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Strain-induced crystallization to prolong the lifetime of pneumatic artificial muscles
Author(s): A. Kojima; M. Okui; I. Hisamichi; N. Tadami; T. Tsuji; T. Nakamura
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Paper Abstract

Various types of soft actuators have been developed for application in wearable movement-assist devices or soft robots. The authors have developed a straight-fiber-reinforced pneumatic rubber artificial muscle (SF-ARM). The SFARM is composed of rubber that is reinforced with fibers aligned only in the axial direction. When air pressure is applied to the SF-ARM, the reinforced fibers limit the rubber expansion to the radial direction so that the muscle contracts in the axial direction. The SF-ARM contracts by 38% at maximum, and this contraction rate exceeds the contraction rate of the McKibben artificial muscle. However, the SF-ARM is not well-suited for practical use because the strain on the SF-ARM while it is actuated is large which can cause fatigue failure of the rubber. This study focuses on suppressing the growth of cracks using strain-induced crystallization of the natural rubber, to prolong the lifetime of the SF-ARM. Natural rubbers form a crystalline layer in the direction perpendicular to the direction of stretching. This crystal layer effectively suppresses the growth of cracks in the SF-ARM when under strain. Deliberately developing a crystal layer should extend the lifetime of the SF-ARM. First, this study confirmed the formation of a crystal layer under extension of natural rubber (NR) and styrene butadiene rubber (SBR) using wide-angle X-ray diffraction measurements. Next, the strain concentration near the crack was analyzed using finite element method simulations. Finally, fatigue-life tests were conducted with SF-ARMs made of NR and SBR.

Paper Details

Date Published: 13 March 2019
PDF: 8 pages
Proc. SPIE 10965, Bioinspiration, Biomimetics, and Bioreplication IX, 109650X (13 March 2019); doi: 10.1117/12.2513246
Show Author Affiliations
A. Kojima, Chuo Univ. (Japan)
M. Okui, Chuo Univ. (Japan)
I. Hisamichi, Chuo Univ. (Japan)
N. Tadami, Chuo Univ. (Japan)
T. Tsuji, Chuo Univ. (Japan)
T. Nakamura, Chuo Univ. (Japan)


Published in SPIE Proceedings Vol. 10965:
Bioinspiration, Biomimetics, and Bioreplication IX
Raúl J. Martín-Palma; Mato Knez; Akhlesh Lakhtakia, Editor(s)

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