Mutual Overlap Coefficient and Wear Debris Motion in Dry Oscillating Friction and Wear Tests

Abstract

In oscillating dry friction and wear tests, mechanical parameters such as degrees of freedom and stroke amplitudes govern the formation of wear debris. A third body is formed by the wear debris within the contact. It is progressively eliminated from the contact area. The volume of wear debris lying outside the contact area corresponds to the total wear between the pin and the counterface. Wear is thus controlled by the elimination of wear debris outside the contact. The overlap of the pin and the friction track on the counterface thus controls the wear debris elimination. That overlap is characterized by the mutual overlap coefficient (MOC) which is defined as the ratio of the pin contact area to the counterface wear track.

Wear debris formation and elimination was simulated with a pin made of a high-wear-rate material rubbing against an oscillating counterface. Widely different wear results and transfer film morphologies are obtained when the MOC varies between 0.66 and 0.99. Wear results are analyzed for small and large MOC. In this study, small values of MOC are defined as being less than 0.8 while large values of MOC are those greater than 0.9. Small and large values of MOC generate characteristic third bodies, and transfer film morphology depends on MOC and load. Related wear mechanism are discussed.