Mechanical Engineering Journal
Online ISSN : 2187-9745
ISSN-L : 2187-9745
Volume 11, Issue 1
Displaying 1-8 of 8 articles from this issue
Solid Mechanics and Materials Engineering (Original Paper)
  • Chaohai LIU, Atsushi IWASAKI, Weimin LIN
    2024 Volume 11 Issue 1 Pages 23-00256
    Published: 2024
    Released on J-STAGE: February 15, 2024
    Advance online publication: December 22, 2023
    JOURNAL OPEN ACCESS

    The objective of the current study is to investigate the mechanical properties of the 180° bending edge of a hot-dip galvanized steel panel with a flat surface edge (as the JISG3302 stander). Our study investigated the relationship between hardness and strain at the cross-section of the panel through numerical simulations. Hardness tests are carried out on the machined cross-sections of the panel, subsequently further hardness and strain conversion equations (based on the ASTM-E140.19(2013) standard), The hardness and strain tests offer valuable insights into the materials’ deformation resistance and its capacity to withstand external loads. The results obtained from these tests, including the hardness and strain values, can be used to develop conversion equations that facilitate the evaluation of the hemmed panel's strength with respect to the metal material used. In addition, the strain results are compared with the numerically simulated strain results (utilized DEFORM Ver.11) to provide a basis for subsequent simulation works. This approach allows for a more comprehensive understanding of the mechanical properties of the cross-section panel and could also validate simulation results: on the reliability and accuracy of the hardness test work. Consequently, this approach allows to predict the behavior of panel material under specific loading conditions in the hemming process. which can be of utmost importance in industrial applications.

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  • Yiji YE, Masakazu ICHIMIYA, Naoto KASAHARA, Yukio TAKAHASHI
    2024 Volume 11 Issue 1 Pages 23-00491
    Published: 2024
    Released on J-STAGE: February 15, 2024
    Advance online publication: January 10, 2024
    JOURNAL OPEN ACCESS

    Buckling is a critical failure mode of the Fast Reactor Main Vessel (FRMV) subjected to seismic load. Post-buckling stability of FRMV is a crucial safety issue during excessive earthquakes. Our prior study revealed that global response becomes stable after buckling by phase-inverse mechanism. However, local fatigue cracks can initiate, penetrate and propagate under cyclic load. In the present study, shaking table experiments using cylindrical models are carried out. The post-buckling crack propagation process is experimentally observed and its mechanism is analyzed. It is shown that dominant cracks always propagate in circumference direction along the diagonal of the diamond-shape buckling dimple. Rapid collapse due to unstable crack propagation never occurs. Instead, a stable propagation mode is observed, where crack growth rate declines with crack circumferential angle. This stability is owing to the displacement-controlled characteristic of dynamic load, which results from the increasing frequency ratio due to crack propagation. Furthermore, a simplified evaluation method based on the estimation of J-integral under displacement-controlled condition is applied to predict the crack growth rate. The comparison with experimental data shows a satisfactory agreement. As a complementary study on global stability of FRMV, the present study confirms a local stability mechanism after buckling, contributing to a more comprehensive understanding on the post-buckling behavior of FRMV.

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  • Satoshi FUJII, Masaru OGAWA
    2024 Volume 11 Issue 1 Pages 23-00546
    Published: 2024
    Released on J-STAGE: February 15, 2024
    Advance online publication: February 03, 2024
    JOURNAL OPEN ACCESS

    In mechanical structures exposed to high temperatures, such as turbine blades for power generation, cracks are detected during in-service inspections. However, there is a risk of fracture owing to the relatively rapid rate of crack propagation, even when a large safety factor is in force. Therefore, a technique is required to estimate the creep-strain distribution before crack initiation and to predict the remaining service life. An inverse analysis method, based on the eigenstrain methodology, has been proposed to estimate the three-dimensional creep-strain distribution using non-destructively measured surface displacements. Three-dimensional creep-strain distributions can be estimated even when the relationship between the creep strain and displacement is non-linear. Through iterative calculations, this method converges to a solution with relatively high estimation accuracy, however, a method for estimating actual complex creep-strain distributions is needed. In this study, a method was proposed to improve the convergence of the iterative calculations. Its effectiveness was demonstrated by numerical analysis using a torsional geometry model that could be used to describe an actual turbine blade. Many unknown values were assumed so that relatively complex creep-strain distributions could be estimated. Convergence calculations were performed to improve the estimation accuracy through iterative calculations, even when displacement measurement errors were considered. The estimation accuracy was improved by using more actual measurements in the inverse analysis.

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Dynamics & Control, Robotics & Mechatronics (Original Paper)
  • Yoshihisa TAKAYAMA, Shinya KIJIMOTO, Satoshi ISHIKAWA
    2024 Volume 11 Issue 1 Pages 23-00207
    Published: 2024
    Released on J-STAGE: February 15, 2024
    Advance online publication: February 02, 2024
    JOURNAL OPEN ACCESS

    In a parallel-motion-type eddy current damper comprising a magnet and conducting plate, the magnet is assumed stationary, and the conductor moves parallel to the xy-plane of a static coordinate system O-xyz. In a previous study, we proved that when an arbitrarily dimensioned rectangular magnet and conductor are symmetrically positioned along both the x- and y- axes at an instant, the condition that “the gradient of scalar potential is zero” (GSPZ condition) is established throughout the conductor in a stationary-conductor coordinate system. For an eddy current damper comprising a ring magnet and conducting disk, the equations of the magnetic vector potential and scalar potential are different from those for an eddy current damper comprising a rectangular magnet and conductor. In this study, we verified whether the GSPZ condition can be applied to an eddy current damper comprising a ring magnet and conducting disk. First, using the three-dimensional finite element method (3D-FEM), we analyzed the eddy current distribution in an eddy current damper comprising a single ring magnet and conducting disk, and we found that the GSPZ condition is valid for an arbitrary diameter of the conducting disk. Second, we verified that the GSPZ condition can be applied to an eddy current damper comprising a combination of ring magnets with oppositely aligned magnetic poles and two conducting disks with arbitrary diameters. Third, we calculated the magnetic damping forces of both eddy current dampers using Fleming’s left-hand rule under the GSPZ condition (GSPZ-A method), and the results were in good agreement with those obtained using the 3D-FEM.

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Dynamics & Control, Robotics & Mechatronics (Selected Paper)
  • Sunao TOMITA, Tomohiko JIMBO
    2024 Volume 11 Issue 1 Pages 23-00513
    Published: 2024
    Released on J-STAGE: February 15, 2024
    Advance online publication: January 05, 2024
    JOURNAL OPEN ACCESS

    Modal parameters such as natural frequencies, modal shapes, and the damping ratio are useful to understand structural dynamics of mechanical systems. Modal parameters need to be estimated under operational conditions for use in structural health monitoring. Therefore, operational modal analysis (OMA) without input signals has been proposed to easily extract modal parameters under operational conditions. Recently, OMA for under-determined systems with more active modes than measurement outputs has been investigated to reduce the number of sensors. This study proposes the OMA framework for under-determined systems based on Bayesian CP (CANDECOMP/PARAFAC) decomposition of second-order statistical data. The proposed method enables us to extract the modal parameters from under-determined systems without tuning the number of active modes, because the rank of the tensor data corresponding to the number of active modes is automatically determined via Bayesian inference. The effectiveness of this method is demonstrated using artificial vibration data of a mass-spring system under operational and under-determined conditions.

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Design, Machine Element & Tribology, Information & Intelligent Technology, Manufacturing, and Systems (Selected Paper)
  • Takuya SEMBA, Yoshifumi AMAMOTO, Hitoshi SUMIYA
    2024 Volume 11 Issue 1 Pages 23-00427
    Published: 2024
    Released on J-STAGE: February 15, 2024
    Advance online publication: February 13, 2024
    JOURNAL OPEN ACCESS

    Dry etching with oxygen plasma was performed on a single-point cutting tool composed of nano-polycrystalline diamond to elucidate the shapeable cutting-edge radius (CER). The tool's CER was measured using an atomic force microscope employing a cantilever made of single-crystal silicon with a tetrahedral shape and a probe tip radius ranging from 4 to 10 nm. The determination of the actual CER involved subtracting the fixed probe tip radius from the measured CER. The dry-etching test results demonstrated a continuous decrease in the measured CER, ultimately converging to a constant value equivalent to the probe tip radius as etching time increased. This phenomenon was utilized to fabricate a standard tool suitable for calibrating the probe tip radius, ensuring a CER and its variation within 0.1 nm. Calibration using the standard tool enabled the identification of the actual CER from the measured values. Notably, the actual CER converged to less than 0.1 nm, with the variation in the converged CER remaining under 0.5 nm. Thus, the shaped actual CER achievable through dry etching with oxygen plasma was less than 0.5 nm.

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Bio, Medical, Sports and Human Engineering (Original Paper)
  • Yang LI, Siying LONG, Tatsuro TERAKAWA, Hirotaka FUJITA, Masaharu KOMO ...
    2024 Volume 11 Issue 1 Pages 23-00547
    Published: 2024
    Released on J-STAGE: February 15, 2024
    Advance online publication: February 05, 2024
    JOURNAL OPEN ACCESS

    The range of motion of the human lower limbs is comparable to that of the upper limbs, which suggests the feasibility of controlling a device with multiple degrees of freedom using the lower limbs. If this can be achieved, it could lead to an extension of human capabilities. In order to ensure accurate control using the user’s feet, it is important to understand the characteristics of foot motions, especially those of the exerted force. This study experimentally investigates the force characteristics of the foot using an isometric device that can measure the exerted force. The experimental results show when intending to exert forward-directed force, downward force is also generated. Additionally, we revealed that when intending to exert downward or sideways forces, forces in other directions also become prominent. Considering the fundamental motion characteristics of the lower limbs, we proposed an operation system and conducted experiments in a virtual space. A method based on conversion equations is proposed to compensate for the unintended force. An experimental comparison of the proposed method and the conventional method shows that the proposed method leads to significant improvements in the clear time, operation path length, and deviation from the ideal path, verifying its effectiveness. Especially during the main stages of the operation, the proposed method allowed for more accurate control, with a maximum enhancement of 16% in accuracy.

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Environmental and Process Engineering, Safety (Original Paper)
  • Yoshiki MAKIHIRA, Yukihiko OKUMURA
    2024 Volume 11 Issue 1 Pages 23-00523
    Published: 2024
    Released on J-STAGE: February 15, 2024
    Advance online publication: February 05, 2024
    JOURNAL OPEN ACCESS

    Measures to prevent the spread of COVID-19 are critical across the globe. A tour bus can carry passengers; however, the small, closed space becomes congested owing to their presence for long periods. Therefore, there is an increased risk of infection on tour buses. The air outlet of the air conditioner in a tour bus was designed to prioritize heating and cooling over ventilation. This study aims to improve the ventilation performance of tour buses. Therefore, a large-scale ventilation simulation was performed using a supercomputer. The results are as follows: (1) when the overall air flow rate of the ventilation is fixed, new outlets must be installed in the upper rear part of the tour bus for rapid ventilation; and (2) the ventilation efficiency was higher when a few high-output outlets were installed instead of several low-output outlets. The reason for the more effective ventilation was to create a large airflow in the tour bus. We proposed the design of a highly efficient ventilation system in an existing bus space and elucidated the appropriate layout of ventilation outlets and the optimal protocol for opening windows.

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