• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2005.05a
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• pp.225-228
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• 2005

The purpose of this study is to investigate effects of the plastic/elastic deformation energy on wet etching characterization on the surface of material by using the nanoindentation and HF wet etching technique. Indents were made on the surface of Pyrex 7740 glass by the hyperfine indentation process with a Berkovich diamond indenter, and they were etched in $50\;wt\%$ HF solution. After etching process, convex structure was obtained due to the deformation-induced hillock phenomena. In this study, effects of indentation process parameters (normal load, loading rate) on the morphologies of the indented surfaces after isotopic etching were investigated from an angle of deformation energies.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2008.05a
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• pp.361-364
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• 2008

Incremental forming path to manufacture a thick concave steel plate using the line array roll set is designed. To find the optimum forming path, the forming processes are simulated by the finite element method. A general-purpose commercial software, MSC.MARC is used. The rolls are modeled as rigid surfaces and the thick plate is modeled as 8-node hexahedral elastic-plastic solid elements to predict accurate springback. It is found that the process can be successfully applied to the fabrication of the dual curvature ship hull plate

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2008.05a
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• pp.383-386
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• 2008

Magnesium alloy sheets have been extending their field of applications to automotive and electronic industries taking advantage of their excellent light weight property. In addition to their excellent light property, magnesium alloys have several other advantages: high specific strength, good welding capability and corrosion resistance. Taking advantage of these benefits, magnesium alloys have also been substituting the polymeric materials in the electronic devices industries. In sheet metal forming application with magnesium alloys, the lower formability and high springback due to the lower elastic property (Young's modulus=45 GPa) at room temperature are major hurdles by which magnesium alloys have limited applications. In this study, commercial notebook case was adopted as the benchmark model, and then design parameters and process conditions are analyzed by the finite element simulation and physical try-outs.

• Transactions of Materials Processing
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• v.12 no.2
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• pp.123-127
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• 2003

The cold rolling conditions for the ultra thin steel for tension mask are very important because the residual stress that affects the flatness of strip is generate during the cold rolling. The residual stress in the sheet causes etching curls when it suffers perforation process. The residual stress through the thickness. To estimate the residual stress and deformation due to etching curl. FEM analysis is performed. Numerical simulation employ a ANSY5 5.6 and an elastic-plastic constitutive equation. The simulation results indicate the distribution of residual stress in the rolled sheet can be controlled by selecting the rolling conditions properly.

• Transactions of Materials Processing
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• v.11 no.4
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• pp.355-362
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• 2002

In this study, an axi-symmetric finite element program for elastic analysis of the die set shrink fitted in cold extrusion was developed. The geometrical constraint according to shrink fit was enforced by employing the Lagrange multiplier method. The numerical results for strain and stress distributions in the die set including single and multi stress rings assembled by shrink fit were compared well with the Lame's equation for thick-walled solution available in the literature. To extend the applicability of the analysis program developed, various cases without or with stress ring and with pre-stress applied on stress ring were numerically investigated as well. This numerical approach enables the optimization study to determine optimal dimensions of die set to improve tool life for practical use in industry.

• Transactions of Materials Processing
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• v.11 no.4
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• pp.363-370
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• 2002

In this study, an optimal design technique was investigated for determining appropriate dimensions of components of the die set used in the extrusion process. For this, an axi-symmetric elastic finite element program for the analysis of deformation of the shrink fitted die set was developed with the Lagrange multiplier method to implement the constraint condition of shrink fit of stress ring. By coupling the rigid-viscoplastic analysis of extrusion process by CAMPform and elastic analysis of the die set, the optimization study was made by employing optimization program DOT. Considering the various assembly conditions, optimal design was determined for a single stress ring case. It is construed that the proposed design method can be beneficial for improving the tool life of cold extrusion die set at practice.

• Proceedings of KOSOMES biannual meeting
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• 2003.05a
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• pp.153-158
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• 2003

Design of general steel structure had applied and achieve elastic design concept mainly so far. Because elastic design supposes that whole structure complies with elasticity formula as that achieve via allowable stress of material is concept that calculate stress distribution of construction about action external load and estimate load of when the maximum stress reaches equally with allowable stress that is established beforehand by maximum safety load of the structure. But, absence that compose actuality structure by deal with external load increase small success surrender and structure hardness falls and tell structure in limit state finally on the whole as showing complicated conduct by interference between these breakdown at buckling by compression. Examined closely about conduct of place since initial buckling through carbon vocal cords transformation finite element analysis series (ANSYS) that place mending condition supposes case that is boundary condition in this investigation.

• Transactions of Materials Processing
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• v.9 no.5
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• pp.486-493
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• 2000

Extrusion die-lip buildup has direct and negative impact on the properties of the final product. At the present time there is no absolute method of die-lip prevention. However, a Periodical shut down of extrusion line for the removal has been the general practice throughout the industry in concern. In this study the die-lip buildup was Investigated with a particular attention paid to the influence of die exit geometry and dimensions on the stresses produced at the point of die exit. To demonstrate the relationship between the stress state and the magnitude of the die-lip buildup, a method of virtual manufacturing was performed, assuming elastic-plastic material behavior for the high-density polyethylene under investigation. The overall numerical results suggested that the longer the die-land and/or the smaller the areal reduction of the die would reduce the tendency for the die-lip formation. Similarly, haying a fillet around the circumferential edge of the die exit would be favorable in decreasing the die-lip buildup.

• Structural Engineering and Mechanics
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• v.5 no.5
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• pp.587-598
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• 1997

A numerical model for masonry is proposed by following an internal variable approach originally developed in the field of elastic-plastic analysis. The general features of the theoretical framework are discussed by focussing on finite element models applicable to incremental elastic-plastic problems. An extremum property is derived and its implications in terms of convergence for convenient algorithms are briefly discussed, by including the case of softening materials and damage effects. Next, a numerical model is presented, which is suitable for masonry, can be developed according to the same internal variable formulation and enjoys similar properties. Some numerical results are presented and compared with the response of a masonry shear wall subjected to pseudodynamic tests.

• Transactions of Materials Processing
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• v.10 no.2
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• pp.130-136
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• 2001

The mathematical set-up model was developed to reduce the mechanical property deviation in annealed and slightly rolled steel strip. The mechanical peculiarities of skin pass rolling process, such as high friction value and non-circular contact arc, low reduction and non-negligible entry and exit elastic zones as well as central restricted deformation zone are all taken into account. The deformation of work rolls is calculated with the influence function method and arbitrary contact arc shape is permitted. The strip deformation is modeled by slab method and the entry and exit elastic deformation zones are included. The strip restricted deformation zone near the neutral point is also considered. It was revealed that the new model has better accuracy than present regression model by statistical analysis with actual mill rolling data.