• Transactions of the Korean Society of Automotive Engineers
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• v.4 no.5
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• pp.16-25
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• 1996

In the present work a rigid-plastic finite element formulation using dynamic explicit time integration scheme is proposed for numerical analysis of auto-body panel stamping processes. The rigid-plastic finite element method based on membrane elements has long been employed as a useful numerical technique for the analysis of sheet metal forming because of its time effectiveness. A damping scheme is proposed in order to achieve a stable solution procedure in dynamic sheet forming problems. In order to improve the drawbacks of the conventional membrane elements, BEAM(abbreviated from Bending Energy Augmented Membrane) elements are employed. Rotational damping and spring about the drilling direction are introduced to prevent a zero energy mode. The lumping scheme is employed for the diagonal mass matrix and linearizing dynamic formulation. A contact scheme is developed by combining the skew boundary condition and the direct trial-and-error method. Computations are carried out for analysis of complicated auto-body panel stamping processes such as forming of an oilpan, a fuel tank and a front fender. The numerical results of explicit analysis are compared with the implicit results with good agreements and it is shown that the explicit scheme requires much shorter computational time, especially when the problem becomes more complicated. It is thus shown that the proposed dynamic explicit rigid-plastic finite element method enables an effective computation for complicated autobody panel stamping processes.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.2
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• pp.248-258
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• 1992

Three-dimensional rigid-plastic finite element formulation based on the membrane theory was described and a computer program for large deformation analysis was developed. In the formulation, normal and planar anisotropy of sheet material and rotation of the principal axes of anisotropy was taken into consideration. Sheet metal was assumed to be rigid-plastic material obeying Hill's quadratic yield criterion and its associated flow rule. Deep drawing process, as a preliminary test, for normal anisotropic material was analyzed in order to examine the validity of developed finite element program. The results were consistent with the existing finite element solutions or experimental data. The present study was mainly concerned with the influence of planar anisotropy on deformation behaviour. Finite element analysis and experiment were carried out for the whole process of deep drawing of planar anisotropic material. The computational and experimental results on the shape of ear, strain distribution and punch load were in good agreement.

• Journal of the Korean Geotechnical Society
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• v.23 no.4
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• pp.79-90
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• 2007

Behaviors of instrumented steel sheet piles which are installed in sand ground by vibratory hammer were investigated. Especially, stresses acting on the pile during vibratory driving, efficiency factor which reflects differences between theoretical driving force and actually delivered acting force, justifiability of rigidity of steel sheet pile, dynamic resistance characteristics of soil and penetration characteristics of sheet pile were analysed. According to the field test results it is justifiable that steel sheet pile behaves as a rigid body during vibratory driving. And it can be seen that maximum stress acting on sheet pile section is far less than tensile strength of the material. Value of the maximum section force at sheet pile head was 72% of that estimated from theoretical equation. Magnitudes of displacement amplitudes computed from displacement-time history curve corresponding to four penetration depths were in the range of 16 $\sim$ 75% of that specified by manufacturer.

• Transactions of Materials Processing
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• v.9 no.6
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• pp.590-597
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• 2000

A finite element formulation lot the simulation of axisymmetric sheet hydroforming is proposed, and an implicit program is coded. In order to describe normal anisotropy of steel sheet, Hill's non-quadratic yield function (Hill, 1979) is employed. Frictional contacts among sheet surface, rigid tool surface, and flexible hydrostatic pressure are considered using mesh normal vectors based on finite element of the sheet. Applied hydraulic pressure is also considered as a function of forming rate and time and treated as an external loading. The complete set of the governing relations comprising equilibrium and interfacial equations is approximately linearized for Newton-Raphson algorithm. In order to verify the validity of the developed finite element formulation, the axisymmetric bulge test is simulated. Simulation results are compared with other FEM results and experimental measurements and showed good agreements. In axisymmetric hydroforming processes of a disk cover, formability changes are observed according to the hydraulic pressure curve changes.

• KIEAE Journal
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• v.7 no.1
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• pp.73-80
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• 2007

This paper aims to develop the diffused reflection material in order to reduce the solar absorption coefficient, and to compare the thermal properties with the different roof structure system; one is using the diffused reflection material applied the upper side of the rigid sheet waterproof system and the other is using the conventional up-side down waterproof system on the roof. For this purpose two experimental test boxes were made of same iso-panel wall and floor with different roof system. The experiment was carried out under these process; measure the surface temperature exposed solar radiation of the variation of the reflection materials(cement paste, silica, galvanized steel and titanium dioxide(TiO2)), measure and analyze the variation of the temperature distribution of the each roof system and indoor air in order to evaluate the thermal properties according to the different roof system. The result shows clearly that using the titanium dioxide(TiO2) might be more effective to reduce the solar insolation.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.12
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• pp.2936-2948
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• 1993

Multi-stage deep drawing is an important sheet metal forming process. The deformation mechanisms of sheet metals during forming processes are complicated mainly due to the geometry and the lubrication of tools involved, the formability and the anisotropic behaviour of the material. The multi-stage deep-drawing processes including normal-drawing, reverse-drawing, and re-drawing are analyzed by use of the rigid-plastic finite element method. The anisotropic behaviour represented by r-value can be incorporated into the formulation. Punch/die loads and thickness distributions were obtained as results of simulating axisymmetric deep drawing processes. The computed results showed good agreements with experiments.

• Transactions of Materials Processing
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• v.5 no.2
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• pp.130-137
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• 1996

The sheet formability can be improved by the optimum drawbeads installation because draw-beads can control the flow of the metal into the die cavity when the punch enters into the die opening, In this study the drawing characteristics for step drawbead are analyzed by 2-D rigid -plastic FEM and also are measured experimentally. In addition for the validity of FEM theoretical results are compared with the experimental results. Especially the draw bead restrain-ing forces and the strain distributions of drawn specimens are obtained in both FEM and experiment. Also the effects of the drawbead dimensions drawing angles and blank holding forces on the drawing characteristics are investigated.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.7
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• pp.2118-2133
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• 1996

A preform is designed by the backward tracing scheme of the rigid-plastic finite element method(FEM) for net-shape shell nosing components without machining after forming. The current process of the shell nosing requires cost-consuming machining to produce final products. Here, the backward tracing scheme of the rigid-plastic FEM, a novel method for preform design of metal forming processes, derives a sound preform for net-shape shell nosing product. The current process is simulated by the rigid-plastic finite element analysis to check the metal flow involved in the forming with a trial preform and its modified preform. The two preforms are found to be inadequate for net-shape shell nosing product. The first application of the back ward tracing scheme derives a preform producing a not-shape shell nosing product. The first application of the backward tracing scheme derives a preform producing a net-shape product numerically, but it is difficult to be formed economically as a preform. Thus an improved preform is designed by the badkward tracing scheme, which is suitable for net-shape manufacturing of the shell nosing components in view of economy of production and forming characteristics of the product. The preform in the current process and a modified preform are confirmed by a series of experiments and the results give the same deformation with the numerical ones. Finally the newly designed preform by the FEM was experimentally proved to be adequate in obtaining net-shape products.

• Journal of the Korean Society for Precision Engineering
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• v.13 no.12
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• pp.86-98
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• 1996

An combined implicit/explicit scheme for the analysis of sheet forming problems has been proposed in this work. In finite element simulation of sheet metal forming processes, the robustness and stability of computation are important requirements since the computation time and convergency become major points of consideration besides the solution accuracy due to the complexity of geometry and boundary conditions. The implicit scheme dmploys a more reliable and rigorous scheme in considering the equilibrium at each step of deformation, while in the explict scheme the problem of convergency is elimented at thecost of solution accuracy. The explicit approach and the implicit approach have merits and demerits, respectively. In order to combine the merits of these two methods a step-wise combined implici/explicit scheme has been developed. In the present work, the rigid-plastic finite element method using bending energy augmented membraneelements(BEAM)(1) is employed for computation. Computations are carried out for some typical sheet forming examples by implicit, combined implicit/explicit schemes including deep drawing of an oil pan, front fender and fuel tank. From the comparison between the methods the advantages and disadvantages of the methods are discussed.

• Transactions of the Korean Society of Mechanical Engineers
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• v.13 no.6
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• pp.1092-1103
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• 1989

본 논문에서는 기존의 금속성형의 유한요소해석에서 사용한 바 있는 기하적경 계조건을 직접 유한요소방정식에 대입하는 방법들을 비교검토하고 3차원박판성형에 적용하기 위하여 개선된 방법을 개발하였다.