The Contact and Sliding Friction of Cellular Materials

Abstract

The mechanics of the contact of a cellular material (open cells) with a compact rough surface (S) is analysed, based on a simple model for the structure of the material. The cell edges (struts) in contact with S bend when the material is compressed against S and their equilibrium configuration depends on the roughness of S and on its friction properties. Under static conditions, the number of edges per unit area in contact with S can be calculated as a function of the compressive stress σ.

When the cellular material slides on S, the bending deflection of the edges varies during sliding and a stick-slip displacement takes place. The friction coefficient depends on the bending stiffness of the edges, on the roughness of the surface and on the friction coefficient of the cell edge material sliding on S. The actual friction coefficient can be much larger than the one of the cell edge material, due to dissipation by bending-unbending. Experimental results for cork sliding on glass are confronted with the predictions of the model.