Friction Dynamics of Geckolike Materials
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Friction Dynamics of Geckolike Materials Jonathan B. Puthoff MRS Advances / FirstView Article / July 2016, pp 1 - 7 DOI: 10.1557/adv.2016.535, Published online: 28 July 2016
Link to this article: http://journals.cambridge.org/abstract_S2059852116005351 How to cite this article: Jonathan B. Puthoff Friction Dynamics of Geckolike Materials. MRS Advances, Available on CJO 2016 doi:10.1557/ adv.2016.535 Request Permissions : Click here
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MRS Advances © 2016 Materials Research Society DOI: 10.1557/adv.2016.535
Friction Dynamics of Geckolike Materials Jonathan B. Puthoff1 1 California State Polytechnic University, Pomona, 3801 West Temple Avenue, Pomona, CA 91768, U.S.A. ABSTRACT The interface between the adhesive toes of geckos and a substrate consists of an array of regularly sized, densely packed, and elastically coupled nanoscopic contacts. The velocitydependent friction exhibited by this system hints at a convolution of various material and structural effects. We explore the dynamics of frictional sliding in these materials using models based on arrays of coupled masses driven by external forces that can become pinned and unpinned to a potential energy landscape. The model system is driven at normalized velocities spanning 6 orders of magnitude, and the output of this model captures both the low-V and high-V behavior of the actual gecko materials. We explore modifications to the essential model that incorporate features more representative of the structure and behavior of the natural gecko system. These results have implications in the design of materials with custom frictional properties. INTRODUCTION The gecko adhesion system provides these animals with an impressive suite of capabilities during climbing, such as robust attachment, easy release, and tolerance to contamination [1]. The system is based on the microscale hair-like protrusions on the underside of the geckos’ toes; these branched keratinous structures, when suitably deployed, securely attach the animal to the underlying surface with weak intermolecular forces acting at the nanoscopic contacts. The mechanisms underpinning this adaptation have considerable relevance to the evolution and biomechanics communities, but a close study of these physical principles can inform the development of synthetic adhesives as well as new theories of tribology [2]. Recent measurements of the dynamic friction produced by natural gecko setal arrays and synthetic geckolike adhesives [3, 4] require an explanation in terms of fundamental tribological principles. Dynamic friction (or rate-dependent friction) is the force response of a system of two bodies in contact moving with some relative velocity V. Traditional teaching on the topic of friction implicitly recognizes this rate dependence, categorizing the friction force as either “static” or “kinetic,” but in
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