• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2003년도 봄 학술발표회 논문집
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• pp.545-552
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• 2003

For temporary excavation support in a congested urban area, the strand of ground anchor should be removed to get permission of the private land to install anchors. But the strand doesn't need to be removed in the outside city area after use. So the anchor body, tension anchor, is fabricated in-situ. The unbonded length of This anchor has several strands, which wrap only one sheath. When the anchor body is carried into job-site or installed in the bore hole, the sheath is torn easily because it is a very week material. So the grout permeate into the torn sheath. Because of that, the load doesn't transfer to the bond length of ground anchors. It may indicate that load is being transferred along the unbonded length and thus within the potential slip surface assumed for overall stability of the anchored system. The load tests were performed on seven low-pressure grouted anchors installed in weathered soil to verify its problems. Four anchors(Type A) have the unbonded length, which consist of five strands and a week sheath and three anchors(Type B) have strands, which is covered by plastic sheath filled with grease, in the unbonded length. Both anchors are compared with load tests results.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2003년도 추계학술대회논문집
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• pp.333-338
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• 2003

Nano-imprint lithography(NIL) is a polymer embossing technique, capable of transferring nano-scale patterns onto a thin film of thermoplastics such as polymethyl methacrylate(PMMA) using this parallel process. Feature size down 10 nm have been demonstrated. In NIL, the pattern is formed by displacing polymer material, which can be squeeze flow of a viscous liquid. Due to the size of the pattern, a thorough understood of the process through experiments may be very different. Therefore we nead to resort to numerical simulation on the embossing process. Generally, there are two ways of numerical simulation on nano-scale flow, namely top-down and bottom-up approach. Top-down approach is a way to simulate the flow assuming that polymer is a continuum. On the contrary, in the bottom-up approach, simulation is peformed using molecular dynamics(MD). However, as latter method is not feasible yet. we chose the top-down approach. For the numerical analysis, two dimensional moving grid was used since the moving grid can predict the flow front. Effects of surface tension as well as the slip at the boundary were also considered.

• 전기학회논문지
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• 제56권1호
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• pp.214-221
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• 2007

This paper presents a myoelectric hand prosthesis(MHP) with two degree of freedom(2-DOF), which consists of a mechanical hand, a surface myoelectric sensor(SMES) for measuring myoelectric signal, a control system and a charging battery. The actuation for the 2-DOF hand functions such as grasping and wrist rotation was performed by two DC-motors, and controlled by myoelectric signal measured from the residual forearm muscle. The grip force of the MHP was automatically changed by a mechanical automatic speed reducer mounted on the hand. The skin interface of SMES was composed of the electrodes using the SUS440 metal in order to endure a wet condition due to the sweat. The sensor was embedded with a amplifier and a filter circuit for rejecting the offset voltage caused by power line noises. The control system was composed of the grip force sensor, the slip sensor, and the two controllers. The two controllers were made of a RISC-type microprocessor, and its software was executed on a real-time kernel. The control system used Force Sensing Resistors, FSR, as slip pick-ups at the fingertip of a thumb and the grip force information was obtained from a strain-gauge on the lever of the MHP. The experimental results were showed that the proposed control system is feasible for the MHP.

• Journal of Advanced Marine Engineering and Technology
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• 제10권2호
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• pp.136-145
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• 1986

The perfect and accurate methods to control the wear are not made clear so far. For this phenomenon only mating surface has been studied. In order to control the wear the essence of it has to be made clear. It is reported that adhesive wear might occure as a result of plastic deformation, the fracture and removal or transfer asperities on close contacting surfaces. On this view point the plastic flow was attempted to compare with fluid or electromagnetic flow. The partial differential equations of equilibrium for the plane strain deformation will make use of the method of characteristics. The characteristic curves or characteristics of the hyperbolic equation coincide with the slip lines by R. Hill's papers. By Hencky's stress equation, it is evident that if P and .phi. are prescribed for a boundary condition then it may be possible to proceed along constant .alpha. and .betha. lines to determine the value of the hydrostatic pressure everywhere in the slip line field net work. A wedge formation mechanism has been considered for an explanation of this matters. The analysis shows that there is a critical value, which depends on the hardness ratio and the shear stress on the interface, for the top angle of asperity is less than this critical value, the asperity can yield plastically despite of being harder than the mating surface.

• Tribology and Lubricants
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• 제34권3호
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• pp.115-122
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• 2018

Chemical mechanical polishing (CMP) is a hybrid processing method in which the surface of a wafer is planarized by chemical and mechanical material removal. Since mechanical material removal in CMP is caused by the rolling or sliding of abrasive particles, interfacial friction during processing greatly influences the CMP results. In this paper, the trend of tribology research on CMP process is discussed. First, various friction force monitoring methods are introduced, and three elements in the CMP tribo-system are defined based on the material removal mechanism of the CMP process. Tribological studies on the CMP process include studies of interfacial friction due to changes in consumables such as slurry and polishing pad, modeling of material removal rate using contact mechanics, and stick-slip friction and scratches. The real area of contact (RCA) between the polishing pad and wafer also has a significant influence on the polishing result in the CMP process, and many researchers have studied RCA control and prediction. Despite the fact that the CMP process is a hybrid process using chemical reactions and mechanical material removal, tribological studies to date have yet to clarify the effects of chemical reactions on interfacial friction. In addition, it is necessary to clarify the relationship between the interface friction phenomenon and physical surface defects in CMP, and the cause of their occurrence.

• 지질공학
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• 제24권3호
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• pp.323-332
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• 2014

The Nobi fault zone, which generated the 1891 Nobi Earthquake (M8.0), includes five or six faults distributed in and around Gifu and Aichi prefectures, Japan. Because large cities are located near the fault zone (e.g., Gifu and Nagoya), and because the zone will likely be reactivated in the future, relatively thorough surveys have been conducted on the 1891 Nobi earthquake event, examining the fault geometry, house collapse rate, and the magnitude and distribution of earthquake intensity and fault displacement. In this study, we calculated the earthquake slip along faults in the Nobi fault zone by applying a 3D numerical analysis. The analysis shows that a zone with slip displacements of up to 100 mm included all areas with house collapse rates of 100%. In addition, the maximum vertical displacement was approximately ${\pm}1700mm$, which is in agreement with the ${\pm}1400mm$ or greater vertical displacements obtained in previous studies. The analysis yielded a fault zone with slip displacements of > 30 mm that is coincident with areas in which house collapse rates were 60% of more. The analysis shows that the regional slip sense was coincident with areas of uplift and subsidence caused by the Nobi earthquake.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2005년도 춘계학술대회 논문집
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• pp.485-488
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• 2005

Most metals are polycrystalline material whose deformation is dominated by the slip system. During the deformation process, orientation of slip systems is rearranged with preferred orientations, leading to deformation-induced crystallographic texture which is called deformation texture. Depending on the texture development, the property of material can be changed. The rate-independent crystal plasticity which is based on the Schmid law as a yield function causes a non-uniqueness in the choice of active slip systems. In this work, to avoid the slip system ambiguity problem, rate-independent crystal plasticity model based on the smooth yield surface with rounded-off corners is adopted. In order to simulate the polycrystalline material under plastic deformation, we employ the Taylor model of polycrystal behavior that all the grains are assumed to be subjected to the macroscopic velocity gradient. Rigid-plastic finite element program based on this rate-independent crystal plasticity is developed to predict the grain-level deformation behavior of FCC metals during metal forming processes. In the finite element calculation, one integration point is considered as a crystalline aggregate which has a number of crystals. Macroscopic behavior of material can be deduced from the behavior of aggregates. As applications, the extrusion processes are simulated and the changes of mechanical properties are predicted.

• 한국결정성장학회지
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• 제20권2호
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• pp.101-105
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• 2010

플라즈마 에쳐 내에 사용되는 실리콘 전극과 링 부품은 사용 중에 강한 플라즈마와 접촉하면서 주기적인 가열과 냉각 과정을 거친다. 이 때 부품의 표면에서는 열 응력으로 인하여 PSB라고 하는 띠 형상의 결함이 생성되며 이로 인하여 그 수명을 다하게 된다. 원료인 실리콘 잉곳의 관점에서 그 수명에 미치는 인자를 살펴보았다. 잉곳의 등급, 즉 S/F와 S/A에 따라 불순물과 결함의 농도를 GDMS와 ${\mu}$-PCD로 평가하여 잉곳의 어떤 요소들에 의하여 수명이 결정되는가를 분석하였다. 그 결과, {001} 면상에서 관찰되는 <110> 방향의 면 결함들이 PSB와 연결될 가능성이 있음을 제안하였다.

• 토지주택연구
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• 제2권4호
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• pp.553-558
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• 2011

말뚝두부와 기초판의 연결방법으로서 기존의 강선남김방식은 시공성이 좋지 않고, 말뚝두부에 파손 및 균열이 발생할 가능성이 높을 뿐만 아니라 현장 인명사고가 자주 발생하여 최근에는 대안적인 방법으로서 원커팅에 의한 철근보강 방식이 제안되어 사용되고 있다. 하지만 이러한 방법들은 역학적인 성능규명에 의하여 그 상세가 구체적으로 제안 또는 검증된 사례가 없다. 이 연구는 원커팅 철근보강 방식에 있어서 최적 보강상세를 제안 할 목적으로 후 타설된 말뚝 내 속채움 콘크리트와 말뚝간의 전단마찰 저항력의 부족으로 인한 파괴를 실험을 통하여 규명하고, 적정 채움 깊이를 제안하였다. 실험결과에 근거하여 말뚝 부착파괴 강도를 안전측의 값으로 0.4MPa를 가정한다면, 부착파괴 이전에 철근이 항복에 도달하도록 하기 위해서 속채움 콘크리트의 깊이는 최소한 PHC 450과 PHC 500의 경우 600mm 이상, PHC 600의 경우 1,000mm 이상 확보하여야 할 것으로 판단된다.

• 한국항공우주학회지
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• 제47권1호
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• pp.9-16
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• 2019

본 연구에서는 중/고고도 영역에서 운행되는 우주발사체 주위 유동에 대한 해석을 효율적으로 하기 위해 삼차원 Navier-Stokes 방정식을 해석하는 비 정렬 격자 기반의 맥스웰의 미끄럼 경계조건이 적용된 유동 해석자를 개발하였다. 유동해석자의 검증은 축대칭 형태의 blunted cone-tip 형상에 대한 해석을 통해 수행하였다. 해석 결과는 타 연구자의 실험 및 직접모사법 해석 결과와 비교를 통해 일치하는 결과를 확인하였고, 속도 슬립 및 온도 점프에 대한 예측을 통해 본 유동해석자의 신뢰성을 확보하였다. 검증된 해석자를 이용하여 고도 86km의 중/고고도 영역에서 마하수 6으로 비행하는 우주발사체에 대한 유동 해석을 수행하였으며, 중/고고도 영역에서 나타나는 유동 현상들에 대해 고찰하였다.