担当区分：責任著者   記述言語：日本語   掲載種別：研究論文（学術雑誌）

道路橋示方書では，せん断遅れによる付加的な応力を有効幅を用いて見かけ上の曲げ剛性を小さくする ことで考慮している. しかしせん断遅れは曲げではなく, せん断変形に起因する断面変形によって生じるこ とが分かっている．これまでにせん断による断面変形の自由度を持つ梁理論が提案され，この断面変形梁 理論では 3 つの断面パラメタを導入することでせん断遅れによる断面変形，ひいてはせん断遅れによる付 加的な応力を高精度に求めることができる．しかし，断面パラメタの決定には代表体積要素の有限要素解 析を行う必要がある．本研究では せん断遅れによる付加的な応力を簡易的かつ高精度で算定するために， 有限要素解析の代わりに機械学習を用いた断面パラメタの推定法を提案する．提案手法を用いた付加的な ひずみの精度を複数の検証用データで評価し，相対差が平均値 0.02%，標準偏差 0.2% 程度であることを確 認した．

DOI： 10.2208/jscejj.22-15009

Kyutacar

担当区分：筆頭著者,　責任著者   記述言語：日本語   掲載種別：研究論文（学術雑誌）

橋梁のように移動荷重を受ける構造物の設計において，着目点の応力等を荷重載荷位置で表した影響線は必要不可欠な概念である．影響線を有限要素モデルで求めようとすると，荷重作用範囲の節点数と同じ数の解析が必要となる．一方，Müller-Breslauの原理を有限要素解析に適用する方法も提案されているが，着目点に不連続変位を与えるため，手間のかかるモデルの修正が必要となる．そこで本論文では，モデルの修正が不要で汎用有限要素解析コードへの実装が容易な影響線の解析手法を提案する．提案手法は有限要素離散化した問題へ直接適用した相反定理に基づいている．平面応力問題および3次元問題の具体例に対して，提案手法により求められた影響線を通常の単位荷重による有限要素解析結果と比較することで提案手法の妥当性を確認した．

DOI： 10.2208/jscejseee.78.3_480

Kyutacar

記述言語：英語   掲載種別：記事・総説・解説・論説等（学術雑誌）

In July 2020, the Kyushu region experienced record-breaking heavy rains from July 4 to7, causing extreme floods in the Kuma and Chikugo Rivers. This was followed by atmospheric instability over a wide area from western Japan to the Tohoku region, resulting in heavy rainfall on July 13-14 in the Chugoku region, and on July 27-28 in the Tohoku region. There was also flooding of large rivers including the Go River and the Mogami River. In recent years, record-breaking torrential rainfall disasters have been occurring every year. The heavy precipitation scale has been increasing in space and time as well as in rainfall intensity, resulting in spatio-temporal expansion of the damage. Furthermore, in 2020, the disaster occurred amidst the restriction of social activities due to the COVID-19 pandemic. The compilation and dissemination of disaster survey data and lessons are essential for the sustainable development of society. Therefore, JSCE has planned a special issue on the July 2020 torrential rain disaster to share and disseminate disaster information and to contribute to the advancement of technology and science related to disaster prevention and mitigation.

DOI： 10.2208/JOURNALOFJSCE.10.1_545

Kyutacar

Scopus

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=85148295769&origin=inward

担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）

Japan   Tokyo   2019年11月09日  -  2019年11月11日

担当区分：最終著者   記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）

Japan   Tokyo   2019年11月09日  -  2019年11月11日

記述言語：英語   掲載種別：研究論文（学術雑誌）

Shear bands with characteristic spatial patterns observed in an experiment for a cubic or parallelepiped specimen of dry dense sand were simulated by numerical bifurcation analysis using the Cam-clay plasticity model. By incorporating the subloading surface concept into the plasticity model, the model became capable of reproducing hardening/softening and contractive/dilative behavior observed in the experiment. The model was reformulated to be compatible with the multiplicative hyperelasto-plasticity for finite strains. This enhanced constitutive model was implemented into a finite-element code reinforced by a stress updating algorithm based on the return-mapping scheme, and by an efficient numerical procedure to compute critical eigenvectors of elastoplastic tangent stiffness matrix at bifurcation points. The emergence of diamond- and column-like diffuse bifurcation modes breaking uniformity of the materials, followed by the evolution of shear bands through strain localization, was observed in the analysis. In the bifurcation analysis of plane strain compression test, unexpected bifurcation modes, which broke out-of-plane uniformity and led to 3-dimensional diamond-like patterns, were detected. Diffuse bifurcations, which were difficult to observe by experiments, have thus been found as a catalyst creating diverse shear band patterns.

DOI： 10.1002/nag.2711

Kyutacar

その他リンク： https://www.scopus.com/pages/publications/85026375110?origin=resultslist

担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）

Japan   Sapporo   2013年09月11日  -  2013年09月13日

Some kinds of element test are generally conducted in order to evaluate mechanical characteristics of structural members that have complex microstructures such as steel and concrete composite beams. However, the element test with a part of the structural member can not faithfully reconstruct deformation state in actual structures. To that end, we formulate a beam with averaged mechanical properties in order to evaluate mechanical properties of Timoshenko beams with microstructures.

その他リンク： https://www.scopus.com/pages/publications/84905248341

記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）

Japan   Sapporo   2013年09月11日  -  2013年09月13日

For better design and construction of steel-concrete hybrid structures, it is important to evaluate the strength and behavior of their joints: e.g. headed studs. However, the contribution of the adhesion and friction along the steel-concrete interface are ignored in such mechanical joints. We here try to propose a new torque shear test system by which the shear strength of the friction and adhesion can be evaluated appropriately. The test specimen has a cylindrical interface in mortar block, and it becomes the interface subjected to the torque shear loading. The results showed that cracks initiated on the side of the specimen were due to the boundary conditions rather than strength of steel-mortar interface and they should be prevented, and the maximum shear stress and residual shear stress were insensitive to the additional reaction force on the steel cylinder of the torque shear test system.

その他リンク： https://www.scopus.com/pages/publications/84905216507

記述言語：英語   掲載種別：研究論文（学術雑誌）

A modification of the Mori–Tanaka method is proposed to evaluate the average elastoplastic behavior of composites and polycrystals in a virtual matrix. The virtual matrix is an elastic material in which real matrix material and inhomogeneities are embedded, and its volume vanishes as a limit after homogenization. With regard to elasticity, depending on the choice of material properties of this virtual matrix, many kinds of average moduli between the classical bounds can be predicted. In this paper, we extend the application of this method to elastoplastic materials. Furthermore, Weng's approximate model of interfacial debonding between the inclusions and the matrix is installed, because of its very simple criterion for the initiation of debonding to simulate progressive debonding phenomena. Several numerical examples without interfacial debonding show the applicability of the virtual matrix concept to elastoplastic materials. The characteristics of the model and its overall behaviors are described through the use of typical numerical simulations with debondings. Finally, comparisons with experimental results including debondings demonstrate the eligibility of the proposed method and models, and the application of the present method to designing a hybrid FRP is overviewed.

DOI： 10.1016/j.mechmat.2011.06.010

DOI： 10.1016/j.mechmat.2011.06.010

その他リンク： https://www.scopus.com/pages/publications/80051576868

記述言語：英語   掲載種別：研究論文（学術雑誌）

The development of plastic deformation after uniaxial plastic strain along [0 0 1] is analyzed in two types of domains in γ–γ′ nickel superalloys. These domains are the horizontal matrix channels normal to [0 0 1] and the vertical channels normal to [1 0 0] and [0 1 0]. By using a mean field method, an elastic energy increase due to the introduction of plastic strain (elongation or compression) in the two types of domains is calculated. The analysis of a mixed mode, where horizontal and vertical channel deformation occurs, is also conducted. Results show that plastic deformation is primarily initiated in a particular type of channel. The choice of the deformation configuration is related to the sign of misfit strain. After a critical amount of plastic strain is reached, the deformation expands through all the matrix channels. This conclusion is supported by the dependence of a flow stress on the deformation mode. FEM calculations are also conducted and compared with the analytical calculation. Except when the strain is extremely small, the two methods give almost the same result.

DOI： 10.1016/j.mechmat.2009.10.001

DOI： 10.1016/j.mechmat.2009.10.001

その他リンク： https://www.sciencedirect.com/science/article/pii/S0167663609001720

担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）

Formulations of linear and nonlinear multiscale analyses for media with lattice periodic microstructures based on the homogenization theory are proposed. For continuum media, the conventional homogenization theory leads to boundary value problems of continuum for both micro- and macroscales. However, it is rational to discretize lattice microstructures, such as cellular solids, by frame elements since they consist of slender members. The main difficulty in utilizing structural elements, such as frame elements, for microscale problems is due to the inconsistency between the kinematics assumed for the frame elements and the periodic displacement field for the microscale problem. In order to overcome this difficulty, we propose a formulation that does not employ the periodic microscale displacement, but the total displacement, including the displacement due to uniform deformation as well as periodic deformation, as the independent variable of the microscale problem. Some numerical examples of cellular solids are provided to show both the feasibility and the computational efficiency of the proposed method.

DOI： 10.1615/IntJMultCompEng.v4.i4.20

DOI： 10.1615/IntJMultCompEng.v4.i4.20

担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）

By virtue of the development of metallurgy and the theory of dislocation, one can qualitatively anticipate the mechanical properties of a material from its microstructure. Moreover, not qualitative but quantitative and precise anticipation is more beneficial for efficient development of new materials. In this context, we utilize a multi-scale method with atomic model, which is a particle system that has potential, and discuss the possibility of quantitative anticipation of material properties including plastic deformation through several representative numerical examples.

DOI： 10.2208/jsceseee.22.209s

DOI： 10.2208/jsceseee.22.209s

Kyutacar

その他リンク： https://www.scopus.com/pages/publications/31444434690