Static aging vs. dynamic rejuvenation in solid friction

Dry friction between macroscopic solids can be understood in terms of the elastic (static regime) versus plastic (dynamic regime) responses to a shear stress of a set of dilute micrometric adhesive contacts. When pinned, such a system is the seat of two distinguishablc slow, quasi-logarithmic aging dynamics: - a “geometric" aging process, originating from the bulk of the contacting asperities, which results in the increase of the real area of contact. - a structural one, taking place within the nm-thick adhesive layers, which behave as 2D confined “soft " structural glasses. Both mechanisms give rise to associated dynamic rejuvenation phenomena, akin to those observed in threshold fluids, which govern the rich variety of frictional dynamics exhibited by extended systems