Lubrication in soft rough contacts: A novel homogenized approach. Part II - Discussion

In M. Scaraggi, G. Carbone, B. N. J. Persson and D. Dini, Soft Matter, 2011, 7, DOI: 10.1039/c1sm05128h (Ref. 1), we have presented a novel mean field theory of mixed lubrication for soft contacts. This theory has been developed within the framework of homogenization techniques. It is based on a perturbation second order accurate expansion; a rigorous averaging process is applied to obtain the average flow equations without the need of any preliminary fully deterministic calculations of the mixed-lubrication problem. The theory allows to calculate the flow factors and the shear stress factors taking into account the coupled effect of asperity–asperity and asperity–fluid interactions occurring at the interface. In this second paper we present the main results of the theory and we discuss the transition from the boundary lubrication regime, where the normal load is supported through asperity–asperity interactions (sometimes mediated by boundary films), to the hydrodynamic regime, where a thin fluid film prevents the surfaces from being in direct contact. We show that fluid-induced asperities flattening, as well as local percolation effects and roughness anisotropic deformation all occur at the contact interface. Finally we describe the origin of the macroscopic friction laws (the so called Stribeck curves) in terms of local average shear stresses.

[1]  H. Cheng,et al.  Application of Average Flow Model to Lubrication Between Rough Sliding Surfaces , 1979 .

[2]  Giuseppe Carbone,et al.  Lubrication in soft rough contacts: A novel homogenized approach. Part I - Theory , 2011 .

[3]  Giuseppe Carbone,et al.  Experimental Evidence of Micro-EHL Lubrication in Rough Soft Contacts , 2011 .

[4]  C J Hooke.  Engineering analysis of rough elastohydrodynamically lubricated contacts , 2009 .

[5]  C J Hooke,et al.  Rapid Calculation of the Pressures and Clearances in Rough, Elastohydrodynamically Lubricated Contacts Under Pure Rolling. Part 1: Low Amplitude, Sinusoidal Roughness , 2006 .

[6]  H. Cheng,et al.  An Average Flow Model for Determining Effects of Three-Dimensional Roughness on Partial Hydrodynamic Lubrication , 1978 .

[7]  C. Venner,et al.  Surface roughness attenuation in line and point contacts , 2000 .

[8]  Duncan Dowson,et al.  Modelling of Elastohydrodynamic Lubrication of Real Solids by Real Lubricants , 1998 .

[9]  B. Mandelbrot,et al.  Fractal character of fracture surfaces of metals , 1984, Nature.

[10]  C J Hooke,et al.  Rapid Calculation of the Pressures and Clearances in Rough, Elastohydrodynamically Lubricated Contacts Under Pure Rolling. Part 2: General Roughness , 2006 .

[11]  B. Persson.  Theory of rubber friction and contact mechanics , 2001 .

[12]  B N J Persson,et al.  On the transition from boundary lubrication to hydrodynamic lubrication in soft contacts , 2009, Journal of physics. Condensed matter : an Institute of Physics journal.

[13]  J. Archard.  Elastic deformation and the laws of friction , 1957, Proceedings of the Royal Society of London. Series A. Mathematical and Physical Sciences.

[14]  Hugh Spikes,et al.  Sixty years of EHL , 2006 .

[15]  G. Carbone,et al.  Adhesive contact of rough surfaces: Comparison between numerical calculations and analytical theories , 2009, The European physical journal. E, Soft matter.

[16]  G. Carbone,et al.  Transition from elastohydrodynamic to mixed lubrication in highly loaded squeeze contacts , 2010 .

[17]  B. Persson,et al.  Theory of the leak-rate of seals , 2008, 0805.0699.

[18]  C. Hooke,et al.  Surface roughness modification in elastohydrodynamic line contacts operating in the elastic piezoviscous regime , 1998 .

[19]  B. Persson.  Contact mechanics for randomly rough surfaces , 2006, cond-mat/0603807.

[20]  B N J Persson,et al.  Fluid dynamics at the interface between contacting elastic solids with randomly rough surfaces , 2010, Journal of physics. Condensed matter : an Institute of Physics journal.

[21]  A. A. Lubrecht,et al.  An Engineering Tool for the Quantitative Prediction of General Roughness Deformation in EHL Contacts Based on Harmonic Waviness Attenuation , 2005 .