• Title/Summary/Keyword: Anisotropic orientation

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Grain Orientation and Electrical Properties of $Sr_2Nb_2O_7$ Ceramics and Thin Films (다결정 및 박막형 $Sr_2Nb_2O_7$의 입자배향과 전기적특성)

  • 손창헌;전상재;남효덕;이희영
    • Journal of the Korean Institute of Electrical and Electronic Material Engineers
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    • v.11 no.4
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    • pp.274-280
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    • 1998
  • Polycrystalline $Sr_2Nb_2O_7$ ceramics with very high Curie temperature were sintered using the powder derived by the chemical coprecipitation method (CCP). The phase evolution and grain-orientation of sintered samples were examined by XRD, while sintering behavior, dielectric properties and polarization were studied by SEM and ferroelectric tester. Extremely high degree of grain-orientation was observed along the (0k0) direction, which resulted in anisotropic dielectric properties of the sintered samples, with the dielectric constant values approaching those for single crystal. Thin film fabrication of $Sr_2Nb_2O_7$ in the pyroniobate family was also attempted on $SiO_2$/Si(100), Pt/$SiO_2$/Si(100), Pt/Ti/$SiO_2$/Si(100) and Pt/$ZrO_2/SiO_2/Si_2(100)$ substrates, using metalorganic decomposition (MOD) process. Neodecanoate precursor solution was prepared by mixing strontium neodecanoate with niobium neodecanoate synthesized from niobium ethoxide. It was found that $Sr_2Nb_2O_7$ single phase appeared in XRD patterns the samples annealed above $950^{\circ}C$. The effect of substrate type on film microstructure and dielectric properties was observed.

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The Effect of Mold Shapes on the Fiber Orientation of Welding Parts for Injectin Molding of Fiber Reinforced Polymeric Composites (섬유강화 고분자 복합재료의 사출성형에 있어서 웰드부의 섬유배향에 미치는 금형형상의 영향)

  • Kang, M. G.;Choi, Y. S.;Kim, H.;Lee, D. G.;Han, G. Y.;Kim, E. G.
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • 2000.11a
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    • pp.457-460
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    • 2000
  • Injection molding is the most widely used process for the industrial forming of plastic articles. During an injection molding process of composites, the fiber-matrix separation and fiber orientation are caused by the flow of molten polymer/fiber mixture. As a result, the product tends to be nonhomogeneous and anisotropic. Hence, it is very important to clarify the relations between separation·orientation and infection molding conditions. So far, there is no research on the measurement of fiber orientation using image processing. In this study, the effects of fiber content ratio and molding condition on the fiber orientation-angle distributions are studied experimentally. Using the image processing method, the fiber orientation distribution of welding parts in injection-molded products is assessed. And the effects of fiber content and injection mold shapes on the fiber orientation in case of fiber reinforced polymeric composites are studied. experimentally.

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The Alignment of Liquid Crystals on the Film Surfaces of Soluble Aromatic Polyimides Bearing t-Butylphenyl and Trimethylsilylphenyl Side Groups

  • Hahm, Suk-Gyu;Jin, Kyeong-Sik;Park, Sam-Dae;Ree, Moon-Hor;Kim, Hyung-Sun;Kwon, Soon-Ki;Kim, Yun-Hi
    • Macromolecular Research
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    • v.17 no.12
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    • pp.976-986
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    • 2009
  • With the study goal of firstly elucidating the anisotropic interactions between oriented polymer chain segments and liquid crystal (LC) molecules, and secondly of determining the contributions of the chemical components of the polymer segments to the film surface topography, LC alignment, pretilt, and anchoring energy, we synthesized three dianhydrides, 1,4-bis(4'-t-butylphenyl)pyromellitic dianhydride (BBPD), 1,4-bis(4'-trimethylsilylphenyl)pyromellitic dianhydride(BTPD), and 2,2'-bis(4"-tert-butylphenyl)-4,4',5,5'-biphenyltetracarboxylic dianhydride (BBBPAn), and a series of their organosoluble polyirnides, BBPD-ODA, BBPD-MDA, BBPD-FDA, BTPD-FDA, and BBBPAn-FDA, which contain the diamines 4,4'-oxydianiline (ODA), 4,4'-methylenediamine (MDA), and 4,4'-(hexafluoroisopropylidene)dianiline (FDA). All the polyimides were determined to be positive birefringent polymers, regardless of the chemical components. Although all the rubbed polyimide films exhibited microgrooves which were created by rubbing process, the film surface topography varied depending on the polyimides. In all the rubbed films, the polymer chains were unidirectionally oriented along the rubbing direction. However, the degree of in-plane birefringence in the rubbed film varied depending on the polyimides. The rubbing-aligned polymer chains in the polyimide films effectively induced the alignment of nematic LCs along their orientation directors by anisotropic interactions between the preferentially oriented polymer chain segments and the LCs. The azimuthal and polar anchoring energies of the LCs ranged from $0.45{\times}10^{-4}\;-\;1.37{\times}10^{-4}\;J/m^2$ and from $0.86{\times}10^{-5}\;-\;4.26{\times}10^{-5}\;J/m^2$, respectively, depending on the polyimides. The pretilt angles of the LCs were in the range $0.10-0.62^{\circ}$. In summary, the soluble aromatic polyimides reported here are promising LC alignment layer candidates for the production of advanced LC display devices.

Fiber orientation distribution of reinforced cemented Toyoura sand

  • Safdar, Muhammad;Newson, Tim;Waseem, Muhammad
    • Geomechanics and Engineering
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    • v.30 no.1
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    • pp.67-73
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    • 2022
  • In this study, the fiber orientation distribution (FOD) is investigated using both micro-CT (computerized tomography) and image analysis of physically cut specimens prepared from Polyvinyl Alcohol (PVA) fiber reinforced cemented Toyoura sand. The micro-CT images of the fiber reinforced cemented sand specimens were visualized in horizontal and vertical sections. Scans were obtained using a frame rate of two frames and an exposure time of 500 milliseconds. The number of images was set to optimize and typically resulted in approximately 3000 images. Then, the angles of the fibers for horizontal sections and in vertical section were calculated using the VGStudio MAX software. The number of fibers intersecting horizontal and vertical sections are counted using these images. A similar approach was used for physically cut specimens. The variation of results of fiber orientation between micro-CT scans and visual count were approximately 4-8%. The micro-CT scans were able to precisely investigate the fiber orientation distribution of fibers in these samples. The results show that 85-90% of the PVA fibers are oriented between ±30° of horizontal, and approximately 95% of fibers have an orientation that lies within ±45° of the horizontal plane. Finally, a comparison of experimental results with the generalized fiber orientation distribution function 𝜌(θ) is presented for isotropic and anisotropic distribution in fiber reinforced cemented Toyoura sand specimens. Experimentally, it can be seen that the average ratio of the number of fibers intersecting the finite area on a vertical plane to number of fibers intersecting the finite area on a horizontal plane (NVtot/NHtot) cut through a sample varies from 2.08 to 2.12 (an average ratio of 2.10 is obtained in this study). Based up on the analytical predictions, it can be seen that the average NVtot/NHtot ratio varies from 2.13 to 2.17 for varying n values (an average ratio of 2.15).

Coupled Analysis with Digimat for Realizing the Mechanical Behavior of Glass Fiber Reinforced Plastics (유리섬유 강화 플라스틱의 역학적 거동 구현을 위한 Digimat와의 연성해석 연구)

  • Kim, Young-Man;Kim, Yong-Hwan
    • Journal of the Computational Structural Engineering Institute of Korea
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    • v.32 no.6
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    • pp.349-357
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    • 2019
  • Finite element method (FEM) is utilized in the development of products to realistically analyze and predict the mechanical behavior of materials in various fields. However, the approach based on the numerical analysis of glass fiber reinforced plastic (GFRP) composites, for which the fiber orientation and strain rate affect the mechanical properties, has proven to be challenging. The purpose of this study is to define and evaluate the mechanical properties of glass fiber reinforced plastic composites using the numerical analysis models of Digimat, a linear, nonlinear multi-scale modeling program for various composite materials such as polymers, rubber, metal, etc. In addition, the aim is to predict the behavior of realistic polymeric composites. In this regard, the tensile properties according to the fiber orientation and strain rate of polybutylene terephthalate (PBT) with short fiber weight fractions of 30wt% among various polymers were investigated using references. Information on the fiber orientation was calculated based on injection analysis using Moldflow software, and was utilized in the finite element model for tensile specimens via a mapping process. LS-Dyna, an explicit commercial finite element code, was used for coupled analysis using Digimat to study the tensile properties of composites according to the fiber orientation and strain rate of glass fibers. In addition, the drawbacks and advantages of LS-DYNA's various anisotropic material models were compared and evaluated for the analysis of glass fiber reinforced plastic composites.

Effects of Humidity and Structure on Friction and Wear Properties of Carbon Fiber/Epoxy Composites (탄소 섬유/에폭시 복합 재료의 마찰 및 마멸 성질에 미치는 습도 및 구조의 영향)

  • 심현해;권오관;윤재륜
    • Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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    • 1990.11a
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    • pp.63-68
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    • 1990
  • Friction and wear behavior of a unidirectional high modulus carbon fiber reinforced epoxy composite exposed to high and low humidity was experimentally examined with various sliding speeds. The results show that the moisture at the sliding surface greatly influences friction and wear properties of the composite. It is also discoverd that the difference in friction and wear behavior between samples with different fiber orientations is mainly due to the anisotropic properties caused by the microstructure of oriented graphite crystals in the carbon fibers and the macrostructure of fiber orientation in the matrix.

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Effects of Humidity and Structure on Friction and Wear Properties of Carbon Fiber/Epoxy Composites (탄소 섬유/에폭시 복합 재료의 마찰 및 마멸 성질에 미치는 습도 및 구조의 영향)

  • 심현해;권오관;윤재륜
    • Tribology and Lubricants
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    • v.6 no.2
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    • pp.88-93
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    • 1990
  • Friction and wear behavior of a unidirectional high modulus carbon fiber reinforced epoxy composite exposed to high and low humidity was experimentally examined with various sliding speeds. The results show that the moisture at the sliding surface greatly influences friction and wear properties of the composite. It is also discoverd that the difference in friction and wear behavior between samples with different fiber orientations is mainly due to the anisotropic properties caused by the microstructure of oriented graphite crystals in the carbon fibers and the macrostructure of fiber orientation in the matrix.

Light diffraction in anisotronic surface relief phase grating (비등방 표면 부조 격자에서의 빛의 회절)

  • 장혜정;강보영;최현희;박병주;우정원
    • Proceedings of the Optical Society of Korea Conference
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    • 2003.07a
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    • pp.166-167
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    • 2003
  • 아조벤젠 그룹의 trans-cis-trans photo isomerization 특성에 의한 광배향 (photoinduced orientation) 성질을 이용하여 아조벤젠이 함유된 폴리머박막에 표면 부조 격자 (surface relief grating)를 만드는 것은 널리 알려져 있다. 특히 최근 들어, 비선형 물질의 주기적인 배열 구조를 만들기 위해서 surface relief grating을 corona poling 하는 방법들이 연구되어 지고 있다. poling된 surface relief grating은 poling 방향으로의 azo분자의 극질서가 유도되기 때문에, $C_{{\infty}v}$점대칭을 가지는 비등방 회절 격자(anisotropic grating)가 되며 2차 비선형 특성 중의 하나인 선형 전기 광학 효과를 나타낼 수 있다. (중략)

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Finite Element Analysis of Thermally-Induced Deformation in SMC Compression Molding (SMC 압축성형공정에서의 열변형에 관한 유한요소해석)

  • Lee, Jae-Hyoung;Lee, Eung-Shik;Youn, Sung-Kie
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.21 no.1
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    • pp.154-163
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    • 1997
  • Thermally-induced deformation in SMC(Sheet Molding Compound) products is analyzed using three dimensional finite element method. Planar fiber orientation, which causes the anisotropic material properties, is calculated through the flow analysis during the compression stage of the mold. Also curing process is analyzed to predict temperature profile which has significant effects on warpage of SMC products. Through the developed procedure, effects of various process conditions such as charge location, mold temperature, fiber contents, and fiber orientations on deformation of final products are studied. and processing strategies are proposed to reduce the warpage and the shrinkage.

Analysis of Flame Generated Turbulence for a Turbulent Premixed Flame with Zone Conditional Averaging (영역분할조건평균법을 이용한 난류예혼합화염내 난류운동에너지 생성에 관한 연구)

  • Im, Yong Hoon;Huh, Kang Yul
    • Journal of the Korean Society of Combustion
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    • v.8 no.4
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    • pp.15-23
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    • 2003
  • The zone conditional two-fluid equations are derived and validated against DNS database of a premixed turbulent flame. The conditional statistics of major flow variables are investigated to understand the mechanism of flame generated turbulence. The flow field in burned zone shows substantially increased turbulent kinetic energy, which is highly anisotropic due to reaction kinematics across thin f1amelets. The transverse component may be larger than the axial component for a distributed pdf of the flamelet orientation angle, while the opposite occurs due to redistribution of turbulent kinetic energy and flamelet orientation normal to the flow at the end of a flame brush. The major source or sink terms of turbulent kinetic energy are the interfacial transfer by the mean reaction rate and the work terms by fluctuating pressure and velocity on a flame surface. Ad hoc modeling of some interfacial terms may be required for further application of the two-fluid model in turbulent combustion simulations.

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