Accueil > A la une > Imagerie des contraintes de frottement

Imagerie des contraintes de frottement

Friction is one of the most longstanding problems in Physics. One of the major origins of the complexity of this problem comes from the roughness of the contacting surfaces. When macroscopic bodies are pressed together, contact only occurs at localized spots between surface asperities. Friction thus involves the shearing of a myriad of micro-contacts which are distributed over length scales ranging from micrometers down to nanometers. Although widely debated, the manner in which these micro-contacts locally dissipate energy remains obscure. As a prerequisite, one should know how frictional stresses are distributed within the highly heterogeneous stress and strain field of macroscopic contact interfaces. Unfortunately, most experiments only rely on measurements of friction force and of its dependence on load and velocity which are averaged quantities of local frictional properties. We recently proposed a method to measure local friction of rubbers by means of a contact imaging approach. Silicon rubber substrates marked beneath their surface by a coloured pattern were prepared in order to measure the displacement field induced by the steady state friction of a glass sphere. As reported in European Journal of Physics E, the deconvolution of this displacement field provides a spatially resolved measurement of the actual shear stress distribution at the contact interface. First results showed that the simple considerations based on actual contact area and constant shear stress hypothesis (often embedded in rough contact models) cannot account for the observed shear stress distribution. Much work remains to be done, but one of the promise of this method is the possibility of investigating local friction between patterned surfaces with well controlled topography at the micrometer level.

 

Friction between a marked silicone rubber and a glass sphere. Deconvolution of the measured surface displacement field provides the distribution of shear stress within the frictional contact.

 

A. Chateauminois and C. Fretigny, ‘Local friction at a sliding interface between an elastomer and a rigid spherical probe’, European Physics Journal E : 27 (2008) 221-227

 

Highlight in Europhysics News,39 (6) 2008