Interaction of displacement amplitude and frequency effects in fretting wear of a high strength steel: Impact on debris bed formation and subsurface damage

Abstract

In previous work, fretting frequency has been observed to have a significant impact not only on wear rates, but also on the nature of fretting debris and the development of subsurface damage; however, while the “frequency effect” has been shown in some cases to be affected by the amplitude of the displacement, the mechanism of the interrelationship is not well understood. The present work presents new insights into the frequency effect by investigating the impact of displacement amplitude on fretting wear over a range of frequencies. Experiments were conducted using like-on-like high strength steel pairs in a cylinder-on-flat configuration. Irrespective of test conditions, the ejected debris was almost entirely made up of iron oxide with only a small fraction of metallic material. It was observed that as displacement amplitude was increased, the debris beds became sparser with a higher proportion of exposed metallic surface in the scar, with extensive deformation and cracking being observed in the metallic material; in contrast, at lower displacement amplitudes, sufficient oxygen is available to continually form oxide throughout the contact, which significantly reduces the development of such sub-surface damage.It is proposed that damage and wear in fretting is controlled by (i) oxygen ingress to the contact; (ii) oxide debris formation; (iii) debris expulsion from the contact. Wear and damage in fretting is controlled by whichever of these processes has the lowest rate under the test conditions being employed, which is then termed the rate-determining process.