• Transactions of the Korean Society of Mechanical Engineers A
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• v.33 no.3
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• pp.276-282
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• 2009

Wrinkling in the flange and wall of a deep-drawn part is one of the major defects in sheet metal processes. Wrinkling is influenced by many factors, such as material properties, shape of the body, forming conditions, stress state and thickness, etc. It is difficult to analyze the wrinkling initiation and growth according to the factors because the effects of the factors are very complex and the wrinkling behavior may show wide variation even though small deviation of factors. In this study, the influence of wrinkling parameters, such as material properties (Al1050, Al5052), the blank holding force and the drawing depth on the wrinkling initiation and growth is investigated by using the experimental method and the dynamic explicit finite element analysis. From the results, it is shown that the dynamic explicit finite element method can be used effectively to prevent the wrinkling problems advancely in the deep drawing process. Also, there is a good agreement between the experimental result and the dynamic explicit finite element analysis.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.14 no.3
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• pp.349-359
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• 2001

An enhanced four-node plate element, which has been developed for explicit dynamic analysis of plate, is described in this paper. Reissner-Mind1in(RM) assumptions are adopted to consider transverse shear deformation effects in the present plate element. RM plate element produces a shear locking phenomena in thin plate so that the substitute natural strains based on assumed strain method are explicitly derived. The present plate element is applied into the explicit transient algorithm and the mass matrix of plate is formulated by using special lumping method proposed by Hinton et al. The performance of the element is verified with numerical examples.

• Journal of Korea Water Resources Association
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• v.30 no.5
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• pp.495-501
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• 1997

Pumping power being given, traditional method requires an iteration process for the solution of discharge and pipe diameter. Yoo and Kang (1996) have developed explicit equations for the estimation of discharge and pipe diameter for the cases of uniformly rough pipe on a sloping bed with a pumping power. The use of poser law for the estimation of friction factor enabled to develop the explicit form of equations. Yoo (1995a) has suggested the mean friction factor method for the estimation of friction factor of commercial pipe or composite surface pipe. With the same approach, the present work has developed the explicit equations of discharge or pipe diameter for the general case of commercial pipe on a sloping bed with a pumping power by adopting the mean friction factor method.

• 제어로봇시스템학회:학술대회논문집
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• 2002.10a
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• pp.80.2-80
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• 2002

The problem of sound source localization is to determine the position of sound sources using the measurement of the acoustic signals received by microphones. To develop a good sound source localization system which is applicable to a mobile platform such as robots, a time delay estimator with low computational complexity and robustness to background noise or reverberations is necessary. In this paper, an explicit adaptive time delay estimation method for a sound source localization system is proposed. Proposed explicit adaptive time estimation algorithm employs direct adaptation of the delay parameter using a transform-based optimization technique, rather than...

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.6 s.177
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• pp.1438-1445
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• 2000

To determine dynamic characteristics of materials, a program was developed under base of stress wave propagation theory for SHPB with explicit finite element method. Through the program, all kinds of quasi-static stress-strain curves can be directly converted to dynamic stress-strain curves at any strain rate. This simulation results were compared with experimental results in the references and they are in a good agreement with each other.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1997.03a
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• pp.188-191
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• 1997

In the recent sheet metal forming simulations, it increases to adopt the dynamic explicit method for an effective computation and the elastic-plastic formulation for stress recovery. It is inevitable in the dynamic explicit method that some noises occur and sometimes partly spoil results of simulations. It is severer when complicated contact conditions are included in simulations. An effective method to control these noises is introduction of damping effects. In this paper, the concept of contact damping is introduced in order to suppress noises due to complicated contact conditions. This is checked by analyzing a simple sheet metal forming process(U-bending). From the computational results, it is shown that the contact damping can effectively control the noises due to contacts and develop more reliable internal stress states.

• Steel and Composite Structures
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• v.13 no.6
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• pp.539-560
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• 2012

This study uses an explicit numerical algorithm to evaluate the ultimate load capacity analysis of a unit Strarch frame, accounting for the initial imperfection effects of the stress-erection process. Displacement-based filament beam element and an explicit dynamic relaxation method with kinetic damping are used to achieve the analysis. The section is composed of the finite number of filaments that can be conveniently modeled by various material models. Ramberg-Osgood and bilinear kinematic elastic plastic material models are formulated to analyze the nonlinear material behaviors of filaments. The numerical results obtained in the present study are compared with the results of experiment for stress-erection and buckling of unit Strarch frames.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1996.06a
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• pp.97-109
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• 1996

In the present work computations are carried out for analysis of complicated sheet metal forming process such as forming of a rear hinge. Finite element formulation using dynamic explicit time integration scheme and step-wise combined Implicit/Explicit scheme are introduced for numerical analysis of sheet metal forming process. 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. The explicit scheme in general use is based on the elastic-plastic modelling of material requiring large computation time. 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 employs a more reliable and rigorous scheme in considering the equilibrium at each step of deformation, while in the explicit scheme the problem of convergency is eliminated at the cost 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 implicit/explicit scheme has been developed.

• 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.

• Journal of Industrial Technology
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• v.20 no.A
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• pp.211-218
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• 2000

It is desirable but difficult to predict springback quantitatively and accurately for successful tool and process design in sheet stamping operations. The result of springback analysis by the finite element method (FEM) is sensitively influenced by numerical factors such as blank element size, number of integration points, punch velocity, contact algorithm, etc. In the present work, a parametric study by Taguchi method is performed in order to evaluate the influence of numerical factors on the result of springback analysis quantitatively and to obtain the combination of numerical factors which gives the best approximation to experimental data. Since springback is determined by the residual stress after forming process, it is important to evaluate stress distribution accurately. The oscillation in the time history curve of stress obtained by the dynamic-explicit finite element method says that the stress solution at termination time is in very unstable state. Therefore, a variability study is also carried out in this study in order to assess the stability of implicit springback analysis starting from the stress solution by explicit forming simulation. The U-draw bending process, one of the NUMISHEET '93 benchmark problems, is adopted as an application model because it is most popular one for evaluating the springback characteristic.