• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1997년도 춘계학술대회 논문집
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• pp.230-235
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• 1997

During laser welding, a laser induced matal vapour and plasuma is formed. The plasma shows strong fluctuation combined with acoustic sound emission. On-line monitoring of the process is possible by measuring and analysing the plasma and acoustic sound emission. This paper introduce the method of on line process monitoring in the laser beam welding and analysis being monitoring signal. The results show the complementary information on the process.

• 한국의학물리학회:학술대회논문집
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• 한국의학물리학회 2002년도 Proceedings
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• pp.407-410
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• 2002

Monochromatic x-ray CT has several advantages over conventional CT, which utilizes bremsstrahlung white x-rays from an x-ray tube. There are several methods to produce such monochromatic x-rays. The most popular one is crystal diffraction monochromatization, which has been commonly used because of the fact that the energy spread is very narrow and the energy can be changed continuously. The alternative method is the use of fluorescent x-ray, which has several advantages such as large beam size and fast energy change. We have developed a parallel-beam and a fan-beam monochromatic x-ray CT, and compared some characteristics such as accuracy of CT numbers between those systems. The fan beam monochromatic x-rays were generated by irradiating target materials by incident white x-rays from a bending magnet beam line NE5 in 6.5 GeV Accumulation Ring at Tukuba. The parallel beam monochromatic x-rays were generated by using a silicon double crystal monochromator at the bending magnet beam line BL-20BM in Spring-8. A Cadmium telluride (CdTe) 256 channel array detector with 512mm sensitive width capable of operating at room temperature was used in the photon counting mode. A cylindrical phantom containing eight concentrations of gadolinium was used for the fan beam monochromatic x-ray CT system, while a phantom containing acetone, ethanol, acrylic and water was used for the parallel monochromatic x-ray CT system. The linear attenuation coefficients obtained from CT numbers of those monochromatic x-ray CT images were compared with theoretical values. They showed a good agreement within 3%. It was found that the quantitative measurement can be possible by using the fan beam monochromatic x-ray CT system as well as a parallel beam monochromatic X-ray CT system.

• Steel and Composite Structures
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• 제21권2호
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• pp.443-460
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• 2016

In this paper, the efficiency and effectiveness of two strengthening methods for upgrading behavior of the two external weak reinforced concrete (RC) beam-column joints were experimentally investigated under cyclic loading. Since two deficient external RC joints with reduced beam height and low strength concrete were strengthened using one-way steel prop and curbs with and without steel revival sheets on the beam. The cyclic performance of these strengthened specimens were compared with two another control external RC beam-column joints, one the standard RC joint that had not two mentioned deficiencies and another had both. Therefore, four half-scale RC joints were tested under cyclic loading.The experimental results showed that these innovative strengthening methods (RC joint with revival sheet specially) surmounted the deficiencies of weak RC joints and upgraded their performance and bearing capacity, stiffness degradation, energy absorption, up to those of standard RC joint. Also, results exhibited that the prop at joint acted as a fuse element due to adding steel revival sheets on the RC beam and showed better behavior than that of the specimen without steel revival sheets. In other words by stiffening of beam, the prop collected all damages due to cyclic loading at itself and acted as the first line of defense and prevented from sever damages at RC joint.

• 한국레이저가공학회지
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• 제17권3호
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• pp.19-23
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• 2014

To directly engrave circuit-line patterns as wide as $6{\mu}m$ in a buildup film to be used as an IC substrate, we applied a projection ablation technique in which an 8 inch dielectric ($ZrO_2/SiO_2$) mask, a DPSS 355nm laser instead of an excimer laser, a ${\pi}$-shaper and a galvo scanner are used. With the ${\pi}$-shaper and a square aperture, the Gaussian beam from the laser is shaped into a square flap-top beam. The galvo scanner before the $f-{\theta}$ lens moves the flat-top beam ($115{\mu}m{\times}105{\mu}m$) across the 8 inch dielectric mask whose patterned area is $120mm{\times}120mm$. Based on the results of the previous research by the authors, the projection ratio was set at 3:1. Experiments showed that the average width and depth of the engraved patterns are $5.41{\mu}m$ and $7.30{\mu}m$, respectively.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1997년도 하계학술대회 논문집 E
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• pp.1779-1781
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• 1997

The 2.0 GeV Pohang Light Source (PLS) is consisted of a full energy Linac and a storage ring. Four kicker magnets are installed in the storage ring tunnel to move the stored beam orbit in the storage ring closer to the injected beam from the beam transfer line. The injected beam then falls into the storage ring beam dynamic aperture. A kicker magnet modulator drives all four kicker magnets to maintain field balance and also synchronized kick of the beam. The kicker modulator can handle 2 GeV full energy beam. The kicker magnet modulator is installed in the storage ring tunnel and under stable operation. Specification of the kicker magnet modulator is ${\sim}6.0{\mu}s$ pulse-width, 200 ns flat-top width with ${\pm}0.2%$ regulation, ${\sim}24\;kA$ peak current, and 10 Hz repetition rate. Two thyratron switches (EEV CX-1536AX) are used in the system. In this article, design, and experimental results of the kicker magnet modulator are discussed.

• 한국기계가공학회지
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• 제11권6호
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• pp.82-87
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• 2012

The purpose of this study is to produce a side impact beam with high tensile steel using a roll forming process. The door side impact beam plays an important roll in a car because it protects passengers from external crash. The roll forming process is a continuous bending process wherein a long metal sheet is bended as it continuously passes several rolls. The characteristic of this study is that an impact beam is produced by a continuous process using a ultra high strength steel without a hardening heat treatment. A model was determined by analysing plasticity of a cross section shape considering high strength. Design parameters of the impact beam was determined by crash-analysing the model. Workpiece products were manufactured by designing dies for roll forming and setting them up in a following process line. Results of a bending test and a FEM analysis was considered and reviewed.

• 한국강구조학회 논문집
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• 제13권1호
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• pp.1-8
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• 2001

본 연구는 콘크리트충전 각형강관을 이용한 기둥-H형 보 접합부에 있어서 시공성과 충전성을 고려하여 강관 기둥을 외부에서 보강한 충전 각형강관 기둥-H형강보접합부를 개발하고자 하며 이러한 접합방식 개발을 위한 기초적 연구로 보의 인장플랜지와 강관기둥 접합부의 인장거동을 실험적으로 관찰하여 제시한 접합부의 내력 및 변형 특성을 파악한다. 시험체의 변수는 각형강관 기둥의 보강 두께(T=9, 18, 27mm)와 높이(H=50, 80mm)로 계획하여 총 4개의 시험체를 제작하였다. 접합부의 항복내력의 평가로 항복선 이론을 적용한 기존의 연구를 수정하여 실험치와 비교한 결과 비교적 좋은 대응을 나타냈다. 본 연구의 접합방식은 외부에서 강관 기둥을 보강하는 간단한 방법으로 보붕괴형의 강접합을 얻을 수 있으며, 콘크리트 충전성을 확보할 수 있어 시공성에 있어서 장점으로 인정된다. 강관기둥의 두께가 8mm 인 것을 고려하면 실제 구조물의 설계에 적용할 수 있는 가능성이 있는 것으로 판단되며, 구체적인 설계방법을 위해서는 추치해석적인 방법에 의한 연구와 보완적인 실험이 필요한 것으로 생각된다.

• 한국레이저가공학회지
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• 제12권3호
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• pp.14-17
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• 2009

The laser welding was performed for the flange joint of two overlapped coaxial circular pipes which serve as the inlet and connector pipes of STS 316L. The laser welding test finally resulted in a good penetration depth of 1.8 to 2.0 mm. On the way to get the good welding quality, two important parameters were found to be optimized. One is the focal positioning which is the offset of the laser beam focus to the exact welding seam line, which is more critical in the inner flange laser welding. When the beam spot size was deviated more than $200\;{\mu}m$ from the seam line, welding of two pipes is failed. The other is a gap size since a certain amount of gap is inevitable due to fabrication tolerance, or artificial allowances for smooth insertion of a pipe. However, it is required to restrict the gap allowance within 0.2mm to avoid undesirable undercut on a welding bead.

• 콘크리트학회지
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• 제10권6호
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• pp.203-211
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• 1998

고체내부의 미소파괴시 발생하는 탄성파 방출을 이용하는 음향방출기법은 구조물 또는 재료 내부의 미시적 변형기구를 이해하는데 매우 유익한 수단으로 최근 각 분야에서 다양하게 응용되고 있다. 따라서 본 연구에서는 모르타르 부재의 휨재하 시험시 부재 내부에 발생하는 미시적 손상거동 및 파괴특성을 시험시 연속적으로 모니터링한 AE 신호특성으로부터 평가하였다. 나아가 삼각법을 이용한 2차원 AE 발생원 위치추정으로부터 시험체 노치선단 주변에 대한 AE 발생원 위치를 명확히 하였으며 이들 결과로부터 미소균열의 성장 거동을 연속적으로 모니터링 하였다.

• Composites Research
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• 제17권4호
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• pp.25-31
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• 2004

본 연구에서는 다중세포로 구성된 타원형 단면 복합재료 블레이드의 정밀 1차원 보 해석모델을 개발하였다. 보의 정식화를 위하여 Reissner의 반보족에너지 함수를 이용하였으며, 고전적인 강성도 및 유연도법을 결합한 혼합보 이론 체계를 구축하였다. 타원단면의 특성계수들을 구하기 위해 단면의 외곽선을 유한개의 선분으로 분할하고 여기에 Gauss 적분을 수행하였다. 또한, 단면을 구성하는 각 세포에 대해 4개의 연속방정식이 충족되도록 구성하였다. 개발된 보 이론을 단일 및 이중세포로 구성된 타원형 복합재료 블레이드에 적용하였으며, 다차원 정밀 유한요소 해석 결과와 비교하여 그 타당성을 확보하였다.