Dry Friction as a Hysteretic Elastic Response

Abstract

The physical mechanisms that control dry friction are still unclear. It is usually assumed that plasticity plays a central role: asperities which provide the contact flow under the effect of both the normal load and the dragging force. There is no doubt that plasticity is important, especially as regards ageing effects — but may be it is not the whole story. Here we propose an alternate possibility in which friction would result from purely elastic response of the asperities, in the presence of multistability and hysteresis. Asperities are treated as point pinning centers that are swept through as the slider moves. For a quasistatic slow sweeping an average drag only appears if the response is multistable and the friction coefficient is proportional to the area of the hysteresis cycle. We treat in detail the case of a single asperity (effect of plasticity, delayed spinodal jump at finite velocities, noise activated depinning). The actual problem of elastic interactions between pinning centers is only touched. We show the existence of a screening length at zero velocity and we discuss briefly cascade jumps and interaction induced multistability. At this stage the analysis remains qualitative.