A new approach to link the friction coefficient with topography measurements during plowing

Running-in of sliding surfaces is a highly complex process that often defines the tribological properties of a contact. With a view to optimizing a tribosystem, more and more industrial research focuses on the mechanisms that occur during running-in. Such studies can nowadays benefit from the progress shown in the field of in situ tribometry. In this work, we present a novel approach to measure and separate the plowing and shear terms of the friction force , in the ideal case of a hard sphere sliding on a plane surface. The experiments were performed with ruby spheres and flat steel pins sliding against a flat copper surface immersed in poly alpha olefin (PAO8). A custom built tribometer was employed to measure the widening of plowing tracks within the wear scar. In these measurements, the relative motion of the surfaces in contact was performed in a linear reciprocating manner. Different methods to distinguish between plowing friction and sliding friction are compared. Our results with spherical sliders show that the widening rate of the wear track is linearly proportional to the plowing term, provided that the spheres do not sink in the Cu sample rapidly. Further experiments with flat on flat demonstrate the potential of expanding this method to multi-asperity systems in order to better understand the dynamics of sliding surfaces during running-in.