• Computational Structural Engineering
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• v.9 no.4
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• pp.173-179
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• 1996

Study of weldment fracture behavior includes thermal analysis, residual stress analysis, and fracture analysis. The J-integral loses its path-independency in a residual stress field. Therefore, it is necessary to develop a program to calculate the J-integral in a welded plate. In this study, theoretical formulation and program were developed for the evaluation of the J-integral at the crack tip of weldments. To verify equations and program, welded thin plate and thick plate were used to calculate residual stress and the J-integral.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2000.11a
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• pp.326-329
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• 2000

Study of Weldment fracture behavior mcludes thermal analysis, residual stress analysis, and fracture analysis The 1-integral loses its path-independency in a res~dual stress field Therefore, it id necessary to develop a program to calculate the J-integral in a welded plate. m this study, theoretical formulation and program were developed for the evaluation of the 1-integral at the crack tip o i weldments. To verify equations and program, welded thin plate and thick plate were used to calculate residual stress and the J-integral.

• Proceedings of the Korean Reliability Society Conference
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• 2004.07a
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• pp.139-145
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• 2004

용접산업이 발전함에 따라 가스메탈아크 용접에서 고내마모성의 콘택트 팁이 요구되어지고 있다. 현재 국내외에서는 콘택트팁에 대한 수명평가 기준이 없으며, 일부 업계에서 자체 규격을 제정하여 운용하고 있지만 근거가 명확하지 않다. 따라서 본 연구에서는 콘택트팁의 신뢰성 평가기준을 제정하고자 하였다. 팁의 주요 파손기구로는 고온 마찰마모, 전기적 에로존, 번백 등이 있다. 신뢰성 평가는 경도 시험, 열처리 후 경도, 용접 마모, 전기전도도를 시험으로 구성되었다. 팁의 수명은 마모가 45%에 도달했을 경우 송급된 와이어 총 길이로 하였으며, 4시간까지 마모시험 한 결과를 근거로하여 한계수명을 추정하였다. 본 연구에서는 세 가지 조성의 다섯 가지의 콘택트팁에 대하여 4시간동안 내마모성 실험을 하였으며, 마모정도는 1시간 단위로 면적비를 백분율로 환산하여 측정하였다. 실험 결과 가공경화형팁은 1시간이내에 재결정 및 입자성장에 의한 경도 저하로 가공경화가 팁 수명에 지속적 영향을 주지 못하였다. 반면, 석출경화형팁은 석출경화 효과가 지속되어 가공경화형팁보다 수명이 향상 되었다.

• Journal of Ocean Engineering and Technology
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• v.22 no.3
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• pp.89-95
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• 2008

Fatigue cracked components often needs to be repaired during service. Standard repair schemes involve strengthening the component by connecting reinforcing members by means of rivets or welding by reducing the crack-tip stress intensity factors. Recent technological advances in fiber reinforced composite materials and adhesive bonding have led to the development of efficient repair schemes. In this study, the influence of various shape parameters on fatigue crack growth in the CCT type uniform thickness plates and the thin-ta-thick type stiffened panels repaired with woven fabric type Kevlar-Epoxy composite patch are studied experimentally.

• Proceedings of the KIEE Conference
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• 2000.07c
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• pp.1800-1802
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• 2000

본 연구에서는 냉음극 발광 소자인 FEA를 이용하여 Cold Cathode Lamp 제작과 그 구조에 대해서 연구하였다. Anode plate에는 ZnO:Zn 형광체를 전기영동법으로 증착한 후 tube slabs와 anode plate를 frit glass를 이용하여 접합하였다. FEA와 substrate의 bonding, addressing을 위한 wire bonding, substrate와 집속전극, setter를 stem base의 외부전극에 연결하기 위한 spot welding, tube와 stem base를 glass melting method로 접합 공정을 하였다. 진공배기 시스템에 배기판을 연결하여 ${\sim}10^{-7}$torr까지 배기한 후 heater를 이용하여 배기관을 tip-off하였다. 최종적으로 진공을 유지하기 위해 getter를 RF 고주파로 활성화하였다. 결론적으로 lamp외 특성을 비교분석한 후 휘도 및 발광효율을 향상시키기 위한 구조절 개선과 방안을 고찰하였다.

• Journal of Ocean Engineering and Technology
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• v.26 no.2
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• pp.33-38
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• 2012

The effects of the diffusible hydrogen content and hardness on the cold cracking in high strength weld metal were investigated. The diffusible hydrogen contents were influenced by welding parameters such as the voltage and contact tip-to-work distance (CTWD). The diffusible hydrogen content increased with an increase in voltage. However, it was decreased with an increase in CTWD. CTWD also influenced the weld metal hardness,especially when the wire used had a higher strength than the base metal. This showed that weld metal hardness had a more powerful effect on weld metal cold cracking than the diffusible hydrogen content in this experiment.

• International Journal of Korean Welding Society
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• v.5 no.1
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• pp.15-28
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• 2005

The ball shear test was investigated in terms of the effects of test parameters, i.e., shear height and shear speed, with an experimental and non-linear finite element analysis for evaluating the solder joint integrity of area array packages. Two representative Pb-free solder compositions were examined in this work: Sn-3.5Ag-0.75Cu and In-48Sn. The substrate was a common SMD type with solder bond pad openings of 460 $\mu$m in diameter. The microstructural investigations were carried out using SEM, and the IMCs were identified with EDS. Shear tests were conducted with the two varying test parameters. It could be observed that increasing shear height, at fixed shear speed, has the effect of decreasing shear force for both Sn-3.5Ag-0.75Cu and In-48Sn solder joints, while the shear force increased with increasing shear speed at fixed shear height. Too high shear height could cause some undesirable effects on the test results such as unexpected high standard deviation values or shear tip sliding from the solder ball. The low shear height conditions were favorable for screening the type of brittle interfacial fractures or the degraded layers in the interfaces. The shear speed conditions were discussed with the stress analyses of the solder ball, and we cannot find any conspicuous finding which is related to optimum shear speed from the stress analyses.

• Proceedings of the KWS Conference
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• 2010.05a
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• pp.97-97
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• 2010

최근 자동차에서 경량화의 방안으로써 높은 강성을 요구하는 고장력강 사용이 증대 되고 있다. 그러나 고장력강은 저항 점용접 시 일반 강에 비해 높은 전류를 요구하며 계면파단 및 expulsion 발생이 용이하기 때문에 가용 전류 구간이 좁은 특성을 가진다. 많은 연구자들이 hold time, tempering 등의 process를 이용하여 고장력강의 저항 점용접성을 개선하고자 하였으나 생산 공정라인에 적용하기는 어려운 실정이다. 본 연구에서는 용접 공정 변수의 변화에 따른 용접성과 전극 형상 변화을 통한 고장력강 점 용접성 향상에 대한 연구를 실시 하였다. 고장력강의 점 용접성 비교하기 위해 표준 전극(S1)과 인위적으로 가공한 전극(M1)을 사용하였으며, 실험에 사용된 판재는 두께 1.4mm의 DP590이며, 그 결과 표준전극(S1) 보다 가공 전극(M1)의 가용 전류 구간이 0.5kA 정도 넓은 것으로 확인 되었다. 두 전극을 사용한 점용접 시험편들의 인장전단강도를 비교 해보면 표준전극(S1)을 적용한 점용접 시 인장전단강도는 KS B 0850 기준에 만족하나 계면 파단이 발생 하였다. 가공 전극(M1)을 적용한 점용접 시 인장전단강도는 규격 기준에 만족하나 버튼 파단이 발생 하였다. 두 전극을 적용한 점용접부 형상 및 용접부 온도 분포에대해 저항점용접 시뮬레이션 프로그램(SORPAS)을 이용하여 실험 결과 값과 비교 분석하였고 파단모드의 변화에 대한 원인 분석을 도출 하였다.

• International Journal of Korean Welding Society
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• v.2 no.2
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• pp.19-25
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• 2002

In recent years, techniques for micro-assembly with high repeatability under a scanning electron microscope (SEM) are required to construct highly functional micro-devices. Adhesion phenomenon is more significant for smaller objects, because adhesional force is proportional to size of the objects while gravitational force is proportional to the third power of it. It is also known that adhesional force between micro-objects exposed to Electron Beam irradiation of SEM increases with the elapsed time. Therefore, mechanical manipulation techniques using a needle-shaped tool by adhesional force are often adopted in basic researches where micro-objects are studied. These techniques, however, have not yet achieved the desired repeatability because many of these could not have been supported theoretically. Some techniques even need the process of trial-and-error. Thus, in this paper, mechanical and adhesional micro-manipulation are analyzed theoretically by introducing new physical factors, such as adhesional force and rolling-resistance, into the kinematic system consisting of a sphere, a needle-shaped tool, and a substrate. Through this analysis, they are revealed that how the micro-sphere behavior depends on the given conditions, and that it is possible to cause the fracture of the desired contact Interfaces selectively by controlling the force direction in which the tool-tip loads to the sphere. Based on the acquired knowledge, a mode diagram, which indicates the micro-sphere behavior for the given conditions, is designed. By referring to this mode diagram, the practical technique of the pick and place manipulation of a micro-sphere under an SEM by the selective interface fracture is proposed.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.17 no.4
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• pp.423-431
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• 2004

For the fracture mechanics analysis of cracks in welds of dissimilar steels, residual stress analysis and fracture analysis must be performed simultaneously. The standard definition of the J -integral leads to a path dependent value in the presence of a residual stress field. And unlike cracks in homogeneous materials, a bimaterial interface crack always induces both opening and shearing modes of stress in the vicinity of the crack tip. Therefore, it is necessary to develope a path independent J-integral definition for a crack in a residual stress field generated by welding of dissimilar steels. This paper addresses the modification of the Rice-J-integral to produce a path independent J -integral when residual stresses due to welding of dissimilar steels and external forces are present. The residual stress problem is treated as an initial strain problem and the J-integral proposed for this class of problems is used. And a program which can evaluate the J -integral for a crack in a weld of dissimialr steels is developed using proposed J integral definition.