Faculty Profiles - OKUMURA, Dai

Papers - OKUMURA, Dai

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The large scale finite element analysis of a charge air cooler using a homogenization method Reviewed

K. Iwahori, N. Ohno, D. Okumura, T. Muraki, S. Miyakawa

SAE Technical Paper Vol. 2013 ( 01 ) page： 1212 2013.8

チューブ-フィン構造体におけるフィン層の均質化弾性剛性（評価と検証） Reviewed

岩堀恵介, 大野信忠, 村木友也, 奥村大, 宮川進

日本機械学会論文集Ａ編 Vol. 79 page： 89-99 2013

Implicit iterative finite element scheme for a strain gradient crystal plasticity model based on self-energy of geometrically necessary dislocations Reviewed

R. Kametani, K. Kodera, D. Okumura, N. Ohno

Computational Materials Science Vol. 53 page： 53-59 2012

Homogenizaed elastic-viscoplastic behavior of anisotropic open-porous bodies with pore pressure Reviewed

N. Ohno, K. Ikenoya, D. Okumura, T. Matsuda

International Journal of Solids and Structures Vol. 49 page： 2799-2806 2012

弾性積層ダンボールの圧縮強度に微視構造の及ぼす影響の均質化解析 Reviewed

奥村　大，大野信忠，小野田孝行，曽我将孝

計算数理工学論文集 Vol. 12 page： 103-108 2012

Plastic size effect analysis of lamellar composites using a discrete dislocation plasticity approach Reviewed

D. Okumura, N. Ohno, K. Yamaguchi

Vol. 27 page： 2040-2055 2011.12

Influence of closed faces on compressive strength of open cell metallic foams Reviewed

Dai Okumura, Yuji Takahashi, Nobutada Ohno

Materials Research Innovations Vol. 15 page： S61-S64 2011

離散転位塑性法を用いたラメラ複合材料の均質化解析 Invited

奥村　大，大野　信忠

計算数理工学レビュー Vol. 2011-1 page： 13-19 2011

離散転位動力学解析のための均質化理論の定式化 Reviewed

奥村　大，大野信忠，片桐慶大

材料 Vol. 59 ( 2 ) page： 149-156 2010.2

Yield and buckling behavior of Kelvin open-cell foams subjected to uniaxial compression Reviewed

Yuji Takahashi, Dai Okumura, Nobutada Ohno

International Journal of Mechanical Sciences Vol. 52 ( 2 ) page： 377-385 2010

幾何学的に必要な転位の自己エネルギーを考慮したひずみこう配結晶組成理論のための陰的有限要素方程式 Reviewed

小寺一輝，亀谷隆真，奥村　大，大野信忠

計算数理工学論文集 Vol. 9 page： 43-48 2009

単軸圧縮を受けるケルビンオープンセルフォームの微視的座屈挙動 Reviewed

奥村　大，岡田篤志，大野信忠

材料 Vol. 57 ( 2 ) page： 126-133 2008.2

Buckling behavior of Kelvin open-cell foams under [0 0 1], [0 1 1] and [1 1 1] compressive loads Reviewed

Dai Okumura, Atsushi Okada, Nobutada Ohno

International Journal of Solids and Structures Vol. 45 ( 13 ) page： 3807-3820 2008

Grain-size dependent yield behavior under loading, unloading, and reverse loading Reviewed

N. Ohno, D. Okumura, T. Shibata

International Journal of Modern Physics B Vol. 22 page： 5937-5942 2008

Higher-Order Stress Due to Self Energy of Geometrically Necessary Dislocations Reviewed

N. Ohno, D. Okumura

Key Engineering Materials Vol. 340-341 page： 173-178 2007

Three-dimensional microscopic interlaminar analysis of cross-ply laminates based on a homogenization theory Reviewed

Tetsuya Matsuda, Dai Okumura, Nobutada Ohno, Masamichi Kawai

International Journal of Solids and Structures Vol. 44 ( 25-26 ) page： 8274-8284 2007

* A homogenization theory of strain gradient single-crystal plasticity and its finite element discretization Reviewed

D. Okumura, Y. Higashi, K. Sumida, N. Ohno

International Journal of Plasticity Vol. 23 page： 1148-1166 2007

Authorship：Lead author Language：English Publishing type：Research paper (scientific journal)

In this study, a homogenization theory based on the Gurtin strain gradient formulation and its finite element discretization are developed for investigating the size effects on macroscopic responses of periodic materials. To derive the homogenization equations consisting of the relation of macroscopic stress, the weak form of stress balance, and the weak form of microforce balance, the Y-periodicity is used as additional, as well as standard, boundary conditions at the boundary of a unit cell. Then, by applying a tangent modulus method, a set of finite element equations is obtained from the homogenization equations. The computational stability and efficiency of this finite element discretization are verified by analyzing a model composite. Furthermore, a model polycrystal is analyzed for investigating the grain size dependence of polycrystal plasticity. In this analysis, the micro-clamped, micro-free, and defect-free conditions are considered as the additional boundary conditions at grain boundaries, and their effects are discussed.

* Higher-order stress and grain size effects due to self-energy of geometrically necessary dislocations Reviewed

N. Ohno, D. Okumura

Journal of the Mechanics and Physics of Solids Vol. 55 page： 1879-1898 2007

Language：English Publishing type：Research paper (scientific journal)

The self energy of geometrically necessary dislocations (GNDs) is considered to inevitably introduce the higher-order stress work-conjugate to slip gradient in single crystals at small strains. It is pointed out that this higher-order stress changes stepwise in response to the in-plane gradient of slip, and thus significantly influences the onset of initial yielding in polycrystals. The self energy of GNDs is then incorporated into the strain gradient plasticity theory of Gurtin (J. Mech. Phys. Solids 50 (2002) 5). The resulting theory is applied to 2D and 3D model crystal grains of size D, leading to the D-1-dependent term of grain yielding with a coefficient determined by grain shape and orientation. This size effect term, which is also derived from a simple energy equation, is discussed using published experimental data of several polycrystalline metals. It is thus shown that the self energy of GNDs quantitatively accounts for not only the grain size dependence of initial yield stress but also the dislocation cell size dependence of flow stress in the submicron to several-micron range of grain and cell sizes.

Long wave-length buckling of periodic open-cell foams subjected to uniaxial compression Reviewed

D. Okumura, A. Okada, N. Ohno

Key Engineering Materials Vol. 345-346 page： 81-84 2007

Microscopic interlaminar stress analysis of CFRP cross-ply laminate using a homogenization theory Reviewed

T. Matsuda, D. Okumura, N. Ohno, M. Kawai

Key Engineering Materials Vol. 340-341 page： 1043-1048 2007

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