論文 - 高野　直樹

Microstructure-based stress analysis and evaluation for porous ceramics by homogenization method with digital image-based modeling

高野 直樹

International Journal of Solids and Structures （International Journal of Solids and Structures）  40 （ 5 ） 1225-1242 - 1242 2003年

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  00207683

　概要を見る

Multi-scale analysis using the asymptotic homogenization method is becoming a matter of concern for microstructural design and analysis of advanced heterogeneous materials. One of the problems is the lack of the experimental verification of the multi-scale analysis. Hence, it is applied to the porous alumina with needle-like pores to compare the predicted homogenized properties with the experimental result. The complex and random microstructure was modeled three-dimensionally with the help of the digital image-based modeling technique. An appropriate size of the unit microstructure model was investigated. The predicted elastic properties agreed quite well with the measured values. Next, a four-point bending test was simulated and finally the microscopic stress distribution was predicted. However, it was very hard to evaluate the calculated microscopic stress quantitatively. Therefore, a numerical algorithm to help understanding the three-dimensional and complex stress distribution in the random porous microstructure is proposed. An original histogram display of the stress distribution is shown to be effective to evaluate the stress concentration in the porous materials. © 2002 Elsevier Science Ltd. All rights reserved.

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Multi-scale finite element analysis of porous materials and components by asymptotic homogenization theory and enhanced mesh superposition method

高野 直樹

Modelling and Simulation in Materials Science and Engineering （Modelling and Simulation in Materials Science and Engineering）  11 （ 2 ） 137-156 - 156 2003年

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  09650393

　概要を見る

To analyse the macroscopic and microscopic behaviours of heterogeneous materials and components, a multi-scale computational method is studied. Although asymptotic homogenization theory has been the main tool during the last decade to solve various multi-scale problems, the assumption of the periodicity of the microscopic unit cell and the incapability of considering the scale effect have resulted in the limitations to this theory's applications. These problems should be overcome because advanced materials are often used as joint or laminated components and the interface crack problem must be analysed. For this sake, a novel multi-scale finite element method is proposed that uses the enhanced mesh superposition method together with the asymptotic homogenization theory. The finite element mesh superposition method uses the global mesh and the local mesh that is superimposed arbitrarily onto the global mesh. The enhanced method allows the adoption of different constitutive laws for the two meshes. The advantage of the homogenization theory to predict the homogenized material model accurately based on the complex microstructure is still utilized. The homogenized material model is used for the global mesh, whilst the microscopic heterogeneity and the crack are considered in the local mesh with the material properties of the constituents. The formulation, modeling strategy, implementation and numerical accuracy of the proposed method is described. A porous ceramic is studied in the numerical example.

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界面き裂を有する不均質接合体のマルチスケール有限要素解析

高野 直樹

材料 52 （ 8 ） 952-957 2003年

研究論文（学術雑誌）, 共著, 査読有り

Three-dimensional microstructural modeling and homogenization of porous alumina with needle-like pores

高野 直樹

Nippon Kikai Gakkai Ronbunshu, A Hen/Transactions of the Japan Society of Mechanical Engineers, Part A （Nippon Kikai Gakkai Ronbunshu, A Hen/Transactions of the Japan Society of Mechanical Engineers, Part A）  46 （ 4 ） 519-526 - 1169 2003年

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  03875008

　概要を見る

In the development of functional ceramics, the study on the relation between the macroscopic properties and the microstructures has been a critical issue. However, it has not been made clear by many experimental works. On the other hand, this paper takes the computational mechanics approach using the homogenization method. To model the very complex microstructure architecture three-dimensionally, the image-based modeling technique is employed. A porous alumina with needle-like random pores with 3.1% porosity ratio is studied in this paper. The effect of the location of extracting the unit cell and its size on the homogenized elastic constants is investigated. Then, the predicted values were compared with the measured ones. As a result, a unit cell region expressed by one million voxel elements with 2 μm resolution provides very accurate prediction regardless of the location of the unit cell in the random microstructures. The error between the numerical prediction and the measurement is only 1%.

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Multi-scale analysis and microscopic stress evaluation for ceramics considering the random microstructures

高野 直樹

Nippon Kikai Gakkai Ronbunshu, A Hen/Transactions of the Japan Society of Mechanical Engineers, Part A （Nippon Kikai Gakkai Ronbunshu, A Hen/Transactions of the Japan Society of Mechanical Engineers, Part A）  46 （ 4 ） 527-535 - 1053 2003年

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  03875008

　概要を見る

A multi scale computational method using the homogenization method is applied to the stress analysis of ceramics considering the random and complex microstructure three-dimensionally. The main purpose of this paper is to propose a numerical method to understand quantitatively the microscopic stress distribution in the random microstructure especially for porous ceramics. The voxel mesh is used to model the microstructure automatically with the help of the image-based modeling technique. In the analysis of porous alumina with needle-like random pores, the distance from the nearest pore is measured for all the voxel elements, which is plotted with the histogram of the microscopic stress distribution. This is of great help to study the relation between the stress concentration and the pore geometry and dispersion.

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Image-based modeling and elastic analysis of porous ceramics by the homogenization method

Keiichi K., Naoki T., Futoshi K., Syusui O., Hiroshi K., Masaru Z.

Journal of the Ceramic Society of Japan （Journal of the Ceramic Society of Japan）  110 （ 1282 ） 567 - 575 2002年06月

ISSN  09145400

　概要を見る

A three-dimensional elastic analysis system for porous ceramics has been built. In this system, three-dimensional morphology of pores is modeled using voxel (volume pixel) elements from digital images. Elastic analysis with this image-based finite element model is performed by the homogenization method. In order to investigate this analysis system, the elastic properties and behavior of porous Al2O3with spherical pores on the order of 1% by volume were computed. Young's moduli obtained by the homogenization method were consistent with both experimental and theoretical values. Using computed moduli of elasticity, the state of local stress concentration around the pores in a bending test was calculated together with the global stress in the sample. It was found that the dependence of the bending strength upon porosity can be described by taking into account local stresses around the pores. The combination of image-based modeling and homogenization method is a useful way to analyze the mechanical behavior of porous ceramics especially with inhomogeneous morphology.

Numerical analysis of permeability tensor for sheared woven fabrics

Takano N., Zako M., Okazaki T.

Nippon Kikai Gakkai Ronbunshu, A Hen/Transactions of the Japan Society of Mechanical Engineers, Part A （Nippon Kikai Gakkai Ronbunshu, A Hen/Transactions of the Japan Society of Mechanical Engineers, Part A）  68 （ 4 ） 529 - 536 2002年04月

ISSN  03875008

　概要を見る

Permeability tensor is a key parameter for Resin Transfer Molding (RTM) of fiber reinforced plastics as well as for its simulation. For sheared textile composites such as woven and knitted fabric composites after preforming or draping, the permeability tensor includes non-diagonal components, which can not be measured easily. This paper describes a numerical evaluation of permeability from both macro- and microscopic standspoints for sheared plain woven fabrics. The asymptotic homogenization theory for solid-fluid mixture is employed to characterize the micro-macro coupling effects. The nature of the macroscopic permeability tensor is discussed first. The microscopic flow field is next evaluated in detail by various ways. The differences of the microscopic flow field was recognized between the undeformed and sheared fabrics. The effects of the macroscopic pressure gradient is also discussed.

せん断変形した織布の樹脂透過テンソルの数値解析

高野 直樹

日本機械学会論文集A編 68 （ 668 ） 529-536 2002年

研究論文（学術雑誌）, 共著, 査読有り

セラミックス多孔体のイメージベースモデリングと均質化法による弾性解析

高野 直樹

日本セラミックス協会学術論文誌 110 （ 1282 ） 567-575 2002年

研究論文（学術雑誌）, 共著, 査読有り

セラミックスのランダムなミクロ構造を考慮したマルチスケール解析とミクロ応力評価

高野 直樹

日本機械学会論文集A編 68 （ 671 ） 1046-1053 2002年

研究論文（学術雑誌）, 共著, 査読有り

Microstructure-based evaluation of the influence of woven architecture on permeability by asymptotic homogenization theory

高野 直樹

Composites Science and Technology （Composites Science and Technology）  62 （ 10-11 ） 1347-1356 - 1356 2002年

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  02663538

　概要を見る

A microstructure-based computational approach is taken to predict the permeability tensor of woven fabric composites, which is a key parameter in resin transfer moulding (RTM) simulation of polymer-matrix composites. An asymptotic homogenization theory is employed to evaluate the permeability from both macro- and microscopic standpoints with the help of the finite-element method (FEM). This theory allows us to study the relation between microscopic woven architecture and macroscopic permeability based on the method of two-scale asymptotic expansions. While the fluid velocity is introduced for Stokes flow microscopically, the macroscopic one is for seepage flow with the Darcy's law. The latter can be characterized for arbitrary configurations of unit microstructures that are analyzed for the former under the assumption of the periodicity. After discussing the validity of this approach, we present a typical numerical example to discuss the permeability characteristics of plain weave fabrics undergoing shear deformation in the preforming in comparison with the underformed one. Another notable feature of the proposed method is that the correlation between the macroscopic behaviors and the microscopic ones can be analyzed, which is important to analyze and/or design the RTM process. Hence, it is also demonstrated that the microscopic velocity field evaluated with macroscopic pressure gradient provides important information about the flow in RTM processes. © 2002 Elsevier Science Ltd. All rights reserved.

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針状気孔を有するアルミナ多孔体の３次元ミクロ構造モデリングと均質化

高野 直樹

日本機械学会論文集A編 68 （ 672 ） 1163-1169 2002年

研究論文（学術雑誌）, 共著, 査読有り

Microstructure-based deep-drawing simulation of knitted fabric reinforced thermoplastic by homogenization theory

Takano N., Ohnishi Y., Zako M., Nishiyabu K.

International Journal of Solids and Structures （International Journal of Solids and Structures）  38 （ 36-37 ） 6333 - 6356 2001年08月

ISSN  00207683

　概要を見る

Process simulation of fiber reinforced composite materials is an important research theme for the development of low-cost and advanced functional composite materials. This paper aims at the simulation of deep-drawing process of knitted fiber reinforced thermoplastics and its verification. The feature of the simulation is that the large deformation of the knitted microstructures can be traced everywhere in the deep-drawn product. The homogenization theory is applied to analyze the micro-macro coupled behaviors of the knitted fabric composite material. By employing a simplified nonlinear computational algorithm, the deep-drawing simulation was carried out on a personal computer. The predicted largely deformed microstructures were compared with the experimental results. The numerical results and experimental ones agreed quite well. This deep-drawing simulation requires us to prepare only the mechanical properties of the constituents, while it provides us all the necessary quantities such as the deformation, strain, stress and stiffness from both microscopic and macroscopic standpoints. © 2001 Elsevier Science Ltd. All rights reserved.

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Deep-drawing simulation of knitted fabric reinforced thermoplastics by homogenization theory and experimental verification

Takano N., Ohnishi Y., Nishiyabu K., Zako M.

Zairyo/Journal of the Society of Materials Science, Japan （Zairyo/Journal of the Society of Materials Science, Japan）  50 （ 5 ） 461 - 467 2001年05月

ISSN  05145163

　概要を見る

A novel computational method for deep-drawing simulation of composite materials has been proposed with taking a three-dimensional continuum mechanics approach. The most notable feature is the consideration of micro-macro coupling effects by the mathematical homogenization theory. The homogenized properties and the constitutive law are evaluated carefully using the three-dimensional microstructure model under the large deformation and biaxial loading conditions. In this paper, the knit reinforcement of aramid fiber is studied, which has very complex microstructure architecture. The polypropylene is used as the matrix. The newly developed deep-drawing simulation provides us the macroscopic deformation, strain, stress and stiffness distribution as well as the largely deformed microstructures in the deep-drawn product. The high-speed computing technique which has been developed in the previous report enables us to carry out the micro-macro coupled nonlinear analysis easily on the personal computer. The experimental work has also been conducted, and the largely deformed microstructures are compared between experiment and simulation. A good coincident was obtained, which implies the validity and reliability of the proposed computational method.

Three-dimensional evaluation of permeability of fiber reinforced composite materials based on their microstructures

Takano N., Terada K., Zako M.

Zairyo/Journal of the Society of Materials Science, Japan （Zairyo/Journal of the Society of Materials Science, Japan）  50 （ 5 ） 488 - 494 2001年05月

ISSN  05145163

　概要を見る

This paper proposes a novel computational method for the evaluation of the permeability of fiber reinforced composite materials with complex microstructures. The homogenization theory for solid-fluid mixture is employed to characterize the micro-macro coupling effects. A characteristic function associated with the flow velocity is derived, whose average is defined as the permeability tensor. The derived relation between the macroscopic velocity and pressure gradient coincides with the conventional Darcy's law. Therefore, the proposed method enables us to predict the permeability tensor numerically without any experimental work. Furthermore, the characteristic function provides useful information to understand the correlation between the microscopic architecture and the macroscopic permeability tensor. Once the permeability tensor is given, we can use a conventional process simulator under the realistic process conditions. The macroscopic pressure gradient is obtained, which leads to the analysis of the actual microscopic flow field in the microstructure. The proposed microstructure-based evaluation can be used as the pre/post-processing of the conventional macroscopic process simulation. Three-dimensional modeling and analysis are shown for textile composites with the help of finite element method.

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重合メッシュ法による不均質体のミクロ応力解析

高野 直樹

日本機械学会論文集A編 67 （ 656 ） 603-610 2001年

研究論文（学術雑誌）, 共著, 査読有り

均質化法による編物強化熱可塑性プラスチックの深絞り成形解析とその検証

高野 直樹

材料 50 （ 5 ） 461-467 2001年

研究論文（学術雑誌）, 共著, 査読有り

繊維強化複合材料のミクロ構造に基づく樹脂透過性の３次元評価

高野 直樹

材料 50 （ 5 ） 488-494 2001年

研究論文（学術雑誌）, 共著

Computational Method for Homogenizatoin of Heterogeneous Materials with Voxel Element Modeling of Their Microstructures

高野 直樹

Materials Science Research International 2   66-71 2001年

研究論文（学術雑誌）, 共著, 査読有り

Finite Element Mesh Superposition Method Applied to Local Stress Analysis of Interphase of Composite Joints

高野 直樹

Materials Science Research International 2   219-224 2001年

研究論文（学術雑誌）, 共著, 査読有り