• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.28 no.12
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• pp.781-786
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• 2015

It is necessary for ferrite sheets to be fabricated with high packing density for excellent electrical properties and high strength. In this study, the relationship between the warpage and the packing density of ferrite green sheet, was investigated with amount variation of organic additives. With 0.4 wt% of dispersant, the packing density was about 48% and warpage appeared 0.5~1.3 mm high. With 1.4 wt% of dispersant, the packing density increased up to 57% and warpage appeared 0.8~2.1 mm high. With high packing density, warpage appeared along the edges of specimen, while with low packing density, deformation appeared over whole specimen inhomogeneously. It is thought that inhomogeneous deformation after sintering came from the inhomogeneity in green sheet prepared with badly dispersed slurry. With good homogeneity in green sheet from well-dispersed slurry, isotropic shrinkage is thought to have occurred along the distance from center to edges of specimen during sintering.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.32 no.4
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• pp.333-339
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• 2008

Densification behavior of copper powder was investigated to study the effect of an aluminum mold under warm pressing. The low flow stress of an aluminum mold is appropriate to apply hydrostatic stress to powder compacts during compaction under high temperature. The suggested powder metallurgy process is very useful under high temperature since copper powder compacts have higher relative density over axial stress of 100 MPa and show more homogeneity as compared with conventional warm pressing. Elastoplastic constitutive equation proposed by Shima and Oyane was implemented into a finite element program (ABAQUS) for densification behavior under warn pressing by using a metal mold. Finite element results agreed well with experimental data for densification and deformation of copper powder compacts in the mold.

• Transactions of Materials Processing
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• v.4 no.2
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• pp.141-150
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• 1995

The purpose of the open die press forging is to maximize the internal deformation for better structural homogeneity and center-line consolidation in case of the ingot. A two and three dimensional viscoplastic finite element analysis is carried out for the plate, cylinder and square forging with the flat die in order to study the forging effects during the process. Effect of width, height reduction, and die staggering are studied through simulation of the process. Thus favorable working conditions are suggested for better and more disirable product quality.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.22 no.1
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• pp.50-55
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• 2013

In order to understand the biomaterial like the blood vessel of artery, there is a need to quantify the biomechanical behavior of the vessel. However, theoretical framework to describe and quantify the behaviour of blood vessel was not well established so far. For studying the biomechanical behavior of artery, Rubber-liked material which is similar to passive artery is selected since conventional theoretical interpretation is very limited to understand and predict the behavior of biomaterial. Rubber-like material is assumed to be very similar to artery and has properties of isotropy, homogeneity and is undergoing large deformation. Based on this assumption, stress developed on Rubber-like material is described by strain energy function and strain invariants which are required to understand the nonlinear elastic behavior of biomaterial. The descriptor which would be used for understanding the biomechanical behavior of artery is studied in this work.

• Structural Engineering and Mechanics
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• v.64 no.1
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• pp.71-79
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• 2017

In this study, interaction of several interface cracks located between a functionally graded material (FGM) layer and an elastic layer under anti-plane deformation based on the distributed dislocation technique (DDT) is analyzed. The variation of the shear modulus of the functionally graded coating is modeled by an exponential and linear function along the thickness of the layer. The complex Fourier transform is applied to governing equation to derive a system of singular integral equations with Cauchy type kernel. These equations are solved by a numerical method to obtain the stress intensity factors (SIFs) at the crack tips. The effects of non-homogeneity parameters for exponentially and linearly form of shear modulus, the thickness of the layers and the length of crack on the SIFs for several interface cracks are investigated. The results reveal that the magnitude of SIFs decrease with increasing of FG parameter and thickness of FGM layer. The values of SIFs for FGM layer with exponential form is less than the linear form.

• Progress in Superconductivity
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• v.3 no.2
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• pp.193-197
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• 2002

There are many problems in wire fabrication of long length Bi-2223 superconductor by using conventional extrusion method. They are mainly due to high surface resistance and inhomogeneous distribution of inner stress. Hydrostatic extrusion process will not only decrease the extrusion pressure but also enhance homogeneous deformation of material by reducing friction force between billet and container Hydrostatic extrusion method is considered to be useful fur fabrication of the homogeneous wire with high density. In this paper, hydrostatic extrusion process is introduced to fabricate Bi-2223 superconducting tape, and also discussed are the interface homogeneity and microstructural aspects of extruded BSCCO/Ag billet.

• Transactions of Materials Processing
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• v.13 no.2
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• pp.148-153
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• 2004

Finite element analysis of open die forging process to make rectangular billet has been performed in this study. Three dimensional rigid-plastic finite element method was used to analyze the effects of process variables, forging pass design and die configurations on the void closure phenomena to maximize the internal deformation for better structural homogeneity and center-line consolidation of the rectangular billet. The effect of anvil width ratio, anvil pitch, anvil shape and number of pass has been estimated by the degree of void closure ratio. Although it is difficult to optimize process parameters in the operational environments, favourable process conditions are suggested for better product quality.

• Journal of the Korean Society for Precision Engineering
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• v.22 no.2
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• pp.79-88
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• 2005

Evaluating the effective properties of materials containing various types of in-homogeneities is an important issue in the analysis of structures composed of those materials. A simple and effective method for the purpose is to impose the periodic displacement boundary conditions on the finite element model of a unit cell. Their theoretical background is explained based on the purely kinematical relations in the regularly spaced in-homogeneity problems, and the strategies to implement them into the analysis and to evaluate the homogenized material constants are introduced. The creep behavior of a thin sheet with square arrayed rectangular voids is characterized, where the orthotropy is induced by the presence of the voids. The homogenization method is validated through the comparison of the analysis of detailed model with that of the simplified one with the effective parameters.

• Journal of Welding and Joining
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• v.30 no.5
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• pp.27-33
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• 2012

Friction stir processing (FSP), developed based on the basic principles of friction stir welding(FSW), a solid-state joining process originally developed for various metal alloys, is an emergingmetalworking technique that can provide localized modification and control of microstructures in near-surface layers of processed metallic components. The FSP causes intense plastic deformation, material mixing, and thermal exposure, resulting in significant microstructural refinement, densification, and homogeneity of the processed zone. The FSP technique has been successfully used for producing the fine-grained structure and surface composite, modifying the microstructure of materials, and synthesizing the composite and intermetallic compound in situ. In this review article, the current state of the understanding and development of FSP is addressed.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.06a
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• pp.93-94
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• 2006

The $I_c$ degradation behavior of YBCO CC tapes due to torsional deformation has been investigated. Particularly, the influence of torsion angle on the $I_c$ in HTS tapes was examined at 77K (self-field). At low torsional angles or shear strains, the $I_c$ degradation was small and gradual. Also, a good consistency of the $I_c$ degradation behaviors was found along the longitudinal direction under torsion when multiple voltage terminals were adopted for investigating the homogeneity of the $I_c$ degradation.