The role of wear particles under multidirectional sliding wear

There is a large number of technical tribosystems like piston/cylinder under a major reciprocating sliding motion, which undergo multidirectional sliding wear by the superpositioning of cyclic loads, e.g. the vibration of the surrounding components. Beside frequency and amplitude of these additional relative movements, the occurrence of wear particles should have a distinct influence on the tribological behaviour [I. Samerski, J. Vdovak, J. Schöfer, A. Fischer, The transition between high and low wear regimes under multidirectional reciprocating sliding, Wear, in press]. Thus a test rig was designed and constructed which allows for a continuous rinsing of lubricants in order to either leave the wear particles inside the contact or wash them away. Polished balls of 52100 bearing steel were slid against ground discs in a self-mated Diesel fuel lubricated contact. The multiaxial movement was brought about by superposition of two oscillations perpendicular to each other, with a primary amplitude of 1000 μm at 1 Hz and a secondary one ranging from 0.0 to 14.3 μm at 100 Hz. Wear depth and friction forces were measured in situ, and wear mechanisms were examined after the tests. At small secondary amplitudes tribochemical reactions prevailed at relatively low wear rates. With increasing the secondary amplitude, surface fatigue by the enhanced movement of wear particles occurred, resulting in higher wear rates. This mechanically dominated wear mechanism could be significantly reduced by rinsing, while tribochemical wear was hardly affected. Additionally, the dissipated friction energy was calculated and energy-based wear rates were determined, which showed a strong dependence on the predominant wear mechanism.