EXPERIMENTAL AND THEORETICAL INVESTIGATION ON WALLING CONTACT FATIGUEOF 52100 AND M50 STEELS UNDER EHL OR MICRO-EHL CONDITIONS

The purpose of this investigation is to clarify the role of roughness on rolling contact fatigue. Tests have been carried out on a two-disk machine, for two rolling bearing steels (52100 and M50), two surface r oughnesses corresponding to EHL and micro-EHL conditions (two differen t surface finishing), three normal loadings (1.5, 2.5 and 3.5 GPa), an d under pure rolling or rolling plus sliding conditions. No surface da mage has been observed up to 50 10(6) cycles for tests with smooth spe cimens. Tests with rough specimens have produced a typical surface dam age, called here surface distress, made of a fat ge population of aspe rity-scale micro-cracks and micro-spalls. The paper describes the surf ace distress observed such as micro-cracks and micro-spalls, Surface d amages obtained are different for tests under pure rolling conditions and rests under rolling plus sliding conditions. Therefore, the role o f the friction direction is underlined. A link is made between our exp erimental observations and calculations that have been carried our usi ng a transient EHL model. The influence of an indent in a line contact , simulating a micro-spall, is studied. Surface pressure and associate d sub-surface stress field are analyzed versus the sliding direction.