DOI： 10.1016/j.commatsci.2023.112281

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Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

DOI： 10.1016/j.msea.2022.144179

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Publishing type：Research paper (scientific journal)   Publisher：MDPI AG  

Due to great interest in the development of electric vehicles and other applications, improving the performances of lithium-ion batteries (LIBs) is crucial. Specifically, components of electrolytes for LIBs should be adequately chosen from hundreds of thousands of candidate compounds. In this study, we aimed to evaluate some physical properties expected for combinations of molecules for electrolytes by microscopic simulations. That is, the viscosity, ionic conductivity, degree of dissociation, diffusion coefficient, and conformation of each molecule were analyzed via molecular dynamics (MD) simulations. We aimed to understand how molecular-sized structures and properties collaboratively affect the behavior of electrolytes. The practical models of molecules we used were ethylene carbonate (EC), fluoroethylene carbonate (FEC), propylene carbonate (PC), butylene carbonate (BC), γ-butyrolactone (GBL), γ-valerolactone (GVL), dimethyl carbonate (DMC), ethyl-methyl carbonate (EMC), diethyl carbonate (DEC), and lithium hexafluorophosphate (LiPF6). Many molecular systems of electrolytes were simulated, in which one molar LiPF6 was mixed into a single or combined solvent. It was found that small solvent molecules diffused with relative ease, and they contributed to the higher ionic conductivity of electrolytes. It was clarified that the diffusion coefficient of lithium (Li) ions is greatly affected by the surrounding solvent molecules. We can conclude that high-permittivity solvents can be selectively coordinated around Li ions, and Li salts are sufficiently dissociated, even when there is only a small content of high-permittivity solvent. Thus, we can confirm solely by MD simulation that one of the better candidates for solvent molecules, formamide (F), will exhibit higher performance than the current solvents.

DOI： 10.3390/batteries8030027

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Publishing type：Research paper (scientific journal)   Publisher：Society of Materials Science, Japan  

DOI： 10.2472/jsms.71.167

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Publishing type：Research paper (scientific journal)   Publisher：Japan Society of Mechanical Engineers  

DOI： 10.1299/transjsme.22-00019

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Publishing type：Research paper (scientific journal)   Publisher：Trans Tech Publications, Ltd.  

Sulfide was used as solid lubricant, and MoS₂ was popular. It was used industry as powder shape. Sulfur as oil additive; ZDDP, MoTDC were also well known. These composites make tribofilm which prevent seizure, scoring and some tribological troubles. In this paper, sulfides were synthesized by powder metallurgy technics. In addition, these sulfides were mixed with bronze powders and sintered as cylindrical specimen. As a result of the friction test in the lubricated condition, tribofilm were covered with specimen surface. By XPS observation, sulfides and oxides were detected on the specimen surface. In the test, additive was not contained in the lubricant because PAO as base oil was adapted. However, sulfide in the specimen affect the making the tribofilm, especially when bornite (Cu₅FeS₄) was used.

DOI： 10.4028/www.scientific.net/kem.901.164

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Publishing type：Research paper (scientific journal)   Publisher：Japan Society of Powder and Powder Metallurgy  

DOI： 10.2497/jjspm.68.317

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Publishing type：Research paper (scientific journal)   Publisher：Hindawi Limited  

As a sustainable ecosystem, the general firing process for ceramics emits large amounts of CO2 gas; thus in ceramics production, the focus is the nonfiring process; however, the solidification and strengthen mechanism of this nonfiring system, which essentially reacts between surface-activated ceramic particles and a solvent, has not been elucidated to date. The nonfiring process had three steps, i.e., particle surface activate process by grinding process, maintaining the active state until starting nonfiring solidification begins, and nonfiring solidification process. Thus, in this study, the reaction of silica and water was simulated by adapting molecular dynamics based on LAMMPS with ReaxFF potentials. Reproducing the activated silica surface state, three ended models called O model, Si model, and OH model were prepared which indicated ended molecules of each surface. These models and a water molecule as a solvent were bonded in the atomic scale, and the energetic state and mechanical properties were evaluated. A reacted or structured O-H-O bond was reproduced in the nonfiring process in the O-ended model. The bond was a hydrogen bond. A Si-O-Si bond was produced when a Si atom was ended on the interface. The bonded interface was able to tensile. However, the tensile strength was weaker than that of the solid silica model. The nonbonded OH model did not have tensile strength.

DOI： 10.1155/2020/8857101

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Other Link： http://downloads.hindawi.com/journals/jnm/2020/8857101.xml

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DOI： 10.4236/jbnb.2020.114017

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DOI： 10.4236/snl.2019.94004

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Malaysian Tribology Society (Mytribos)  

Replacement of exhaustible and harmful resources used as solid lubricants is required for sliding elements such as plain bearings. In particular, the substitution of lead containing in the lead bronze is considered an urgent task. Therefore, in this study, attention was focused on metal sulfides (Cu2S, Cu5FeS4, SnS, TiS2, etc) as a substitute material for lead. After synthesis of sulfide and preparation of sintered body, friction and abrasion test was carried out and applicability as solid lubricant was investigated. The tribological properties of the dry conditions were evaluated by a journal type high speed tester. As a result, the friction coefficient of the bronze specimen without sulfide was about 0.3, whereas the bronze specimen containing sulfide showed a friction coefficient of about 0.1, indicating that the sulfide reduced the frictional resistance. Among them, the specimens containing Cu2S and Cu5FeS4 exhibited a lower friction coefficient. It is considered that this is influenced not only by the effect of hardness but also by film formation by sulfide.

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DOI： 10.1088/1757-899X/461/1/012074

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Publishing type：Research paper (scientific journal)   Publisher：Japan Society of Mechanical Engineers  

DOI： 10.1299/transjsme.19-00206

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：European Powder Metallurgy Association (EPMA)  

In recent years, with the development of powder metallurgy technology, sintered materials have been tried for bearings. However, parts made by powder metallurgy are porous and therefore have low strength. Therefore, this research was conducted using bimetal which is excellent in strength and sliding property. In this experiment, a friction test was carried out using sulfide bronze and metallic powder of brass and phosphor bronze with blended solid lubricant (graphite or sulfide) These materials were sintered in vacuum condition. As a result, in the friction test, the phosphor bronze had the lowest coefficient of friction and a stable friction. Also the amount of wear on phosphor bronze was small. This is thought to be due to the improvement of the abrasion resistance by adding phosphorus and the solid lubricant. In conclusion, among these three copper alloys, phosphor bronze was found to be the most excellent in wear resistance.

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Institute of Physics Publishing  

The process of nano-sized wiredrawing is investigated by using molecular dynamics (MD) simulation in this study. The authors have constructed novel computation models of wiredrawing, in which a single wire of just a several nanometers in diameter is smoothly drawn through a perfectly rigid die together with lubrication mechanism and is forced to be shaped into thinner one. Interatomic potentials used in MD simulation is a conventional pairwise type useable for iron-carbon binary system (for pearlitic steel). For MD model of pearlite steel wire, it is recognized that ferrite-cementite interface effectively offers high-speed diffusion path for carbon atoms from cementite side to ferrite side (elementary mechanism of cementite decomposition). As conclusion, we showed by using atomistic simulation that nano-sized wiredrawing process is theoretically quite possible.

DOI： 10.1088/1757-899X/307/1/012039

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DOI： 10.1155/2018/4153464

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

The time-dependent crack initiation from the interface free-edge of adhesively bonded axisymmetric columnar butt joints (epoxy/SUS, edge shape: 90 degrees/90 degrees) was investigated in detail. With the change of applied stress level, sigma(n), the butt joints exhibited crack initiation life, t(C), that varied about four orders of seconds (10(2)-10(6) s). Such a clear time-dependent life property was then studied in terms of the fracture mechanics. The near-edge stress/strain field at the crack initiation was numerically evaluated with the finite element method (FEM) by applying the time-hardening creep law to the epoxy resin. It was found that the critical asymptotic stress field along the interface represented by the combination of two parameters, lambda(cr)(sigma) (creep stress singularity index) and K-sigma(cr) (creep stress intensity factor), satisfies a unique relation irrespective of (sigma(n), t(C)) sets. The same tendency was also confirmed when the near-edge total strain field parameters were employed. These results indicate that the K-lambda criterion, originally developed for static fracture problems, still holds its validity in the time domain. (C) 2017 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.engfracmech.2017.08.017

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

Sufides as MoS₂ are known as solid lubricants. These materials are also known as thermoelectric materials. However, there is no materials satisfied both functions at the same time. In this study, sulfides powders such Cu₂S (chalcocite), SnS, Cu₅FeS₄ (bornite) were synthesized under vacuum condition. Some specimens were evaluated by friction tester and their lubricity, not only sintered sulfied but also blended and sintered sulfides with bronze powders were compared. Other specimens were evaluated their seebeck coefficients, that is one of the thermoelectric properties. Experiments results of the seebeck coefficients were compared with simulation results. As a result, it was found that SnS and blended SnS with bronze had indicated better friction properties. For thermoelectric properties, seebeck coefficient of Cu₂S had matched with experiments and simulation. Totally, Cu₂S (chalcocite) has superior properties as both solid lubricant and thermoelectric material.

DOI： 10.1299/jsmeiip.2017.A-14

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

DOI： 10.1299/jsmecmd.2017.30.108

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：European Powder Metallurgy Association (EPMA)  

Sufides as MoS2 are known as solid lubricants. These materials are also known as thermoelectric materials. However, there is no material satisfying both functions at the same time. In this study, sulfides powders such as Cu2S (chalcocite), TiS2, SnS, Cu5FeS4 (bornite) were synthesized under vacuum condition. Some specimens of sintered sulfides were evaluated by friction tester and their lubricity. As a result it was found that SnS had indicated better friction properties. Other specimens were evaluated in terms of Seebeck coefficients, which is one of the thermoelectric properties. Experimental results of the Seebeck coefficients were compared with simulation results. For thermoelectric properties, the Seebeck coefficient of Cu2S had matched with experiments and simulation. Totally, Cu2S (chalcocite) and SnS has superior properties both, as solid lubricant as well as thermoelectric material.

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Journal of the Japan Society of Powder and Powder Metallurgy  

Copper (Cu) alloys are used as sliding materials. Especially, bronze (Cu-Sn alloy) is popular material for sintered bearings. In the sintering process, the reductive atmosphere is generally adopted on an industrial field to reduce the oxide which exists on the surface of Cu-Sn alloy powders as atomized. However, sintering in the vacuum atmosphere is useful because of disusing any kinds of gases. It was reported that sintering in the vacuum atmosphere gives better properties unless the alloy powder is heavily oxidized. In this report, the radial crushing strengths was investigated for the sintered Cu-Sn alloys which were the bronze and the sulfide dispersed bronze (Sulfide bronze). Especially tin powder and fine tin powder were used as the additives mixed for the Cu-Sn alloys to compare the radial crushing strengths. With increasing compacting pressure and sintering temperature, the pores in the sintered specimen were decreasing, and the sintered specimen which had lower porosity indicated high radial crushing strength. And on the sulfide bronze the feature of the fracture surface depended on tin content. In the specimen with lower tin content the interface between the bronze matrix and sulfide particle became the origin of the fracture, while in the one with higher tin content the Cu-Sn intermetallic compound which was so hard and brittle became the origin of the fracture.

DOI： 10.2497/jjspm.63.255

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Japanese Society of Tribologists  

In order to clarify the plastic deformation mechanism of silicon carbide in cubic phase (3C-SiC), molecular dynamics (MD) simulations are performed on the nanoindentation using a spherical indenter. Transition from elastic deformation to plastic deformation has been confirmed by the phenomenon called pop-in in the load-displacement curves during nanoindentation. Dislocations on {1 1 1} slip planes are found during indentation. In order to analyze internal defects, common neighbor analysis (CNA) is slightly modified so that it is suitable for the analysis of slips of zinc-blend structure. In our method, the CNA is applied separately to sub-lattice of Si or C in the same SiC. By this method, structural changes are confirmed in a region with the shape of square pyramid when the pop-in behavior occurs. By measuring the atomic distances along the region of misalignment, it was confirmed that there is certainly atomic sliding by crystalline slip. Furthermore, it is found that, with increase of loading, dislocation loops spread along {1 1 1} slip planes.

DOI： 10.2474/trol.11.183

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：ELSEVIER SCIENCE BV  

The strength against fracture nucleation from an interface free-edge of silicon-nitride (SiN)/copper (Cu) micro-components is evaluated. A special technique that combines a nano-indenter specimen holder and an environmental transmission electron microscope (E-TEM) is employed. The critical load at the onset of fracture nucleation from a wedge-shaped free-edge (opening angle: 90 degrees) is measured both in a vacuum and in a hydrogen (H-2) environment, and the critical stress distribution is evaluated by the finite element method (FEM). It is found that the fracture nucleation is dominated by the near-edge elastic singular stress field that extends about a few tens of nanometers from the edge. The fracture nucleation strength expressed in terms of the stress intensity factor (K) is found to be eminently reduced in a H-2 environment. Copyright (C) 2016 The Authors. Published by Elsevier B.V.

DOI： 10.1016/j.prostr.2016.06.174

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Trans Tech Publications Ltd  

The strength against interfacial fracture initiation from a free-edge of Si/Cu micro-components was evaluated. The micro-scale cantilever specimens containing dissimilar interfaces were fabricated with a focused-ion-beam (FIB) technique, and they were loaded with a quantitative nanoindenter holder operated in a transmission electron microscope (TEM). The specimens were successfully fractured along the Si/Cu interface, and the critical loads at fracture were measured. The critical stress distribution near the free-edge was evaluated with the finite element method (FEM). The near-edge stress distributions of 90°/90°-shaped specimens were scattered while those of 135°/135°-shaped specimens were in good agreement despite the difference in specimen dimensions. Such a difference was discussed in terms of the relation between the magnitude of stress singularity and the microstructures of material.

DOI： 10.4028/www.scientific.net/KEM.665.169

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

<p>Recently, the fuel consumption improvement by weight saving is required in transportation machine. Therefore, Mg alloy is expected as the alternative material of Al alloy and resin material, because it is the lightest in the practical metals and its specific intensity is high. However, twin crystal deformation occurs easily, and there are the two kinds types (i.e. {10<span style="text-decoration: overline;">1</span>2} and {10<span style="text-decoration: overline;">1</span>1} twin crystal) in that deformation. It has been reported that the {10<span style="text-decoration: overline;">1</span>2} twin crystal has work to relax the stress concentration and the {10<span style="text-decoration: overline;">1</span>1} twin crystal has close relation to fracture. Our aim is to evaluate the kinds and the conditions of those types with AE method. In this study, Mg alloy AZ31 was used, and the AE signals of the alloy were detected in compression, tensile and CT test. After that, the analysis of those signals were done. From the results obtained under this experimental conditions, the following things became clear. (1) The frequency components near 250, 550 and 850 kHz are caused by slip, twin crystal deformation and crack growth respectively. (2) It is possible that the two kinds crystal deformation types are discriminated by the identification standards decided by the AE count and fractal dimension Fd of the detected signals.</p>

DOI： 10.1299/transjsme.16-00027

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

Magnesium alloy is the lightest material in all practical metals, and has the excellent mechanical properties. From such reasons, the alloy is noticed as the attractive material in various fields. However, the alloy has the weak points that are inferior for heat and corrosion resistance. Therefore, it will be possible to guarantee the safety security of structure parts, if the information on the fracture strain and life, etc. are evaluated by the signals detected from the alloy under those use environment. The three type specimens of the virgin, the heat history (<i>i.e.</i> repeatedly gave the heating to the virgin specimen) and the corrosion specimen (<i>i.e.</i> immersed the virgin specimen into solution) are prepared in this study. Then, the tensile test was carried out for each specimen, and the AE signals emitted in the testing were detected. Frequency and fractal dimension analysis were carried out in order to extract the features of those signals. From such analysis results, the feature extraction of the signal by the elasticity twin deformation was done, because that deformation participates in the degradation of mechanical properties. As the result, the following things became clear under the experimental condition in this study: The frequency component of the signals caused by that deformation is near 550 kHz. The fractal dimensions <i>Fd</i> of those signal show the value over 1.85. Then, it was examined whether the fracture strain is evaluated by the <i>Ib</i> value (Improved <i>b</i>-value) led from the frequency distribution of the <i>Fd</i>. As the result, the effectiveness of this method proposed under the experimental conditions in this study was confirmed. Therefore, the possibility for the prediction of that strain by the AE signal detected in elastic region was shown.

DOI： 10.1299/transjsme.14-00541

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

A6061-T6 alloy has been used in the liner material of high-pressure hydrogen gas storage container that is mounted on a fuel cell vehicle. The degradation of the properties such as strength, toughness and hydrogen embrittlement resistance, etc., has been pointed out, because the grain structure of the mouthpiece part of the liner becomes coarse in the manufacturing process. The tensile and fatigue test for the specimens with different grain size were done, and the detected AE signals during the testing were analyzed. In the tensile test, the characteristics of the signals on dislocation motion, transgranular and intergranular fracture were extracted. In the fatigue test, it was shown that the possibility of which the damage is evaluated by the spectral analysis that utilizes the slope of an approximation straight line in the both logarithmic scale display of FFT analysis result. Then we proposed the amplitude ratio R_v that is the parameter which divided the maximum amplitude of signal for intergranular fracture by that of detected signal, and the correlation between the grain size and the R_v was recognized. These proposed information are able to be utilized in order to evaluate the damage of the container.

DOI： 10.1299/transjsme.2014smm0292

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：HINDAWI PUBLISHING CORPORATION  

Fiber Bragg grating (FBG) is an optical fiber sensor and is suitable for acoustic emission (AE) measurements of structures such as chemical plants that require water resistance, explosion proofing, and so forth, However, directionality has been a problem in conventional usage which glues the grating range of an FBG to the inspection surface. This study proposes a cylinder-FBG (C-FBG) sensor with the FBG glued to a cylindrical sensor holder. Effectiveness of the sensor was evaluated by characterizing directionality and frequency sensitivity of the sensor and by comparing the detected AE signals in a 3-point bending test of a carbon fiber reinforced plastic (CFRP) laminate against a conventional wide-band piezoelectric AE sensor. The features of the detected signals were similar to the signals detected by the wide-band AE sensor. These results show that it is possible to produce a wide-band cylindrical sensor without the directionality limitations of the conventional usage of FBG.

DOI： 10.1155/2014/274071

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Language：Japanese   Publisher：The Japan Society for Precision Engineering  

DOI： 10.11522/pscjspe.2013A.0.559.0

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Materials Research Society  

Many industries have developed new materials as substitutes for lead in solid lubricants. For example, lead bronze, a Cu-Pb alloy that has been used for slide bearings, has been replaced by a Cu alloy containing sulfide. The development of Pb-free Cu alloys has received considerable attention recently. Pb and sulfide are types of solid lubricants
in particular, MoS 2(molybdenum disulfide) is a popular sulfide lubricant. This study focuses on a material that contains Cu2S. The properties of Cu 2S as a solid lubricant are unknown. First principles (FP) and molecular dynamics (MD) are used to clarify the lubrication mechanism of Cu 2S. The atomic-level stable structure of Cu2S is evaluated by FP under specific sliding conditions. The Cu2S lubrication mechanism is clarified by MD using the FP results for the interatomic potential functions. It is clarified that there is a specific slip system and the Cu-S bonds that exists above and below the layers of the slip system are very strong. © 2013 Materials Research Society.

DOI： 10.1557/opl.2013.563

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

The simple method to analyze atomistic strain in molecular dynamics (MD) simulation is studied. The proposed method, here called atomic strain measure (ASM), is based on Green-Lagrangian strain measure which is traditionally defined in continuum mechanics. The ASM is formulated for the use in atomic system with some adequate assumptions. In our formulation, pairwise interatomic vectors of finite length are approximately substituted for infinitesimal continuum line segments between material's points. The obtained expression of ASM is very simple and easy to use. The authors are checking the validity, limitation and usefulness of ASM by actual MD models of aluminum. A perfect-crystal model results in qualitatively good results for strain evaluation, as for the response to homogenous deformation. The ASM is also applied to a polycrystal model, which has a lot of inhomogeneous nanostructures, i.e. crystalline defects such as grain boundaries (GBs) and triple junctions (TJs) among them. It is confirmed that a certain concentration of strain onto the vicinity of GB plane or TJ point is able to be clearly captured by using ASM. It is concluded that approach of the present ASM analysis for atomic simulation is very effective to obtain change of nanostructure. © 2012 The Society of Materials Science, Japan.

DOI： 10.2472/jsms.61.162

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：AMER SOC MECHANICAL ENGINEERS  

The concept of micro-electro-mechanical systems (MEMS) sensors directly fabricated on a ceramic substrate, which can be used for a package of end product, was proposed. As demonstrations of the sensors directly fabricated on a ceramic package, an accelerometer and a magnetoresistive (MR) sensor are focused on, and their fabrications on a ceramic substrate is investigated. The accelerometer utilizes a fringe capacitance formed in a ferroelectric material. For this sensor, in stead of a previously used bulk PZT plate, a screen-printed BaTiO3 (BTO) film on a ceramic alumina substrate was herein employed. An accelerometer using a BTO film was practically fabricated. The sensitivity of it was estimated as 0.1 pF/g, which is degraded a little compare with the previously developed accelerometer using a PZT plate; however, the order is the same. The magnetoresistive (MR) sensor can detect not only x- and y-axes magnetic field intensities but also z-axis one, where all fields are based on the sensor coordinate system. Namely, not only azimuth but also angle of elevation of the sensor can be detected from triaxis components of geomagnetic field. The principle is as follows: a permalloy (FeNi) plate is stood aside MR element. The plate distorts magnetic field and generates x- (or y-) component from originally z-directional field. So, the resistance of MR element changes in proportional to z-axis field intensity, provided that other axes intensities are kept constant.

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

Multi-phase-field (MPF) method which is capable of using several phase-field variables is applied to simulate martensitic transition in micro-scale Ni-Ti shape-memory alloy (SMA). By modeling Ni-Ti SMA specimen in MPF simulation assuming only three major variants of martensite crystal in monoclinic structure, the detailed manner of forming martensite variants and interaction between them are observed. We adjust several free energy (densities) usually used for the phase-field functional to Ni-Ti SMA properties, e.g. chemical free energy, elastic strain energy, gradient energy, and double-well potential energy. Especially in the formulation of elastic strain energy, to express austenite (cubic)-to-martensite (monoclinic) transition of Ni-Ti alloy, microscopic parameter available from experimental result for lattice mismatch between austenite and martensite is brought into free energy functional. We discuss the different growth of martensite variants depending on initial condition for martensite nucleus, in which some arbitrary area in the computation domain is provided with random number. It is confirmed that a martensite variant with a positive lattice mismatch (i.e. the direction of larger edge in monoclinic unit) grows preferentially in the case of tensile loading in that direction. In compression, a variant with the most negative mismatch in the compressive direction grows strongly. The starting time of loading is sometimes a factor for the resulted variant structures. We found that, once a lamellae structure is formed, the relation between direction of further loading and that of lamellae interface plane dominates the resulted structural combination of variants. © 2011 The Japan Society of Mechanical Engineers.

DOI： 10.1299/kikaia.77.1320

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN SOC MECHANICAL ENGINEERS  

Inelastic deformation of gold (Au) atomic cluster is investigated by using molecular dynamics (MD) simulations. We performed compression and unloading tests in which silicon (Si) plates approach each other and push single Au cluster of 4 nm diameter in between. Possibility of super-elastic (hyper-elastic) behavior is first discussed in the present study. The potential function of embedded atom method is adopted inside Au cluster, whereas other interactions are formulated by simplified Lennard-Jones interaction. The cluster in MD simulation shows large recovery strain which is reversible in unloading process after compression. The recovery strain is estimated on average from 5 to 10%. It is found that there are deformation mechanisms depending on temperature of the cluster. Mechanism for low temperature is based on slip motion and that for high temperature is dominated by surface reconstruction. The strength of interaction energy between Si plate and the Au cluster which may cause pulling force and produce tensile state is investigated, referring to our AFM experiment.

DOI： 10.1299/jamdsm.4.405

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Molecular dynamics (MD) study of martensitic transformation (MT) in nickel and aluminum alloy is performed. The behavior focused on is transformation between crystalline structures from B2 cubic cell to body-centered tetragonal cell, which is simply realized by uniaxial tensile loading. The potential function used is Finnis-Sinclair type having only single energy minimum where B2 structure exists. The availability of this specific many-body potential for stress-induced MT phenomena under uniaxial loading is fully discussed. In MD simulations, martensite phase is induced by tensile stress or strain in the atomic system, as predicted by a potential energy map. It is understood that the characteristic of the potential energy function with regard to deformation is crucial for MT studies and investigating energy-strain or stress-strain map is worthwhile. The MT behavior in the atomic system occurs during a plateau region of stress-strain (S-S) curve of the whole specimen, that is typical for experimental superelastic or shape-memory alloys under uniaxial loading. It is found that, during each MT event large jump of atomic strain is observed. Owing to single energy minimum, the atomic system shows almost perfect recovery in S-S curve, where the graph comes completely back to initial state after unloaded. Besides, the present paper focuses on surface effect for MT behavior. Since the surface effect is dominant in MT phenomena especially in microscopic specimens, a novel computational scheme for stabilizing condition in which uniaxial loading is always applied together with arbitrary periodic boundary condition(s) is devised. By comparing one-, two-, and three-dimensional models under uniaxial loading, it is recognized that the nucleation behavior depends strongly on the existence of free surface region (including corner edge). When there is no surface, a chaotic nucleation of martensite is observed. On the other hand, the free surface induces first martensite because of less constraint in tensile deformation of unit cells. It is confirmed that the tendency toward MT nucleation corresponds to yield stress or strain of the specimen. In order to define and detect martensite structure as for each atom, an atomic strain measure (ASM) with our own formation is introduced. It is shown that the ASM is very effective to distinguish martensite bct unit structure from others. (C) 2009 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.commatsci.2009.04.025

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN INST METALS  

Plastic working of metals using severe plastic deformation (SPD) recently attracts interest of researchers, because it is a method that will improve the toughness as well as the strength just by applying enormously large strain oil the material. In this study, deformation, stress and strain of aluminum in ECAP (equal channel angular pressing) are analyzed computationally by using smoothed particle hydrodynamics (SPH) method which is one of particle methods. In addition to elastic-plastic constitutive relation, a newly developed theoretical framework in which grain refinement process is involved is proposed here. We try to implement the framework into the SPH computation. The main idea to conduct grain refinement in the material is that applied energy by plastic working causes continuous change in the total area of grain boundaries and averaged diameter in the material becomes smaller and smaller. The reasonable change can be observed by using such simple but theoretical framework. The present paper is focused on implication, formulation and possibility of the grain refinement model. [doi: 10.2320/matertrans.MD200814]

DOI： 10.2320/matertrans.MD200814

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE SA  

Ni-Ti thin films for micro actuators is the focus of intense research. Such films have precipitates with a unique micro-structure. By molecular dynamics simulation (MDS) using embedded-atom potentials, we construct nano-sized Ni-Ti model systems including plate shape precipitates. First, the energetics of such plate precipitates is evaluated. The simulations show that there is a lower energy precipitate which is actually observed in experimental studies. Second, uniaxial-tensile loading is conducted for the MDS model which contains the precipitate. For the relaxed state, the precipitate sufficiently matches the Ni-Ti parent phases at the interfaces, whereas during the loading, mismatch as well as nucleation of martensite occurs there. (C) 2007 Published by Elsevier B.V.

DOI： 10.1016/j.msea.2007.01.190

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

The mechanism of stress-induced amorphization and martensite transformation is analyzed at an atomic level by using molecular dynamics (MD). Calculation model for MD is made of Ni-Ti (B2 structure) alloy which has edge cracking. The framework of modified embedded atom method (MEAM) potential and its approximated expression are attempted to be adopted in order to reproduce amorphous structure. The pentagonal bipyramid which is used as one of noncrystalline models is focused on, and short-range order of amorphous is distinguished by detecting indices of (1551) and (1541) for bond pairs defined in CNA. Martensite phase (B19' structure) is distinguished by the analysis of lattice constants of primitive crystal unit. As a result, it is found that amorphous structure has concentrated on nearby crack. The change of shear component in stress tensor shows very similar trend for change of amorphization ratio defined here. On the other hand, the results show that tensile stress plays an important role in martensite transformation.

DOI： 10.1299/jsmemecjo.2008.1.0_11

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

Morphology and mechanical properties of atomic-cluster-assembled structures, which are generated from nanosize cluster of metallic atoms, are studied by using molecular dynamics with many-body interatomic potential. Generation of the structures is carried out by configuring copper clusters (made up of 683 atoms) in regular array with initial approaching velocities. It is confirmed that one-dimensional, two-dimensional, and three-dimensional structures can be designed and fabricated from clusters. Shape of the structures is largely dependent on initial velocities, that is, initial kinetic energy attributed to clusters. In two-dimensional model with low approaching velocity, some structures have voids and show large surface ratio. Subsequently, tensile test is conducted on the structures. By chucking two end regions and pulling them in opposite direction, tensile straining of the structures is carried out. Strain energy calculated from stress-strain curve over testing process can be used as an effective evaluation value for distinguishing ductile structures from brittle structures. On the other hand, tensile strength (maximum stress) does not have marked variation as to the shape of structures. It is found that, in two-dimensional structures, existence of voids enhances the brittleness. It is because, when the structure has void inside, stacking faults appear and disappear more easily than when the structure gets rid of void by clusters being packed closely. Strain rate, as another factor which may alter the mechanical properties, is diminished from that of principal result to smaller value, corresponding to tensile velocity from 100 m/s to 5 m/s. Though the tensile strength and strain energy are influenced slightly by strain rate, they are always low for the structure with voids.

DOI： 10.2472/jsms.55.746

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

Molecular dynamics simulation (MDS), using the embedded atom method for interatomic interactions, is performed to reveal the microscopic mechanism of stress-induced martensitic transformation of Ni - Ti alloys. Stress-induced martensitic transformation was observed for tensile simulation using four different strain rates. The relationship between stress and martensite ratio does not depend on the strain rate. Investigation of the results of MDS for the transformation pathway makes it clear that there are multiple pathways between the parent phase and the martensite phase regardless of the strain rate. Multiple pathways appear owing to differences in the relationship ( angle) between the tensile direction and the specific lattice lengths of the parent or martensite unit cell. Increase and decrease in the martensite ratio during tensile simulation varies according to the pathways, depending on the strain rate.

DOI： 10.1088/0965-0393/14/5/S05

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN INST METALS  

Microscopic mechanism of martensitic transformation in nickel (Ni)-titanium (Ti) alloy is investigated by molecular dynamics (MD) simulation using embedded atom method (EAM) potentials. The computational parallelepiped specimen with nano-size dimension is surrounded by Ti-terminated free surfaces and constrained regions for loading. The detection method of martensite phase is newly exploited. The crystalographic B19' monoclinic crystal form can be identified as martensite phase by checking up atomic lengths and angles of neighborhood and by comparing them with possible values of lattice parameters already proposed. In tensile loading, the specimen shows a kind of stress-induced transformation from parent phase (B2 structure) to martensite phase (B19' structure). Outbreak of martensitic transformation occurs immediately after stress reaches maximum value. In outbreak of martensite, distortion of unit structure is observed as an actual change in atomic coordinates. It is found that there are two major transformation paths both resulting in martensite structure, each of which has contrary sequence of changes in atomic length or angle. There is also the other route of atomic movement for completing martensitic transformation with relatively long-range atomic migration. The EAM potential used in the present study is discussed as to crystalline energies of periodic B2 or B19' unit structures. Dynamic energies in transformation are also obtained from MD results and they show that there are energy barriers in martensitic transforming. Static evaluation of energy, on the assumption of uniform transformation, is carried out and is compared with energy change obtained by MD method.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

The melting and softening behavior of nano-size silica (SiO) was studied using the molecular dynamics method. Energy supply was simulated by considering radiative heat transfer. The potential function of silica includes three-body interaction as well as two-body interaction. Initially, thermal treatment for making the amorphous state was performed for both thin film-type and sphere-type nano-size specimens. Then, pre-determined radiative energy, estimated by the spectroscopic concept of electromagnetic waves which are reflecting and refracting in the nano-size material, was applied to the specimen continuously. Depending on the temperature rise, each specimen exhibited softening or melting accompanied by dissociation of silicon oxide molecules. A change in the atomic structure was mainly recognized in the Si-O-Si bonding angle, which was effectively assessed using a novel parameter named the "B parameter". By using this "B parameter", both the strained state of SiO4 tetrahedra and their interconnection become obvious simultaneously. Regardless of the specimen shape, the coordination number and the "B parameter" have a certain relationship depending on the characteristic atomic-scale local structure of silica, such as SiO4, SiO3, or SiO2. It was found that a wide distribution of the "B parameter" for the Si-O-Si angle and increase in the distribution for the O-Si-O angle together indicate melting or softening of the nano-size silica. (C) 2004 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.commatsci.2004.06.003

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PROFESSIONAL ENGINEERING PUBLISHING LTD  

The atomic structure of grain boundaries generated in the process of coalescence between copper atom clusters is investigated using the molecular dynamics method. The effective medium theory is adopted as interatomic interaction for precise estimation of surface and defect energies. The effects of cluster size, velocity and crystalline orientation on the atomic behaviour are studied. When cluster size is relatively small, dislocations (detected as stacking faults) generated in the contact region develop throughout the cluster body. On the other hand, in larger-size clusters, stacking faults are multiple and they interact with each other inside clusters. The local atomic structure is effectively assessed by a topological method, by which atoms are recognized as a face-centred cubic (fee) structure or a hexagonal close-packed (hcp) structure. Large approaching velocity results in a flattened shape of clusters and induces complicated propagation of stacking faults, where the critical speed for this transition is estimated at 600-700 m/s approximately. When a slight orientation angle is applied to clusters, the difference in angle is cancelled by the spontaneous spin of clusters. However, when a large orientation mismatch is given to clusters, nucleation and growth of stacking faults are obstructed according to the Schmid factor of slip.

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

Appearance and subsequent behavior of lattice defects induced by coalescence between copper atom clusters are investigated by molecular dynamics method. Since mechanical properties of atomic-cluster-assembled structure are supposed to be largely dominated by interface phenomena, elementary knowledge on atomic rearrangement near the boundary is required. The Effective Medium Theory (EMT) is adopted as interatomic interaction of the present problem because of demand for sensitivity to surface energy and stacking fault energy. Main defects detected are stacking faults (SFs), i. e. planar spreading of local h. c. p. structures. Static energy of SF in the range of 30-90 mJ/m<SUP>2</SUP> is computed, which agrees well with experimental data. Transition in deformation mechanism of cluster is found by means of computational configuration, where approaching velocity between 0 K clusters varies from 20 to 1000m/s. In general, larger velocity results in flattened structure of clusters. High energy regime, where SF extends all over clusters, consumes kinetic energy at least 9-16 times as large as static energy of isolated SF. When slight orientation angle in-plane is applied to clusters before their adhering, the mismatch in angle is canceled by spontaneous rotation of clusters unless the orientation angle exceeds 15 degrees. On the other hand, larger difference in orientation angle prevents SF from occurring and moving. This degradation in amount of SF due to orientational mismatch is nicely predicted by considering Schmid factor, which is calculated from configuration of slip directions and clusters' approaching direction.

DOI： 10.1299/kikaia.70.183

CiNii Books

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Other Link： https://jlc.jst.go.jp/DN/JALC/00237187550?from=CiNii

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPRINGER  

Mechanical properties of unique-shaped nano materials called "atomic-cluster-assembled" structure are studied by using molecular dynamics (MD) simulation and adopting effective medium theory (EMT) potential function. First, copper clusters with stable globular shape are computationally arranged on 1-D, 2-D, or 3-D regular array in artificial manner and then their gathering behavior is observed. Piled-up clusters become one specimen, which is sometimes left with internal voids. It is found that morphology of the product is largely dependent on initial kinetic energy attached to clusters. Secondly, strength of the "atomic-cluster-assembled" structures is evaluated by tensile loading test. Analysis of tensile strength and strain energy shows that defects introduced at the generating process markedly alter the behavior of the structure in the breakage. Brittle fracture tends to occur when the specimen includes initial imperfection such as void structure between clusters.

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Language：Japanese   Publisher：The Visualization Society of Japan  

Atomic structure of gold nanowire with sub-nanometer diameter is investigated by interactive molecular dynamics (IMD). IMD is developed as original code using OpenGL graphics and computation of conventional molecular dynamics (MD) based on FS-type interatomic potential. Tensile testing of 7-3 type nanowire is performed, where comparison between results obtained by ordinary MD and by IMD is done. Necking before breakage is observed in both cases, but unique long one-dimensional atomic chain is realized by IMD more easily. This is owing to ability of delicate steering furnished by interactive simulation, which is realized conceptionally by exchange of physical information between simulator and computing system and technically by real-time visualization and easy-to-use device.

DOI： 10.3154/jvs.23.Supplement1_323

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科研費奨励研究

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Grant-in-Aid for Encouragement of Young Scientists 20030401-20030331

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Japan Society of Mechanical Engineers  

The heat transfer is enhanced in curved pipes by the secondary flow. Its stirring effect is expected to be more augmented in multiple pipe bends which form a coiled pipe with periodically canging the plane of curvature. Numerical investigations of flow and temperature field including the developing region in such a pipe are carried out in laminar flow regime using parabolized governing equations. The calculation method has been validated for coiled pipes. In multiple pipe bends, Coriolis force due to the change of curvature plane causes complicated secondary flow pattern, realizing more homogeneous mixing. In the case of high Prandtl number fluids, the heat transfer is more enhanced in multiple pipe bends compared with in ordinary coiled pipes. Meanwhile, this is not the case for low Prandtl number fluids. The mechanism which causes this opposite effect is also discussed.

DOI： 10.1299/kikaib.69.2664

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Japan Society of Mechanical Engineers  

The heat transfer is enhanced in curved pipes by the secondary flow. Its stirring effect is expected to be more augmented in multiple pipe bends which form a coiled pipe with periodically canging the plane of curvature. Numerical investigations of flow and temperature field including the developing region in such a pipe are carried out in laminar flow regime using parabolized governing equations. The calculation method has been validated for coiled pipes. In multiple pipe bends, Coriolis force due to the change of curvature plane causes complicated secondary flow pattern, realizing more homogeneous mixing. In the case of high Prandtl number fluids, the heat transfer is more enhanced in multiple pipe bends compared with in ordinary coiled pipes. Meanwhile, this is not the case for low Prandtl number fluids. The mechanism which causes this opposite effect is also discussed.

DOI： 10.1299/kikaib.69.2664

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：TRANS TECH PUBLICATIONS LTD  

Coalescence phenomena among copper clusters is investigated by using molecular dynamics method. The Effective Medium Theory (EMT) is adopted as interatomic interaction. When cluster size is relatively small, dislocations (or stacking fault) generated in contact region can develop through cluster body. In larger clusters, on the other hand, there remains partial dislocations chiefly near contact region, which is recognized as local transformation from f.c.c. structure into h.c.p. structure. A method of identifying local structure of atoms is effective and is confirmed to be effective to analysis of the boundary. It is also found that a lot of stacking faults are generated and flattened structure is obtained, when collision velocity exceeds some limit. When large orientation mismatch is given to clusters initially, development of stacking fault is obstructed.

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Japan Society of Mechanical Engineers  

The longitudinal heat transfer in capillary pipes is enhanced by fluid oscillation. The analytical solution to this phenomenon is obtained considering the wall thermal conductivities. Based on this solution, the effects of wall conductivity and thickness are investigated for the case of large amplitude of fluid motion. The longitudinal heat transfer through the fluid part is more enhanced with highly conductive thick pipes. This is because the radial region where the heat is transferred backward is smaller with these pipes. The direction of longitudinal heat transfer depends on the phase difference of temporal change between the velocity and temperature
whether it exceeds π/2, or not. From this point of view, the most effective wall to this problem is presented, where the wall temperature does not change preserving the mean temperature of the location during the oscillation.

DOI： 10.1299/kikaib.68.3439

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Japan Society of Mechanical Engineers  

The longitudinal heat transfer in capillary pipes is enhanced by fluid oscillation. The analytical solution to this phenomenon is obtained considering the wall thermal conductivities. Based on this solution, the effects of wall conductivity and thickness are investigated for the case of large amplitude of fluid motion. The longitudinal heat transfer through the fluid part is more enhanced with highly conductive thick pipes. This is because the radial region where the heat is transferred backward is smaller with these pipes. The direction of longitudinal heat transfer depends on the phase difference of temporal change between the velocity and temperature
whether it exceeds π/2, or not. From this point of view, the most effective wall to this problem is presented, where the wall temperature does not change preserving the mean temperature of the location during the oscillation.

DOI： 10.1299/kikaib.68.3439

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

Sintering process of copper atom clusters is investigated by multi-resolution molecular dynamics (MRMD) simulation. This MRMD method is constructed as combination between calculation of atomic motion in boundary regions being done by ordinary MD method and calculation of rigid body motion of clusters being done by another kind of equation. Two dimensional array of 683 copper atom-clusters is studied, and it is found that adequate reappearance of the behavior about translation, collision, coalescence, and oscillation of clusters is capable to be obtained by MRMD method with new algorithm in determination of MD region.

DOI： 10.1299/jsmezairiki.2002.0_67

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

Coalescence process of metallic atom clusters is studied by newly devised multi-resolution molecular dynamics (MRMD) method which combines ordinary molecular dynamics (MD) method with rigid body dynamics. Based on the concept that molecular or atomic motion is important and effective only in a surface region in which clusters are contacting, a set of equations of motion are derived from a single Lagrangian composed of whole variables in atomic system by using assumptions of rigid body motion according to accuracy required in each region. In simulation of two equivalent clusters' collision, comparison of MRMD results with ordinary MD results is made in respect to trajectories of cluster center, energies, and angular momentums. It is found that these methods produce coincident shapes and motions of cluster. Increase of kinetic energy obtained by using MRMD method when clusters coalesce, however, is smaller than that obtained by using ordinary MD method. It is also found that proper transmission of rotational motion in clusters' system can be possible by adopting a conservation scheme of angular momentum in rigid body dynamics. As a result, contraction of calculation time is realized by the MRMD method.

DOI： 10.1299/kikaia.68.210

CiNii Books

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Other Link： https://jlc.jst.go.jp/DN/JALC/00155463187?from=CiNii

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

The effect of the sectional shape of pipes on the enhancement of longitudinal heat transfer by fluid pulsation in pipe bundles has been investigated. Bundles of circular, triangular, square and hexagonal pipes are considered. Heat transfer characteristics of each pipe and the gross performance as a pipe bundle including the heat conduction in pipe walls, are discussed. The local distribution of longitudinal heat transfer in pipe section reveals the existence of a region where heat is transferred toward the higher temperature end when the pulsation frequency is sufficiently high. As a pipe bundle, only a circular one has narrow gaps among each three pipes, which deteriorate the gross performance of heat transfer. But in the case of the present investigation which assumes acrylic pipes of the same wall thickness, the circular pipe bundle is advantageous to other ones as for the global performance of longitudinal heat transfer including the wall thermal conduction, because the area ratio of pipe walls, whose low thermal conductivity lowers the performance, is least when the pipes are circular.

DOI： 10.1299/jsmeb.43.460

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Language：Japanese   Publisher：The Visualization Society of Japan  

Multi-resolution (MR) molecular dynamics (MD) method is developed for the investigation of nano-scale atomic cluster in collision and coalescence processes. Lennard-Jones interatomic potential for copper crystal is used. Equations of motion both for ordinary MD particles and for clusters treated as rigid bodies are derived from the same Lagrangian, and are solved simultaneously. It is found that ordinary MD regions and rigid body regions should be adequately bounded. To cope with this difficulty, interactive molecular dynamics method using computer graphics is adopted to MRMD algorithm for the selection of adequate MD region. In the interactive simulation, intentional shift of each atom or cluster is also possible. This enables one to set up various initial conditions of calculation and to simulate any possible physical process. It is recognized that real-time nature and interactivity are advantageous and vital to enhance the reality and familiarity in the atomic or molecular simulation. It is concluded that, for more efficient interactive visualization, graphics ability of computer is further required.

DOI： 10.3154/jvs.20.1Supplement_43

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Soc Mater Sci, Japan  

Coalescence process of copper nano-clusters is investigated by molecular dynamics simulation using inter-atomic interaction based on effective-medium theory. Stable atomic configuration at 0 K is determined for several spherical clusters and icosahedral structure composed of 13, 55, or 147 atoms is obtained. Excess energy of clusters averaged over approximated surface area is larger than that of a flat surface. Compressive stress and high atomic energy exist near center in small clusters. By interaction simulation between two equivalent clusters, in which they approach each other with some offset distance or some initial rotation motion and coalesce, it is found that rotation motion of the whole body is generated as a consequence and that rotational kinetic energy obtained after coalescence is affected by size of the original cluster and initial offset distance. Transition from translational kinetic energy to rotational kinetic energy completes in less than 1 picosecond. In clusters system composed of 1366 atoms, it is shown, by the analysis of coordination number or atomic configurations and trajectories, that compressive deformation in coalescence process becomes smaller with increasing initial offset distance. In the system with small number of atoms, lattice vibration is large and it is supposed that rearrangement of atomic structure is relatively easy.

DOI： 10.2472/jsms.49.263

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

In this paper, atomic migration near grain boundary of aluminum wiring line in micro-electronic device is analyzed by molecular dynamics (MD) simulation. Interatomic potential used is based on effective-medium theory (EMT). It is shown that junction point composed of grain boundary and surface is a region where active movement of atoms (atomic diffusion) appears. Under tensile loading, not only atomic diffusion but also slip between atomic layers (dislocation movement) is activated in the junction region. If there exists a certain constraint on the surface due to, for example, a passivation film attached on the aluminum line, atomic rearrangement near the junction changes remarkably. (C) 1999 Elsevier Science B.V. All rights reserved.

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Japan Society of Mechanical Engineers  

The enhancement of longitudinal heat transfer by means of fluid pulsation in pipe bundles has been investigated. Bundles of circular, triangular, square and hexagonal pipes are considered. Heat transfer characterisitics of each pipe and the gross performance as pipe bundles including the heat conductance in pipe walls are discussed. The distribution of the longitudinal heat transfer intensity across the pipe section reveals the existance of a region where heat is transferred toward the high temperature end when the pulsation frequency is high. Although the gaps between three circular pipes deteriorate the heat transfer characteristics by fluid in a circular pipe bundle, when acrylic pipes are assumed, the gross performance is the best with a circular pipe bundle, because the area ratio occupied by pipe wall in a cross-section, where the low thermal conductance deteriorates the performance, is least when the pipes are circular.

DOI： 10.1299/kikaib.65.2821

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN SOC MECHANICAL ENGINEERS  

Atomic diffusion near an aluminum grain boundary is analyzed in order to investigate the basic mechanism of stress-induced migration (SM) in a thin wiring line in LSI. Molecular dynamics based on effective-medium theory (EMT) is applied to a model consisting of a surface and Sigma=5[001] symmetrical tilt grain boundary with a bamboo-like structure. EMT is derived without any empirical knowledge and is known to be effective for analysis of an inhomogeneous atomic structure. Above the transition temperature from low-to high-temperature modes of SM, jump motion of atoms near the grain boundary occurs and the diffusion coefficients (DCs) which are estimated from the mean square displacement of atoms increase markedly. DC is largest in the region where the grain boundary intersects the surface. The magnitude of DC in the grain boundary region and its temperature dependence agree well with the results obtained by Plimpton and Wolf [Phys. Rev., B, Vol. 41, No. 5 (1990), p. 2712], who used several pair-wise interatomic potentials. It is proven that DC increases exponentially with tensile strain and decreases with compressive strain.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Characterization of Al Sigma = 5 tilt and twist grain boundaries are performed by means of molecular dynamics simulations based on DFT (density functional theory), EMT (effective medium theory) and EAM (embedded atom method) and effect of a Si precipitation into the grain boundary is examined. EMT gives more accurate estimation than EAM concerning the excess energy. A remarkable difference is observed for atomic structure between FP-MD and EMT in the case of tilt grain boundary. Precipitated Si-atom on the Sigma = 5 tilt grain boundary forms a hard structure which has a triangle shape. It brings about little effect on the grain boundary stiffness in the normal direction, but increases remarkably the shear resistance of the grain boundary.

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Society of Materials Science Japan  

Atomistic simulation of coincidence grain boundary (CSL grain boundary) on tensile strength is executed. Molecular dynamics based on the effective-medium theory (EMT) for aluminum which contains no empirical parameter is applied. For two tilt axes, which are chosen to be [100] and [110], the CSL grain boundary with ∑=5-41 and ∑=3-33, respectively, are investigated. The estimated grain boundary energy and the surface energy agree well with the previous studies. For the fracture energy estimated from tensile loading simulation, Griffith's criterion for brittle fracture gives the lower limit. And for ∑=3(A) and ∑=11(A) grain boundaries, which have extraordinarily small grain boundary energy, the amount of plastic work is several times larger than that for the other grain boundaries. It is also supposed that deformation constraint influences the brittleness and ductility of bicrystal enormously. And it is demonstrated that, when brittle fracture occurs, the effect of pre-existing grain boundary energy on the fracture strength becomes prominent.

DOI： 10.2472/jsms.46.238

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Japan Society of Mechanical Engineers  

Atomic diffusion near an aluminum grain boundary is analyzed in order to investigate a basic mechanism of stress-induced migration (SM) in a thin wiring line in LSI. Molecular dynamics which is based on the effective-medium theory (EMT) is applied to a model containing a surface and Σ=5[001] symmetrical tilt grain boundary with bamboo-like structure. EMT is constructed using no empirical knowledge and is known to be effective for analysis of inhomogeneous atomic structure. Above the transition temperature from low-to high-temperature modes of SM, jump motion of atoms near the grain boundary occurs and the diffusion coefficients (DC) which are estimated from the mean square displacement of atoms increase remarkably. DC has the largest value in the region where the grain boundary intersects the surface. The magnitude of DC in the grain boundary region and its temperature dependence agree well with the results obtained by Plimpton et al., who have used several pair-wise interatomic potentials. It is proven that DC increases with an exponential function of the tensile strain.

DOI： 10.1299/kikaia.62.2358

CiNii Books

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Other Link： https://jlc.jst.go.jp/DN/JALC/00042808916?from=CiNii

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

CiNii Books

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

CiNii Books

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

CiNii Books

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

CiNii Books

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

CiNii Books

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Language：English   Publisher：IOP PUBLISHING LTD  

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Language：Japanese   Publishing type：Book review, literature introduction, etc.   Publisher：Japan Society of Mechanical Engineers  

Ni-Ti alloy, one of well-known shape memory alloys, attracts attention by their functional advantages in thin films or their nanostructures. Stress induced martensitic transformation (SIMT) is recognized as a principal deformation mechanism, while its atomistic view on nucleation or prematensitic transformation is left unrevealed. Therefore, we computationally investigate microscopic mechanism of SIMT in Ni-Ti alloy using molecular dynamics simulation (MDS) with embedded atom metod (EAM) potential function. The Ni-Ti simulation model consisted of 19 404 atoms and surrounded by free surfaces is subjected to loading and unloading with appropriate structural relaxations. To identifying crystalline phase changes from B 2 (parent) to B 19′ (martensite) in the alloy under loading, we monitor lattice parameters, ratio of two lattice parameters, and their angles from instantaneous atomic positions. We define the martensite phase by specifying possible combination of the parameters according to literatures. In loading process, with rapid stress descent, the MDS model deforms and shows maximal ratio of martensite phase. We find that there are two major paths of atomic configurational change from H 2 to B 19′ in these martensite structures and there is also another kind of long-range atomic migration whose distance is larger than single lattice constant. The separation into these multiple paths is caused by discrepancy in angles between interatomic connecting line in unitcell and the tensile direction. It is also find that each paths have characteristic activation energies during configurational change (i.e. during phase transformation). It is ensured that SIMT is microscopically constructed by various types of structural changes and their energetics.

DOI： 10.1299/kikaia.72.232

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Language：Japanese   Publisher：Kansai University  

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Language：Japanese   Publisher：関西大学  

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Event date： 2019.12

Venue：Taipei, Taiwan  

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Event date： 2019.12

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Event date： 2019.12

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Event date： 2019.12

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Event date： 2019.12

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Event date： 2019.10

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Event date： 2019.10

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Event date： 2019.10

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Event date： 2019.10

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Event date： 2019.6

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Event date： 2019.3

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Event date： 2019.3

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Event date： 2018.12

Venue：京都大学宇治キャンパス, 宇治市  

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Event date： 2018.12

Venue：京都大学宇治キャンパス, 宇治市  

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Event date： 2018.12

Venue：京都大学宇治キャンパス, 宇治市  

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Event date： 2018.12

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Event date： 2018.11

Venue：産総研つくば,つくば市  

[学生優秀発表賞 受賞] 分子シミュレーション学会誌 アンサンブル, Vol.21,No.1(通巻85号),(2019-1), pp.75.

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Event date： 2018.11

Venue：産総研つくば,つくば市  

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Event date： 2018.11

Venue：Pilzen,Czech Rep.  

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Event date： 2018.10

Venue：Osaka, Japan  

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Event date： 2018.10

Venue：Osaka, Japan  

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Event date： 2018.10

Venue：Osaka, Japan  

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Event date： 2018.10

Venue：Osaka, Japan  

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Event date： 2018.10

Venue：Osaka, Japan  

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Event date： 2018.7

Venue：NewYork, U.S.A.  

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Event date： 2018.6

Venue：Melbourne, Australia  

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Event date： 2018.6

Venue：Melbourne, Australia  

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