JOURNAL OF JAPANESE SOCIETY OF TRIBOLOGISTS
Online ISSN : 2189-9967
Print ISSN : 0915-1168
ISSN-L : 0915-1168
Volume 65 , Issue 7
Special Issue on Focus on Sports and Athletes from Engineering Perspectives
Showing 1-13 articles out of 13 articles from the selected issue
Announcement
Contents
The Valediction by the Ex-President
The Inaugural Address by the President
Special Issue on Focus on Sports and Athletes from Engineering Perspectives
Explanation
  • Toshiaki NISHI
    2020 Volume 65 Issue 7 Pages 398-403
    Published: July 15, 2020
    Released: July 15, 2020
    JOURNALS RESTRICTED ACCESS

    To achieve human movement, an external force is often required via contact between the human body and another surface, thus inducing friction and wear. It is therefore reasonable to design sports and active gear based on tribology. Considering shoes alone, many interfaces must be considered; e.g., outer sole and floor, inner lining and sock, and shoelaces with themselves. Each interface relates to the shoe performance, including slip resistance, wear resistance, and fitting. In particular, the slip and wear resistance are directly determined by the friction and wear behaviors of the outer sole, generally constructed of rubber. A common method used to decrease weight and eliminate the bonding process labor is to mount a single piece of foam resin as the mid- and outer soles, designated as a unisole. Because the low elastic modulus inherent in a porous structure induces a high real contact area, the foam resin exhibits high friction; while the high porosity also decreases wear resistance. Further, the foam resin porosity distribution is not uniform, especially near the interface with a skin layer. Previous reports show that friction and wear behaviors of cross-linked ethylene vinyl acetate foam with a skin layer are sensitive to the foam porosity of the wear surface, which varies during the wear process, and that decreasing the foam bulk porosity and the contact pressure improves wear resistance. Considering these reports, a new unisole material for volunteer shoes in Tokyo 2020 was developed exhibiting reduced porosity and elastic modulus. The low porosity also achieves a high settling resistance, which allows the unisole structure to be fitted with holes for improved breathability.

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  • Hiroo OKANAGA
    2020 Volume 65 Issue 7 Pages 404-409
    Published: July 15, 2020
    Released: July 15, 2020
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    In soccer and volleyball games, there is the phenomenon that the non-spinning or low-spinning ball orbit changes unpredictably. In badminton, the shuttlecock has high air-friction properties due to its special shapes. The investigation of these phenomena is important to enjoy these games. Many studies have been carried out to clarify the aerodynamics characteristics of soccer ball, volleyball and badminton shuttlecock. In this paper, the aerodynamic characteristics for various soccer balls and volleyball without rotation are explained. And furthermore, the effects of a feather shuttlecock and a nylon shuttlecock on the aerodynamic characteristics with rotation are explained.

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  • Hideyuki NATORI, Atsushi YAMAMOTO
    2020 Volume 65 Issue 7 Pages 410-415
    Published: July 15, 2020
    Released: July 15, 2020
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    As the Tokyo Paralympic Games approached, the opportunity to see the Para-athlete wearing artificial ʻprosthetic limbsʼincreased in various media. These athletes overcame their injuries and disabilities to turn themselves into some of the best athletes in the world. On the other hand, there are many staffs who works and supports them at the backyard. In this article, research and developments for the artificial legs, especially for prosthetic adapter components, for Para-athlete with lower extremity amputation is presented.

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  • ―Towards the Tokyo Paralympic Games―
    Akira SHIONOYA
    2020 Volume 65 Issue 7 Pages 416-423
    Published: July 15, 2020
    Released: July 15, 2020
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    It is about six months before the Tokyo Paralympic Games. As well as daily training of players aiming to participate in the tournament, the development of equipment to support the players is progressing at a rapid pace. This article focuses on wheelchairs for competition, introduces wheelchairs for competition especially item characteristics, structure, materials and so on by introduction, and summarizes the development process and evaluation of badminton competition wheelchairs being developed for Tokyo.

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  • Takeshi YAMAGUCHI, Daiki NASU
    2020 Volume 65 Issue 7 Pages 424-430
    Published: July 15, 2020
    Released: July 15, 2020
    JOURNALS RESTRICTED ACCESS

    The control of slippage between a hand and an object is fundamental to improving athletic performance in sports that require a strong grip, such as baseball and rock-climbing. In order to prevent slippage between a hand and an object, athletes often use grip-enhancing powders to maintain grip in both dry and wet conditions. In baseball pitching, rosin powder, which comprises magnesium carbonate powder and pine resin, is often used as grip-enhancing agent. In this review, the normal force range applied at the finger during ball releasing process in fastball pitching is introduced and the effect of rosin powder application at the finger tip on the frictional characteristics between finger and baseball leather sheet is described. The friction coefficient is not necessarily increased by the presence of rosin powder at the finger pad-leather sheet interface under dry conditions. However, under wet conditions, rosin powder application increases the friction coefficient relative to the nonpowdered condition in the large normal force condition, indicating the efficacy of rosin powder as a grip-enhancing agent.

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Explanation
  • Akemi ITO
    2020 Volume 65 Issue 7 Pages 431-439
    Published: July 15, 2020
    Released: July 15, 2020
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    Friction reduction is strongly required for engines to reduce CO2 emission. Measurements for factors relating friction losses, which are the shape of sliding surface, temperature, oil film thickness, oil film pressure, and so on, are essential to investigate optimum design of moving parts of engines. Measurement techniques for piston friction, cam friction, bearing friction, shape of sliding surface, oil film thickness, oil film pressure, and so on are described in this paper. It was shown that friction must be measured directly for estimating friction losses of engine moving parts. The remaining subject for such measurements is that for supply oil volume.

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Original Contribution on Science
  • Haruna ISHIZUKA, Youichi WATANABE, Masao TAKEYAMA
    2020 Volume 65 Issue 7 Pages 440-449
    Published: July 15, 2020
    Released: July 15, 2020
    [Advance publication] Released: May 12, 2020
    JOURNALS FREE ACCESS

    The purpose of this study is to investigate the microstructural wear behavior of the surface of steel oxy-nitrocarburized in a Li-added salt bath. JIS SKD61 was oxy-nitrocarburized or nitrocarburized at 823 K for 300 min. A ball-on-disk type wear test was conducted at 0.10‒4.90 N without lubrication using a Al2O3 ball. After oxy-nitrocarburizing, an outer oxide layer (OOL) and an inner oxide layer (IOL), following a nitrogen compound layer (NCL), were formed on the surface. The nitrocarburized steel had a porous NCL (PNCL). The grain size of the Li-Fe oxide in the OOL was a few μm. The IOL consisted of an Li-Fe oxide layer with alloy oxides, the grain size was smaller. As a result of the wear test, IOL had highest wear resistance. Both oxide layers are thermodynamically stable, but cracks propagated at the grain boundaries of the oxide in the OOL, the layer was worn. On the other hand, cracks did not propagate in the IOL. The NCL without void had better wear resistance than PNCL, but it was oxidized by friction heat easily and was worn. It is suggested that oxy-nitrocarburizing makes wear resistance of die improve as compared to conventional nitrocarburizing.

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