• 한국전기전자재료학회:학술대회논문집
• /
• 한국전기전자재료학회 2009년도 추계학술대회 논문집
• /
• pp.41-41
• /
• 2009

We utilized atomic layer deposition (ALD) for the growth of the ZnO channel layers in the oxide thin-film-transistors (TFTs) with a bottom-gate structure using a $SiO_2/p-Si$ substrate. For fundamental study, the effect of the channel thickness and thermal treatment on the TFT performance was investigated. The growth modes for the ALD grown ZnO layer changed from island growth to layer-by-layer growth at thicknesses of > 7.5 nm with highly resistive properties. A channel thickness of 17 nm resulted in the good TFT behavior with an onloff current ratio of > $10^6$ and a field effect mobility of 2.9 without the need for thermal annealing. However, further increases in the channel thickness resulted in a deterioration of the TFT performance or no saturation. The ALD grown ZnO layers showed reduced electrical resistivity and carrier density after thermal treatment in oxygen.

• 한국정밀공학회지
• /
• 제18권8호
• /
• pp.32-39
• /
• 2001

This paper presents the synchronous vibration control of a rotor system using an Active Air Bearing(AAB). In order to suppress the synchronous vibration, it is necessary to actively control the air film pressure or the air film thickness. In this study, active pads are used to control the air film thickness. Active pads are supported by the pivots containing piezoelectric actuators and their radial positions can be actively controlled by applying voltage to the actuators. Disturbances and various kinds of external force can cause the shaft vibration as well as the change of the air film thickness. The dynamic behaviors of a rotary system supported by two tilting-pad gas bearings and its active stabilization using the tilting-pads as actuators are investigated numerically. The PID controller is applied to the tilting-pad gas bearing system with three pads, two of which contain piezoelectric actuators. To test the vapidity of the theoretical method, the performance of this control method is evaluated through experiments. The experimental results show the effectiveness of the control system for suppressing the unbalanced response of the rigid modes.

• 한국정밀공학회지
• /
• 제18권8호
• /
• pp.182-192
• /
• 2001

During the deep drawing process an initially flat blank is clamped between the die and the blank holder after which the punch moves down to deform the clamped blank into the desired shape. In general, sheet metal forming may involve stretching, drawing, bending or various combinations of those basic modes of deformation. The deformation problems of sheet metal working involve non-linearity in geometry and material. In this work, The punch load and thickness strain of electro-galvanized sheet steel (SECD) for elliptical deep drawing are examined under the various process conditions including, punch shape radius, die shape radius. The changes of punch load and thickness strain distribution of the deformed elliptical cup are affected by the size of each die shape radius.

• Earthquakes and Structures
• /
• 제12권2호
• /
• pp.153-163
• /
• 2017

The underlying goal of the present paper is to investigate soil and structural uncertainties on impedance functions and structural response of soil-shallow foundation-structure (SSFS) system using Monte Carlo simulations. The impedance functions of a rigid massless circular foundation resting on the surface of a random soil layer underlain by a homogeneous half-space are obtained using 1-D wave propagation in cones with reflection and refraction occurring at the layer-basement interface and free surface. Firstly, two distribution functions (lognormal and gamma) were used to generate random numbers of soil parameters (layer's thickness and shear wave velocity) for both horizontal and rocking modes of vibration with coefficients of variation ranging between 5 and 20%, for each distribution and each parameter. Secondly, the influence of uncertainties of soil parameters (layer's thickness, and shear wave velocity), as well as structural parameters (height of the superstructure, and radius of the foundation) on the response of the coupled system using lognormal distribution was investigated. This study illustrated that uncertainties on soil and structure properties, especially shear wave velocity and thickness of the layer, height of the structure and the foundation radius significantly affect the impedance functions, and in same time the response of the coupled system.

• 한국강구조학회 논문집
• /
• 제14권1호
• /
• pp.113-120
• /
• 2002

프리캐스트 바닥판 합성형 교량의 전단연결부는 전단포켓과 베딩층이 존재하여 현장타설 강합성 교량과는 다른 구조적 특징을 갖고 있다. 따라서 프리캐스트 바닥판의 전단연결재 설계의 기초를 수립하기 위해서는 실험을 통한 연구가 수행되어야 한다. 프리캐스트 바닥판 합성형 교량의 전단연결재의 피로수명을 평가하기 위하여 베딩층의 두께를 변수로 한 전단연결재의 push-out 피로 시험을 수행하였다. push-out 피로 시험의 수행 결과, 전단연결재의 파괴모드를 확인하였고, 이를 통해 프리캐스트 바닥판 합성형 교량의 전단연결재의 피로수명 곡선식을 유도하였다.

• Structural Engineering and Mechanics
• /
• 제74권2호
• /
• pp.175-187
• /
• 2020

The theories having been developed thus far account for higher-order variation of transverse shear strain through the depth of the beam and satisfy the stress-free boundary conditions on the top and bottom surfaces of the beam. A shear correction factor, therefore, is not required. In this paper, the effect of surface on the axial buckling and free vibration of nanobeams is studied using various refined higher-order shear deformation beam theories. Furthermore, these theories have strong similarities with Euler-Bernoulli beam theory in aspects such as equations of motion, boundary conditions, and expressions of the resultant stress. The equations of motion and boundary conditions were derived from Hamilton's principle. The resultant system of ordinary differential equations was solved analytically. The effects of the nanobeam length-to-thickness ratio, thickness, and modes on the buckling and free vibration of the nanobeams were also investigated. Finally, it was found that the buckling and free vibration behavior of a nanobeam is size-dependent and that surface effects and surface energy produce significant effects by increasing the ratio of surface area to bulk at nano-scale. The results indicated that surface effects influence the buckling and free vibration performance of nanobeams and that increasing the length-to-thickness increases the buckling and free vibration in various higher-order shear deformation beam theories. This study can assist in measuring the mechanical properties of nanobeams accurately and designing nanobeam-based devices and systems.

• 대한기계학회논문집A
• /
• 제26권4호
• /
• pp.711-719
• /
• 2002

This paper presents the synchronous vibration control of a rotor system using an active air bearing(AAB). In order to suppress the synchronous vibration, it is necessary to actively control the air film pressure or the air film thickness. In this study, active pads are used to control the air film thickness. Active pads are supported by pivots containing piezoelectric actuators and their radial position can be actively controlled by applying voltage to the actuators. Thus, disturbances, i. e. various kinds of external force can cause shaft vibration as well as change of the air film thickness. The dynamic behavior of a rotary system supported by two tilting-pad gas bearings and its active stabilization using the tilting-pads as actuators are investigated numerically. The $\mu$ synthesis are applied to the AAB system with three pads, two of which contain piezoelectric actuators. To test the validity of the theoretical method, the performance of this control method is evaluated through experiments. The experimental results also show the effectiveness of the control system for suppressing the unbalanced response of the rigid modes.

• Steel and Composite Structures
• /
• 제50권4호
• /
• pp.419-428
• /
• 2024

Prefabricated partially-encased composite (PEC) structural component is widely used in construction industry due to its superior structural performance and easy assembly characteristic. However, the solid web in traditional PEC components tends to split concrete into two halves, thus potentially reduces structural integrity and requires double concrete pouring. To overcome the above disadvantages, a new PEC beam with open-web π-shaped steel is proposed in this paper. Four open-web PEC beams with varying sectional height, flange thickness and web void rate were constructed and tested under flexural loads. During experimental tests, all beams exhibited typical flexural failure modes with strong moment capacities and excellent ductility. Owing to the unique construction form of web opening, steel-concrete bonding properties were enhanced and very small relative steel-concrete slips were observed. Experimental results also showed that the flexural capacity of such PEC beams increased with the increase of the sectional height and flange thickness, while was not affected by the web void rate. At last, a flexural capacity formula of the open-web PEC beam was proposed based on the whole section plastic rule. The formula results agreed well with experimental results.

• 비파괴검사학회지
• /
• 제32권1호
• /
• pp.34-40
• /
• 2012

본 연구에서는 FRP 보강판 부착 콘크리트에서의 유도초음파 기본 모드의 전파 특성에 부착제인 epoxy의 두께와 물성이 미치는 영향을 알아보고자 하였으며, 이를 위해 FRP-epoxy-concrete로 구성된 다층 유도초음파 시스템을 모델링하고 모드 해석을 수행하였다. Epoxy 층의 두께와 탄성계수를 변수로 하여 해석을 수행한 결과, A0 모드에 비해 S0 모드가 epoxy 층의 두께와 탄성계수 변화에 큰 영향을 받으며, 이로부터 경계층인 Epoxy 층의 상태 평가에는 A0 모드에 비해 S0 모드가 유효하리라는 결론을 얻었다.

• 비파괴검사학회지
• /
• 제21권4호
• /
• pp.406-414
• /
• 2001

폴리에틸렌 코팅 가스배관의 결함탐상을 위해 광범위 비파괴탐상기법인 유도초음파를 적용하였다. 가스배관의 내경은 190.7mm, 두께는 5.3mm, 그리고 바깥 표면은 $1.9{\pm}0.5mm$의 폴리에틸렌 층으로 코팅되어 있다. 폴리에틸렌 코팅 배관의 외면에 0.5MHz 탐촉자와 가변각 웨지를 사용하여, 비축대칭 유도초음파를 가진 시켰다. 주파수와 위상속도 조정을 통하여 가스배관의 결함 탐상을 위한 적절한 모드를 찾아내고, 모드의 특성을 단시간 퓨리어 변환을 이용하여 분석하였다. 결함탐상 결과를 두께 손실 및 원통형 관통결함에 대한 인위결함에 대해 나타내었다. 그리고 가스배관에 인위적으로 삽입한 두께 손실과 원통형 관통결함에 대한 검출 성능을 평가하였다.