• Smart Structures and Systems
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• 제23권1호
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• pp.31-44
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• 2019

The present study investigate the compressive stress, shear stress, tensile stress, vertical electrical displacement and horizontal electrical displacement induced due to a load moving with uniform velocity on the free rough surface of an irregular transversely isotropic functionally graded piezoelectric material (FGPM) substrate. The closed form expressions ofsaid induced stresses and electrical displacements for both electrically open condition and electrically short condition have been deduced. The influence of various affecting parameters viz. maximum depth of irregularity, irregularity factor, parameter of functionally gradedness, frictional coefficient of the rough upper surface, piezoelectricity/dielectricity on said induced stresses and electrical displacements have been examined through numerical computation and graphical illustration for both electrically open and short conditions. The comparative analysis on the influence of electrically open and short conditions as well as presence and absence of piezoelectricity on the induced stresses and induced electrical displacements due to a moving load serve as the salient features of the present study. Moreover, some important peculiarities have also been traced out by means of graphs.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2009년도 정기 학술대회
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• pp.488-491
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• 2009

본 논문에서는 응력함수와 Kantorovich method를 이용하여 기저판(substrate)에 인장과 굽힘이 작용할 때 복합재 패치의 3차원 응력을 해석하였다. 면내 방향과 면외 방향의 두 응력함수에 가상 공액일의 법칙(Complementary virtual work principle)을 적용하였으며 복합재 패치의 자유 경계조건과 바닥의 기저판으로부터 전달되는 전단 수직 응력 조건을 부여하였다. 이를 통해서 패치 구조물의 지배방정식을 연립 미분 방정식 형태의 고유치 문제로 변환하여 응력함수를 구하였다. 위 방법의 타당성과 효용성을 검증하기 위한 수치 예제로 cross-ply, angle-ply, quasi-isotropic의 패치 적층 배열을 고려하였으며, 층간 응력함수 값이 자유 경계에서 최고치를 나타내고 패치 중심부로 갈수록 급격히 감소하는 모습을 확인하였다. 제안된 기법은 기저판에 인장하중이 작용하는 경우뿐만 아니라 굽힘 하중이 작용하는 경우에도 정확한 예측이 가능하여, 패치 구조물의 층간 응력을 포함한 3차원 응력을 해석하는데 있어서 효율적인 해석 도구로서 사용할 수 있을 것이라 사료된다.

• 한국결정학회지
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• 제5권1호
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• pp.7-13
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• 1994

구조물에 매설된 광센서나, 기판위에 필름상으로 성장시켜 제조한 광디바이스등에서 보이는 바와 같이 변 형이나 온도변화가 존재할 경우 이방성을 가진 일반적인 결정 내에서의 빛의 진행의 변화를 검토하였다. 이방 성을 가지는 결정 내에서의 빛의 진행을 나타내는 굴절율을 계산하였고 변형이나 온도변화가 존재할 경우 이 복굴절율들의 변화를 표시하였다. 그리고 등방성 매질로 모델을 단순화하였을 경우에 빛의 진행을 검토하여 선행연구자들의 결과와 비교 검토하였다

• 한국세라믹학회지
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• 제32권10호
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• pp.1103-1110
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• 1995

Silicon carbide (SiC) films have been deposited on the isotropic graphite by chemical vapor deposition. Change of deposition parameters affected significantly the microstructure and preferred orientation of SiC films. Preferred orientation of SiC films was (111) or (220), and microstructure showed the startified structure consisting of small crystallite or faceted columnar structure depending on the deposition parameters. For microhardness, (111) oriented film and stratified structure were superior to (220) oriented film and faceted columnar structure, respectively. Surface of (111) oriented films was less rough than that of (220) oriented films. Adhesion force between graphite substrate and SiC films was above 100N for crystalline films and 49N for amorphous film.

• 한국표면공학회지
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• 제35권4호
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• pp.211-217
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• 2002

Ti-Si-N films were deposited onto WC-Co substrate by a RF-PECVD technique. The deposition behaviors of Ti-Si-N films were investigated by varying the deposition temperature, RF power, and reaction gas ratio (Mx). Ti-Si-N films deposited at 500, 180W, and Mx 60% had a maximum hardness value of 38GPa. The microstructure of films with a maximum hardness was revealed to be a nanocomposite of TiN crystallites penetrated by amorphous silicon nitride phase by HRTEM analyses. The microstructure of maximum hardness with Si content (10 at.%) was revealed to be a nanocomposite of TiN crystallites penetrated by amorphous silicon nitride phase, but to have partly aligned structure of TiN and some inhomogeniety in distribution. and At above 10 at.% Si content, TiN crystallite became finer and more isotropic also thickness of amorphous silicon nitride phase increased at microstructure.

• 한국세라믹학회지
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• 제30권5호
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• pp.389-396
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• 1993

We studied the crystallization behavior of amorphous PbTiO3 thin film grown at 30$0^{\circ}C$ by RF magnetron sputtering on Pt substrate. Crystallization to full perovskite phase was observed after annealing at 475$^{\circ}C$, for 9min, without PbO volatilization. The higher the annealing temperature, the shorter the time required for crystallization. The isothermal kinetic study at 475$^{\circ}C$ showed that the Avrami constant was approximately 4, which implies that the crystallization can be characterized by isotropic 3-dimensional growth with a constant nucleation rate. The TEM study revealed that the crystallized thin film was composed of very fine (20~100nm) grains oriented randomly without any evidence of 90$^{\circ}$domain boundaries.

• 한국광학회:학술대회논문집
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• 한국광학회 2003년도 하계학술발표회
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• pp.168-169
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• 2003

We have determined the orientational distribution functions (OBFs) at both air and substrate isotropic interfaces of a chiral chitosan bio-polymer film by the measurements of surface second-harmonic generation (SHG). It was shown that the simultaneous SHG analysis of both interfaces, based on the macroscopic and microscopic relations, provides all the informations on the nonlinear optical (NLO) activity. (omitted)

• 한국산학기술학회논문지
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• 제18권11호
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• pp.762-769
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• 2017

준등방성 라미네이트내의 확장강성 계수는 방사방향으로균일하지만, 굽힘강성 계수는 플라이 적층순서에 의해 방사방향으로 변화한다. 이 논문에서는 복합재 광학에서 사용되는 단방향섬유 복합재료와 무작위로 분포된 단섬유 복합재료로 이루어진 세 가지 유형의 준 등방성 라미네이트 반사경내의 굽힘강성 계수의 방사방향의 변화량을 비교하였다. 단섬유 복합재료 반사경 방사방향의 확장강성 계수와 굽힘강성 계수는 균일하게 나타나는 반면, 단방향섬유 복합재료 반사경의 경우에는 굽힘강성 계수의 방사방향으로의변화량이 11%에서 많게는 26%까지 변화하는 것으로 나타났다. 또한 강성계수의 차이로 인한 굽힘-비틀림-커플링 효과 등 강성 민감도 또한 큰 것으로 나타났다. 이러한 요소는 정밀성이 요구되는 광학분야에 복합재 반사경의 적용을 어렵게 할 커다란 문제점으로 인식되며, 이러한 복합재료의 이방성 성질로 인한 필연적인방사형 방향으로의 강성계수의 변화 및 그 영향성을 줄이기 위해서는 단섬유나 무작위로 공간에 흩어져있는 섬유 복합재료를 사용하는 것이 복합재 반사경내에 존재하는 굽힘강성 계수의 변화를 제거하는 하나의 방법이다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1998년도 하계학술대회 논문집 G
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• pp.2518-2520
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• 1998

Silicon can be reactive ion etched (RIE) either isotropically or anisotropically. In this paper, a new micromachining technology combining these two etching characteristics is proposed. In the proposed method, the fabrication steps are as follows. First. a polysilicon layer, which is used as the bottom electrode, is deposited on the silicon wafer and patterned. Then the silicon substrate is etched anisotropically to a few micrometer depth that forms a cavity. Then an PECVD oxide layer is deposited to passivate the cavity side walls. The oxide layers at the top and bottom faces are removed while the passivation layers of the side walls are left. Then the substrate is etched again but in an isotropic etch condition to form a round trench with a larger radius than the anisotropic cavity. Then a sacrificial PECVD oxide layer is deposited and patterned. Then a polysilicon structural layer is deposited and patterned. This polysilicon layer forms a pivot structure of a rocker-arm. Finally, oxide sacrificial layers are etched away. This new micromachining technology is quite simpler than conventional method to fabricate joint structures, and the devices that are fabricated using this technology do not require a flexing structure for motion.

• 한국세라믹학회지
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• 제32권4호
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• pp.419-428
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• 1995

Polycrystalline silicon carbide (SiC) thick films were depostied by low pressure chemical vapor deposition (LPCVD) using CH3SiCl3 (MTS) and H2 gaseous mixture onto isotropic graphite substrate. Effects of deposition variables on the SiC film were investigated. Deposition rate had been found to be surface-reaction controlled below reactor temperature of 120$0^{\circ}C$ and mass-transport controlled over 125$0^{\circ}C$. Apparent activation energy value decreased below 120$0^{\circ}C$ and deposition rate decreased above 125$0^{\circ}C$ by depletion effect of the reactant gas in the direction of flow in a horizontal hot wall reactor. Microstructure of the as-deposited SiC films was strongly influenced by deposition temperature and position. Microstructural change occurred greater in the mass transport controlled region than surface reaction controlled region. The as-deposited SiC layers in this experiment showed stoichiometric composition and there were no polytype except for $\beta$-SiC. The preferred orientation plane of the polycrystalline SiC layers was (220) plane at a high reactant gas concentration in the mass transfer controlled region. As depletion effect of reactant concentration was increased, SiC films preferentially grow as (111) plane.