• Journal of the Korean Wood Science and Technology
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• 제15권2호
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• pp.99-104
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• 1987

Fiber mats were made at various density levels, using fibers from papermill sludge, ricestraw and various mixtures of the two. The paper mill sludges were collected from Moorim Papermill Co, and Jeonjoo Papermill Co. They were soaked in the liquid sulfur compounds, sulfur-tall oil and sulfurpolyester compounds, and made into fiber-reinforced, sulfur-based composition board. Under optimum conditions of fiber mat preparation and saturation with molten sulfur and modified sulfur, the Young's moduls of the manufactured tiber-reinforced composition board are superior to those of conventional wood-based composition boards. For example, the moduli of elasticity of the composition board made from papermill sludge, with a density of 0.40gm/$cm^3$, were greater than 1,400,000psi as compared 800,000psi for high density hardboard(1.28gm/$cm^3$). The modulus of rupture of the best reinforced composition board manufactured was over 9000psi, comparable to 6000psi of high density hardboard. The proposed Bryant and Lee's theory, "Modified Rule of Mixtures" can be applicable to the nonoriented and short fibrous composition board, when it was modified from "Rule of Mixtures" established by Paul an Jones, and supplemented by Smith and Cox's theory, In the Bryant and Lee's theory of $E_c=\frac{1}{3}aE_fV_f+bE_mV_m$, the constants "a" and "b" for the composition boards made from papermill sludge and the mixtures of ricestraw and the sludge were identified to be in the ranges of 3.29~3.54 and -2.47~-2.80 respectively.

• 한국세라믹학회지
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• 제37권3호
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• pp.240-246
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• 2000

The microwave dielectric properties of the complex perovskite (Pb0.5Ca0.5)(Fe0.5Ta0.5)O3 ceramics were investigated with the porosity and the dielectric mixing rule. Assuming that the specimens were mixtures of real dielectrics and pores, with 3-0 connectivity, the ionic polarizabilities modified by Maxwell's equation were more close to the theoretical values rather than those modified by Wiener's equation in porous specimens. The theoretical dielectirc loss were obtained with the infrared reflectivity spectra from 50 to 4000cm-1, which were calculated by Kramers-Kronig analysis and classical osciallator model. The relative tendency of dielectric loss calculated from the theoretical value and Maxwell's equation in the specimens with different porosities was in good agreement with the one by the post resonant method.

• Journal of the Korean Wood Science and Technology
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• 제12권3호
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• pp.3-8
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• 1984

섬유의 방향성이 무질서한 composites에 적용되는 Smith와 Cox의 이론(理論)을 포함한 Paul과 Jones의 혼합이론식(混合理論式)은 유황(硫黃) 화합물(化合物)을 사용하여 제조한 목재섬유 복합재(複合材)에도 일차적(一次的)인 liner regression constant가 주어질 때는 사용할 수가 있음을 보여준다. $E_c=\frac{1}{3}aE_fV_f+bE_mV_m$으로 표시된 이 liner regression from에 math. rom pack을 사용한 Hewlett Packard 75C(HP 75C) computer의 계산 결과는 목재 섬유 복합재(複合材)에 사용된 matrix의 종류, 섬유판의 밀도와 목재 밑 목질 섬유의 종류에 관계없이 a=3.27~3.54와 b=-2.47~-2.80의 일정한 범위의 값을 보여주므로, 지금까지 무(無)질서한 방향성을 지닌 장(長)섬유로 된 복합재(複合材)에만 적용되어 왔던 Paul과 Jones의 혼합이론(混合理論)과 이것과 같은 방향을 지닌 단(短) 섬유로 된 목재(木材)나 목질(木質) 섬유 composites에도 적용될 수 있음을 증명하고 있다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 춘계학술대회논문집A
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• pp.399-404
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• 2000

Functionally graded materials(FGMs) involve dual-phase graded layers in which two different constituents are mixed continuously and functionally according to a given volume fraction. For the analysis of their thermo-mechanical response, conventional homogenized methods have been widely employed in order to estimate equivalent material properties of the graded layer. However, such overall estimations are insufficient to accurately predict the local behavior. In this paper, we compare the thermo-elastic behaviors predicted by several overall material-property estimation techniques with those obtained by discrete analysis models utilizing the finite element method, for various volume fractions and loading conditions.

• 한국가스학회:학술대회논문집
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• 한국가스학회 2000년도 추계학술발표회 논문집
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• pp.148-151
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• 2000

• Composites Research
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• 제13권1호
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• pp.50-60
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• 2000

본 연구는 섬유/입자 혼합금속복합재료의 강화기구를 분석하는 이론적 해석방법을 제시하였다. 혼합금속복합재료의 인장강도 및 탄성계수는 같은 보강재의 부피분율 가진 단섬유복합재료에 비해서 강도가 최대 20%까지 증가한다. 이러한 증가효과는 본 연구에서 새로이 제안된 클러스터 모델을 도입한 후 이에 따른 강화효과를 Modified Rule of Mixture을 적용하여 분석하였다. 해석결과 클러터구조는 인장강도에 대해서 섬유의 효율을 탄성계수에 대해서는 배향인자를 증가시키는 것으로 나타났다. 이론적 해석 결과는 $Al_2O_3$섬유/입자 예비성형체에 AC8A를 침투시켜 제조한 금속복합재료에 대한 실험결과와 비교되었으며 이를 통해 해석이론이 타당함을 확인하였다.

• 한국전산구조공학회논문집
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• 제21권1호
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• pp.13-20
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• 2008

기능경사 소재(FGM)에는 서로 다른 두 가지 구성입자들이 혼합되어 있는 경사층(graded layer)이 삽입되어, 소재 전 영역에 걸쳐 구성입자의 체적분율이 연속적이고 기능적으로 변화하도록 되어있다. 이러한 이상(dual-phase) 입자복합재의 열 기계적 거동을 해석함에 있어 필수적인 경사층의 물성치는 전통적으로 균질화 기법을 이용하여 예측되었다. 하지만, 이러한 균질화 기법은 구성입자의 형태, 분산구조 등과 같은 상세 형상을 반영하지 못하지 때문에 복합재의 총체적인 등가 물성치 예측에만 국한 되어왔다. 이러한 맥락에서 본 연구에서는 경사층을 미시역학적으로 이산화 모델링하고, 다양한 체적분율과 외부 하중조건에 대해 유한요소해석을 실시하여 이러한 균질화 기법들의 특성을 분석하였다.

• 대한기계학회논문집A
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• 제25권6호
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• pp.988-995
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• 2001

Functionally graded materials(FGMs) are highlighted to be suitable for high temperature engineering due to their continuous distribution of material properties. In this paper, an optimal design is executed for determining the optimal material volume distribution pattern that minimizes the steady-state thermal stress of FGM heat-resisting composites. The interior penalty function method and the golden section method are employed as optimization techniques while the finite element method is used for thermal stress analysis. Through numerical simulations we suggest the volume fraction distributions that considerably improve initial thermal stress distributions.

• Steel and Composite Structures
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• 제25권3호
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• pp.347-360
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• 2017

The goal of this study is to fill this apparent gap in the area about vibration analysis of multiwalled carbon nanotubes (MWCNTs) curved panels by providing 3-D vibration analysis results for functionally graded multiwalled carbon nanotubes (FG-MWCNTs) sandwich structure with power-law distribution of nanotube. The effective material properties of the FG-MWCNT structures are estimated using a modified Halpin-Tsai equation. Modified Halpin-Tsai equation was used to evaluate the Young's modulus of MWCNT/epoxy composite samples by the incorporation of an orientation as well as an exponential shape factor in the equation. The exponential shape factor modifies the Halpin-Tsai equation from expressing a straight line to a nonlinear one in the MWCNTs wt% range considered. Also, the mass density and Poisson's ratio of the MWCNT/phenolic composite are considered based on the rule of mixtures. Parametric studies are carried out to highlight the influence of MWCNT volume fraction in the thickness, different types of CNT distribution, boundary conditions and geometrical parameters on vibrational behavior of FG-MWCNT thick curved panels. Because of using two-dimensional generalized differential quadrature method, the present approach makes possible vibration analysis of cylindrical panels with two opposite axial edges simply supported and arbitrary boundary conditions including Free, Simply supported and Clamped at the curved edges. For an overall comprehension on 3-D vibration analysis of sandwich panel, some mode shape contour plots are reported in this research work.

• Steel and Composite Structures
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• 제29권5호
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• pp.569-578
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• 2018

This paper aims to investigate the transient vibration behavior of functionally graded carbon nanotube (FG-CNT) reinforced nanocomposite plate resting on Pasternak foundation under pulse excitation. The plate is considered to be composed of matrix material and multi-walled carbon nanotubes (MWCNTs) with distribution as per the functional grading concept. The functionally graded distribution patterns in nanocomposite plate are explained more appropriately with the layer-wise variation of carbon nanotubes weight fraction in the thickness coordinate. The layers are stacked up in such a way that it yields uniform and three other types of distribution patterns. The effective material properties of each layer in nanocomposite plate are obtained by modified Halpin-Tsai model and rule of mixtures. The governing equations of an illustrative case of simply-supported nanocomposite plate resting on the Pasternak foundation are derived from third order shear deformation theory and Navier's solution technique. A converge transient response of nanocompiste plate under uniformly distributed load with triangular pulse is obtained by varying number of layer in thickness direction. The validity and accuracy of the present model is also checked by comparing the results with those available in literature for isotropic case. Then, numerical examples are presented to highlight the effects of distribution patterns, foundation stiffness, carbon nanotube parameters and plate aspect ratio on the central deflection response. The results are extended with the consideration of proportional damping in the system and found that nanocomposite plate with distribution III have minimum settling time as compared to the other distributions.