Research Papers

Mechanism Maps for Frictional Attachment Between Fibrillar Surfaces

[+] Author and Article Information
Robert M. McMeeking

Department of Mechanical Engineering, and Department of Materials, University of California, Santa Barbara, CA 93106; and Leibniz Institute for New Materials (INM), Campus D2 2, 66123 Saarbruecken, Germany

Lifeng Ma

MOE Key Laboratory for Strength and Vibration, Department of Engineering Mechanics, Xi’an Jiaotong University, Xi’an 710049, China

Eduard Arzt

 Leibniz Institute for New Materials (INM), Campus D2 2, 66123 Saarbruecken, Germany

J. Appl. Mech 76(3), 031007 (Mar 09, 2009) (8 pages) doi:10.1115/1.3002760 History: Received July 15, 2007; Revised June 18, 2008; Published March 09, 2009

The mechanics of frictional attachment between surfaces with pillars, inspired by the head fixation system of dragonflies, is analyzed. The system consists of two surfaces of interdigitating pillars held together through friction, as by the densely packed bristles of two brushes when pressed together. The adhesive strength of the system is promoted by high elastic modulus, high friction coefficient, large aspect ratio, and dense packing of the fibers. However, the design is limited by the compressive buckling, the compressive indentation or cracking of the contacting pillars, yielding in shear or similar mechanisms that limit the achievable friction stress, and tensile failure of the pillars upon pull-out. Maps, which summarize the strength of the adhesive system and the failure limits and illustrate the trade-off among the design parameters, are presented. Case studies for steel, nylon, and ceramic pillars show that useful strength can be achieved in such attachments; when buckling during assembly and contact failure can be avoided, adhesive performance as high as 30% of the tensile strength of the pillar material may be possible.

Copyright © 2009 by American Society of Mechanical Engineers
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Figure 1

Schematic of the head stabilization mechanism in a dragonfly

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Figure 2

Attachment system consisting of two pillar arrays to be pressed together so that the pillars intersect and contact each other. The pull-off strength is due to the interpillar friction.

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Figure 3

Plan view of the pillar array: the dashed circle corresponds to one interdigitating pillar

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Figure 4

Schematic of the attachment device: (a) prior to being engaged to create the attachment, (b) after displacement by a distance Δ, and (c) the zone of contact between two touching pillars

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Figure 5

Approximate deformed cross-section of a pillar when constrained by three pillars from the opposite surface

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Figure 6

Map of attachment strength of the fibrillar system with failure limits: i.e., normalized contact stress p(1−ν2)/E versus aspect ratio L/D of the pillar. The curved contours are lines of equal normalized attachment strengths K=Σc(1−ν2)/μE. (a) The case of sufficient tensile strength (corresponding to K=0.01) where buckling upon engagement of the attachment system and compressive failure at the contacts together determine the optimum. (b) The case where the tensile strength of the pillars determines the optimum attachment strength (K=0.003).

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Figure 7

Two pillars sliding against each other to depict the unit problem for buckling during engagement of the attachment system by compression: (a) The pillars sliding past each other while straight. (b) A buckled pair of pillars.




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