• 소성∙가공
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• 제22권8호
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• pp.456-462
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• 2013

Compression tests were conducted at the various temperatures and strain rates to investigate void formation and microstructures behavior of a 1.9wt%C ultrahigh carbon steel used in forged workrolls. The microstructure, grain size and volume fraction of cementite were determined using specimens deformed in the temperature range from 800 to $1150^{\circ}C$ and strain rates from 0.01 to 10/s. It was found from the microstructural analysis that the grain size is larger at higher temperatures and lower strain rate deformation conditions. In addition, a higher volume fraction of cementite was measured at lower temperatures. The brittle blocky cementite was fractured at $800^{\circ}C$ and $900^{\circ}C$ regardless of strain rate. As a result, numerous new micro voids were formed in the fragmented blocky cementite. It was also found that local melting can occur at temperatures of more than $1130^{\circ}C$. Therefore, the forging temperature should be controlled between $900^{\circ}C$ and $1120^{\circ}C$. The temperature rise, which depends on the anvil stroke and velocity, was estimated through cogging simulation to find the appropriate forging temperature and to prevent local melting due to plastic work.

• Geomechanics and Engineering
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• 제16권5호
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• pp.463-469
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• 2018

In offshore engineering, lateral cyclic loading may induce excessive lateral movement and bending strain in pile foundations. Previous studies mainly focused on deformation mechanisms of single piles due to lateral cyclic loading. In this paper, centrifuge model tests were conducted to investigate the response of a $2{\times}2$ pile group due to lateral cyclic loading in clay. After applying each loading-unloading cycle, the pile group cannot move back to its original location. It implies that residual movement and bending strain are induced in the pile group. This is because cyclic loading induces plastic deformation in the soil surrounding the piles. As the cyclic load increases from 62.5 to 375 kN, the ratio of the residual to the maximum pile head movements varies from 0.30 to 0.84. Moreover, the ratio of the residual to the maximum bending strains induced in the piles is in a range of 0.23 to 0.82. The bending strain induced in the front pile is up to 3.2 times as large as that in the rear pile. Thus, much more protection measures should be applied to the front piles to ensure the serviceability and safety of pile foundations.

• 대한금속재료학회지
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• 제46권7호
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• pp.449-457
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• 2008

Compression deformation behaviors at high temperature as a function of temperature and strain rate were investigated in the 6061 aluminum alloy, which is used for automobile wheel. Compression tests were carried out in the range of temperatures $300{\sim}475^{\circ}C$ and strain rate $10^{-3}{\sim}10^{-1}sec^{-1}$. By analyzing these results, strain rate sensitivity, deformation temperature sensitivity, the efficiency of power dissipation, Ziegler's instability criterion, etc were calculated, which were plastic deformation instability parameters as suggested by Ziegler, Malas, etc. Furthermore, deformation processing map was drawn by introducing dynamic materials model (DMM) and Ziegler's Continuum Criteria. This processing map was evaluated by relating the deformation instability conditions and the real microstructures. As a result, the optimum forging condition for the automobile wheel with the 6061 aluminum alloy was designed at temperature $450^{\circ}C$, strain rate $1.0{\times}10^{-1}sec^{-1}$. It was also confirmed by DEFORM finite element analysis tool with simulation process.

• 한국해양공학회지
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• 제9권2호
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• pp.112-122
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• 1995

In this work, prediction of fatigue life and fatigue crack growth are studied. 4th order polynominal function is presented to describe the crack growth behaviors from artifical pit of SM45C steel. Crack growth curves obtained from 4th order polyminal growth equations are in good agreement with experimental data The crack growth behaviors at arbitrary stress levels and investigated by the concept of elastic-plastic fracture mechanics using ${\Delta}J$. Fatigue life prediction are carried out by numerical integral method. Prediction lives obtained by proposed method in this study, is in good agreement with the experimental ones. Life prediction results calculated by using of ${\Delta}J$ better than those of ${\Delta}K$.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2003년도 춘계학술대회논문집
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• pp.319-322
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• 2003

For the analysis of leveling process by the 3-dimensional elastic-plastic finite element method, a finite element analysis program modeling large deformation of shell has been developed. This program fur analyzing large deformation of sheet during leveling includes spring-back analysis as well as efficient contact treatment between sheet and rolls of leveler. This is verified by the simple leveling experiment with 5 rolls at laboratory. Besides the leveling examples, problems within the category of large strain and rotation, such as 3-dimensional roll-up and gutter occurrence at continuous bending-unbending process are also tested for verification of the program. The residual curvatures of strip predicted by finite element analysis are within 20% error range of the experiment. The formation and direction of anticlastic curvature or gutter during bending-unbending under tension is predicted and this agrees with the experimental results.

• 한국산학기술학회논문지
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• 제10권2호
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• pp.407-411
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• 2009

본 논문에서는 전편에 개발된 간단한 전단속도 의존적 구성모델의 각 모델변수에 대한, 정의, 값 결정법 및 결과에 미치는 영향 등에 대하여 분석하였다. 분석결과, 특히 전단속도 및 점성 핵 관련 모델변수의 영향이 보편적 범위 내에 있는 것으로 나타났다 이러한 관점에서 점성 및 소성 항복면을 동일시하는 개념의 모델 간략화 수정을 하였으며, 결과는 비교적 성공적으로 나타났다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회A
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• pp.1813-1817
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• 2007

The present work presents plastic limit load solutions for piping branch junctions with local wall-thinning, based on detailed three-dimensional (3-D) and small strain FE limit analyses using elastic-perfectly plastic materials. Three types of loading are considered; internal pressure, in-plane bending on the branch pipe and in-plane bending on the run pipe. The wall-tinning located on variable area of the piping branch junction is considered. A wide range of piping branch junction and wall-thinning geometries are considered. Comparison of the proposed solutions with FE results shows good agreement

• 한국농공학회논문집
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• 제46권4호
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• pp.75-84
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• 2004

The evaluation technique of seismic performance on agricultural infrastructure based on dynamic numerical simulations, which Included a cyclic elasto-plastic and a viscoelastic-viscoplastic constitutive model to actual multi-layered ground conditions during large earthquake were performed by a liquefaction analysis in the present study. From the liquefaction analysis, it was verified that the models can give a good description of the damping characteristics and liquefaction phenomena of ground accurately during large event which induces plastic deformation in large strain range.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2006년도 춘계학술대회 논문집
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• pp.59-62
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• 2006

Mg alloys have drawn a huge attention in the field of transportation and consumer electronics industries since it is the lightest alloy which could be industrially applicable. Most Mg alloy components have been fabricated by casting method. However, there have been a lot of research activities on the wrought alloys and their plastic forming process recently. The deformation behavior of an AZ31 Mg alloy at the elevated temperature was examined firstly to find out the optimum plastic forming range in terms of temperature and strain rate. During high temperature deformation, AZ31 alloy is usually undergone the dynamic recrystallization which influence the deformation behavior in turn. In the present study, the effect of deformation on dynamic recrystallization of an AZ31 alloy was investigated to clarify the relation between the deformation and recrystallization. In an AZ31 alloy system, the dynamic recrystallization was found to occur continuously. Recrystallized grain size was dependent on the stress level.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2003년도 춘계학술대회논문집
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• pp.240-243
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• 2003

Finite element analyses for bursting failure prediction in bulge forming under combined internal pressure and independent axial feeding are carried out. By means of the FEM combined with Oyane's ductile fracture criterion based on Hills quadratic plastic potential, the forming limit and bursting pressure level are investigated for a seamed tube that comprises of weldment, heat affected zone(HAZ) and base material parts. Especially, in order to determine the material property of HAZ tensile tests for the base material and the weld metal are executed based on iso-strain approach. Finally, through a series of bulge forming simulations with consideration of the weldment and HAZ it is concluded that the proposed method would be able to predict the bursting pressure and fracture initiation site more realistically, so the approach can be extended to a wide range of practical bulge forming processes.