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Local friction of rubber with rough surfaces

This project is devoted to the local analysis of steady-state friction within contact interfaces formed between smooth rubber surfaces and rigid rough counterfaces. The local friction law is determined from spatially resolved measurements of the displacement field at the surface of the soft rubber substrate.

with Christian Fretigny, D.T. Nguyen, V. Romero, M. Trejo, and S. Yashima

 

Collaboration with Alexis Prevost, Elie Vandersman (Laboratoire Jean Perrin, UPMC), Manoj Chaudhury (Lehigh Univ, USA) and et Nic Spencer (ETH Zürich)

 

We are investigating the friction of rubber with rough rigid surfaces at length scales ranging from the macroscopic contact size (i.e. in the millimeter range) down to micrometer scale. For that purpose, we have developed contact imaging techniques which allow to determine the friction induced surface displacement field within contacts between rubbers and glass surfaces. Then, the corresponding interface stress field is determined from an inversion of the measured displacement field.

Using this methodology, we investigate the local friction law, i.e. the relationship between the local shear stress and contact pressure, within frictional contacts between a smooth silicone rubber and randomly rough (Gaussian) glass surfaces. Independently of the statistical characteristics of the rough surfaces (Gaussian or not) the local frictional shear stress is found to vary sub-linearly with the local contact pressure, demonstrating that, for such multi-contact interfaces, Amontons-Coulomb’s friction law does not prevail at the local scale. More generally, these experimental results establish the existence of scale effects in friction laws.

 


Local friction law within a frictional contact between a smooth silicone rubber and a sand blasted lens (rms roughness about 1 µm). Each color corresponds to a different experiments carried out at increasing normal loads.

 

Recently, this approach has been extended to :

Friction of viscoelastic rubbers with statistically rough surfaces

Using similar contact imaging approaches we have also investigated the friction of viscoelastic rubbers with rough surfaces. We have established the relationship between the velocity dependence of the frictional stress and fluctuations in the actual contact area which are induced by viscoelastic effects at the microasperities scale.
Within the framework of a collaboration with S. Ramakrishna and N. Spencer at l’ETH Zürich, we have also investigating the friction of rubbers with surfaces patterned with monodisperse colloidal nano-asperities. We are especially interested in the contribution of nanoscale viscoelastic dissipation to friction. Using such nano-patterned surfaces, this processes can be investigated with well mastered surface topographies.

Contact and friction of model statistically rough surfaces

we are also investigating normal contact and friction of model multicontact interfaces formed between smooth surfaces and substrates textured with a statistical distribution of spherical micro-asperities. Measurements of the real area of contact A versus normal load P are performed by imaging the light transmitted at the microcontacts. Comparison with two multi-asperity contact models, which extend the Greenwood–Williamson (J. Greenwood and J. Williamson, Proc. Royal Soc. London Ser. A, 295, 300(1966)) model by taking into account the elastic interaction between asperities at different length scales, are performed, and allows their validation for the first time. We find that long range elastic interactions arising from the curvature of the nominal surfaces are the main source of the non-linearity of A(P). At a shorter range, and except for very low pressures, the pressure dependence of both density and area of microcontacts remains well described by Greenwood-Williamson’s model, which neglects any interaction between asperities.

 

Model rough surface textured with spherical micro-asperities (size about 30 µm).
 


Related Publications

 

Non-Amontons-Coulomb local friction law of randomly rough contact interfaces with rubber
D.T. Nguyen, E. Wandersman, A. Prevost, Y. Le Chenadec, C. Frétigny, A. Chateauminois
EPL 104 (2013) 64001

 

Friction of viscoelastic elastomers with rough surfaces under torsional contact conditions.
M. Trejo, C. Frétigny and A. Chateauminois
Physical Review E 88 (2013) 052401

 

Friction of rubber with surfaces patterned with rigid spherical asperities.
D.T. Nguyen, S. Ramakrishna, C. Fretigny, N.D. Spencer,Y. Le Chenadec, A. Chateauminois
Tribology Letters 49 (2013) 135-144

 

Surface pressure and shear stress field within a frictional contact on rubber.
D.T. Nguyen, P. Paolino, M-C. Audry, A. Chateauminois, C. Frétigny, Y. Le Chenadec, M. Portigliatti and E. Barthel
Journal of Adhesion 87 (2011) 235-250

 

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