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Local friction of rubbers with rough surfaces

Antoine Chateauminois, 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)

The fundamentals of friction are a longstanding problem in Physics. We are especially interested in the relationship between the friction of macroscopic systems and interface processes taking place at length scales intermediate between the contact size and the micrometer scale. This processes involve, for example, the role of micro-asperities within rough contact interfaces or the dynamics of stick slip motions.

Friction of rubbers with randomly rough rigid surfaces

Using recently developed contact imaging techniques, we are investigating the distribution of shear stress within frictional interfaces between rubber substrates and rigid (glass) lenses. Friction-induced surface displacement fields are measured from the deformation of a markers’ lattice. From an inversion procedure based on contact mechanics, the shear stress distribution at the surface of the rubber is deduced.

 

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Deformation of a surface marked silicone rubber within a frictional contact with a glass lens (steady state sliding).

 

 

Displacement (left) and shear (right) field measured along the sliding direction. The silicone rubber substrate is moving from bottom top with respect to the fixed glass lens.

 

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 rough 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). Colors correspond to different experiments carried out at increasing normal load.

 

Using these approaches, we have also evidenced an overlooked dependence of friction on the deformation of rubber substrates : In smooth glass/rubber contact interfaces, the local frictional stress is found to depend on the local in-plane stretch of the elastomer surface. These effects have also some implications in the friction of rough contact interfaces and remain to be accounted for in theoretical models.

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

With Alexis Prevost, Elie Vandersman (LJP, UPMC) and Manoj. K. Chaudhury (Lehigh Univ.) 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).
 


Publications

A. Chateauminois, D.T. Nguyen and C. Frétigny, Effects of local stretch on the frictional stress of rubber, submitted

 

C. Frétigny and A. Chateauminois, contact on a stretched rubber, Physical Review E to appear (2017)

 

S. Biswas, A. Chakrabarti, A. Chateauminois, E. Wandersman, A. M. Prevost and M.K. Chaudhury, Soft Lithography Using Nectar Droplets, Langmuir 31 (2015) 13155−13164

 

S. Yashima, V. Romero, E. Wandersman, C. Frétigny, M.K. Chaudhury, A. Chateauminois and A.M. Prevost, Normal contact and friction of rubber with model randomly rough surfaces, Soft Matter 11 (2015) 871 - 881

 

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

 

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

 

D.T. Nguyen · S. Ramakrishna · C. Fretigny · N.D. Spencer · Y. Le
Chenadec · A. Chateauminois, Friction of rubber with surfaces patterned with rigid spherical asperities, submitted to Trib. Letters (08/2012)

 

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

 

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