Hysteresis and recovery length in a dry solid friction experiment

We report an experiment on dry friction between two elastic surfaces made of millimetric steel spheres embedded in an elastic medium. We study the hysteresis cycle of the tangential force induced by a quasi-static cyclic displacement. At low velocities, hysteresis effects are fully characterized by a recovery length comparable to the size of the steel spheres. This length is independent of the velocity and of the normal load. We propose an interpretation for this recovery length with a simple model of discrete contacts.