• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1999.03b
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• pp.14-17
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• 1999

The wrinkling behavior of a thin sheet with perfect geometry is a kind of compressive instability. The compressive instability is influenced by many factors such as stress state mechanical properties of the sheet material geometry of the body contact conditions and plastic anisotropy. The analysis of compressive instability in plastically deforming body is difficult considering all the factors because the effects of the factors are very complex and the instability behavior may show wide variation for small deviation of the factors. In this study the bifurcation theory is introduced for the finite element analysis of puckering initiation and growth of a thin sheet with perfect geometry. All the above mentioned analysis and the post-bifurcation behavior is analyzed by introducing the branching scheme proposed by Riks. The finite element formulation is based on the incremental deformation theory and elastic-plastic material modeling. in order to investigate the effect of plastic anisotropy on the compressive instability a square plate that is subjected to compression in one direction and tension in the other direction is analyzed by the above-mentionedfinite element analysis. The critical stress ratios above which the buckling does not take place are found for various plastic anisotropic modeling method and discussed. Finally the effect of plastic anisotropy on the puckering behavior in the spherical cup deep drawing process is investigated.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2004.05a
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• pp.190-193
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• 2004

Ever since the ideal forming theory has been developed fur process design purposes, application has been limited to sheet forming and, for bulk forming, to two-dimensional steady flow. Here, application for the non-steady case was performed under the plane-strain condition based on the theory previously developed. In the ideal flow, material elements deform following the minimum plastic work path (or mostly proportional true strain path) so that the ideal plane-strain flow can be effectively described using the two-dimensional orthogonal convective coordinate system. Besides kinematics, for a prescribed final part shape, schemes to optimize a preform shape out of a class of initial configurations and also to define the evolution of shapes and boundary tractions were developed. Discussions include the two problematic issues on internal tractions and the non-monotonous straining. For demonstration purposes, numerical calculations were made for a bulk part under forging.

• Journal of the Korean Wood Science and Technology
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• v.45 no.1
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• pp.28-35
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• 2017

In this study, specimens of rigid frame joint were produced by integrating joints with adhesive and other specimens were produced by inserting a wooden gusset integrated with a column member into a slit-processed beam member and joining them with pins. Then the moment resistance performances of the specimens were examined. For the wooden gusset, a GFRP-reinforced wooden gusset was used. The calculation results of perfect elasto-plasticity for the frame specimens for which a GFRP-reinforced wooden gusset was inserted into and joined with the slit-processed beam member by pins were 20-80% lower compared to the control group which consisted of steel plate-inserted frame specimens. The rigid frame specimens for which the column and beam members have been integrated with adhesive showed almost no initial residual transformations, as well as 38% greater initial rigidity and 41% greater plasticity compared to the steel plate-inserted joint.

• Fibers and Polymers
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• v.5 no.3
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• pp.209-212
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• 2004

A nonsteady axi-symmetric ideal flow solution is obtained here. It is based on the rigid perfect-plastic constitutive law with the Tresca yield condition and its associated flow rule. The process is to deform a circular solid disk into a spherical shell of prescribed geometry. It is assumed that there are no rigid zones and friction stresses. The solution obtained provides the distribution of kinematic variables and involves one undetermined function of the time. This function can be in general found by superimposing an optimality criterion.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.32 no.1
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• pp.37-44
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• 2019

A bond-based peridynamic model has been reported dynamic fracture characteristic of brittle materials through a simple constitutive model. In the model, each bond is assumed to be a simple spring operating independently. As a result, this simple bond interaction modeling restricts the material behavior having a fixed Poisson's ratio of 1/4 and not being capable of expressing shear deformation. We consider a state-based peridynamics as a generalized peridynamic model. Constitutive models in the state-based peridynamics are corresponding to those in continuum theory. In state-based peridynamics, thus, the response of a material particle depends collectively on deformation of all bonds connected to other particles. So, a state-based peridynamic theory can represent the volume and shear changes of the material. In this paper, the perfect plasticity is considered to express plastic deformation of material by the state-based peridynamic constitutive model with perfect plastic flow rule. The elastic-plastic behavior of the material is verified through the stress-strain curves of the flat plate example. Furthermore, we simulate the high-speed impact on 3D granite model with a nonlocal contact modeling. It is observed that the damage patterns obtained by peridynamics are similar to experimental observations.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2007.05a
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• pp.229-232
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• 2007

In hot strip rolling, the work roll profile is one of the main factors in predicting and correcting the strip profile. Various studies concerning the wear profile and the thermal crown of work roll have been performed, and the results of these studies have shown that the work roll profile must be predicted accurately so as to efficiently control the strip qualities such as thickness, crown, flatness, and camber. Therefore, a precise prediction model of roll profile is called for in a perfect shape control system. In this paper, a genetic algorithm was applied to improve on the roll profile prediction model in hot strip rolling. In this approach, the optimal design problem is formulated on the basis of a numerical model so as to cover the diverse design variables and objective functions. A genetic algorithm was adopted for conducting design iteration for optimization to determine the coefficient of the numerical model for minimization of errors in the result of the calculated value and the measured data. A comparative analysis showed a satisfactory conformity between them..

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2003.05a
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• pp.434-438
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• 2003

The shearing process for the sheet metal is normally used in the precision elements such as semi-conductor components. In these precision elements, the burr formation brings a bad effect on the system assembly and demands the additional de-burring process. In this paper, we have developed the desktop-type precision punching system to investigate the burr formation mechanism and present kinematically Punch-die auto aligning methodology, for the purpose of burr unifomizing and minimizing, between the rectangular shaped punch and die. By using the scanning electron microscope, the aligned punching results are compared with the miss-aligned ones. Also, we measured the relative burr heights using the self-designed laser measuring device for insitu self aligning. Since it is hard to get the perfect, so called, burr-free edges during the shearing process, we introduced the ultrasonic do-burring machine. The de-burring operation was carried out by a novel do-burring method, the reversal flow resistance method, under different machining loads and abrasive types. The final do-burring results show the validity of our punching do-burring system pursuing the burr-free punched elements.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2003.10b
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• pp.94-106
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• 2003

In recent years, the production value of Taiwanese mold and die industries have reached to a high peak in 1998, in amount of NT 604 hundred million dollars. But in recent years production value are going down year by year, till year of 2001 the production value have down to NT 394 hundred million dollars. Its main reason might be the major product were following in medium and low price category, the high accuracy and high cost mold and die still rely on import aboard. Therefore how to made the related technical database system on various field to provide the industry user to promote industries competition ability in mold and die is really urgent matter at this moment. In this research, we will offer how to apply the Visual Basic program language to edit a set of more perfect database system of mold and die material selection. At the present time, we have constructed complete Knowledge-Base-System of intelligence for forging mold and die material, the most related data from the existed data, the others are through our additional experimental results. By using this system by the user can got the related and need data easily, we hope it will reduce designing time and cost for mold and die.

• Transactions of Materials Processing
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• v.13 no.6 s.70
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• pp.540-545
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• 2004

Ever since the ideal forming theory has been developed for process design purposes, application has been limited to sheet forming and, fur bulk forming, to two-dimensional steady flow. Here, application for the non-steady case was performed under the plane-strain condition based on the theory previously developed. In the ideal flow, material elements deform following the minimum plastic work path (or mostly proportional true strain path) so that the ideal plane-stram flow can be effectively described using the two-dimensional orthogonal convective coordinate system. Besides kinematics, fur a prescribed final part shape, schemes to optimize a preform shape out of a class of initial configurations and also to define the evolution of shapes and boundary tractions were developed. Discussions include the two problematic issues on internal tractions and the non-monotonous straining. For demonstration purposes, numerical calculations were made for a bulk part under forging.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1999.03b
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• pp.173-178
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• 1999

In this study MD simulations have been performed to observe the behavior of a grain boundary in an a-Fe plate under 2-dimensional loading. In MD simulation the acceleration of every molecule can be achieved from the potential energy and the force interacting between each molecule and the integration of the motion equation by using Verlet method gives the displacement of each molecule. Initially four a-Fe rectangular plates having different misorientation angles of grain boundary were modeled by using the Johnson potential and Morse potential We compared the potential energy of the grain boundary system with that of the perfect structure model. Also we could obtain the width of the grain boundary by investigating the local potential energy distribution. The tensile loading for each grain boundary models was applied and the behavior of grin boundary was studied. From this study it was clarified that in the case using Johnson potential the obvious fracture mechanism occurs along the grain boundary in the case of Morse potential the diffusion of the grain boundary appears instead of the grain boundary fracture.