• Transactions of Materials Processing
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• v.28 no.3
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• pp.145-153
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• 2019

The objective of this study is to analyze the mechanical splicing characteristic of the threaded bar according to the contact conditions of the transverse rib. In order to consider the contact conditions of the rib, selection of the main variables including the gap of the core diameter ($l_c$), rib angle (${\theta}$), and the number of contacts ($C_N$) of transverse rib was done. So as to analyze the splicing characteristic of the D51 threaded bar, a finite element (FE) simulation of the tensile test was conducted using the designed D51 threaded bar and coupler. Through FE simulation results, it was verified that the mechanical slicing characteristics varied based on the main design variables ($l_c$, ${\theta}$, and $C_N$). It was further confirmed that it was important to determine the $C_N$ in consideration of $l_c$. Additionally, the tensile test results of the D25 and D51 threaded bar combined with the couplers were similar to FE simulation results. Furthermore, to quantitatively evaluate FE simulation and test results, the calculation equation for the contacted projection area ratio (R) of the transverse rib was proposed. To secure a mechanical splicing joint of the threaded bar, it was established that the R calculated using the proposed equation had to be greater or equal to 40%.

• Structural Engineering and Mechanics
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• v.32 no.1
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• pp.95-126
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• 2009

The present contribution addresses the parallelization of advanced simulation methods for structural reliability analysis, which have recently been developed for large-scale structures with a high number of uncertain parameters. In particular, the Line Sampling method and the Subset Simulation method are considered. The proposed parallel algorithms exploit the parallelism associated with the possibility to simultaneously perform independent FE analyses. For the Line Sampling method a parallelization scheme is proposed both for the actual sampling process, and for the statistical gradient estimation method used to identify the so-called important direction of the Line Sampling scheme. Two parallelization strategies are investigated for the Subset Simulation method: the first one consists in the embarrassingly parallel advancement of distinct Markov chains; in this case the speedup is bounded by the number of chains advanced simultaneously. The second parallel Subset Simulation algorithm utilizes the concept of speculative computing. Speedup measurements in context with the FE model of a multistory building (24,000 DOFs) show the reduction of the wall-clock time to a very viable amount (<10 minutes for Line Sampling and ${\approx}$ 1 hour for Subset Simulation). The measurements, conducted on clusters of multi-core nodes, also indicate a strong sensitivity of the parallel performance to the load level of the nodes, in terms of the number of simultaneously used cores. This performance degradation is related to memory bottlenecks during the modal analysis required during each FE analysis.

• Journal of the Korean Society for Precision Engineering
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• v.13 no.11
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• pp.114-123
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• 1996

The major objective of the present paper is to estabilish analytical technique in order to closely understand and analyze the actual shearing process. First of all, isothermal and non-isothermal FE-simulation of the shearing process are carried out using finite element software DEFORM. Based on preliminary simulation using DEFORM, the finite element program to analyze two dimensional shearing process is developed. The ductile fracture criterion and the element kill method are also used to estimate if and where a fracture will occur and to investigate the features of the sheared surface in shearing process. It can be seen that the developed program combined with the ductile fracture criterion and element kill method has enabled the achievement of FE-simulation from initial stage to final stage of shearing process. The effects of punch-die clearance on shearing process are also investigated. In order to verify the effectiveness of the proposed technique the simulation results are compared with the known expermental data. It is found that the results of the present work are in close agreement with the published experimental results.

• Korean Journal of Optics and Photonics
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• v.28 no.3
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• pp.97-102
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• 2017

In this paper, we investigate the optical properties of $Ag@Fe_3O_4$ nanoparticles (NPs) composed of a plasmonic core and a magnetic shell. As the $Fe_3O_4$ shell with high refractive index (~2.42) is formed on the surface of the silver NPs having diameter of 60 nm, the wavelength of the localized surface-plasmon resonance (LSPR) is shifted from 420 nm to 650 nm, a so-called "redshift". Furthermore, through the use of three simulation models ($Ag@Fe_3O_4$ NP, $Fe_3O_4$ shell NP, and silver NP), the peak at 410 nm is seen to be the result of scattering by the $Fe_3O_4$ shell with 60 nm thickness, which would be useful in comprehending the complex optics in various nanoscale assemblies using similar NPs.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2009.10a
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• pp.425-428
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• 2009

Aerospace engine application needs to stand high temperature and pressure. Because of its mechanical properties such as high strength at high temperature, Alloy 718 is used aerospace engine application about 80%. But alloy 718's mechanical properties cause some problem to manufacturing profile ring like damage of material and mold. In this study, alloy 718's mechanical properties investigated for knowing its formability and using FE-Simulation for designing profile ring roll process and mold shape. Profile ring rolling processing is designed with "Initial material$\rightarrow$Blank$\rightarrow$Linear Ring$\rightarrow$Profilering". Blank's heating temperature is setting $1100^{\circ}C$ for manufacturing a trial profile ring on the basis of FE-Simulation. As a result of manufacturing alloy 718 profile ring, it is possible to make near target profile shape ring with all of the processing condition which gives in this study.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1996.04a
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• pp.191-195
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• 1996

Conventional single-side straight cutting of sheet metal is analyzed by the rigid-thermoviscoplastic finite element method. The FE-simulation is performed from initial stage to final stage of shearing process. The ductile fracture criterion and element kill method are used in the present work to estimate if and where a fracture occurs and to investigate the features of sheared surface in shearing process. The FE-simulation results are obtained for different clearances and these are compared with published experimental results. It is found that the results of the present work are in close agreement with published experimental results.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2002.10a
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• pp.296-299
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• 2002

The precision blanking of thin sheet metal is important process on production of precision electronic machine parts such as IC leadframe. In the blanking process, the factors that friction coefficient, tool clearance, material properties are the most important factors in the precision blanking process, because these factors affect the sheared face of product, side forces to punch during blanking process and surface condition after blanking process. So, many investigations have been performed. But, the former studies did not take up the characteristic of material. In this paper, in order to investigate the characteristic of blank, such as K(strength coefficient) and n(strain hardening coefficient), on the sheared face of blank and the side force to punch, FE-simulation has been analyzed by means of DEFORM-2D. To obtain input Parameters on FE-simulation, tensile and friction test has been done.

• Transactions of Materials Processing
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• v.25 no.6
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• pp.396-401
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• 2016

Recently, Multi-strength hot stamping process has been widely used to achieve lightweight and crashworthiness in automotive industry. In concept of multi-strength hot stamping process, process design of tailor rolled blank(TRB) in partial heating is difficult because of thickness and temperature variation of blank. In this study, springback prediction of TRB in partial heating process was performed considering its thickness and temperature variation. In partial heating process, TRB was heated up to $900^{\circ}C$ for thicker side and below $Ac_3$ transformation temperature for thinner side, respectively. Johnson-Mehl-Avrami-Kolmogorov(JMAK) equation was applied to calculate austenite fraction according to heating temperature. Calculated austenite fraction was applied to FE-simulation for the prediction of springback. Experiment for partial heating process of TRB was also performed to verify prediction accuracy of FE-simulation coupled with JMAK equation.

• Transactions of Materials Processing
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• v.29 no.6
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• pp.338-346
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• 2020

A V-bending test was performed in order to predict springback of high-strength steel sheets under various conditions. The results of V-Bending test were analyzed with artificial neural networks and FE-simulation, respectively, for the tool design. The results of design are discussed. The bending test result using the tool designed with artificial neural networks was about 92˚. However, the bending test result using the tool designed FE-simulation was about 94.5˚. Artificial neural networks are a useful tool along with FE-simulation in predicting springback.

• Nuclear Engineering and Technology
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• v.52 no.2
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• pp.337-343
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• 2020

Oxide dispersed strengthened (ODS) steel is an important candidate for Gen-IV reactors. Oxide embedded in Fe can help to trap irradiation defects and enhances the strength of steel. It was observed in this study that the size of oxide has a profound impact on the depinning mechanism. For smaller sizes, the oxide acts as a void; thus, letting the dislocation bypass without any shear. On the other hand, oxides larger than 2 nm generate new dislocation segments around themselves. The depinning is similar to that of Orowan mechanism and the strengthening effect is likely to be greater for larger oxides. It was found that higher shear deformation rates produce more fine-tuned stress-strain curve. Both molecular dynamics (MD) simulations and BKS (Bacon-Knocks-Scattergood) model display similar characteristics whereby establishing an inverse relation between the depinning stress and the obstacle distance. It was found that (110)_oxide || (111)_Fe (oriented oxide) also had similar characteristics as that of (100)_oxide || (111)_Fe but resulted in an increased depinning stress thereby providing greater resistance to dislocation bypass. Our simulation results concluded that critical depinning stress depends significantly on the size and orientation of the oxide.