• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 1994년도 추계학술대회 논문집
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• pp.80-94
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• 1994

As for axisymmetirc sheet metal forming, a kind of pick-up apparatus for body-wrinkling is deviced. Experiments with both hemispherical and flat headed punches, with various clearances between punch and die, with respect to three kinds of materials each of which has two thicknesses, are performed. Firstly the process of evolution of body-wrinkling is observed. Then the critical blank-holding force (or meridional tensile force) for suppression of body-wrinkling at a specified punch-stroke is measured for all cases mentioned above. An empirical formula for it is proposed. Deformation patterns and stress distributions are analysed by the use of FEM. A simplified critical condition for body-wrinkling is formulated and introduced into the FEM program. And its effectiveness is checked by comparison with the experimental results. Using this FEM system, the governing factors of body-wrinkling are cleared up.

• 소성∙가공
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• 제9권2호
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• pp.128-139
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• 2000

Wrinkling is one of the major defects in sheet metal products and may be also attributable to the wear of the tool. The initiation and growth of wrinkles are influenced by many factors such as stress state, mechanical properties of the sheet material, geometry of the body, and contact condition. It is difficult to analyze the wrinkling initiation and growth considering the factors because the effects of the factors are very complex and the wrinkling behavior may show a wide variation for small deviations of the factors. In this study, the bifurcation theory is introduced for the finite element analysis of wrinkling initiation and growth. All the above mentioned factors are conveniently considered by the finite element method. The finite element formulation is based on the incremental deformation theory and elastic-plastic elements considering the planar anisotropy of the sheet metal. The proposed method is verified by employing a column buckling problem. And then, the initiation and growth of wrinkling in deep drawing of cylindrical cup are analyzed.

• 소성∙가공
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• 제20권1호
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• pp.42-47
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• 2011

Recently, with the merits of simplicity, ease of mass production and cost effectiveness, a roll-to-roll (R2R) forming process is tried to be employed in the manufacturing of the circuit board, barrier ribs and other electronic device. In this study, the roll-to-roll process for the forming of micro-pattern in electronic device panel is designed and analyzed. In the preliminary experiments, two major defects, i.e., crack near the dimple wall and wrinkling on outside region of dimple, are found. The study on the crack prevention is carried out in previous works by authors. In this study, the cause of wrinkling and modification of tooling to prevent the wrinkling is studied. The main cause of wrinkling is considered to be the uneven material flow along the rolling direction. To reduce or to retard the wrinkling initiation, a dummy shape on outside the pattern is introduced. From the finite element analysis results, it is shown that the dummy shape can reduce the uneven material flow significantly. Finally the effect of dimensions of the dummy shape on material flow is investigated and the optimum dimensions are found.

• 한국항공우주학회지
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• 제31권5호
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• pp.44-54
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• 2003

샌드위치 보의 포옴심재와 면재에 대한 물성치 실험을 통해 이들의 기계적 특성을 파악하였다. 이들로부터 포옴심재 및 적층면재로 제작된 샌드위치 보의 굽힘 국소좌굴현상을 고찰하였다. 좌굴전 양상을 고려한 굽힘 국소좌굴해석이 3점 굽힘시험을 통한 실험값에 더 근접함으로서 이를 고려한 굽힘 국소좌굴해석의 타당함을 보였고 그 양상도 고찰하였다.

• Structural Engineering and Mechanics
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• 제12권4호
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• pp.363-376
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• 2001

Sandwich plates are widely used in lightweight design due to their high strength and stiffness to weight ratio. Due to the heterogeneous structure of sandwich plates, they can exhibit local instabilities (wrinkling), which lead to a sudden loss of stiffness in the structure. This paper presents an analytical solution to the wrinkling problem of sandwich plates. The solution is based on the Rayleigh-Ritz method, by assuming an appropriate deformation field. In contrast to the other approaches up to now, this model takes arbitrary and different orthotropic face layers, finite core thickness and orthotropic core material into account. This approach is the first to cover the wrinkling of unsymmetric sandwiches and sandwiches composed of orthotropic FRP face layers, which are most common in advanced lightweight design. Despite the generality of the solution, the computational effort is kept within bounds. The results have been verified using other analytical solutions and unit cell 3D FE calculations.

• Structural Engineering and Mechanics
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• 제21권4호
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• pp.407-422
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• 2005

Plate elements in fully profiled sandwich panels are generally subjected to local buckling failure modes and this behaviour is treated in design by using the conventional effective width method for plates with a width to thickness (b/t) ratio less than 100. If the plate elements are very slender (b/t > 1000), the panel failure is governed by wrinkling instead of local buckling and the strength is determined by the flexural wrinkling formula. The plate elements in fully profiled sandwich panels do not fail by wrinkling as their b/t ratio is generally in the range of 100 to 600. For this plate slenderness region, it was found that the current effective width formula overestimates the strength of the fully profiled sandwich panels whereas the wrinkling formula underestimates it. Hence a new effective width design equation has been developed for practical plate slenderness values. However, no guidelines exist to identify the plate slenderness (b/t) limits defining the local buckling, wrinkling and the intermediate regions so that appropriate design rules can be used based on plate slenderness ratios. A research study was therefore conducted using experimental and numerical studies to investigate the effect of plate slenderness ratio on the ultimate strength behaviour of foam supported steel plate elements. This paper presents the details of the study and the results.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1996년도 추계학술대회 논문집
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• pp.123-127
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• 1996

The tendency of wrinkling formation on the flange of a deep-drawn rectangular container was investigated experimentally under different process conditions. Such process variables as blank size, sheet thickness, blank-holding force, and depth of drawing are chosen to examine their effects on the flange wrinkles of the products. Number and amplitudes of the wrinkles are measured along the periphery of the flange and compared between each case of process condition.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 1999년도 추계학술대회논문집
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• pp.18-21
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• 1999

The wrinkling of thin sheet metal induced by compressive instability is one of major defects in sheet metal forming processes. compressive instability is influence by many factors such as mechanical properties of the sheet material geometry of the sheet contact conditions and plastic anisotropy. The analysis of compressive instability in a plastically deforming body is rather difficult because the effects of the above-mentioned factors are rather complex and the instability behavior may show swide variations even for small deviations of the factors. in this work the bifurcation theory is introduced for the finite elemental analysis of the instability behavior of a thin sheet with initially sound geometry and property. All the above-mentioned factors are conveniently considered by the finite element method. The instability limit is found by introducing a criterion scheme into the incremental analysis and the post-bifurcation behavior is analyzed by introducing the branching scheme. Wrinkling initiation and growth in the deep drawing process are analyzed.

• 한국항공우주학회지
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• 제33권12호
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• pp.33-38
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• 2005

본 연구에서는 팽창형 막 구조물의 대변형 특성을 수치적 그리고 실험적으로 살펴보았다. Miller와 Hedgepeth의 막 이론을 이용하여 주름 효과를 고려한 막재료 구성방정식을 FORTRAN으로 해석 알고리즘을 만들어 user material(UMAT) subroutine을 개발하였다. 개발된 주름 해석 UMAT subroutine을 상용 해석 프로그램 ABAQUS와 연계 해석하여 팽창형 막 구조물의 주름 영역과 변형된 형상 특성 연구를 수행하였다.

• 오토저널
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• 제11권4호
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• pp.35-42
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• 1989

The major purpose of this paper is a study on the effect of die profile radius on the formability of spring-type blankholder system in deep drawing process. By drawing the various materials, formability is studied by means of checking the drawing force, blankholding force variation, limiting drawing ratio and wall wrinkling phenomenon. As the die profile radius increases, the maximum drawing force and maximum blankholding force decrease regardless of lubrication condition. Because better lubrication induces blankholding force to rise, spring type blankholder system is better to protect flange wrinkling phenomenon than constant pressure type. And wall wrinkling phenomenon was not detected in experimental die radius range, so the Miyakawa's upper wrinkling limit is understimated in case of material tested.