Lift-up Hysteresis Butterflies in Friction
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Charles-Augustin de Coulomb postulated that the act of rubbing of surfaces against each other leads the asperities on the surfaces to deform and mount each other. Thus, in order for tangential motion to ensue, an associated lift-up in the direction normal to the surface, will take place. Although this behavior has been sporadically pointed out in literature, we believe that the butterfly curves associated with it during presliding have not been reported before. We have performed dry, presliding rubbing experiments that show that there is a regular, relative normal displacement associated with the tangential motion; in particular, that normal motion describes rate-independent, hysteresis, butterfly curves (similar in nature to those found in piezo-electric and magnetic materials), in the tangential displacement and in the tangential force, respectively. This communication outlines and explores the basic behavior of those butterfly curves experimentally.