• Structural Engineering and Mechanics
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• 제78권4호
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• pp.379-386
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• 2021

A numerical and computer simulation for dynamic stability analysis of graded porous nanoplates has been provided using a Chebyshev-Ritz-Bolotin approach. The nanoplate has been formulated according to the nonlocal elasticity and a 3-unkown plate model capturing neutral surface location. All of material properties are assumed to be dependent of porosity factor which determines the amount or volume of pores. The nano-size plate has also been assumed to be under temperature and moisture variation. It will be shown that stability boundaries of the nanoplate are dependent on static and dynamical load factors, porosity factor, temperature variation and nonlocal parameter.

• Advances in aircraft and spacecraft science
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• 제3권4호
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• pp.471-502
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• 2016

This paper presents the dynamic instability analysis of un-damped elastically supported piezoelectric functionally graded (FG) beams subjected to in-plane static and dynamic periodic thermomechanical loadings with uncertain system properties. The elastic foundation model is assumed as one parameter Pasternak foundation with Winkler cubic nonlinearity. The piezoelectric FG beam is subjected to non-uniform temperature distribution with temperature dependent material properties. The Young's modulus and Poison's ratio of ceramic, metal and piezoelectric, density of respective ceramic and metal, volume fraction exponent and foundation parameters are taken as uncertain system properties. The basic nonlinear formulation of the beam is based on higher order shear deformation theory (HSDT) with von-Karman strain kinematics. The governing deterministic static and dynamic random instability equation and regions is solved by Bolotin's approach with Newmark's time integration method combined with first order perturbation technique (FOPT). Typical numerical results in terms of the mean and standard deviation of dynamic instability analysis are presented to examine the effect of slenderness ratios, volume fraction exponents, foundation parameters, amplitude ratios, temperature increments and position of piezoelectric layers by changing the random system properties. The correctness of the present stochastic model is examined by comparing the results with direct Monte Caro simulation (MCS).

• 대한기계학회논문집A
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• 제37권9호
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• pp.1151-1158
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• 2013

습기 수착 물성은 전자 패키징 장치의 신뢰성에 있어서 층간의 수증기 압력에 의해 공정과정 동안 발생되는 박리 불량의 고장 분석 및 최적의 재료 개발에 있어서 필수적이다. 본 논문에서는 온습도 모델에 따른 전자 패키징 재료의 온도 의존적인 흡습 및 탈습 물성을 변수화 하였고 이에 대한 온도 및 습도의 영향에 대해 고찰하였다. 변수화된 확산성에서 얻어진 확산 활성화 에너지는 등가의 습기 수착 수준을 위한 가속 수명 비율을 결정하고 신뢰 수명 평가에 요구되는 등가의 소요 시험 시간에 미치는 습기 확산성의 영향을 예측할 수 있게 한다. 신뢰성 시험 표준에서 평가된 유연 전자 모듈의 가속 수명비율을 예시하였다.

• Advanced Composite Materials
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• 제18권3호
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• pp.233-249
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• 2009

Safe installation and operation of high-pressure composite cylinders for hydrogen storage are of primary concern. It is unavoidable for the cylinders to experience temperature variation and significant thermal input during service. The maximum failure pressure that the cylinder can sustain is affected due to the dependence of composite material properties on temperature and complexity of cylinder design. Most of the analysis reported for high-pressure composite cylinders is based on simplifying assumptions and does not account for complexities like thermo-mechanical behavior and temperature dependent material properties. In the present work, a comprehensive finite element simulation tool for the design of hydrogen storage cylinder system is developed. The structural response of the cylinder is analyzed using laminated shell theory accounting for transverse shear deformation and geometric nonlinearity. A composite failure model is used to evaluate the failure pressure under various thermo-mechanical loadings. A back-propagation neural network (NNk) model is developed to predict the maximum failure pressure using the analysis results. The failure pressures predicted from NNk model are compared with those from test cases. The developed NNk model is capable of predicting the failure pressure for any given loading condition.

• 한국전기전자재료학회논문지
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• 제30권11호
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• pp.705-709
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• 2017

Effective surface area and morphology of a sensitive thin film are important factors for its applications in sensor systems for the analysis of physical properties. In this study, we investigated the morphologies, electrochemical properties, and applicability of zinc oxide multilayer thin films fabricated by electrodeposition and annealing. The microstructure and electrochemical properties of the zinc oxide films were dependent on temperature and applied voltage. The best characteristics were obtained at an applied voltage of -1.4 V and a temperature of $50^{\circ}C$. The morphologies also changed upon annealing. The results suggest that the zinc oxide films fabricated by electrodeposition and annealing can be applied as various sensor materials.

• 한국전기전자재료학회논문지
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• 제20권8호
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• pp.661-665
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• 2007

This paper presents the electrical properties of SiGe HBTs designed with bottom collector and single metal layer structure for RF power amplifier. Base layer was formed with graded-SiGe/Si structures and the collector place to the bottom of the device. Bottom collector and single metal layer structures could significantly simplify the fabrication process. We studied about the influence of SiGe base thickness, number of emitter fingers and temperature dependence $(<200^{\circ}C)$ on electrical properties. The feasible application in $1{\sim}2GHz$ frequency from measured data $BV_{CEO}{\sim}10V,\;f_T{\sim}14GHz,\;{\beta}{\simeq}110,\;NF{\sim}1dB$ using packaged SiGe HBTs. We will discuss the temperature dependent current flow through the e-b, b-c junctions to understand stability and performance of the device.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 1999년도 춘계학술대회 논문집
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• pp.665-668
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• 1999

Thin films of Pb(Zr,Ti)O$_3$ were fabricated by means of the sol-gel spin-coating method and the multi-coating of eight coating numbers. The thin films were dried on the temperature range of 250 ~ 400($^{\circ}C$), whenever the specimens were dried after each coating Processing. The fabricated ferroelectric thin films of lead zirconate titanate(PZT) were treated with the rapid thermal annealing(RTA) at 650($^{\circ}C$),or 3(min), and direct insertion thermal annealing(DITA) at 650($^{\circ}C$), for 30(min). The measured properties of dielectric thin films were following: The good results of dielectric properties were shown by the RTA specimen. The saturation polarization(Ps), remanent polarization(Pr), coercive field (Ec), dielectric constant and dielectric loss factor of the RTA specimen were estimated to be about 27.1[ $\mu$ C/$\textrm{cm}^2$], 13.7[ $\mu$ C/$\textrm{cm}^2$], 55.6(kV/cm), 786 and 6.4(%) respectively.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2006년도 하계학술대회 논문집 Vol.7
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• pp.138-139
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• 2006

Metal organic chemical vapor deposition has been investigated for growth of $Sb_{2-x}Bi_xTe_3$ films on (001) GaAs substrates using diisopropyltelluride, triethylantimony and trimethylbismuth as metal organic sources. The thermoelectric properties were measured at room temperature and include Seebeck coefficient, electrical conductivity and Hall effect. In-plane carrier concentration and electrical Hall mobility were highly dependent on precursor's composition ratio and deposition temperature. The thermoelectric Power factor($={\alpha}^2{\sigma}$) was calculated from theses properties. The best Power factor was $2.6\;{\times}\;10^{-3}W/mK^2$, given by grown $Sb_{1.6}Bi_{0.4}Te_3$ at $450^{\circ}C$. These materials could potentially be incorporated into advanced thermoelectric unicouples for a variety of power generation applications.

• Computers and Concrete
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• 제32권2호
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• pp.207-215
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• 2023

This paper investigates wave propagation in functionally graded carbon nano-reinforced composite (FG-CNTRC) plates under the influence of temperature based on Reddy' plate model. The material properties of Carbon Nanotubes (CNTs) are size-dependent, and the volume fraction of CNTs varies only along the thickness direction of the plate for different CNTs reinforcement modes. In addition, the material properties of CNTs can vary for different temperature parameters. By solving the eigenvalue problem, analytical dispersion relations can be derived for CNTRC plates. The partial differential equations for the system are derived from Lagrange's principle and higher order shear deformation theory is used to obtain the wave equations for the CNTRC plate. Numerical analyses show that the wave propagation properties in the CNTRC plate are related to the volume fraction parameters of the CNTRC plate and the distribution pattern of the CNTs in the polymer matrix. The effects of different volume fractions of CNTs and the distribution pattern of carbon nanotubes along the cross section (UD-O-X plate) are discussed in detail.

• 한국전산구조공학회논문집
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• 제24권4호
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• pp.383-389
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• 2011

본 논문에서는 통계적인 방법을 이용하여 점탄성 제진재인 합성고무의 물성에 대한 변동성을 평가하는 방법을 제안하고 측정데이터를 이용하여 합성고무에 대한 평가를 수행하고 합성고무로 이루어진 고무 마운트에 대한 동특성 해석을 수행하였다. 고무 물성의 불확실성 인자로는 외기 온도의 변화와 실험 데이터의 오차 및 점탄성 물질모델의 오차를 고려하였다. 고무는 분수차 미분모델로 표현되었고, 온도의 영향은 비선형 이동계수모델을 도입하여 복소계수로 나타내어 동강성과 감쇠를 표현하였다. 이러한 물성모델을 바탕으로 고무에 대한 물성 실험데이터와 물성계수의 확률밀도함수 사이에 정의된 우도함수를 최대화하는 통계적 보정방법을 이용하여 물성모델의 물질계수들에 대한 변동성을 추정하였다. 합성고무로 이루어진 제진용 고무 마운트에 대하여 유한요소모델을 이용하여 동특성을 계산하였다. 동특성의 계산시 추정된 물성의 통계값을 적용하고 몬테카를로 해석을 통하여 동강성의 변동성을 살펴서 그 변동성이 매우 큼을 확인하였다.