ABSTRACT
Surface roughness has a huge impact on many important phenomena. The most important property of rough surfaces is the surface roughness power spectrum C(q). We present surface roughness power spectra of many surfaces of practical importance, obtained from the surface height profile measured using optical methods and the atomic force microscope. We show how the power spectrum determines the contact area between two solids. We also present applications to sealing, rubber friction and adhesion for rough surfaces, where the power spectrum enters as an important input.
ABSTRACT
Loss of braking power and rubber skidding on a wet road is still an open physics problem, as neither the hydrodynamic effects nor the loss of surface adhesion that are sometimes blamed really manage to explain the 20-30% observed loss of low-speed tyre-road friction. Here we report a novel mechanism based on sealing of water-filled substrate pools by the rubber. The sealed-in water effectively smoothens the substrate, thus reducing the viscoelastic dissipation in bulk rubber induced by surface asperities-well established as a major friction contribution. Starting with the measured spectrum of asperities one can calculate the water-smoothened spectrum and from that the predicted friction reduction, which is of the correct magnitude. The theory is directly supported by fresh tyre-asphalt friction data.
Subject(s)
Accidents, Traffic , Hydrocarbons/chemistry , Materials Testing/methods , Models, Chemical , Rheology/methods , Water/chemistry , Computer Simulation , Elasticity , Friction , Hardness , Surface Properties , ViscosityABSTRACT
We study the time-dependent contact area as a viscoelastic solid is squeezed against a randomly rough substrate. Using a recently developed contact mechanics theory we study how the contact area depends on time and on the magnification zeta. Numerical results are presented for self-affine fractal surfaces, and applications to tack, rubber friction, and sealing are given.
