Designing, Processing and Properties of Advanced Engineering Materials

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Authors: Yun Hee Lee, Jae Il Jang, Dong Il Kwon
Abstract: A theoretical model has been proposed to assess quantitative residual stress from a stress-induced shift in an indentation curve, but the assumption in this model of equibiaxial surface stress has obstructed its application to real structures in complex stress states. Thus we investigated the influence of non-equibiaxial surface stress on contact deformation through instrumented indentations of a biaxially strained steel plate in order to extend the model to a general surface stress by considering a ratio of two principal stresses.
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Authors: Ju Young Kim, Baik Woo Lee, Ho Seok Nam, Dong Il Kwon
Abstract: Amorphous silicon carbide (a-SiC) films were deposited using molecular dynamics simulations employing the Tersoff potential. The structure and intrinsic stress of a-SiC films changed dramatically with changes in such principal deposition process parameters as substrate temperature and incident energy. Changes in structure and intrinsic stress with deposition process parameters were analyzed.
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Authors: Hyoung Jin Choi, Beong Bok Hwang, B.D. Ko, Joong Yeon Lim, D.H. Jang
Abstract: The dissimilar channel angular pressing (DCAP or CCSS) based on the equal channel angular pressing (ECAP) was numerically modeled and analyzed by means of a rigid-plastic two-dimensional finite element method. Multi-pass rolling is performed in two different manners; the feeding direction of samples into the DCAP-channel is maintained in Route A and the feeding direction is reversed in the Route B. The deformation of AA1100 sheets during the DCAP process comprises three distinct processes of rolling, bending and shearing. The shear deformation of an amount of 0.5 was concentrated at the corner of the DCAP-channel where the abrupt change in the direction of material flow occurred. Because differences in the shear deformation in Route A and Route B led to the different strain states throughout the thickness of the aluminum sheet, the strain history in the DCAP-channel was analyzed in various thickness layers by the shear and effective strain components.
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Authors: Hyoung Jin Choi, Beong Bok Hwang, B.D. Ko, D.H. Jang, Joong Yeon Lim
Abstract: The cold forging processes of automobile parts such as piston-pin, valve-spring retainer(VSR) and power-assisted steering part (PAS) are analyzed by the rigid-plastic finite element method. The results of the simulation on the piston-pin are summarized in terms of the strain distribution and load-stroke relationship. Based on the analysis on the current processes of VSR and PAS, the new novel processes for improving the conventional process sequences are designed. As a design criterion, the improved processes satisfy the new condition such as an initial billet size, the production time and the limit value of forming load and pressure etc. The present simulation results and the newly developed process gave rise to an improvement in manufacturing processes for cold-forged automobile parts. Furthermore, the numerical analysis for the processes in this study provides a new design concept for forming processes and a basis for the selection of forging equipments.
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Authors: B.D. Ko, D.H. Jang, Hyoung Jin Choi, Joong Yeon Lim, Beong Bok Hwang
Abstract: A finite element method for the compaction process of metallic powder is introduced in the present work. Basic equations for the finite element formulation are summarized. A yield criterion, which is modified by describing asymmetric behavior of powder metal compacts, is introduced and applied to various classes of powdered metal compaction processes. Three material parameters are involved in the yield function and determined from the behavior of sintered powder compacts as a function of relative density. The FEM simulation includes single-action and double-action pressings of solid cylinders as well as cylindrical rings of relatively long parts (Class II parts). The compaction process for multi-level flanged components (Class III and Class IV parts) is also analyzed. The predicted results from simulations are summarized in terms of density distributions within the compacts and pressure distributions exerted on the die-wall interfaces, and also in terms of effectiveness with increased relative motions with in the compacts and the effect of various compaction schemes of combination of punch motions. Results obtained in the multi-level compaction process are discussed in terms of average relative density distributions at each height.
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Authors: Jong Heun Lee, Soo Ho Park, Moo Young Huh
Abstract: In order to optimize the recrystallization texture of ferritic stainless steel sheets, the crystallographic texture was modified by means of cross rolling. The as-received hot band displayed pronounced through-thickness texture gradients with a strong rotated cube orientation in the sheet center layer. After the conventional normal rolling, the strong initial texture was retained. Pronounced{001}<110> in the rolling textures led to the formation of {334}<483> in the final recrystallization texture. Cross rolling in the present work was performed by a 45° rotation of RD around ND. Cross-rolling led to a weakening of {001}<110> orienations. After recrystallization annealing the cross-rolled samples displayed stronger {111}//ND orientations. The orientation stability during the rolling deformation was tackled by means of Taylor deformation model.
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Authors: Hyoung Seop Kim, Min Hong Seo, Sun Ig Hong, Sung Ho Kim, Woo Seog Ryu
Abstract: In order to analyze the creep behaviour of Cr-Mo steels, an elasto-viscoplastic constitutive model based on dislocation density considerations is described. A combination of a kinetic equation, which describes the mechanical response of a material at a given microstructure in terms of dislocation glide, and evolution equations for internal variables characterising the microstructure provide the constitutive equations of the model. Microstructural features of the material are implemented in the constitutive equation. The internal variables are associated with the total dislocation density. The model has a modular structure and can be adjusted to describe a particular type of materials behaviour and metal forming processes. In this paper, the predicted creep behaviour of Cr-Mo steels is compared with the experimental results.
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Authors: Bong Ki Ji, Jun Hyung Lim, Dong Wook Lee, Min Woo Kim, Byung Hyuk Jun, Chan Joong Kim, Jin Ho Joo
Abstract: We studied the effects of the processing variables on the texture development of Ni tapes prepared from Ni powder compact rods. The Ni power was compacted into rods by cold isostatic pressing(CIP). The CIP-processed Ni rods were sintered for densification and made into Ni tapes of 100 microns by cold rolling. For the development of a cube texture, the rolled Ni tapes were annealed at various temperatures. The brass texture was converted into a cube texture during annealing and the degree of the formed cube textured was dependent on the annealing temperature. We analyzed the (200) cube texture by X-ray diffraction and pole figure analysis and EBSD(Electron beam backscattered diffraction pattern).
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Authors: Jin Seok Oh, Myung Hyun Lee, J.D. Kim, J.Y. Lee
Abstract: Cathodic protection is a system of preventing corrosion by forcing all surfaces of a hull to be cathode by providing external anodes. A metal can be made cathodic by electrically connecting it to a more anodic metal within the electrolyte. Anodes of these metals corrodepreferentially, the corrosion current of the anode achieving cathodic protection of the underwater hull to which they are connected. This paper presents a new current control algorithm for ICCP (Impressed Current Cathodic Protection) system. The anode of ICCP system is controlled by an external DC source with converter. The function of anode is to conduct the protective current into seawater. The DC source is generally obtained from main power system that contains a transformer, converter and etc. The proposed algorithm can operate AC-DC converter with current link. This algorithm includes the harmonic suppression control strategy and the optimum protection strategy and has tried to test the requirement current density for protection, the influence of voltage, the protection potential. Also, the properties of ICCP protected hull of ship in seawater are evaluated.
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Authors: Sang Yun Cha, I.B. Chudakov, Jong S. Woo, Jong Kweon Kim, Young Rae Cho
Abstract: The effects of magnetic annealing on a magnetiostriction in commercial grain-oriented 3.2 at.% Si steels were investigated. A combined (constant+strong pulsed) magnetic field during the magnetic annealing played a significant role in reducing the magnetostriction. The reduction ratio in magnetostriction was greatly dependent on surface conditions such as whether it was a bare metallic, tension coated and laser-scribed surface for grain-oriented electrical steels. For all three samples, the effect of the magnetic annealing on reduction in maganetostriction is more clearly observed in the compressive stress rather than in the tensile stress region.
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