• 한국방재학회 논문집
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• 제7권5호
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• pp.61-71
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• 2007

Navier 해 및 유한요소 해를 두께 방향으로 재료의 성질이 변하는 점진기능재료 판 및 쉘의 해석을 위해 제시하였다. 판과 쉘의 두께를 따라 완만하게 변하는 등방성 구조물의 두께방향에 따른 역학적 특성을 고려하기 위하여 S 형상 함수를 적용한 점진기능재료를 고려하였다. 비선형 9 절점 요소기저 Lagrangian 쉘 요소의 정식화를 기하학적 비선형 해석을 위해 제시하였다. 자연 좌표계에 의한 변형률이 본 연구의 쉘요소에 사용된다. 1차 전단변형이론에 의한 수치 해석 예제로 상면과 하면의 탄성 계수의 변화, 하중조건, 형상 비 그리고 폭-두께 비에 따른 역학적 거동을 연구하였다. 또한 거듭제곱 매개 변수의 변화에 따른 점진기능재료 구조물의 결과들을 조사하였다.

• Earthquakes and Structures
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• 제15권4호
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• pp.369-382
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• 2018

A free vibration analysis and wave propagation of functionally graded porous beams has been presented in this work using a high order hyperbolic shear deformation theory. Unlike other conventional shear deformation theories, a new displacement field that introduces indeterminate integral variables has been used to minimize the number of unknowns. The constituent materials of the beam are assumed gradually variable along the direction of height according to a simple power law distribution in terms of the volume fractions of the constituents. The variation of the pores in the direction of the thickness influences the mechanical properties. It is therefore necessary to predict the effect of porosity on vibratory behavior and wave velocity of FG beams in this study. A new function of the porosity factor has been developed. Hamilton's principle is used for the development of wave propagation equations in the functionally graded beam. The analytical dispersion relationship of the FG beam is obtained by solving an eigenvalue problem. Illustrative numerical examples are given to show the effects of volume fraction distributions, beam height, wave number, and porosity on free vibration and wave propagation in a functionally graded beam.

• Journal of Electrochemical Science and Technology
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• 제1권1호
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• pp.50-56
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• 2010

$La_{0.6}Sr_{0.4}Co_{0.2}Fe_{0.8}O_{3-\delta}$ (LSCF) powders with different particle sizes, synthesized through a citrate complexation method and a gel-casting technique, are used to fabricate porous LSCF cathodes with graded microstructures via tape casting. To create porous electrodes with desired porosity and pore structures, graphite and starch are used as pore former for different layers of the graded cathode. Examination of the microstructures of the as-prepared LSCF cathode using an SEM revealed that both grain size and porosity changed gradually from the catalytically active layer (near the electrodeelectrolyte interface) to the current collection layer (near the electrode-interconnect interface). Impedance analysis showed that a 3-layer LSCF cathode with graded microstructures exhibited much-improved performance compared to that of a single-layer LSCF cathode, corresponding to interfacial resistance of 0.053, 0.11, and 0.27 $\Omega{\cdot}cm^2$ at 800, 750, and $700^{\circ}C$ respectively.

• 한국전기전자재료학회논문지
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• 제21권9호
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• pp.853-858
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• 2008

The structure of organic light-emitting diodes(OLEDs) with typical heterostructure consists of anode, hole injection layer, hole transport layer, light-emitting layer, electron transport layer, electron injection layer, and cathode. 4,4bis[N-(1-napthyl)-N-phenyl-amino]-biphenyl(NPB) used as a hole transport layer and 4'4-bis(2,2'-diphenyl vinyl)-1,1'-biphenyl(DPVBi) used as a blue light emitting layer were graded-mixed at selected ratio. Interface at heterojunction between the hole transport layer and the elecrtron transport layer restricts carrier's transfer. Mixing of the hole transport layer and the emitting layer reduces abrupt interface between the hole transport layer and the electron transport layer. The operating voltage of OLED devices with graded mixed-layer structure is 2.8 V at 1 $cd/m^2$ which is significantly lower than that of OLED device with typical heterostructure. The luminance of OLED devices with graded mixed-layer structure is 21,000 $cd/m^2$ , which is much higher than that of OLED device with typical heterostructure. This indicates that the graded mixed-layer enhances the movement of carriers by reducing the discontinuity of highest occupied molecular orbital(HOMO) of the interface between hole transport layer and emitting layer.

• Advances in nano research
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• 제12권5호
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• pp.467-482
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• 2022

In the current work, static and free torsional vibration of functionally graded (FG) nanorods are investigated using Fourier sine series. The boundary conditions are described by the two elastic torsional springs at the ends. The distribution of functionally graded material is considered using a power-law rule. The systems of equations of the mechanical response of nanorods subjected to deformable boundary conditions are achieved by using the modified couple stress theory (MCST) and taking the effects of torsional springs into account. The idea of the study is to construct an eigen value problem involving the torsional spring parameters with small scale parameter and functionally graded index. This article investigates the size dependent free torsional vibration based on the MCST of functionally graded nano/micro rods with deformable boundary conditions using a Fourier sine series solution for the first time. The eigen value problem is constructed using the Stokes' transform to deformable boundary conditions and also the convergence and accuracy of the present methodology are discussed in various numerical examples. The small size coefficient influence on the free torsional vibration characteristics is studied from the point of different parameters for both deformable and rigid boundary conditions. It shows that the torsional vibrational response of functionally graded nanorods are effected by geometry, small size effects, boundary conditions and material composition. Furthermore, for all deformable boundary conditions in the event of nano-sized FG nanorods, the incrementing of the small size parameters leads to increas the torsional frequencies.

• Steel and Composite Structures
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• 제44권1호
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• pp.81-89
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• 2022

The purposes of the present work it to study the effect of shear deformation on the static post-buckling response of simply supported functionally graded (FGM) axisymmetric beams based on classical, first-order, and higher-order shear deformation theories. The behavior of postbuckling is introduced based on geometric nonlinearity. The material properties of functionally graded materials (FGM) are assumed to be graded in the thickness direction according to a simple power law distribution in terms of the volume fractions of the constituents. The equations of motion and the boundary conditions derived using Hamilton's principle. This article compares and addresses the efficiency, the applicability, and the limits of classical models, higher order models (CLT, FSDT, and HSDT) for the static post-buckling response of an asymmetrically simply supported FGM beam. The amplitude of the static post-buckling obtained a solving the nonlinear governing equations. The results showing the variation of the maximum post-buckling amplitude with the applied axial load presented, for different theory and different parameters of material and geometry. In conclusion: The shear effect found to have a significant contribution to the post-buckling behaviors of axisymmetric beams. As well as the classical beam theory CBT, underestimate the shear effect compared to higher order shear deformation theories HSDT.

• Journal of Oral Medicine and Pain
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• 제30권3호
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• pp.353-360
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• 2005

측두하악장애 연구진단기준 (Research Diagnostic Criteria for Temporomandibular Disorders; RDC/TMD)을 이용하여 측두하악장애 환자들에서 심리학적 상태 및 턱기능장애의 정도가 통증의 정도 및 지속기간, 통증과 관련된 일상생활 장애의 정도 및 기간, 만성통증척도에 미치는 영향 등을 알아보기 위하여 RDC/TMD axis I criteria에 따라 측두하악장애로 진단받은 평균연령 30.1$\pm$12.5 세인 93 명의 환자들(남성 17명, 여성 76명)을 대상으로 RDC/TMD axis II 병력 설문지를 작성하게 한 뒤, 우울증점수, 신체화장애점수, 턱기능장애점수와 만성통증척도의 통증 강도, 통증 지속기간, 통증과 연관된 장애 점수, 통증과 연관된 장애의 기간 및 만성통증척도 사이의 연관성을 분석하여 다음과 같은 결론을 얻었다. 1. 93명의 측두하악장애 환자들에서 만성통증척도의 경도의 장애를 보이는 군 (low disability group, grade I and II)은 42.0% 이었으며, 심도의 장애를 보이는 군 (high disability group, grade III and IV)은 51.5% 이었다. 2. 우울증점수는 통증 강도, 통증 지속기간, 통증과 연관된 장애 점수, 통증과 연관된 장애의 기간, 만성통증척도 모두에 통계적으로 유의한 영향을 미치지 않았다. 3. 신체화장애점수는 통증 강도 (p<0.01), 통증과 연관된 장애의 기간 (p<0.01), 만성통증척도 (p<0.01)에 유의한 영향을 미쳤으나, 통증 지속기간이나 통증과 연관된 장애 점수에는 통계적으로 유의한 영향을 미치지 않았다. 4. 턱기능장애점수는 통증 강도 (p<0.001), 통증과 연관된 장애의 기간 (p<0.01), 만성통증척도 (p<0.001)에 유의한 영향을 미쳤으나, 통증 지속기간이나 통증과 연관된 장애 점수에는 통계적으로 유의한 영향을 미치지 않았다. 측두하악장애환자에서 신체화장애와 턱기능장애는 환자가 느끼는 통증의 강도 및 장애의 정도와 밀접하게 관련되어 나타날 수 있으며, 환자가 호소하는 정서적 스트레스에 대한 포괄적인 이해와 기능장애에 대한 적절한 관리가 측두하악장애 환자의 성공적인 치료에 매우 중요하리라 생각된다.

• 자원환경지질
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• 제34권6호
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• pp.627-648
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• 2001

Skaergaard 암체의 중대에는 사장석 우세대와 휘석 우세대가 교대하는 macro-rhythmic layers와 modally-graded, rhythmic lace론 비롯한 최소 두 가지 종류 이상의 layering 발견된다 Macro-rhythmic layers는 LS의 중대에서만 빈번히 발견된다. 두게는 0.3에서 3.3m에 이르고 명확한 상하부 경계를 가지며 노두에서 2km 이상 휭으로 연장된다. 자기 macro-rhythmic layer에서는 내부적인 점이층리 구조를 보이지는 않으나 소규모 modally-graded layer 빈번히 발견된다. Modally-graded, rhythmic layer는 LS의 흔히 발견되나 UBS나 MBS에서는 드물게 관찰된다. 두에는 떼서 50cm에 이르고 노두에서 최대 100m 까지 횡으로 연속된다. 횡적으로 갑자기 혹은 서서히 사라지며 종종 기칠 메우기 구조나 사층리 구조를 수반한다. 명확한 하부 경계와 점이적인 상부 경계와 함께 강한 층간 modal grading이나 size grading이 특징이다. 중대 modally-graded layering중 사장석 우세와 휘석 우세 macro-rhythmic layer두개를 상세하게 조사하였다. 일반적으로 사장석 내의 $K_2$O와 Ba, 휘석, 티탄철석, 그리고 자철석 내의 MgO와 FeO*를 제외한 광물성분변이는 보이지 않는다. 티탄철석과 자철석이 풍부한 layer기저에 산출되는 휘석, 티탄철석, 그리고 자철석의 성분은 MgO가 더 많고 FeO*는 더 적은 경향을 보여준다. 이와 같은 성분변이는 기존의 결정과 Fe가 많은 melt의 상호반응의 결과로 생각되며 Layer 기저에서는 상부보다 적은 re-equilibration를 겪은 것으로 생각된다. 개개 상이나 휘석과 oxide의 비와 reequilibration의 정도 간에는 직접적인 상관관계는 보이지 않는다 휘석 우세 layer거 사장석에 비해 사장석 우세 layer 의 사장석은 UBS의 사장석과 유사하게 상대적으로 적은 $K_2$O와 Eu/Sm를 보이며 이는 사장석 우세 layer는 암체 상부에서 유래한 과외의 사장석에 기인함을 시사한다. 사장석 우세 layer는 대류기에 휘석 우세 layer는 비대류기에 형성되었음을 시사한다. $K_2$O가 적은 사장석 우세 layer의 사장석은 layer내로 통과하는 $K_2$O가 풍부한 liquid와의 reequilibration 에 기인한 것으로 생각된다.

• Structural Engineering and Mechanics
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• 제45권3호
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• pp.355-371
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• 2013

Single- and multi-span orthotropic functionally graded hollow cylinders subjected to axisymmetrical bending are investigated on the basis of a unified shear deformable shell theory, in which the transverse displacement is expressed by means of a general shape function. To approach the through-thickness inhomogeneity of the hollow cylinder, a laminated model is employed. The shape function therefore shall be determined for each fictitious layer. To improve the computational efficiency, we resort to a transfer matrix method. Based on the principle of minimum potential energy, equilibrium equations are established, which are then solved analytically using the transfer matrix method for arbitrary boundary conditions. Numerical comparisons among a third-order shear deformable shell theory, an exact elastic theory and the present theory are provided for a simply supported hollow cylinder, from which the present theory turns out to be superior in stress estimation. Distributions of displacements and stresses in single- and three-span hollow cylinders with different boundary conditions are also illustrated in numerical examples.

• Structural Engineering and Mechanics
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• 제58권3호
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• pp.423-442
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• 2016

This study considers a functionally graded (FG) elastic layer resting on homogeneous elastic substrate under axisymmetric static loading. The shear modulus of the FG layer is assumed to vary in an exponential form through the thickness. In solution, the FG layer is approximated into a multilayered medium consisting of thin homogeneous sublayers. Stiffness matrices for a typical homogeneous isotropic elastic layer and a half-space are first obtained by solving the axisymmetric elasticity equations with the aid of Hankel's transform. Global stiffness matrix is, then, assembled by considering the continuity conditions at the interfaces. Numerical results for the displacements and the stresses are obtained and compared with those of the classical elasticity and the finite element solutions. According to the results of the study, the approach employed here is accurate and efficient for elasto-static problems of FGMs.