Working group 1

Today, the phenomenological macroscopic or mesoscopic description of sliding friction cannot be linked yet to the fundamental mechanisms occurring at the molecular level. Bridging the different length scales by properly relating the atomistic processes with the macroscopically observed effects is the challenge of modern tribology which WG1 will address.

Main objectives

  • Enrich the description of mesoscopic sliding fiction by overcoming the single-asperity level description, addressing tribological problems in relevant multi-contact systems, where both single-asperity dynamics and collective interaction mechanisms should play a crucial role.
  • Analyse the complex variation in the interfacial separation between rough surfaces, extending over several decades in length scales and its effects on friction and on the flow of a fluid in between the surfaces.
  • Investigate and control the mechanism of energy dissipation due to wear and plastic deformations.
  • Correlate atomistic studies of friction and the macroscopic friction and wear tests.
  • Study the behaviour of nanowires/nanotubes as candidate objects (micro/mesoscale in one dimension and nanoscale in others) for bridging the tribological properties at the small length scales.
  • Elucidate the origin of certain friction laws (rate-and-state), which yield a good phenomenological description of systems as different as granular media and solid on solid.
  • Address the microscopic origin of interface “ageing” and of slow relaxations.

Methods A

Experimental: *Tribological test methods, from nanonewtons to newtons, to explore lubricated and dry systems where roughness size scale varies continuously over many orders of magnitude. *Combined microtribometry and surface analytical techniques. *On-line topography and wear measurements for friction experiments at micro/macroscopic scales. *In-situ friction measurements between nanowires/nanotubes and substrate in longitudinal/lateral directions. *Experiments on granular media and solid-on-solid friction, measuring the time/length scales involved, and the influence of disorder on the parameters of rate-and-state laws. *Direct measurements of single-particle and cooperative motion in molecules in contact with a surface; benchmark data on energy landscapes and dissipative mechanisms.

Methods B

Theoretical: *Implementation of specific approaches to model dynamics in multicontact systems, linking descriptions of single contact, discrete arrays and extended systems. *Development of unconventional multiscale/hybrid simulation techniques to bridge the atomic level of investigation with coarse-grained or continuum analysis at larger scales.