• Journal of Welding and Joining
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• 제11권1호
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• pp.52-61
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• 1993

Laser welding of ASTM no. 1060 Al plate with a pulsed Nd: YAG laser of 200W average power was performed for end capping of KMRR nuclear fuel elements In this research, we performed basic welding experiments. Firstly, laser output parameters which affect laser welding parameters were studied by changing laser input parameters for effective welding of 1060 Al plates. We found that laser power density and pulse energy are important parameters for smooth bead shape. Secondly, welding parameters which affect weld width-to-depth ratio were studied by changing power density and pulse energy, shielding gas, and defocusing. We found that power density must be higher than 0.3 Mw/cm$^{2}$ pulse energy must be higer than 3 J. travel speed must not exceed 200mm/sec, laser focus must be existed beneath 2-3mm from plate surface and helium is proper shielding gas. Thirdly, we studied the weld defects of Al-1060 such as crack and porosity in lap-joint welding. We designed new welding geometry for crack free welding of Al-1060 plates, and obtained crack free weldment but with lack of fusion. However, with Ti, Zr grain refiner elements, we can weld Al plates without solidification hot crack. Finally, we studied the origin of porosity by changing shielding gas. And we found that porosity was resulted from entrapment of shielding gas by the collapsing keyhole.

• 한국생산제조학회지
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• 제25권5호
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• pp.329-337
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• 2016

The demand for the eco-friendly vehicles is skyrocketing because of the increasing $CO_2$ emissions and global warming. In the industrial field, the battery process, a core part of an eco-friendly vehicle, is drawing increased attention; its weight lightening as well as high energy density are becoming increasingly important. In this study, pure Ni plates that were used as the battery pole plate were welded using the laser. The lab joint welding was conducted on ten pure Ni plates at a laser power of 1900 W and a feed speed of 2.8-3.4 m/min. As observed in the experiment, a faster feed speed reduced the bead width, but the laser did not penetrate all ten specimen plates. In addition, pores were trapped when protective gas was used, but they were not trapped when the welding was conducted in atmospheric condition.

• Journal of Welding and Joining
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• 제15권6호
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• pp.57-65
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• 1997

A study was undertaken to determine the influence of welding variables such as shielding and plasma gases, torch standoff, travel speed and heat input, etc. on the quality of plasma arc welds in Zircaloy-4 sheet, 2mm thick. Effect of shielding gases and their flow rates on the mechanical properties of Zircaloy-4 welds by plasma arc welding were determined in terms of tensile, bardness and bend tests. The microstructure and fracture surface of Zircaloy-4 welds were investigated by optical and scanning electron microscopies. In addition, the causes of porosity and undercut in plasma arc welds of Zircaloy-4 were also investigated. Zircaloy-4 weld bead width and depth by helium shielding gas showed a wider and deeper than those by argon. It was found that Zircaloy-4 welds with shielding gas of helium did dxhibit a little smoother and uniform weld beads than those with shielding gas of argon. It was also found that the optimum gas flow rates for Zircaloy-4 welding were 0.45l/min for plasma gas with Ar and 4.5 - 6 l/min for shielding gas with He. In addition, there was no big difference in the microstructure and fracture surface of the weld metals made by either Ar shielding gas or He shielding gas.

• Journal of Welding and Joining
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• 제10권2호
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• pp.51-62
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• 1992

A torch was designed and fabricated in order to develope the technology of "locally drying underwater welding" by water curtain method. The condition for the formation of the possible local cavity, the mechanical properties and the thermal cycle of welds were investigated in the developed welding equipment compared with in-air welding. The possibility of highly reliable and practical underwater welding was found. The proper local cavity was formed above the water flowrate of 30l/min and CO$_{2}$ gas flowrate of 100l/min. The bead width and penetration depth were increased with increasing welding current. The hardness of weldments is about 160Hv in air welding, but about 210Hv in underwater welding. The elongation and the impact value of underwater weldments are 15% and 6Kg/cm$^{2}$ respectively, which are only half as much as the values of in-air welding. The cooling time in the temperature range from 800.deg.C to 500.deg.C affecting the structure and the hardness of weldments is about 22sec. in air welding while about 10sec. in underwater welding.r welding.

• Interaction and multiscale mechanics
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• 제6권2호
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• pp.157-172
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• 2013

This paper presented an investigation of macromolecular suspension in a grooved channel by using the dissipative particle dynamics (DPD) with finitely extensible non-linear elastic (FENE) bead spring chains model. Before studying the movement and evolution of macromolecules, the DPD method was first validated by modeling the simple fluid flow in the grooved channel. For both simple fluid flow and macromolecular suspension, the flow fields were analyzed in detail. It is found that the structure of the grooved channel with sudden contraction and expansion strongly affects the velocity distribution. As the width of the channel reduces, the horizontal velocity increases simultaneously. Vortices can also be found at the top and bottom corners behind the contraction section. For macromolecular suspension, the macromolecular chains influence velocity and density distribution rather than the temperature and pressure. Macromolecules tend to drag simple fluid particles, reducing the velocity with density and velocity fluctuations. Particle trajectories and evolution of macromolecular conformation were investigated. The structure of the grooved channel with sudden contraction and expansion significantly influence the evolution of macromolecular conformation, while macromolecules display adaptivity to adjust their own conformation and angle to suit the structure so as to pass the channel smoothly.

• Journal of Magnetics
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• 제5권1호
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• pp.19-22
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• 2000

The effects of a hard-biased Held on the magnetic and magnetoresistive properties of a crossed spin-valve head are investigated by computer simulation with particular emphasis on the asymmetry of the output signal. The spin-valve considered in this work is NiMn (25 nm)/NiFe (2.5 m)/Cu (3 nm)/NiFe (5.5 m), with a length of 1500 m and a width of 600 nm. A simple model is used where each magnetic layer consists of a single domain, and the magnetoresistance is a function of the angle between the magnetization directions of the two magnetic layers. The ideal crossed spin-valve structure is not realized with the present model and magnetic parameters, but the deviation from ideality is decreased by the hard-biased field. This results in the improvement of the linearity of the output signal with the use of the bias field. The magnetoresistance ratio and magnetoresistive sensitivity, however are reduced. The magnetic properties including the magnetoresistance are found to be strongly affected by magnetostatic interactions, particularly the inter-layer magnetostatic field.

• 반도체디스플레이기술학회지
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• 제17권3호
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• pp.36-40
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• 2018

We have developed a nonlithographic patterning technique using polystyrene nanoparticles to form nanonet channel structures which is promising for high-performance TFT applications. Nanoparticles assisted patterning (NAP) is a technique to form uniform nano-patterns by applying lift-off and dry etch process. Oxygen plasma treatment was used to control the diameters of nanonet hole size to realize a branch width down to 100 nm. NAP technology can be very promising to fabricate nanonet structure with advantages of lower manufacturing cost and large-area patterning capability.

• 한국자기학회지
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• 제25권5호
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• pp.162-168
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• 2015

광 리소그래피 공정을 이용하여 반강자성체 IrMn 층을 기반으로 하는 GMR-SV(giant magnetoresistance-spin valve) 소자 위에 ${\mu}m$ 선폭 크기의 코일을 적층하여 미크론 크기 코일을 제작하였다. GMR-SV 박막일 때와 소자 제작 후의 자기저항비와 자장감응도는 각각 4.4 %, 2.0 %/Oe와 1.6 %, 0.1 %/Oe로 나타났다. 여러 개의 $1{\mu}m$ 크기인 자성비드가 붙은 적혈구 바로 아래 위치에 놓일 소자와 10번 감은 미크론 크기 코일에 흐르는 AC 및 DC 전류 크기에 따른 자기장 분포를 유한요소법 전산모사로 분석하였다. 코일 중심인 $z=0{\mu}m$에서 주파수 20 kHz인 AC 전류가 0.1 mA에서 10.0 mA로 증가하면 이 값에 비례하여 자기장의 크기는 $30{\mu}T$에서 $3060{\mu}T$로 증가하였다. 그리고 코일 중심에서부터 $z=10{\mu}m$에서 자기장 크기는 $z=0{\mu}m$인 중심에서 보다 1/6배로 줄어들었다. 미크론 크기 코일에 흐르는 전류에 의해 생성되는 자기장은 적혈구 포획용으로 충분한 크기를 갖고 있어서 검출용 바이오센서로 활용 가능함을 확인 할 수 있었다.

• 대한기계학회논문집A
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• 제34권1호
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• pp.79-83
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• 2010

최근 원자력발전소 배관계의 용접 시 결함 발생의 원인이 되는 용접변형과 용접잔류응력을 감소시키고 용접 효율도 증가시키기 위해 협개선 용접법이 적용되고 있다. 협개선 용접법은 기존 용접법에 비해 상대적으로 입열량이 적고 용접변형과 용접잔류응력도 감소시킬 수 있기 때문에 배관 건전성 관점에서 많은 이점이 있을 수 있다. 그러나 실제 협개선 용접부 결함에 대한 정확한 파괴역학적 분석 등을 위해서는 용접 특성을 고려하여 변형 및 용접잔류응력 특성을 정확하게 예측해야 한다. 따라서 본 논문에서는 협개선 용접부에 대한 상세 2차원 유한요소해석을 수행하여 협개선 용접부의 용접잔류응력 분포를 결정하였으며, 이를 일반적인 용접법에 대한 특성과 비교하였다. 본 논문의 결과는 향후 협개선 용접부의 결함 평가와 용접방법 개선 등을 위해 적용될 수 있다.

• Journal of Welding and Joining
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• 제33권2호
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• pp.14-17
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• 2015

Cleaning effect is well known mechanism of oxide layer removal in DCEP polarity. It is also known that DCEN has higher heat input efficiency than DCEP in GTAW process. Based on these two renowned arc theories, conventional variable polarity arc for aluminum welding was set up to have minimum DCEP and maximum DCEN duty ratio to achieve the highest heat input efficiency and weldability increase. However, recent several variable polarity GTA research papers reported unexpected result of proportional relationship between DCEP duty ratio and heat input. The authors also observed the same result then suggested combination of tunneling effect and random walk of cathode spot to fill up the gap between experiment and conventional arc theory. In this research, suggested combinational work of tunneling effect and rapid cathode spot changing is applied to another unexpected phenomena of variable polarity aluminum arc welding. From previous research, it is reported that wider oxide removal range, narrower bead width and shallower penetration depth are observed in thin oxide layered aluminum compared to the case of thick oxide. This result was reported for the first time and it was hard to explain the reason at that time therefore the inference by the authors was hardly acceptable. However, the suggested combinational theory successfully explains the result of the previous report in logical way.