Kris De Moerlooze

A Model of the Transient Behavior of Tractive Rolling Contacts

When an elastic body of revolution rolls tractively over another, the period from commencement of rolling until gross rolling ensues is termed the prerolling regime. The resultant tractions in this regime are characterized by rate-independent hysteresis behavior with nonlocal memory in function of the traversed displacement. This paper is dedicated to the theoretical characterization of traction during prerolling. Firstly, a theory is developed to calculate the traction field during prerolling in function of the instantaneous rolling displacement, the imposed longitudinal, lateral and spin creepages, and the elastic contact parameters. Secondly, the theory is implemented in a numerical scheme to calculate the resulting traction forces and moments on the tractive rolling of a ball. Thirdly, the basic hysteresis characteristics are systematically established by means of influence-parameters simulations using dimensionless forms of the problem parameters. The results obtained are consistent with the limiting cases available in literature and they confirm experimental prerolling hysteresis observations. Furthermore, in a second paper, this theory is validated experimentally for the case of V-grooved track.

Experimental Investigation into the Tractive Prerolling Behavior of Balls in V-Grooved Tracks

In a rolling element system, the period of transition between motion commencement and the attainment of steady state, gross rolling, and termed prerolling is of common concern to many engineering applications. This region is marked by hysteresis friction behavior, with a characteristic friction-displacement curve, which is in particular relevant to motion characterization and control issues. In a previous paper, the authors carried out a theoretical analysis of tractive prerolling, leading to a model for simulating this phenomenon. The present paper is dedicated to the experimental investigation of tractive prerolling friction behavior, including validation of the theoretical model. Firstly, a kinematic analysis of the rolling motion in V-grooved tracks is carried out. Secondly, the influence of the normal load on the frictional behavior, in prerolling up to the attainment of gross rolling, is investigated on a dedicated test setup. Finally, the newly developed theoretical model is validated by comparison with the experimental results. Satisfactory agreement is obtained between theory and experiment.

Lift-up Hysteresis Butterflies in Friction

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.