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Lecture

Controlling Friction Anisotropy: Effects of Material Elasticity, Surface Geometry and Substrate Roughness

Tuesday (21.02.2017)
16:50 - 17:15 Rohrersaal
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Surfaces with anisotropic friction properties are very common in biological systems. Friction anisotropy can be achieved on various length scales from the atomic scale, such as crystal lattice structures, to the micro/macro scale, such as surface microstructures and can, thus, often be regarded as a geometry-induced property. Here, we use a simple model system for friction anisotropy, which consisted of a sawtooth-shaped surface profile. We tested tribological properties of sawtooth surfaces of three different aspect ratios made of a soft silicone rubber and a stiff epoxy resin against substrates with different roughness also made of a soft silicone rubber and a stiff epoxy resin. By changing these key factors of the material and substrate properties, it was possible to not only change the amount of anisotropy, but even to reverse it, i.e. inverting the preferred direction of motion. This can be explained by the ability of the polymer sawtooth surface to deformation. The hard epoxy resin samples do not deform during sliding, therefore mechanical interlocking occurs when pulling against the sawtooth structures, resulting in higher friction, while there is lower friction when pulling with the sawtooth structures due to easy sliding over the surface asperities. The soft silicone rubber samples deform well during sliding. This leads to less mechanical interlocking as well as lower contact area when pulling against the sawtooth structures. When sliding with the sawtooth structures, the contact area between sample and substrate greatly increases due to sample deformation, resulting in an increase of the friction coefficient. These effects can be used for many potential applications, one of which is robot locomotion. Here, movement direction as well as movement efficiency can be greatly tuned without high control effort by using the proper combination of surface geometry, material elasticity and substrate roughness.

 

Speaker:
Halvor Tramsen
Christian-Albrechts-Universität zu Kiel
Additional Authors:
  • Dr. Lars Heepe
    CAU Kiel
  • Prof. Hao Zhang
    Nanjing University of Aeronautics and Astronautics
  • Prof. Dr. Zhendong Dai
    Nanjing University of Aeronautics and Astronautics
  • Prof. Dr. Poramate Manoonpong
    University of Southern Denmark
  • Prof. Dr. Stanislav N. Gorb
    CAU Kiel