Details of a Researcher - Takano, Naoki

Papers - Takano, Naoki

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

Naoki Takano, Masaru Zako, Toru Okazaki and Futoshi Kubo

Materials Science Research International 2 219-224 2001

Research paper (scientific journal), Joint Work, Accepted

Microstructure-based Deep-drawing Simulation of Knitted Fabric Reinforced Thermoplastics by Homogenization Theory

Naoki Takano, Yoshihiro Ohnishi, Masaru Zako and Kazuaki Nishiyabu

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

Research paper (scientific journal), Joint Work, Accepted

Microscopic stress analysis of heterogeneous media by finite element mesh superposition method

Takano N., Zako M.

Nihon Kikai Gakkai Ronbunshu, A Hen/Transactions of the Japan Society of Mechanical Engineers, Part A (Nihon Kikai Gakkai Ronbunshu, A Hen/Transactions of the Japan Society of Mechanical Engineers, Part A) 67 ( 656 ) 603 - 610 2001

ISSN 03875008

Multiscale Modeling for heterogeneous media such as fiber or particulate reinforced composite materials and porous materials is one of the recent topics in computational mechanics and materials science. Homogenization technique has been, studied and used for the micro-macro bridging under the conditions of periodicity of the microstructures and of uniformity of macroscopic field. However, these two conditions make the evaluation of microscopic stresses using the homogenized model useless in the real applications, because the stresses with high gradient at the interface, edge or surface as well as the stress concentration due to voids etc. must be calculated. To solve this problem, in this paper, the finite element mesh superposition method is employed to calculate the microscopic stresses directly for local heterogeneity without the periodicity under non-uniform macroscopic strain field. Through two numerical examples, the efficiency of the modeling and the effectiveness of the microscopic stress evaluation are discussed.

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Formulation of homogenization method applied to large deformation problem for composite materials

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

International Journal of Solids and Structures (International Journal of Solids and Structures) 37 ( 44 ) 6517 - 6535 2000.11

ISSN 00207683

In order to analyze the mechanical behaviors of composite materials under large deformation, the formulation of the homogenization method is described. In this formulation, assuming that the microstructures in a local region of the global structure are deformed uniformly and that consequently the microscopic periodicity remains in the local region under large deformation, the microscopic deformation is precisely defined by the perturbed displacement and product of macroscopic displacement gradient and microscopic coordinates. Finally, microscopic and macroscopic equations are obtained. The above mentioned assumption of the periodicity of microstructures is experimentally validated. The computer program is also developed according to this formulation, and the large deformation is analyzed for the unidirectional fiber reinforced composite material and the knitted fabric composite material.

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傾斜ミクロ構造設計による材料機能化

TAKANO Naoki

日本複合材料学会誌 26 ( 1 ) 9-16 2000

Research paper (scientific journal), Joint Work, Accepted

局所的不均質部を有する構造体のグローバル／ローカルモデリング

TAKANO Naoki

日本機械学会論文集A編 66 ( 642 ) 220-227 2000

Research paper (scientific journal), Joint Work, Accepted

The Formulation of Homogenization Method Applied to Large Deformation Problem for Composite Materials

Naoki Takano, Yoshihiro Ohnishi, Masaru Zako and Kazuaki Nishiyabu

International Journal of Solids and Structures 37 ( 44 ) 6517-6535 2000

Research paper (scientific journal), Joint Work, Accepted

均質化法によるテキスタイル複合材料の樹脂浸透係数の評価

TAKANO Naoki

日本複合材料学会誌 26 ( 5 ) 171-178 2000

Research paper (scientific journal), Joint Work, Accepted

Integrated Design of Graded Microstructures of Heterogeneous Materials

Naoki Takano and Masaru Zako

Archive of Applied Mechanics (Archive of Applied Mechanics) 70 ( 8-9 ) 585-596 - 596 2000

Research paper (scientific journal), Joint Work, Accepted, ISSN 09391533

This paper proposes a novel, integrated, computational design methodology of graded microstructures of heterogeneous materials for the emergence of macroscopic function. In the first step of the design procedure, some discrete microstructures among a large number of graded microstructures are determined by the genetic algorithm as the optimization method. In this determination procedure, the homogenized modeling is adopted considering the micro-macro coupling by the homogenization method. This method enables us to study complex microstructures. Homogenized properties such as elastic properties, coefficient of thermal expansion and thermal conductivity can be calculated rigorously based on continuum mechanics. Calculated homogenized properties are stored in the micro-macro correlative database. The genetic algorithm can select the best geometrical arrangement of multiple microstructures from the pre-calculated database to construct the graded microstructure architecture. By using the database, the microscopic and macroscopic analyses are separated from each other, which reduces considerably the computational cost for the micro-macro coupled design. In the second step, continuously graded microstructures are designed using a feature-based 3D-CAD system by interpolating the discretized graded microstructures. In addition, a solid model is produced by the stereolithography technique to help in understanding the computationally designed complex microstructures. Brief descriptions of the formulation of the homogenization method for heat conduction and thermal stress problems are shown. A design problem for a plate with graded microstructures in its thickness direction is shown. The objective function for this example is the control of the wrap of the plate under the condition of temperature distribution. © Springer-Verlag 2000.

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Multi-scale Computational Method for Elastic Bodies with Global and Local Heterogeneity

Naoki Takano, Masaru Zako and Manabu Ishizono

Journal of Computer-Aided Materials Design (Journal of Computer-Aided Materials Design) 7 ( 2 ) 111-132 - 132 2000

Research paper (scientific journal), Joint Work, Accepted, ISSN 09281045

A multi-scale computational method using the homogenization theory and the finite element mesh superposition technique is presented for the stress analysis of composite materials and structures from both micro- and macroscopic standpoints. The proposed method is based on the continuum mechanics, and the micro-macro coupling effects are considered for a variety of composites with very complex microstructures. To bridge the gap of the length scale between the microscale and the macroscale, the homogenized material model is basically used. The classical homogenized model can be applied to be case that the microstructures are periodically arrayed in the structure and that the macroscopic strain field is uniform within the microscopic unit cell domain. When these two conditions are satisfied, the homogenization theory provides the most reliable homogenized properties rigorously to the continuum mechanics. This theory can also calculate the microscopic stresses as well as the macroscopic stresses, which is the most attractive advantage of this theory over other homogenizing techniques such as the rule of mixture. The most notable feature of this paper is utilize the finite element mesh superposition technique along with the homogenization theory in order to analyze cases where non-periodic local heterogeneity exists and the macroscopic field is non-uniform. The accuracy of the analysis using the finite element mesh superposition technique is verified through a simple example. Then, two numerical examples of knitted fabric composite materials and particulate reinforced composite material are shown. In the latter example, a shell-solid connection is also adopted for the cost-effective multi-scale modeling and analysis.

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Global/local modelling of structures with local heterogeneity

Takano N., Zako M., Ishizono M.

ISSN 03875008

For the numerical simulation of mechanical behaviors of structures with local heterogeneity, a global/local modelling technique using the finite element mesh superposition technique and shellsolid connection is proposed. Not only the global deformation but also three-dimensional stresses nearby the local heterogeneity can be analyzed precisely with less efforts than conventional methods. The finite element mesh superposition technique makes it possible to overlay local fine solid mesh which considers the local heterogeneity on global rough solid mesh which neglects the local heterogeneity. A plate structure that contains dissimilar material in a local portion is analyzed by the proposed modelling technique. The results agreed well with those calculated using the conventional three-dimensional fine mesh model.

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Hierarchical modelling and local stress analysis of composite materials and structures

Takano N., Kashiwagi Y., Ohnishi Y., Zako M.

ISSN 03875008

In the numerical simulation of mechanical behaviors of composite materials and structures, a novel hierarchical modelling technique is proposed. Not only the global deformation but also the mesoscopic stresses are analyzed precisely with less human efforts than conventional methods. Four level hierarchy is defined for the textile composites, and the homogenization method and finite element mesh superposition technique are adopted. The latter technique makes it possible to overlay arbitrary local fine mesh on the global rough mesh. A panel with a rib made of knitted fabric composite material is analyzed by the proposed method. Three-dimensional modelling of the mesostructure of knitted fabric composite material is also shown. The validity of the proposed method was examined, and the mesoscopic stresses are calculated easily.

カップリング効果を考慮した曲げ試験法

TAKANO Naoki

強化プラスチックス 45 ( 3 ) 84-87 1999

Research paper (scientific journal), Joint Work, Accepted

複合材料構造物の階層モデリングと局所的応力解析手法

TAKANO Naoki

日本機械学会論文集A編 65 ( 631 ) 498-505 1999

Research paper (scientific journal), Joint Work, Accepted

Hierarchical Modelling of Textile Composite Materials and Structures by the Homogenization Method

Naoki Takano, Yasutomo Uetsuji, Yukio Kashiwagi and Masaru Zako

Modelling and Simulation in Materials Science and Engineering (Modelling and Simulation in Materials Science and Engineering) 7 ( 2 ) 207-231 - 231 1999

Research paper (scientific journal), Joint Work, Accepted, ISSN 09650393

For the simulation of mechanical behaviours of textile composite materials and structures, a novel hierarchical modelling technique is proposed. Not only the global deformation but also the stresses at multiscales are analyzed precisely. Four-level hierarchy is defined for the textile composites such as woven and knitted fabric composites. The stresses at the mesostructure, which is a periodic unit cell of textile composite materials consisting of fibre bundles and matrix, can be evaluated accurately by the homogenization method and finite-element mesh superposition technique. The latter technique makes it possible to overlay arbitrary local fine mesh on the global rough mesh. Anisotropic damage mechanics is also utilized for strength evaluation at the mesoscale. Three-dimensional modelling of the mesostructure of woven and knitted fabric composite materials is shown. Localization analysis has been carried out within practical computational time and cost by the proposed hierarchical modelling.

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Intelligent Material Systems Using Epoxy Particles to Repair Microcracks and Delamination Damage in GFRP

Masaru Zako and Naoki Takano

Journal of Intelligent Material Systems and Structures (Journal of Intelligent Material Systems and Structures) 10 ( 10 ) 836-841 - 841 1999

Research paper (scientific journal), Joint Work, Accepted, ISSN 1045389X

The objective of this study is to propose an intelligent material system that can perform a self-repairing operation against initial damage that might occur in GFRP laminates. Specifically, we highlight the development of a novel actuator to be used in such self-repairing operations. There has been much research on sensor systems to detect damage and some actuators to control the shape of the structure or to control the vibration. However, no literature can be found on the actuator aiming at the self-repair of damage. For this purpose, a small grain particle-type adhesive is embedded in a glass/epoxy composite (GFRP) laminate. The diameter of the particle is approximately 50 μm. Hence, in the developed intelligent material system, coldsetting epoxy resin is used as the matrix, uni-directionally arranged glass fiber is used as the reinforcement, and a thermosetting epoxy particle is used as a repairing actuator. The volume fraction of the particles in the matrix was approximately 40%. The embedded particles can repair the damage, when melted by heat. Basic characteristics of the particles were investigated first, and we confirmed that the embedded particles in the matrix can melt by heat and flow to repair the crack. We also confirmed that the embedded particles do not deteriorate the stiffness of the GFRP laminate. Then we investigated the efficiency of the repairing operation against initial damage such as microscopic matrix cracks and delamination, by conducting two typical tests, i.e., static three-point bending of [0/90] laminate and tensile fatigue of [0/90]slaminate. Damage was observed by CCD camera. As a result, the decrease in the stiffness due to initial damage has been recovered and consequently increased, the residual fatigue life.

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On an intelligent structure of concrete reinforced by CFRP

Zako M., Takano N., Fujioka H.

Zairyo/Journal of the Society of Materials Science, Japan (Zairyo/Journal of the Society of Materials Science, Japan) 47 ( 11 ) 1183 - 1187 1998.11

ISSN 05145163

An intelligent structure of concrete reinforced by CFRP which can detect and repair the delamination of CFRP from the surface of concrete has been proposed and the performance has been evaluated in this paper. In order to investigate the effect of repair, three-point bending test has been performed on the test piece. When the optical fiber sensor detects the delamination during the test, the processor judges the damage to be repaired. The embedded Ni-Cr wire is heated to release the epoxy resin in the capsule, it spreads into the delamination to adhere the damage. The result of three-point bending test after repair showed better performance than that of a specimen of non-repaired. In case the repair was delayed, however, reasonable repairing cannot be expected. Therefore, delamination must be detected and repaired in the early stage of fracture. As a result, it was recognized that the delamination of CFRP on mortar concrete can be repaired with the proposed system.

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On sensor and actuator for intelligent structure of concrete reinforced by CFRP

Zako M., Takano N., Fujioka H.

Zairyo/Journal of the Society of Materials Science, Japan (Zairyo/Journal of the Society of Materials Science, Japan) 47 ( 11 ) 1178 - 1182 1998.11

ISSN 05145163

When CFRP lamina is applied for the reinforcement of concrete structures, the lamina has a possibility to delaminate from the surface of concrete. The delamination must be detected and be repaired as soon as possible for the reliability of structures. In pursuit of this, an intelligent structure was proposed in this paper. Both sensor and actuator are required to detect and to repair the delamination, respectively. As the intelligent structure, optical fiber was used to detect the delamination of CFRP as a sensor. Epoxy resin adhesive in a capsule was used to repair the delamination as an actuator. In the first paper, characteristics of both sensor and actuator were investigated. The brightness of transmitted light in the optical fiber was decreased at bended point caused by delamination of CFRP. On the other hand, the capsuled epoxy resin has been spreaded widely into delaminated interface. As a result, it was recognized that the proposed sensor and actuator can be used to detect and repair the delamination of CFRP.

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Design procedure for laminated composites based on genetic algorithm with function approximation

Zako M., Takano N., Takeda N.

Zairyo/Journal of the Society of Materials Science, Japan (Zairyo/Journal of the Society of Materials Science, Japan) 47 ( 5 ) 446 - 451 1998.05

ISSN 05145163

In this paper, a design procedure for laminated composite structures based on GA (Genetic Algorithms) with function approximations is proposed. Design variables considered to enhance the rigidity of the laminated composite structure are the number of laminae, the fiber orientations and the stacking sequence. The fiber orientations are chosen from some prepared angles. In the proposed procedure, the rigidity of laminated composites is approximated by means of weighing coefficients and transformed elastic constants at the prepared angles. The proposed approximate function can be thought of response surfaces, because the weighing coefficients are adjusted with pairs of input and output data. The effective approximation is generated using auxiliary information about the principal stress distribution. The approximate function is used as the objective function of GA and can be evaluated without finite element analysis. As a result, the proposed procedure can reduce computational cost remarkably. In this paper, the detail of our developed design procedure and data sampling scheme are described.

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Development of design margin decision system considering fatigue limit

Zako M., Takano N., Hanaki S.

Zairyo/Journal of the Society of Materials Science, Japan (Zairyo/Journal of the Society of Materials Science, Japan) 47 ( 1 ) 90 - 94 1998.01

ISSN 05145163

The experimental results of fatigue at low stress levels around the fatigue limit have large scatter. For the design of structures and machines, it is important to evaluate the scatter and to decide the design margin. In this paper, the statistical method to decide the fatigue limit is proposed. In the proposed method, the fatigue limit is decided with considering the distribution of fatigue strength. Because each fatigue data is transformed into normalized fatigue strength, this method has the advantage point that the distribution of fatigue strength and the fatigue limit can be found by relatively small samples. Using the proposed method, the computer system to decide the design margin for fatigue is developed. In this system, the S-N curve with fatigue limit and the distribution of fatigue strength are obtained at first. Then the design margin with a given probability of failure and a confidence level is calculated. The developed system is applied to some experimental results for fatigue test. As a result, the S-N curve with the design margin has obtained easily. It is recognized that the obtained S-N curve is decided after consideration of scatter.

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