• 한국항공우주학회지
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• 제30권7호
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• pp.113-122
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• 2002

KSR-III 로켓의 자세제어 시스템 모델링과 최적 벤딩 필터 설계가 이루어졌다. 모델링에는 로켓 강체 동역학, 공력, 슬로싱, 구조적 벤딩, 구동기 동역학, 센서 동역학, 그리고 탑재 컴퓨터 특성이 고려되었다. 시간의 변화에 따른 자세제어 시스템 파라미터들의 변화를 보상하기 위하여 이득 스케쥴링 기법이 사용되었다. 벤딩 모드를 안정화시키기 위한 필터가 매개변수 최적화 방법을 이용하여 설계되었다. 설계된 자세제어 시스템은 주파수 영역에서 요구되는 이득 및 위상 안정성 여유를 가지게 되었다.

• Structural Engineering and Mechanics
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• 제53권1호
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• pp.17-26
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• 2015

The cross sections of hollow cylindrical tubes ovalise under a pure bending condition, and this reduces their flexural stiffness as their curvatures increase. It is important to accurately evaluate this phenomenon, known as the 'Brazier effect', to understand the bending behaviour of the systems considered. However, if the tubes are supported by an elastic medium or foundation, the ovalisation displacements of their cross sections may decrease. From this point of view, the purpose of this research is to analytically investigate the bending characteristics of single- and double-walled elastic tubes contacted by an elastic material by considering the Brazier effect. The Brazier moment, which is the maximum moment-carrying capacity of the ovalised cross section, can be calculated by introducing the strain energy per unit length of the tube in terms of the degree of ovalisation for the tube and the curvature. The total strain energy of the double-walled system is the sum of the strain energies of the outer and inner tubes and that of the compliant core. Results are comparatively presented to show the variation in the degree of ovalisation and the Brazier moment for single- and double-walled tubes.

• Advances in materials Research
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• 제9권1호
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• pp.63-98
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• 2020

The novelty of this paper is the use of a simple higher order shear and normal deformation theory for bending and free vibration analysis of functionally graded material (FGM) beams on two-parameter elastic foundation. To this aim, a new shear strain shape function is considered. Moreover, the proposed theory considers a novel displacement field which includes undetermined integral terms and contains fewer unknowns with taking into account the effects of both transverse shear and thickness stretching. Different patterns of porosity distributions (including even and uneven distribution patterns, and the logarithmic-uneven pattern) are considered. In addition, the effect of different micromechanical models on the bending and free vibration response of these beams is studied. Various micromechanical models are used to evaluate the mechanical characteristics of the FG beams for which properties vary continuously across the thickness according to a simple power law. Hamilton's principle is used to derive the governing equations of motion. Navier type analytical solutions are obtained for the bending and vibration problems. Numerical results are obtained to investigate the effects of power-law index, length-to-thickness ratio, foundation parameter, the volume fraction of porosity and micromechanical models on the displacements, stresses, and frequencies.

• Steel and Composite Structures
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• 제38권5호
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• pp.583-597
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• 2021

This article develops a nonclassical model to analyze bending response of squared perforated microbeams considering the coupled effect of microstructure and surface stress under different loading and boundary conditions, those are not be studied before. The corresponding material and geometrical characteristics of regularly squared perforated beams relative to fully filled beam are obtained analytically. The modified couple stress and the modified Gurtin-Murdoch surface elasticity models are adopted to incorporate the microstructure as well as the surface energy effects. The differential equations of equilibrium including the Poisson's effect are derived based on minimum potential energy. Exact closed form solution is obtained for bending behavior of the proposed model considering the classical and nonclassical boundary conditions for both uniformly distributed and concentrated loads. The proposed model is verified with results available in the literature. Influences of the microstructure length scale parameter, surface energy, beam thickness, boundary and loading conditions on the bending behavior of perforated microbeams are investigated. It is observed that microstructure and surface parameters are vital in investigation of the bending behavior of perforated microbeams. The obtained results are supportive for the design, analysis and manufacturing of perforated nanobeams that commonly used in nanoactuators, nanoswitches, MEMS and NEMS systems.

• 마이크로전자및패키징학회지
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• 제18권1호
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• pp.55-59
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• 2011

유연성 기판 상의 동박의 반복 굽힘 변형에 따른 절곡 빛 굴곡 신뢰성과 인장 특성과의 관계를 규명하기 위해 4종류의 동박 시편의 절곡 신뢰성 실험, 굴곡 선뢰성 실험과 인장 실험을 실시하였다. 절곡 신뢰성 실험은 동박에 5.3%의 굽힘 변형률을, 굴독 선뢰성 실험은 동박에 2.0%의 굽힘 변형률을 반복적으로 인가하면서 전기 저항 변화를 관찰하고 피로 수명을 평가하였다. 또한, 4가지 시편의 인장 실험을 통해 탄성 계수, 항복 강도, 연장 강도, 인성 등의 재료 물성을 구한 결과, 연성과 인성이 우수한 시편의 경우 절곡 및 굴곡 신뢰성이 크게 우수한 것으로 나타났다. 반면, 탄성 계수, 항복 강도의 경우 절곡 및 굴곡 신뢰성과 큰 연관성을 보이지 않았다. 이는 절곡 및 굴곡 변형에 의한 금속의 피로 파괴 거동은 재료의 파괴 인성과 밀접한 관계를 가지기 때문으로 판단된다.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2010년도 추계학술대회 논문집
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• pp.124-129
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• 2010

Wind load characteristics is investigated for vibration analysis of wind turbine gearbox. A normal wind model assumed, of which the wind velocity is increased according to the height from ground. A blast wind model is assumed, of which the maximum velocity is located at the center and the velocity profile is normally distributed. The periodical torque and bending moments transmitted to the main shaft of wind turbine are investigated. The average values and the harmonic terms of the transmitted moments are studied on the wind direction of range $-45^{\circ}{\sim}45^{\circ}$ and the bending moment characteristics are examined, which is regarded as the main source of the misalignment of gear train.

• 한국염색가공학회지
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• 제6권4호
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• pp.54-61
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• 1994

The study has been conducted to investigate the relationship between yarn structural parameters such as diameter, twist multiplier and linear density, and mechanical properties of yarns measured by KES-F System. Each mechanical characteristic values per tex have non-linear relationship to the increment of yarn diameter, but as the linear density has increased, the mechanical characteristic values except for the bending characteristics have decreased linearly. It is, however, difficult to analyze obviously on the effects of twist multiplier even though the bending and the shear characteristic values were inclined to decrease. The effect of dyeing has also considered. The results are showing that yarn-dyed samples had higher effects than top-dyed ones on the mechanical characteristics.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 2001년도 추계학술대회(한국공작기계학회)
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• pp.172-178
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• 2001

Titanium alloys have lightness, high strength and good corrosion resistant characteristics, and broadly used in manufacturing parts for military and aerospace industries. And these alloys also are recognized for organism materials comparatively and used as fixing ones in the human body. Nevertheless thess alloys have excellent properties such as corrosion resistance, heat resistance, and good tensile strength, it is difficult to machine by traditional methods because of high hardness and chemically activated property. So higher tool wear is expected when cutting by tools. Therefore, it is required nontraditional machining process. And the mechanical characteristics such as surface structure and shape, hardness and bending strength are studied for wire electrical discharge machined and surface ground titanium alloys for various heat-treated conditions.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2001년도 춘계학술대회 논문집
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• pp.683-686
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• 2001

The thermomechanical characteristics of NITINOL shape memory alloy were evaluated using DSC with small samples and DMA with three-point bending specimens. The shape memory alloy of 54.4Ni/45.5Ti wt.% was used so that the austenite finish temperature was in the range of $50~100^{\circ}C$. Two types of sample were tested in the experiments corresponding to as-received and annealed conditions. Simple beam bending theory was used to calculate the dynamic moduli of the shape memory alloy. According to the results, a large discrepancy in transformation temperatures was found between DSC and DMA techniques. Annealing treatment was found to suppress the R-phase transformation during cooling and the secondary plateau in the austenite transformation. Such a heat treatment was also significantly influenced to raise the transformation temperatures and the moduli of the shape memory alloy.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 1998년도 추계학술대회 논문집
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• pp.248-253
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• 1998

Recently, the uses of Ceramic/metal bonded joints, resin/metal joints, adhesive joints, composite materials which are composed of dissimiliar materials have increased in various industry fields. Since the ceramic/metal bonded joints material is made at a high temperature, residual stress distributions due to differences in material properties were investigated by varying material parameters. The two dimensional finite element analysis was performed to study residual stress distribution in Si3N4/SM45C bonded joint with a copper interlayer between the silicon nitride(Si3N4) and the structural carbon steel(SM45C) and 4-point bending tests were carried out under room temperature. Fracture surface and crack propagation path were observed using scanning electron microscope and characteristics of its fracture was discussed.