• 한국생산제조학회지
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• 제21권6호
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• pp.932-937
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• 2012

In the presented study, SM45C carbon steel parts were joined by friction welding. The welding process was carried out under optimized conditions using statistical approach. The study of SM45C is conducted with various combinations of process parameters. Parameter optimization, microstructure and mechanical property correlation are the major contribution of the study. The welded joints were produced by varying spindle revolution speed, friction pressure, upset pressure and burn-off length. Tension tests were applied to welded parts to obtain the strength of the joints. Fracturs properties were additionally obtained experimentally under fluctuated tensile loads. Microstructures using microphotographs were examined in the weld interface and weld region and heat affected zone and base metal and flash zone of welded parts. Finally, Hardness variations in welding zone and base metal were also obtained. Through these tests, the optimum conditions of parameters for ${\phi}20$ SM45C in friction welding were obtained when the friction spindle revolution was 1,950 rpm, the friction pressures was 30 MPs, upset pressures was 50 MPs.

• Nuclear Engineering and Technology
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• 제55권4호
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• pp.1269-1279
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• 2023

Pool boiling experiments are performed within an isolated bubble regime at inclination angles of 0° and 45°. When a bubble grows and departs from the heating surface, the pressure, buoyancy, and surface tension force play important roles. The curvature and base diameter are required to calculate the pressure force, the bubble volume is required to calculate the buoyancy force, and the contact angle and base diameter are required to calculate the surface tension force. The contact angle, base diameter, and volume of the bubbles are evaluated using images captured via a high-speed camera. The surface tension force equation proposed by Fritz is modified with the contact angles obtained in this study. When the bubble grows, the contact angle decreases slowly. However, when the bubble departs, the contact angle rapidly increases owing to necking. At an inclination angle of 0°, the contact angle is calculated as 82.88° at departure. Additionally, the advancing and receding contact angles are calculated as 70.25° and 82.28° at departure, respectively, at an inclination angle of 45°. The dynamic behaviors of bubble growth and departure are discussed with forces by pressure, buoyancy, and surface tension.

• Ocean Systems Engineering
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• 제13권1호
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• pp.57-77
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• 2023

In the present study, the total hydrodynamic pressure exerted by the fluid on walls of rectangular tanks due to horizontal excitations of different frequencies, is investigated by pressure based finite element method. Fluid within the tanks is invisid, compressible and its motion is considered to be irrotational and it is simulated by two dimensional eight-node isoparametric. The walls of the tanks are assumed to be rigid. The total hydrodynamic pressure increases with the increase of exciting frequency and has maximum value when the exciting frequency is equal to the fundamental frequency. However, the hydrodynamic pressure has decreasing trend for the frequency greater than the fundamental frequency. Hydrodynamic pressure at the free surface is independent to the height of fluid. However, the pressure at base and mid height of vertical wall depends on height of fluid. At these two locations, the hydrodynamic pressure decreases with the increase of fluid depth. The depth of undisturbed fluid near the base increases with the increase of depth of fluid when it is excited with fundamental frequency of fluid. The sloshing of fluid with in the tank increases with the increase of exciting frequency and has maximum value when the exciting frequency is equal to the fundamental frequency of liquid. However, this vertical displacement is quite less when the exciting frequency is greater than the fundamental frequency.

• 한국강구조학회 논문집
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• 제16권4호통권71호
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• pp.463-470
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• 2004

본 연구에서는 중심축하중을 받는 각형강관기둥의 베이스플레이트의 지압응력의 분포와 설계에 대하여 조사하였다. 일반적으로 강구조 기둥의 베이스플레이트는 지압응력이 등분포하다고 가정하고 그 크기와 두께를 결정한다. 그러나 축하중이 적으면 베이스플레이트의 크기도 작아지고 두께도 얇아지며 지압응력은 등분포하게 되지 않으며 기둥단면의 하부에 집중된다. 본 연구에서는 실험적 방법과 해석적 방법으로 지압응력의 분포에 대하여 조사하고 그 결과를 이용하여 설계법을 검토하였다. 4개의 각형강관기둥 베이스플레이트 시험체를 제작하여 실험을 수행하였다. 또한 유한요소해석프로그램인 ANSYS를 이용하여 베이스플레이트의 지압응력의 분포를 해석하였다. 연구결과 축하중이 적은 경우 지압응력은 기둥단면의 하부에 집중되고 등분포하지 않으므로 유효폭의 개념을 이용하여 베이스플레이트를 설계하는 방법이 적절함을 나타내었다.

• 한국지반공학회논문집
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• 제20권8호
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• pp.193-203
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• 2004

표면이 거친 강성옹벽의 경우 뒷채움재에서 발생하는 아칭효과로 인해 옹벽에는 비선형의 토압분포가 작용하며, 아칭효과가 비선형의 토압분포에 미치는 영향은 옹벽의 변위 형태에 따라 달라진다. 따라서 강성옹벽에 작용하는 주동토압의 크기와 비선형의 토압분포를 정확하게 산정하기 위해서는 옹벽의 변위형태에 따라 달라지는 뒷채움재에 서 발생하는 실제적 인 파괴면 형상과 아칭효과를 고려해야만 한다. 따라서 본 연구에서는 강성옹벽이 저점을 중심으로 회전하는 경우에 뒷채움재에서의 아칭효과와 비선형의 파괴면 형상을 고려함으로써 비선형의 주동토압을 산정할 수 있는 토압산정식을 제안하였다. 이 과정에서 토압산정식이 수학적으로 복잡해지는 것을 피하기 위하여 뒷채움재에서 발생하는 비선형의 파괴면 형상은 4개의 직선으로 구성되는 가상의 파괴면으로 대체하였다. 그리고 제안식으로부터 구한 예측치를 기존의 모형시험 결과와 비교한 결과 제안식은 만족스런 토압 예측치를 제공하는 것으로 나타났다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1999년도 하계학술대회 논문집 D
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• pp.1523-1525
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• 1999

ZnO is a wide-bandgap II-VI semiconductor and has a variety of potential application. ZnO exhibits good piezoelectric, photoelectric and optic properties, and is good for a electroluminescence device. ZnO films have been deposited at (0001) shappire by PLD technique. Chamber was evacuated by turbomolecular pump to a base pressure of $1{\times}10^{-6}$ Torr Nd:YAG pulsed laser was operated at ${\lambda}=355nm$. The ZnO films were deposited at oxygen pressures from base to 500 mTorr. The substrate temperatures was increased from $200^{\circ}C$ to $700^{\circ}C$. At aleady works, UV emission and green-yellow PL was observed. In this work, ZnO films showed UV, violet, green and yellow emissions. UV emission was enhanced by increasing partial oxygen pressure. We investigated relationship between partial oxygen pressure and UV emission.

• 대한기계학회논문집A
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• 제26권3호
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• pp.544-552
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• 2002

Recommended seismic design guide for the flat bottom vortical-cylindrical oil storage tanks in KS B 6225 is presented. Under earthquake excitations, the hydrodynamic pressure exerted on the tank walls produces overturning moment which may cause either a failure of the anchors or a buckling of the tank shell near its base. The basis for establishing design loads due to hydrodynamic pressure is described including seismic zone risk map in Korea, zone coefficients and the essential facilities factor. This procedure for calculating applied compressive stress on the shell base subjecting to seismic load and for estimating the allowable buckling stress is described.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 추계학술대회논문집A
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• pp.166-173
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• 2001

Recommended seismic design guide for the flat bottom vertical-cylindrical oil storage tanks in KS B 6225 is presented. Under earthquake excitations, the hydrodynamic pressure exerted on the tank walls produces overturning moment which may cause either a failure of the anchors or a buckling of the tank shell near its base. The basis for establishing design loads due to hydrodynamic pressure is described including seismic zone risk map in Korea, zone coefficients and the essential facilities factor. This procedure for calculating applied compressive stress on the shell base subjecting to seismic load and for estimating the allowable buckling stress is described.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1997년도 추계학술대회 논문집
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• pp.551-555
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• 1997

IJnder earthquake excitations, the hydrodynamic pressure exerted on the flat bottom vertical-cylindrical oil storage tank walls produces overturning moment which may cause either a failure of the anchors or a buckling of the tank shell near its base. The basis for establishing design loads due to hydrodynamic pressure is described including seismic zone risk map in Korea. zone coefficients and the essential facilities factor. This procedure for calculating applied compressive stress on the shell base subjecting to seismic load and for estimating the allowable buckling stress is described. And seismic design program for the tanks is presented.

• 소성∙가공
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• 제25권4호
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• pp.254-260
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• 2016

In this study, hot isostatic pressed Ni-base superalloy was subjected by high-pressure torsion process to improve the dispersion of gamma prime phase, mechanical properties and remove prior particle boundaries. The resulting microstructural size decreases and prior particle boundaries removed with increasing strain by high-pressure torsion process. Moreover, the microhardness values and room temperature tensile strength were enhanced. However, the tensile elongation was decreased as increasing strain due to fast crack propagation along the refined and well dispersed gamma prime particles.