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Particle Modeling Based on Interatomic Potential and Crystal Structure: A Multi-Scale Simulation of Elastic-Plastic Deformation of Metallic Material

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World Journal of Nano Science and Engineering 2021年第3期11卷 45-68页

作者： ken-ichi saitoh Naoya Hanashiro Department of Mechanical Engineering Faculty of Engineering Science Kansai University Suita Japan

We formulate a macroscopic particle modeling analysis of metallic materials (aluminum and copper, etc.) based on theoretical energy and atomic geometries derivable from their interatomic potential. In fact, particles in this framework are presenting a large mass composed of huge collection of atoms and are interacting with each other. We can start from cohesive energy of metallic atoms and basic crystalline unit (e.g. face-centered cubic). Then, we can reach to interparticle (macroscopic) potential function which is presented by the analytical equation with terms of exponent of inter-particle distance, like a Lennard-Jones potential usually used in molecular dynamics simulation. Equation of motion for these macroscopic particles has dissipative term and fluctuation term, as well as the conservative term above, in order to express finite temperature condition. First, we determine the parameters needed in macroscopic potential function and check the reproduction of mechanical behavior in elastic regime. By using the present framework, we are able to carry out uniaxial loading simulation of aluminum rod. The method can also reproduce Young’s modulus and Poisson’s ratio as elastic behavior, though the result shows the dependency on division number of particles. Then, we proceed to try to include plasticity in this multi-scale framework. As a result, a realistic curve of stress-strain relation can be obtained for tensile and compressive loading and this new and simple framework of materials modeling has been confirmed to have certain effectiveness to be used in materials simulations. We also assess the effect of the order of loadings in opposite directions including yield and plastic states and find that an irreversible behavior depends on different response of the particle system between tensile and compressive loadings.

关键词： Molecular Dynamics Particle Method Elasticity Plasticity Nanostructure Multi-Scale Modeling

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Molecular Dynamics Study on Mechanical Properties in the Structure of Self-Assembled Quantum Dot

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World Journal of Nano Science and Engineering 2012年第4期2卷 189-195页

作者： Tatsuya Yamaguchi ken-ichi saitoh Department of Mechanical Engineering Faculty of Engineering Science Kansai University Suita Japan System Design Major Graduate School of Science and Engineering Kansai University Suita Japan

Stress and strain in the structure of self-assembled quantum dots constructed in the Ge/Si(001) system is calculated by using molecular dynamics simulation. Pyramidal hut cluster composed of Ge crystal with {105} facets surfaces observed in the early growth stage are computationally modeled. We calculate atomic stress and strain in relaxed pyramidal structure. Atomic stress for triplet of atoms is approximately defined as an average value of pairwise (virial) quantity inside triplet, which is the product of vectors between each two atoms. Atomic strain by means of atomic strain measure (ASM) which is formulated on the Green’s definition of continuum strain. We find the stress (strain) relaxation in pyramidal structure and stress (strain) concentration in the edge of pyramidal structure. We discuss size dependency of stress and strain distribution in pyramidal structure. The relationship between hydrostatic stress and atomic volumetric strain is basically linear for all models, but for the surface of pyramidal structure and Ge-Si interface. This means that there is a reasonable correlation between atomic stress proposed in the present study and atomic strain measure, ASM.

关键词： Molecular Dynamics Self-Assembled Quantum Dot Germanium Silicon Mechanical Property

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Nano-Scale Modelling and Simulation of Metal Wiredrawing by Using Molecular Dynamics Method

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World Journal of Nano Science and Engineering 2014年第2期4卷 70-83页

作者： ken-ichi saitoh Youhei Sameshima Syuhei Daira Department of Mechanical Engineering Kansai University Suita Japan Graduate School of Science and Engineering Kansai University Suita Japan Graduate School of Science and Engineering Kansai University Suita Japan Denso Techno Co. Ltd. Obu Japan

In this paper, molecular dynamics (MD) simulations of nano-sized wiredrawing are performed. The wiredrawing is a traditional plastic working method, but there has not been any insight to develop it in a nano-sized scale. Therefore, to materialize the concept of the nano-sized wiredrawing, a numerical modelling is pursued at first in this paper, and the interatomic potential, a crystalline orientation, the drawing condition realized by a die geometry are thoroughly investigated. In particular, to reduce the friction between a wire and a die, a simple friction model for the MD analysis is newly proposed, where the interatomic interaction is adequately modified by a single factor ω. Then, the fruitful results are obtained by using ω = 0.1. We checked the availability of such nano-sized MD simulation by constructing a two-dimensional wiredrawing model, at first. The analysis of atomic stress during drawing is also assessed. It is useful to use invariant of the atomic stress tensor, such as hydrostatic stress (average stress, σm) or von Mises equivalent stress (σeq). The former is related to the phase transformation from the body-centered-cubic (bcc) structure to the face-centered-cubic (fcc) one, which is found in the present MD simulation. It is observed that an initial α-iron crystal with bcc structure changes partially into the fcc phase. It is recognized that the phase transformation is caused by the positive hydrostatic stress values, which is occurring especially inside the die region. We observed that a lot of dislocation core structures occur in wiredrawing process and their existence and evolution are well related to the equivalent stress values.

关键词： Molecular Dynamics Iron and Steel Wiredrawing Plastic Working Nanotechnology Materials Processing Crystalline Structure

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Structure and Mechanical Behavior of Cellulose Nanofiber and Micro-Fibrils by Molecular Dynamics Simulation

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Soft Nanoscience Letters 2013年第3期3卷 58-67页

作者： ken-ichi saitoh Haruhiko Ohno Syunichiro Matsuo Department of Mechanical Engineering Faculty of Engineering Science Kansai University Suita Japan KYOCERA Corporation Kyoto Japan.

Cellulose nanofiber (CNF) and CNF micro-fibrils (CNF-MFs) are computationally modeled by molecular dynamics with united atom (UA) methodology of polymers. Structural stability and mechanical properties of these materials are focused on. Diffusion coefficient decreases with increase of the number of shells in CNF-MF. The structure of CNF-MFs with crystalline alignment is totally stabilized with twist which is an accumulation of torsion angles at Glycosidic bonds between monomers inside CNFs. Unique fiber drawing simulation, where a single CNF fiber is taken out of CNF-MF structure, is first conducted. The CNF fiber which is drawn out stretches up to relatively large strain, with linear increase of tensile stress. The computation results show that, the larger the number of shell structure of CNF-MF is, the larger the stretch and the stress of drawn fibers are.

关键词： Cellulose Nanofiber Molecular Dynamics Wiredrawing Mechanical Properties Biomaterial Twist Angle

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Molecular Dynamics Study of Collagen Fibrils: Relation between Mechanical Properties and Molecular Chirality

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Journal of Biomaterials and Nanobiotechnology 2020年第4期11卷 260-278页

作者： ken-ichi saitoh Tomohiro Sato Masanori Takuma Yoshimasa Takahashi Department of Mechanical Engineering Faculty of Engineering Science Kansai University Suita Osaka Japan

Collagen is a basic biopolymer usually found in animal bodies, but its mechanical property and behavior are not sufficiently understood so as to apply to effective regenerative medicine and so on. Since the collagen material is composed of many hierarchical structures from atomistic level to tissue or organ level, we need to well understand fundamental and atomistic mechanism of the collagen in mechanical response. First, we approach at exactly atomistic level by using all-atom modeling of tropocollagen (TC) molecule, which is a basic structural unit of the collagen. We perform molecular dynamics (MD) simulations concerning tensile loading of a single TC model. The main nature of elastic (often superelastic) behavior and the dependency on temperature and size are discussed. Then, to aim at coarse-graining of atomic configuration into some bundle structure of TC molecules (TC fibril), as a model of higher collagen structure, we construct a kind of mesoscopic model by adopting a simulation framework of beads-spring model which is ordinarily used in polymer simulation. Tensile or compression simulation to the fibril model reveals that the dependency of yield or buckling limit on the number of TCs in the model. Also, we compare the models with various molecular orientations in winding process of initial spiral of TC. The results are analyzed geometrically and it shows that characteristic orientational change of molecules increases or decreases depending on the direction and magnitude of longitudinal strain.

关键词： Collagen Molecular Dynamics Coarse-Graining All-Atom Modeling Mechanical Properties

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Molecular Dynamics Study on Transmission Mechanism of Torsional Deformation in Cellulose Nanofibers with Hierarchical Structure

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Soft Nanoscience Letters 2019年第4期9卷 45-57页

作者： kentaro Takada ken-ichi saitoh Tomohiro Sato Masanori Takuma Yoshimasa Takahashi Engineering Science Major Graduate School of Science and Engineering Kansai University Suita Osaka Japan Kawasaki Heavy Industries Ltd. Hyogo Japan Department of Mechanical Engineering Faculty of Engineering Science Kansai University Suita Osaka Japan.

Cellulose nanofiber (CNF) is a fibrous and nano-sized substance produced by decomposition of bulk-type cellulose which is a main component of plants. It has high strength comparable to steel, and it shows low environmental load during a cycle of production and disposal. Besides it has many excellent properties and functions such as high rigidity, light-weight, flexibility and shape memory effect, so it is expected as a next-generation new material. Usually it is composed of many cellulose micro fibrils (CMFs) in which molecular chains of cellulose are aggregated in a crystal structure, the knowledge of mechanical properties for each CMF unit is important. Since actual fibrils are complicatedly intertwined, it is also crucial to elucidate the transmission mechanism of force and deformation not only in one fibril but also in between fibrils. How the dynamic and hierarchical structure composed of CMFs responds to bending or torsion is an interesting issue. However, little is known on torsional characteristics (shear modulus, torsional rigidity, etc.) concerning CMF. In general, in a wire-like structure, it is difficult to enhance torsional rigidity and strength, compared with tensile ones. Therefore, in this study, we try to build a hierarchical model of CNF by multiplying CMF fibers and to conduct molecular dynamics simulation for torsional deformation, by using hybrid model between all-atom and united-atoms model. First, shear modulus was estimated for one CMF fibril and it showed a value close to the experimental values. Also, we assume a state in which two CMFs are ideally arranged in parallel, and create a hierarchical structure. We evaluate the dependence on the temperature for the bond strength and toughness in the hierarchical structures. Furthermore, we mentioned the transmission mechanism between components of a hierarchical structure.

关键词： Molecular Dynamics Cellulose Nanofibers Composite Materials Torsion Hi-erarchical Structure

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Renal amyloidosis as a late complication of Crohn's disease:a case report and review of the literature from Japan

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World Journal of Gastroenterology 2000年第3期6卷 461-464页

作者： Osamu saitoh Keishi Kojima Tsutomu Teranishi ken Nakagawa Masanobu Kayazawa Masashi Nanri Yutaro Egashira ichiro Hirata ken-ichi Katsu Second Department of Internal Medicine Osaka Medical CollegeTakatsukiJapan First Department of Pathology Osaka Medical CollegeTakatsukiJapan

INTRODUCTION Secondary amyloidosis is a rare but seriouscomplication of Crohn’s disease(CD).Theincidence of the association of secondaryamyloidosis in patients with CD has been reportedto be 0.5%-8% in Western ***,in Japan,the number of patients with CDcomplicated by amyloidosis is *** of their clinical manifestations andthe incidence of association are ***,we report herein a patient with

关键词： Crohn’s disease/complication renal amyloidosis amyloid deposits

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Improving the performance of conventional base isolation systems by an external variable negative stiffness device under near-fault and long-period ground motions

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Earthquake Engineering and Engineering Vibration 2020年第4期19卷 985-1003页

作者： Sandhya Nepal Masato saitoh Graduate School of Science and Engineering Saitama University255 Shimo-OkuboSakura-kuSaitamaJapan

Recent studies have shown that base-isolated objects with long fundamental natural periods are highly influenced by long-period earthquakes. These long-period waves result in large displacements for isolators, possibly leading to exceedance of the allowable displacement limits. Conventional isolation systems, in general, fail to resist such large displacements. This has prompted the need to modify conventional base isolation systems. The current work focuses on the development of an external device, comprising a unit of negative and positive springs, for improving the performance of conventional base isolation systems. This unit accelerates the change in the stiffness of the isolation system where the stiffness of the positive spring varies linearly in terms of the displacement response of the isolated objects. The target objects of the present study are small structures such as computer servers, sensitive instruments and machinery. Numerical studies show that the increase in the damping of the system and the slope of the linear function is effective in reducing the displacement response. An optimal range of damping values and slope, satisfying the stability condition and the allowable limits of both displacement and acceleration responses when the system is subjected to near-fault and long-period ground motions simultaneously, is proposed.

关键词： base isolation near-fault earthquakes long-period earthquakes negative stiffness variable stiffness

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A VASUALIZATION FOR THE DYNAMIC BEHAVIORS OF THE MIXTURE OF WATER MASS FOR NORTHWESTERN PACIFIC NEAR JAPAN

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International Journal of Modeling, Simulation, and Scientific Computing 2013年第S1期4卷 86-103页

作者： KUN ZHAO SATOSHI NAKADA NAOHISA SAKAMOTO KOJI KOYAMADA CHANDRAJIT BAJAJ YOichi ISHIKAWA TOSHIYUKI AWAJI TEIJI IN SEI-ichi saitoh Graduate School of Engineering Kyoto University KyotoKyoto Prefecture606-8501Japan Institute for the Promotion of Excellence in Higher Education Kyoto University KyotoKyoto Prefecture606-8501Japan Department of Computer Science The Institute for Computational Engineering and Sciences University of Texas at Austin AustinTexas78712USA Department of Geophysics Division of Earth and Planetary Sciences Kyoto University KyotoKyoto Prefecture606-8501Japan Data Research Center for Marine-Earth Sciences Japan Agency for Marine-Earth Science and Technology Yokosuka Kanakawa Prefecture237-0061Japan Japan Marine Science Foundation Tokyo Tokyo Metropolis110-0008Japan Laboratory of Marine Bioresource and Environment Sensing Faculty of Fisheries Sciences Hokkaido University SapporoHokkaido Prefecture060-0808Japan

Recent studies are focusing on the distribution of water mass because the mixture region of water mass is highly related to the rich fishing grounds[Yasuda I.,Watanabe Y.,***.3(3):172–181,1994].Due to the large data size and time-varying property,efficient exploration and visualization of the ocean data is always extremely *** extract the dynamic behaviors of the water mass and its mixture from a large-scale simulated ocean dataset,we developed an efficient visualization system by applying our volume compression method and our volume rendering *** system allows us to investigate the time-varying distributions of ocean physical properties,additionally from the user’s perspective and *** the experiments,we show the generality and expressiveness by applying our system for single-and multi-property visualizations to find some significant ocean water ***,we could obtain a clear visualization result to show the dynamic behaviors of the mixture of water mass for simulation data regarding a location in the northwestern Pacific near Japan.

关键词： Oceanography water mass visualization.

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Model tests and numerical analyses on horizontal impedance functions of inclined single piles embedded in cohesionless soil

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Earthquake Engineering and Engineering Vibration 2013年第1期12卷 143-154页

作者： Chandra Shekhar Goit Masato saitoh Department of Civil and Environmental Engineering Saitama University

Horizontal impedance functions of inclined single piles are measured experimentally for model soil-pile systems with both the effects of local soil nonlinearity and resonant *** practical pile inclinations of 5掳 and 10掳 in addition to a vertical pile embedded in cohesionless soil and subjected to lateral harmonic pile head loadings for a wide range of frequencies are *** obtained with low-to-high amplitude of lateral loadings on model soil-pile systems encased in a laminar shear box show that the local nonlinearities have a profound impact on the horizontal impedance functions of *** impedance functions of inclined piles are found to be smaller than the vertical pile and the values decrease as the angle of pile inclination *** values of horizontal impedance functions are obtained for the ＇positive＇ and ＇negative＇ cycles of harmonic loadings,leading to asymmetric force-displacement relationships for the inclined *** of these experimental results is carried out through three-dimensional nonlinear finite element analyses,and the results from the numerical models are in good agreement with the experimental *** analyses conducted on the numerical models suggest that the consideration of local nonlinearity at the vicinity of the soil-pile interface influence the response of the soil-pile systems.

关键词： inclined single piles harmonic loads horizontal impedance functions local nonlinearity finite element model

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