A model of friction with plastic contact nudging: AmontonsCoulomb laws, aging of static friction, and nonmonotonic Stribeck curves with finite quasistatic limit
Abstract
We introduce a model of friction between two contacting (stationary or cosliding) rough surfaces, each comprising a random ensemble of polydisperse hemispherical bumps. In the simplest version of the model, the bumps experience on contact with each other only pairwise elastic repulsion and dissipative drag. These minimal ingredients are sufficient to capture a static state of jammed, interlocking contacting bumps, below a critical frictional force that is proportional to the normal load and independent of the apparent contact area, consistent with the AmontonsCoulomb laws of friction. However, they fail to capture two widespread observations: (i) that the dynamic friction coefficient (ratio of frictional to normal force in steady sliding) is a roughly constant or slightly weakening function of the sliding velocity $U$, at low $U$, with a nonzero quasistatic limit as $U\to 0$, and (ii) that the static friction coefficient (ratio of frictional to normal force needed to initiate sliding) increases ("ages") as a function of the time that surfaces are pressed together in stationary contact, before sliding commences. To remedy these shortcomings, we incorporate a single additional model ingredient: that contacting bumps plastically nudge one another slightly sideways, above a critical contactcontact load. With this additional insight, the model also captures observations (i) and (ii).
 Publication:

arXiv eprints
 Pub Date:
 June 2022
 arXiv:
 arXiv:2206.15185
 Bibcode:
 2022arXiv220615185F
 Keywords:

 Condensed Matter  Soft Condensed Matter;
 Condensed Matter  Materials Science
 EPrint:
 5 pages, 5 figures