Friction force oscillations in the pin-on-disc configuration

Friction force oscillations occurring in a pin-on-disc configuration, widely used to test tribological properties af engineering materiais, have been experimentally observed. It is argued that these ascillations are not an artefact of a parlicular design of the pin-on-disc apparatus but result from the nature of motion within the region of cantact between the pin and the disc. Moreover, it is postulated that the shape and the rotation of the contact area abaut its geometric centre additionally amplify friction oscillations. The paper is an attempt to provide a rational explanation at the fundamental level for friction force fluctuations in the pin-on-disc configuration. lt is based on the analysis of motion within the contact region.