• 한국재료학회지
• /
• 제6권6호
• /
• pp.576-584
• /
• 1996

The zirconia-alumina composite, a low loss material, was sucessfully sintered using a 2.45 GHz microwave radiation. The dense zirconia was used as a microware coupling aid. The effect of microwave power level on the heating rates of samples and the feasibility of microwave energy use in processign ceramec materials were obtained. It was also obtained how to accurately measure the temperature. According to the microwave heating theory, heating mechanisms were discussed.

• 한국콘크리트학회:학술대회논문집
• /
• 한국콘크리트학회 2004년도 추계 학술발표회 제16권2호
• /
• pp.425-428
• /
• 2004

Nonlinear finite element analysis is conducted to predict the structural behavior of precast concrete column and steel beam connected by using bolted connections. The Nonlinear FEM program is based on the modified compression field theory which has good accuracy in the concrete structures. The link element is properly used to model the discontinuity between precast concrete column and steel beam. Predictions from the proposed model are compared with experimental results and it is concluded that structural behaviors of the composite structures, such as strength capacity, crack pattern and failure mode, can be predicted quite successfully.

• 한국콘크리트학회:학술대회논문집
• /
• 한국콘크리트학회 2006년도 추계 학술발표회 논문집
• /
• pp.317-320
• /
• 2006

In order to determine a minimum thickness of the pultruded GFRP panel as a structural member, some experimental studies were performed. GFRP tubes with 2mm, 4mm, 6mm thickness were manufactured by pultrusion process. First, coupon tests for finding mechanical properties were carried out. Comparisons between test results and analysis results based on classical laminate theory showed large differences in case of 2mm, 4mm specimens. The reason is that it is difficult to apply appropriate pultruding force and keep layered stitched fabric flat for the pultrusion process of complex shaped FRP member with small thickness. On the consequence, we decide 6mm as a minimum thickness of FRP member. Second, 4-point bending tests were performed and the results with compared with numerical analysis. The behavior of FRP tube can be exactly predicted by numerical analysis if buckling analysis is included.

• 한국진공학회:학술대회논문집
• /
• 한국진공학회 2009년도 제38회 동계학술대회 초록집
• /
• pp.112-112
• /
• 2010

최근 세라믹스의 고온소결과정 없이 상온 후막제조가 가능한 에어로졸 데포지션법이 개발되어 이를 응용한 다양한 연구들이 진행되고 있다. 본 연구에서는 차세대 3차원 초고밀도 집적용연성(flexible)기판재료로서 $Al_2O_3$-PTFE(polytetrafluoroethylene) 복합체를 에어로졸 데포지션을 이용하여 상온제조 하였으며, 제조된 복합체 내의 $Al_2O_3$ 함량계산에 관한 연구를 진행하였다. 제조된 복합체는 기존의 세라믹만의 $Al_2O_3$ 후막에 비하여 PTFE의 첨가로 인한 잔류응력 감소효과가 있음이 확인되었으며 SEM, TEM 등 미세구조 분석을 통하여 충격고화 시 파우더의 미립화감소를 확인할 수 있었다. 또한, 공정의 최적화를 위한 분석 시 중요한 요소인 복합체 내의 세라믹 함량을 간편한 전기적 특성 측정을 통하여 계산하는 방법에 대한 연구를 진행하였다. 이를 위하여 이종 물질의 혼합에 관한 이론인 Hashin-Shtrikman bound theory와 3차원 정전장 해석 시뮬레이션을 병행하여 계산의 오차범위를 산출하고 실제 제조된 복합체 내의 $Al_2O_3$ 함량을 5 vol.% 이내의 오차로 측정할 수 있었다.

• 한국소음진동공학회:학술대회논문집
• /
• 한국소음진동공학회 2005년도 추계학술대회논문집
• /
• pp.217-222
• /
• 2005

Active vibration control of smart hull structure using Macro Fiber Composite (MFC) actuator is performed. Finite element modeling is used to obtain governing equations of motion and boundary effects of end-capped smart hull structure. Equivalent interdigitated electrode model is developed to obtain piezoelectric couplings of MFC actuator. Modal analysis is conducted to investigate the dynamic characteristics of the hull structure, and compared to the results of experimental investigation. MFC actuators are attached where the maximum control performance can be obtained. Active controller based on Linear Quadratic Gaussian (LQG) theory is designed to suppress vibration of smart hull structure. It is observed that closed loop damping can be improved with suitable weighting factors in the developed LQG controller and structural vibration is controlled effectively.

• 한국표면공학회지
• /
• 제36권4호
• /
• pp.347-355
• /
• 2003

Roughening of metal surfaces frequently enhances the adhesion strength of metals to polymers by mechanical interlocking. When a failure occurs at a roughened metal/polymer interface, the failure prone to be cohesive. In a previous work, an adhesion study on a roughened metal (oxidized copper-based leadframe)/polymer (Epoxy Molding Compound, EMC) interface was carried out, and the correlation between adhesion strength and failure path was investigated. In the present work, an attempt to interpret the failure path was made under the assumption that microvoids are formed in the EMC as well as near the roots of the CuO needles during compression-molding process. A simple adhesion model developed from the theory of fiber reinforcement of composite materials was introduced to explain the adhesion behavior of the oxidized copper-based leadframe/EMC interface and failure path. It is believed that this adhesion model can be used to explain the adhesion behavior of other similarly roughened metal/polymer interfaces.

• Journal of Power Electronics
• /
• 제17권4호
• /
• pp.953-962
• /
• 2017

Momentum flywheels are widely applied for the generation of small and precise torque for the attitude control and inertial stabilization of satellites and space stations. Due to its inherited system nonlinearity, the tracking performance of the flywheel torque/speed in dynamic/plug braking operations is limited when a conventional controller is employed. To take advantage of the well-separated two-time-scale quantities of a flywheel driving system, the singular perturbation technique is adopted to improve the torque tracking performance. In addition, the composite control law, which combines slow- and fast- dynamic portions, is derived for flywheel driving systems. Furthermore, a novel control strategy for plug braking dynamics, which considers couplings between the Buck converter and the three-phase inverter load, is designed with easy implementation. Finally, experimental results are presented to demonstrate the correctness of the analysis and the superiority of the proposed methods.

• Steel and Composite Structures
• /
• 제34권2호
• /
• pp.289-297
• /
• 2020

In the present research post-buckling of a cut out plate reinforced through carbon nanotubes (CNTs) resting on an elastic foundation is studied. Material characteristics of CNTs are hypothesized to be altered within thickness orientation which are calculated according to Mori-Tanaka model. For modeling the system mathematically, first order shear deformation theory (FSDT) is applied and using energy procedure, the governing equations can be derived. With respect to Rayleigh-Ritz procedure as well as Newton-Raphson iterative scheme, the motion equations are solved and therefore, post-buckling behavior of structure will be tracked. Diverse parameters as well as their reactions on post-buckling paths focusing cut out measurement, CNT's volume fraction and agglomeration, dimension of plate and an elastic foundation are investigated. It is revealed that presence of a square cut out can affect negatively post-buckling behavior of structure. Moreover, adding nanocompsits in the matrix leads to enhancement of post-buckling response of system.

• Steel and Composite Structures
• /
• 제33권2호
• /
• pp.163-180
• /
• 2019

A semi analytical method is employed to analyze free vibration characteristics of uniform and stepped functionally graded circular cylindrical shells under complex boundary conditions. The analytical model is established based on multi-segment partitioning strategy and first-order shear deformation theory. The displacement functions are handled by unified Jacobi polynomials and Fourier series. In order to obtain continuous conditions and satisfy complex boundary conditions, the penalty method about spring technique is adopted. The solutions about free vibration behavior of functionally graded circular cylindrical shells were obtained by approach of Rayleigh-Ritz. To confirm the dependability and validity of present approach, numerical verifications and convergence studies are conducted on functionally graded cylindrical shells under various influencing factors such as boundaries, spring parameters et al. The present method apparently has rapid convergence ability and excellent stability, and the results of the paper are closely agreed with those obtained by FEM and published literatures.

• Steel and Composite Structures
• /
• 제33권1호
• /
• pp.123-131
• /
• 2019

The present investigation is concerned with two dimensional deformation in a homogeneous nonlocal thermoelastic solid with two temperature. The nonlocal thermoelastic solid is subjected to inclined load. Laplace and Fourier transforms are used to solve the problem. The bounding surface is subjected to concentrated and distributed sources. The analytical expressions of displacement, stress components, temperature change are obtained in the transformed domain. Numerical inversion technique has been applied to obtain the results in the physical domain. Numerical simulated results are depicted graphically to show the effect of angle of inclination and nonlocal parameter on the components of displacements, stresses and conductive temperature. Some special cases are also deduced from the present investigation.