Mechanical Engineering Journal
Online ISSN : 2187-9745
ISSN-L : 2187-9745
Advance online publication
Displaying 1-7 of 7 articles from this issue
  • Naoki MORITA, Tomoya TAKAHASHI, Tetsuya MATSUDA, Masahito UEDA, Tomohi ...
    Article ID: 24-00013
    Published: 2024
    Advance online publication: May 23, 2024
    JOURNAL OPEN ACCESS ADVANCE PUBLICATION

    In this study, a parallel three-scale homogenization analysis simulator that accounts for macro-, meso-, and micro-scale structures was developed for the carbon-fiber-reinforced plastics (CFRPs) used in high-pressure hydrogen storage vessels manufactured using the filament winding (FW) method. The developed simulator enables detailed analysis that accounts for fiber irregularities in the fiber bundle tapes of FW-CFRP. Because numerical simulations that consider fiber irregularities increase computational time and memory usage, we developed a parallel computation system for three-scale homogenization using the domain decomposition method. Numerical examples using large-scale computers verified that our parallel three-scale homogenization analysis has parallel computing performance close to the ideal acceleration ratio. We then investigated the effects of fiber waviness in fiber bundle tapes on the macro-scale properties of FW–CFRP by considering waviness as an initial irregularity in the carbon fiber arrangement. Our analysis of fiber irregularities revealed that fiber waviness has a significant effect on macroscopic stiffness and stress. Within the scope of this study, the macroscopic stiffness and stress were reduced by 40% and 57%, respectively, compared to the results without irregularities.

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  • Jiajun HONG, Takuya YOSHIMURA
    Article ID: 23-00007
    Published: 2024
    Advance online publication: May 01, 2024
    JOURNAL OPEN ACCESS ADVANCE PUBLICATION

    This work investigates the availability of the baseline approach proposed in the previous researches, and expands the applicability of the method for noise and vibration optimization. Based on the s-plane extension theory, baseline was formed by introducing a virtual damping in the transfer function calculation formula. Sensitivity analysis based on baseline was conducted to predict the changing tendency by structure modification in the target frequency range. The validity of the proposed method is examined through numerical simulation with two finite element (FE) models. A simple hollow rectangular parallelepiped model was constructed for confirming the effect of baseline sensitivity analysis as a structural vibration reduction treatment. And a vehicle frame-panel structure was constructed for confirming the proposed method as a noise optimization example. In view of the model in discussion, the sum of squares sensitivity or root-mean-square sensitivity was calculated to determine the mass attachment location. The conventional sensitivity values using FRFs without virtual damping(FRF method) were also calculated for comparing with baseline sensitivity results. The FE models with mass attachment based on sensitivity analysis results were calculated for confirming the vibration reduction effects. The result shows that FRF method has a greater decrease at some single peak in the target frequency range, while the baseline method has a better reduction performance at multiple peaks in the target frequency range. The selection strategies of the two methods for the mass attachment location and the change of mode shape after mass attachment were discussed. The baseline sensitivity method presented in this study provides a feasible approach for noise and vibration performance improvement in the medium frequency band.

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  • Chihaya HOSHIKAWA, Akinori YOSHIMURA, Keita GOTO, Masahiro ARAI
    Article ID: 24-00012
    Published: 2024
    Advance online publication: April 24, 2024
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    Progressive damage behavior of woven composite structure is simulated, based on decoupled multi-scale damage analysis to consider microscopic woven structure. Since woven composites have complex microstructure, it is difficult to predict their damage behavior by only experimental approaches. Evaluating damage process is important for the assessment of safety, and numerical method of simulating damage behavior is demanded. In this paper, decoupled multi-scale analysis method was adopted. The constitutive law used in analysis of structural member scale (macroscopic scale) was identified by analysis of weave-structure scale (microscopic scale) and two-scale simultaneous analyses are no longer necessary. In microscopic scale, representative unit cell (RUC) of woven structure was considered, and in-plane periodicity was assumed to reflect inhomogeneity caused by woven structure. Microscopic analysis was carried out to identify the constitutive law which is used in the macroscopic analysis. Transverse crack of fiber bundle was modeled using enhanced continuum damage mechanics (ECDM) model. Fiber/matrix interface debonding was also modeled by cohesive zone model (CZM). In the macroscopic scale, structural member was modeled. Macroscopic analysis was carried out to investigate initial damage occurrence location and damage process. Damage progress was modeled by stiffness degradation, using CDM model and microscopic analysis results were reflected to determination of macroscopic damage variables. Four-point bending test of macroscopic specimen was carried out for validation of the analysis. Damage observation showed the macroscopic analysis effectively simulated damage occurrence and propagation. Localization analysis was then carried out to investigate damage behavior of woven structure, reflecting deformation history of macroscopic initial damage occurrence location to microscopic analysis. By comparing the analysis to cross-section observation, initial damage simulation showed good agreements with experiment.

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  • Sungmin YOON, Masato MORII, Yasuhiro KIMURA, Yuhki TOKU
    Article ID: 24-00015
    Published: 2024
    Advance online publication: April 24, 2024
    JOURNAL OPEN ACCESS ADVANCE PUBLICATION

    In the present paper, the multiple applications of high-density pulsed electric current (HDPEC) with current densities between 100 and 200 A/mm2 made fatigue crack growth (FCG) slow, in which a current density of more than 150 A/mm2 provided high efficiency to refrain from FCG. The application of multiple HDPECs under the current density of 200 A/mm2 showed a significantly reduced fatigue crack growth rate (FCGR). The fracture surfaces without the HDPEC effect showed signs of FCG along the crystal structure elongated in the rolling direction, on the other hand, a series of welded joints were formed at the crack tips due to the effect of applying multiple HDPECs, which provided different patterns of FCG leading to crack arrest. When initial HDPEC is applied in a short crack under the same HDPEC condition, it shows partial welding at the crack tip, while more concentrated welding at the crack tip by moderate Joule-heating is shown as fatigue progresses and the fatigue crack length increases. Elemental analysis by energy-dispersive X-ray spectroscopy and crystallographic analysis by electron backscatter diffraction also provided the microstructure features at the crack tip subjected to the application of multiple HDPECs. It is most efficient to perform in a short crack with multiple applications, and applying multiple manners as the crack progresses contributes to the accumulated improvement of fatigue properties by slowing the FCGR based on each application.

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  • Hiroyuki TAKANASHI
    Article ID: 23-00490
    Published: 2024
    Advance online publication: April 18, 2024
    JOURNAL OPEN ACCESS ADVANCE PUBLICATION

    This study modeled the behavior of pedestrians who avoids moving obstacles, especially other pedestrians or bicycles are approaching, which are common in daily life. In our previous research, we modeled the behavior of a pedestrian when they avoided a static obstacle, such as a parked car, parked bicycle, or poles on a roadside. However, pedestrian motion might be affected by movement of an obstacle or its size. Accurate behavior modeling of pedestrians should include these factors. Typically, previous studies have treated pedestrian motion as a deterministic model. However, human behavior should be considered as stochastic motion even though deviations, such as walking speed, are not very large when considering local motion. When pedestrians avoid an obstacle, their motion or behavior is determined by their own individual factors, such as age, sex, etc. In this paper, we focus on the effect of obstacle speed and relative distance. To model pedestrian behavior during avoidance of a moving obstacle, walking loci were measured at first. Then, we derived and evaluated differences in avoidance behavior with respect to the obstacle speed. One result showed that the speed of a moving obstacle is one of the most important factors as the pedestrian begins avoidance, that is, the time factor that is determined by the relative speed and the relative distance affects the timing of avoidance behavior of a pedestrian.

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  • Sungmin YOON, Yasuhiro KIMURA, Yuhki TOKU
    Article ID: 23-00551
    Published: 2024
    Advance online publication: April 06, 2024
    JOURNAL OPEN ACCESS ADVANCE PUBLICATION

    In this paper, a series of molecular dynamics (MD) simulations was performed to identify the high-temperature tensile properties of nanostructured polycrystalline CoCrCuFeNi high entropy alloy (HEA). The mechanism of strength reduction at elevated temperatures was understood through nanostructure observation such as phase transformation and dislocation evolution in MD simulation. The applicability of this material from room temperature to 1200 ℃ as a high-temperature use of structural material was identified. The stress-strain curve was found to gradually decrease ultimate tensile strength and yield stress as the temperature applied to the material increases. The elastic modulus decreases rapidly at slightly high temperatures but decreases gradually as it goes to the extremely high temperatures. Face-centered cubic (FCC)→hexagonal close-packed (HCP) phase transformation, which is energetic process between atoms due to tensile loading, was revealed. From the vicinity of the yield stress to the quasi-plastic regime, it competitively contributes to tensile properties between FCC→HCP phase transformation and growth of voids. In dislocation analysis, the typical partial dislocations such as perfect, Shockley, stair-rod and others were measured, in which Shockley and stair-rod partial dislocations show its characteristics that contribute to tensile properties. The results in this study contribute to understanding the high-temperature applicability of nanostructured polycrystalline CoCrCuFeNi HEA.

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  • Takeshi EMOTO, Takanori EMARU, Ankit RAVANKAR, Abhijeet RAVANKAR, Yuki ...
    Article ID: 23-00352
    Published: 2024
    Advance online publication: April 05, 2024
    JOURNAL OPEN ACCESS ADVANCE PUBLICATION

    Skilled technicians primarily use manual tools to maintain the geometry and surface conditions of railcar wheels. To ensure efficient wheel maintenance, the development of an automated inspection system is required. Herein, an inspection method for railcar wheels is proposed based on the assessment of wheel tread dimensions and surface conditions and investigation results of the method are presented. The parameters of wheel tread dimensions and surface conditions are considered because they are crucial for railway operation safety and manually inspecting them requires a large workforce. To improve the efficiency of the system, a combined inspection method through laser measurement and machine vision is used, both the techniques compensate for each other’s shortcomings. The experiments are conducted using laser sensors and machine vision techniques, including defect detection using AI model based on YOLOv5, as well as image data captured via a digital video camera to obtain high-accuracy automatic measurements and determine the feasibility of such measurements. Additionally, the measurement accuracy of the proposed method is verified based on experiments on sample wheel having wheel tread surface defects. In this paper, sample wheel including various wheel tread surface defects is used.

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