材料
Online ISSN : 1880-7488
Print ISSN : 0514-5163
ISSN-L : 0514-5163
最新号
選択された号の論文の17件中1~17を表示しています
論文
  • 塩谷 光平, 新山 友暁, 下川 智嗣
    2024 年 73 巻 2 号 p. 101-108
    発行日: 2024/02/15
    公開日: 2024/02/20
    ジャーナル フリー

    High-entropy alloys (HEAs) are multicomponent alloys composed of five or more than five elements with near equimolar concentrations. In this study, molecular dynamics (MD) simulations of grain boundary (GB) migration in HEAs were performed in order to systematically investigate the concentration dependence of the constituent elements on its migration behavior. We found that the driving force required for GB migration in the model HEAs reaches the maximum when the GB migration becomes intermittent or the velocity reduces. The maximum driving force is achieved at the maximum degree of GB segregation, showing that GB segregation, which can be controlled by the element composition in the HEAs, strongly affects the GB migration behavior such as the required force for the migration and the velocity. Our study indicates that the element composition in HEAs plays an important role in determining the GB migration behavior and the obtained results contribute to designing the HEAs with superior mechanical properties.

  • 藤本 一郎, 岡山 竜也, 松本 龍介
    2024 年 73 巻 2 号 p. 109-114
    発行日: 2024/02/15
    公開日: 2024/02/20
    ジャーナル フリー

    It is well known that carbon addition enhances the strength of steel, but it also increases the sensitivity to delayed fracture. The origin of increased sensitivity to delayed fracture at a higher carbon content is not clarified yet. In this report, high-strength steels with different carbon contents were fabricated, and their delayed fracture properties were firstly evaluated. As the amount of carbon in the material increased, the amount of carbon concentration at the grain boundaries and the dislocation density also increased, and the material became more sensitive to delayed fracture. Then, a grain boundary (GB) model was created based on the samples used in the experiments, and the hydrogen effect on the cohesive energy of GB was evaluated using first principles calculations. The cohesive energy without carbon atoms was 3.47 J/m2 in the presence of hydrogen, while it with one additional carbon atom was 3.70 J/m2. This result was inconsistent to the experiment. Therefore, based on the results of dislocation density measurements, we assumed that more vacancies are generated in materials with a higher carbon content. By adding vacancy at GB, the cohesive energy decreased to 1.79 J/m2, and showed the same tendency as in the experiment. This suggests that not only hydrogen and carbon, but also vacancies, are responsible for the decrease in delayed fracture resistance.

  • 久保 淳, 河合 江美, 梅野 宜崇
    2024 年 73 巻 2 号 p. 115-120
    発行日: 2024/02/15
    公開日: 2024/02/20
    ジャーナル フリー

    In this study, we carried out molecular dynamics simulations of fatigue of single-crystal copper nanowires for the purpose of revealing the fatigue mechanisms of metal nanowires. We examined four nanowire models with different crystal orientations to investigate the effect of the single- and multi-slip deformation. Cyclic tension and compression were applied to the nanowire models. As a result, we observed that atomic vacancies were formed by dislocation motion during cyclic deformation. We found two types of the vacancy formation mechanisms, i.e., motion of a jogged screw dislocation and intersection of two stacking faults in different slip systems, which are the possible causes of fatigue in nanomaterials.

  • 河合 江美, 久保 淳, 梅野 宜崇
    2024 年 73 巻 2 号 p. 121-128
    発行日: 2024/02/15
    公開日: 2024/02/20
    ジャーナル フリー

    The purpose of this study is to quantitatively evaluate the effect of three factors (Factor-1: Surface of nanoscale materials, Factor-2: Atomistic structure of surfaces, and Factor-3: Normal stress on active slip planes) on critical resolved shear stress (CRSS) of dislocation nucleation in nanoscale materials. We conducted atomistic simulations of tensile or compressive deformation for copper single-crystal nanowire models with different surface structure by varying the cross-section shape and crystal orientation. In all models, stacking faults occurred at the dislocation nucleation. Thus, we discussed the effect of the three factors on CRSS of the nanowire models by considering with the ideal shear strength along the Burgers vector of the partial dislocation under the effect of normal stress. The reduction of the ideal strength due to the presence of surfaces was estimated to be about 30 %. Our analyses revealed that CRSS in most of the models can be explained by considering Factor-1 and Factor-3 alone. CRSS in the other models much deviated (-20 ~ +200 %) from the projection by Factor-1 and Factor-3, suggesting that Factor-2 can play a major role in some cases.

  • 鈴土 知明, 海老原 健一, 都留 智仁, 森 英喜
    2024 年 73 巻 2 号 p. 129-135
    発行日: 2024/02/15
    公開日: 2024/02/20
    ジャーナル フリー

    It is well known that body-centered cubic (bcc) transition metals such as α-Fe become brittle below the ductile to brittle transition temperature (DBTT). Although the fracture occurs on a macroscopic scale, it consists of a series of interatomic bond breaking events; therefore, accurate atomistic modeling is critical to understanding this phenomenon. In this work, atomistic simulations of curved crack fronts of α-Fe were performed using an interatomic potential generated by a machine learning technique. For this purpose, large simulation boxes consisting of ∼26 million atoms were used. We obtained evidence that the cleavage plane is {100}, and the cleavages are accompanied by crack tip plasticity at elevated temperature.

  • 森 英喜
    2024 年 73 巻 2 号 p. 136-140
    発行日: 2024/02/15
    公開日: 2024/02/20
    ジャーナル フリー

    Accurate investigation of the energetics of screw dislocation in body-centered cubic iron is important for strength evaluation of steel materials. For accurate atomic modeling of screw dislocations due to the long-range elastic interac-tions produced by dislocations, it is important to establish atomic models and boundary conditions. Recently, Helicoidal Boundary Conditions (HBCs), a new treatment of boundary conditions for screw dislocations in cubic metal, have been proposed by Savvidi et al. In this study, we implemented HBCs in LAMMPS as fix function. We also investigated the energetics of screw dislocations in BCC iron under HBCs. The Peierls barrier and Peierls stress predicted by our developed artificial neural network potential are 36.9 meV/b and 1440MPa, where b in magnitude of Burgers vector, respectively. These results are consistent with previous studies and allow us to confirm the advantages of HBCs.

  • 岩崎 富生, 坪内 繁貴, 浅利 裕介, 磯部 隆史, 黒川 麗, 青木 大輔
    2024 年 73 巻 2 号 p. 141-148
    発行日: 2024/02/15
    公開日: 2024/02/20
    ジャーナル フリー

    Polylactic acid (PLA) resin has been attracting more and more attention because it is not only a biomass-based carbon-neutral material, which does not increase CO2 emission, but also an eco-friendly biodegradable plastic, although the mechanical strength and biodegradability of PLA is not very high. So, by using Chemicals Informatics (CI) based on public literature data, additives effective for improving the mechanical strength and biodegradability of the PLA resin were explored in order to make the PLA resin available for wider use. As a result, adipic acid and 3,3'-dithiodipropionic acid were discovered as effective additives. To clarify the mechanism that improves the mechanical strength and biodegradability with these additives, molecular simulations were conducted. As a result of the simulation, it was found that the lattice matching between PLA and the additives (adipic acid and 3,3'-dithiodipropionic acid) is very good and that this lattice matching increases adhesion between PLA and the additives and improves the mechanical strength. It was also found that the lattice matching constructs the diffusion path of water molecules and enhances the hydrolysis, which accelerates the biodegradability. The effects of the additives were confirmed by tensile testing and hydrolysis tests.

  • Tomio IWASAKI, Yosuke KAWAHITO
    2024 年 73 巻 2 号 p. 149-156
    発行日: 2024/02/15
    公開日: 2024/02/20
    ジャーナル フリー

    The adhesion strength and wettability at the interfaces between a polyetheretherketone (PEEK) resin and titanium dioxide (TiO2), which have become more important for direct joining of PEEK resin and titanium (Ti), is investigated by using molecular simulations. Especially, the dependence of the adhesion strength and wettability on crystal orientations of rutile TiO2 were investigated to realize strong joint between the PEEK resin and TiO2. By putting a PEEK-resin sphere on a rutile TiO2 surface and by heating the system to 650 K, the contact angles at the interfaces were calculated to evaluate the wettability. After the system is cooled to 300 K from 650 K, the adhesive fracture energy is calculated to evaluate the adhesion strength. The results of the contact angles showed that PEEK resin on the TiO2(100) and that on the TiO2(001) surface have low wettability with large contact angles. On the other hand, PEEK resin on the TiO2(110) surface has high wettability with a small contact angle. The results of the adhesive fracture energies showed that the adhesion at the PEEK-resin/TiO2(100) and PEEK-resin/TiO2(001) interfaces are weak. On the other hand, the adhesion at the PEEK-resin/TiO2(110) interface is strong. To clarify the reason that the higher wettability and higher adhesion strength are obtained at the PEEK/TiO2(110) interface, atomic configurations were visualized. The atomic configuration showed that the lattice-matched coherent interface is realized and the surface atomic density is high only at the PEEK/TiO2(110) interface. Therefore, the lattice matching and the high surface atomic density at the PEEK/TiO2(001) interface are considered to be dominant factors in the high wettability and strong adhesion. The experimental results show that the wettability and critical load of scratch tests increase in the order: PEEK/TiO2(100)< PEEK/TiO2(001)<< PEEK/TiO2(110).

論文
  • 上杉 徳照, 大倉 直也, 中島 智晴, 小川 耕平, 堤 親平, 澤田 健二, 中本 光二
    2024 年 73 巻 2 号 p. 157-164
    発行日: 2024/02/15
    公開日: 2024/02/20
    ジャーナル フリー

    Due to the complexity and variations in defects, surface inspection of casting relies on human vision. However, this approach becomes unstable due to human fatigue. Additionally, the lack of a standardized communication method for surface inspection criteria impedes accurate quantification. With recent advancements in machine learning and artificial intelligence, specifically with deep learning and Convolution Neural Networks (CNN), the automation of the surface inspection for castings is becoming feasible. We have developed an image analysis method based on deep learning to automate the inspection of the cast surfaces of ductile cast iron pipes. Ductile cast iron pipe is a crucial component in social infrastructure, and we must identify defective products reliably. To reliably identify defective products, it is imperative to merge quantitative grade regression with the classification of defects, ensuring no flaws are overlooked. Images of the cast surfaces underwent preprocessing and data augmentation before being input into the CNN. We compared twelve pre-trained CNN architectures based on ImageNet, eventually utilizing fine-tuned DenseNet201. For grade regression and defect classification, we proposed an ensemble learning approach, integrating a weighted average of the regressor and classifier with weighted cross-entropy as the loss function. By adjusting the weights in the proposed method, we attained grade regression while maintaining a 100% recall rate for defect classification.

  • 河村 力, 森田 泰博, 深堀 貢, 本田 正徳, 荒川 仁太, 曙 紘之, 菅田 淳
    2024 年 73 巻 2 号 p. 165-171
    発行日: 2024/02/15
    公開日: 2024/02/20
    ジャーナル フリー

    Injection molded composites, which are increasingly being applied to automobiles, have a distribution of fiber orientation within the part, making it difficult to ensure the accuracy of structural analysis. In particular, it is necessary to correctly predict edge stresses in order to predict bending strength properties. To this end, we proposed in a previous report a coupled forming and structural analysis method that can account for heterogeneity in fiber orientation in the thickness direction, and demonstrated its superiority in three-point bending of a flat plate in the out-of-plane direction. However, we have not been able to verify the accuracy of the analysis for in-plane direction loading or the accuracy when the orientation is uniform in the plate thickness direction. Therefore, the validity of this method was verified on an H-shaped material intended for automotive parts. Talbot-Law imaging and micro X-ray CT imaging were used to ensure the accuracy of the fiber orientation tensor of the entire structure and the flange ends, and then coupled analysis was performed. The analysis error of the conventional method for both maximum generated load and rupture displacement was around 30%, whereas the new method was within 4%, confirming its significance.

  • 和田 英男, 扶川 泰斗, 廣芝 伸哉, 小池 一歩, 河原 正美
    2024 年 73 巻 2 号 p. 172-177
    発行日: 2024/02/15
    公開日: 2024/02/20
    ジャーナル フリー

    The metal-organic decomposition (MOD) method is a promising method for the deposition of VO2 thin films, which are expected to be used as material for smart window. However, a serious problem for such applications is that the minimum baking temperature in the previous study is 580℃ under nitrogen (N2) atmosphere, which exceeds the softening point of soda glass of ~500℃. In this study, we successfully reduced the baking temperature to 450℃ for forming polycrystalline VO2 thin films on glass substrates in N2 atmosphere added with 4% H2. When the transmittance of VO2 thin films between the visible and near-infrared regions around the phase transition temperature was measured with a spectrophotometer, maximum values of the average transmittance at 90℃ between 400 and 800 nm was 54.4% and the maximum dimming rate for transmittance change at 1600 nm was 36.8%. Furthermore, the substitutional doping of Nb ions effectively lowered the phase transition temperature from 68℃ to 49℃ at the baking temperature of 450℃.

  • 川上 瑞人, 原田 幸弘, 朝日 重雄, 喜多 隆
    2024 年 73 巻 2 号 p. 178-182
    発行日: 2024/02/15
    公開日: 2024/02/20
    ジャーナル フリー

    We theoretically studied the electron density dependence of the electric field enhancement effect caused by the localized surface plasmon resonance in heavily-doped InAs/GaAs quantum dots (QDs). The resonant wavelength of the field enhancement factor in spherical and semi-ellipsoid QDs shows a shift toward shorter wavelengths with increasing the electron density at mid-to-near infrared wavelengths. Semi-ellipsoid QDs have a resonance at a longer wavelength than spherical QDs and show stronger electric field enhancement. Furthermore, the multiple resonant wavelengths appear in semi-ellipsoid InAs/GaAs QDs due to the lowered symmetry, which is promising for the electric field enhancement at the infrared wavelength for increasing the energy conversion efficiency of photovoltaics.

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