• Journal of Welding and Joining
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• v.33 no.6
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• pp.60-66
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• 2015

Molten zone shape of pulse laser welding is affected by welding conditions such as beam power, beam speed, irradiation time, pulse frequency, etc. and is divided into conduction type and keyhole type. It is necessary to design heat source model for irradiation of laser beam in the pulse laser welding. Shape variables and the maximum energy density value of the heat source model are different depending on the molten zone shape. In this paper, pulse laser welding simulation for joining of cylindrical part and circular cover was carried out. The heat source model for pulse laser beam with circular path was applied to the heat input boundary condition, radiative and conductive heat transfer were considered for the thermal boundary condition. For each phase, thermal and mechanical properties according to temperature were also applied to analysis. Analytical results were in good agreement with the molten zone size of specimen under the same welding conditions. So, the reliability of the welding simulation was verified. Finally, the improvements for reducing residual deformation after cover welding could be reviewed analytically.

• The Korean Journal of Rheology
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• v.8 no.3_4
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• pp.207-214
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• 1996

사출성형은 많은 장점과 유용성에도 불구하고 싱크마크나 휨과 같은 변형문제를 피 하기 어렵다. 이것은 성형품의 부위별 온도분포 및 냉각속도 차이에 의한 잔류응력에 기인 하는 것으로 구조가 복잡하거나 크기가 쿤 경우에 더욱 더 문제가 되기 쉽다. 이와 같은 문 제를 해결하기 위하여 성형품의 내부에 기포를 형성시켜 수지의 수축분을 기포의 성장으로 보상하여 주는 가스사출성형이 개발되어 많이 활용되고 있는 실정이다. 한편 일반 가스성형 과 달리 수지를 완전히 채운후 저압의 공기를 이용하여 기포를 발생시켜 수지의 체적수축분 을 보상해주는 PFP성형기술은 가스사출의 나점인 공기의 유동조절문제를 해결하고 비용이 저렴한 등의 잇점을 가지고 있다. 이 과정은 가스성형공정의 2차 침투과정과 매우 유사하나 아직까지 이에대한 이해나 연구는 매우 부족한 실정이다 본 연구는 기포의 성장이 수지의 체적수축에 의한 것이라는 가정에 근거하여 기포성장길이에 관한 모델링을 수행한 것이다. 실험결과와의 비교를 통하여 기본 가정에 대한 타당성을 검증하고 여러 인자들의 영향을 살 펴보았다. 본 연구는 PFP성형공정에 대한 이해를 증진시켜 금형설계 및 성형조건 설정에 대한 가이드라인을 제시하며 아울러 PFP공정에 대한 보다 체계적인 이해 및 일반가스성형 의 2차 침투과정 등의 관련 현상에 대한 이해 및 연구에 도움이 될것으로 기대된다.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2006.05a
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• pp.145-148
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• 2006

Cold gas dynamic spray is a relatively new coating process by which coatings can be produced without significant heating during the process. Cold gas dynamic spray is conducted by powder sprayed by supersonic gas jet, and generally called the kinetic spray or cold-spray. Cold-spray was developed in Russia in the early 1980s to overcome the defect of thermal spray method. Its low process temperature can minimize thermal stress and also reduce the deformation of the substrate. Most researches on cold-spray have focused on micro scale coating, but our research team tried to apply this method to macro scale deposition. The macro scale deposition causes deformation of a thin substrate which is usually convex to the deposited side. In this research, the main cause of the deformation was investigated using 6061-T6 aluminum alloy and properties of deposited aluminum layer such as coefficient of thermal expansion, Elastic modulus, hardness, electric conductivity were measured. From the result of the analysis, it was concluded that compressive residual stress was the main reason of substrate deformation while CTE had little effect.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2014.05a
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• pp.102-103
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• 2014

Due to the nature of the existing load, the criteria of assessing the intensity of the lightweight wall's impact resistance has been though of as obscure. The current study, therefore, focuses on the standardized assessment of the impact resistance to the force of the large soft body applying to the lightweight wall. The gypsum board wall showed a low level of the maximum residual displacement. It is, however, required to be careful about the selection of the finishing process since the high level of the maximum displacement is likely to cause harm to finishing materials. Unlike the gypsum board, the ALC block wall displayed a considerable rigidity while showing almost no maximum residual displacement. Even with the low level of the maximum displacement due to the stiffness, the ALC block wall is still likely to be affected by the vibration derived from any impact on the surface, which demands a need for additional study. The future experimental study, accordingly, will focus on the impact of the vibration on finishing materials, consequently leading to the accurate prediction of the possibility of potential damage to the lightweight wall caused by the large soft body.

• Proceedings of the KSME Conference
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• 2001.11a
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• pp.186-191
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• 2001

Tensile residual stress happen by difference of coefficients of thermal expansion between fiber and matrix is one of the serious problems in metal matrix composite(MMC). In this study, TiNi alloy fiber was used to solve the problem of the tensile residual stress as the reinforced material. TiNi alloy fiber improves the tensile strength of composite by occurring compressive residual stress in matrix using shape memory effect of it. Pre-strain was added to generate compressive residual stress inside TiNi/A16061 shape memory alloy(SMA) composite. It was also evaluated the effect of compressive residual stress corresponding to pre-strains variation and volume fraction of TiNi alloy. AE technique was used to clarify the microscopic damage behavior at high temperature and the effect of pre-strain difference of TiNi/A16061 SMA composite. In addition, two dimensional AE source location technique was applied to inspect the crack initiation and propagation in composite.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2003.06a
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• pp.1799-1802
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• 2003

The commercial success of a new product is influenced by the time to market. Shorter product leadtimes are of importance in a competitive market. This can be achieved only if the product development process can be realized in a relatively small time period. New cutting inserts are developed by a time consuming trial and error process guided by empirical knowledge of the mechanical cutting process. The effect of previous cutting on chip formation and the surface residual stresses has been studied. The chip formation is not affected much. There is only a minor influence from the residual stress on the surface from tile first cutting on the second pass chip formation. Thus, it is deemed to be sufficient to simulate only the first pass. The influence of the cutting speed and feed on the residual stresses has been computed and verified by the experiments. It is shown that the state of residual stresses in the workpiece increases with the cutting speed. This paper presents experimental results which can be used for evaluating computational models to assure robust solutions. The general finite element code ABAQUS/Standard has been used in the simulations. A quasi-static simulation with adiabatic heating was performed. The path for separating the chip from the workpiece is predetermined. The agreement between measurements and calculation is good considering the simplifications introduced.

• Journal of the Korean Magnetics Society
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• v.12 no.3
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• pp.88-93
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• 2002

Rapidly solidified NdFeB powders were mixed with fine powders of pure metal elements before CA-press employed to obtain a fully dense isotropic precursor. Subsequently, the precursor was deformed by CA-deformation to obtain an anisotropic magnet. The CA-deformed anisotropic NdFeB magnets with 0.3 wt.% Zn or Sn exhibited the coercivities about 80% higher (11.4. and 11.2 kOe, respectively) than that (6.4 kOe) of the additive-free magnet.

• Transactions of Materials Processing
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• v.24 no.6
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• pp.395-399
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• 2015

A microstructure-based finite element simulation was conducted to predict the plastic strain ratio (R-value) of a dual-phase (DP) steel. The representative volume elements (RVEs) concept was adopted for the image-based FE modeling and a 3D model was constructed using sequential 2D images. Each phase was considered with the von-Mises yield criterion and the Swift model. The Swift parameters were defined by the empirical equations based on the chemical composition. The developed model was applied to analyze the effect of residual stress on the R-value and stress distribution. In order to consider the residual stress development after cold rolling, 10 % compression was applied in the thickness direction and unloaded before the tensile stress was applied in the rolling direction. The results showed a reasonable prediction for the R-value evolution: a sharp increase at small strains was well described and a transition followed in the downward direction. The R-value evolution was analyzed using the stress distribution change on the π-plane

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.7 s.178
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• pp.1740-1747
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• 2000

Under repeated rolling, initial plastic deformation introduces residual stresses which render the steady cyclic state purely elastic. This is called the process of shakedown. Many studies have been done about the shakedown in semi-infinite half space using calculated Hertizian pressure. In this paper shakedown processes in a shaft are studied by finite element analyses of a two dimensional(plane strain) model with elastic-linear-kinematic-hardening-plastic material subjected to repeated, frictionless rolling contact. Symmetric and non-symmetric pressure distributions are obtained using a simplified model of the bearing-shaft assembly. The rolling contact is simulated by repeatedly translating both pressure distributions along the surface of the shaft. By the influence of the non-symmetric pressure, larger residual radial tensile stress is generated in the immediate subsurface layer, which may make a crack propagate and, the subsurface undergoes a zigzag plastic deformation during the shakedown process, which may lead to a crack initiation.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.479.2-479.2
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• 2014

자가 세정 및 김서림 방지가 가능한 투명 코팅 소재로써 $TiO_2$ 코팅박막을 제안하였으며, $TiO_2$ 코팅박막은 스퍼터링 방식으로 제작하였다. 낮은 표면 에너지를 갖는 물질을 화학적으로 변형시키고 유리기판 위 텍스쳐링을 형성함으로써, 수분에 대해 완전히 다른 특성을 갖는 표면을 유도하며, 김서림 방지 기능과 자가세정, 그리고 높은 빛 투과 특성으로 스마트 표면 코팅을 구현할 수 있다. $TiO_2$ 자가세정 코팅기술은 설치 후 1년 안에 먼지 및 오염에 따라 최대 40%의 효율 저하가 나타나는 태양전지, 디스플레이 패널 분야에서 매우 중요한 요소로 자리 잡을 것으로 기대되어진다. 본 연구에서는 $TiO_2$ 세라믹 타겟이 부착된 비대칭 마그네트론 스퍼터링 장치를 이용하여 $TiO_2$ 박막을 증착하였으며 증착되어진 $TiO_2$ 박막의 광촉매 특성과 트라이볼로지 특성을 고찰하였다. 광촉매 특성으로는 표면 접촉각 분석을 통하여 고찰하였으며, 트라이볼로지 특성으로는 경도, 잔류응력, 마찰계수, 표면 거칠기 등을 평가하였다. 또한 XRD, FESEM 분석등 구조분석을 통하여 광촉매 특성과 트라이볼로지 특성등과의 연관성을 규명하였다.