics
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• 제60권1호
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• pp.91-110
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• 2016

Tube hydroforming (THF) under pulsating hydraulic pressures is a novel technique that applies pulsating hydraulic pressures that are periodically increased to deform tubular materials. The deformation behaviours of tubes in pulsating THF may differ compared to those in conventional non-pulsating THF due to the pulsating hydraulic pressures. The equivalent stress-strain relationship of metal materials is an ideal way to describe the deformation behaviours of the materials in plastic deformation. In this paper, the equivalent stress-strain relationships of SS304 tubes in pulsating hydroforming are determined based on experiments and simulation of free hydraulic bulging (FHB), and compared with those of SS304 tubes in non-pulsating THF and uniaxial tensile tests (UTT). The effect of the pulsation parameters, including amplitude and frequency, on the equivalent stress-strain relationships is investigated to reveal the plastic deformation behaviours of tubes in pulsating hydroforming. The results show that the deformation behaviours of tubes in pulsating hydroforming can be well described by the equivalent stress-stain relationship obtained by the proposed method. The amplitude and frequency of pulsating hydraulic pressure have distinct effects on the equivalent stress-strain relationships-the equivalent stress becomes augmented and the formability is enhanced with the increase of the pulsation amplitude and frequency.

• 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.