The effects of tribological factors and load sequence on surface pitting and cracks in bearing steel

This paper presents an investigation of the influence of various tribological parameters on surface initiated damage through Rolling Sliding Tests (RSTs) using bearing steel specimens. The RSTs were conducted on a benchtop twin-disc machine, consisting of a tribometer and a rolling contact fatigue testing system. The parameters investigated were contact pressure, slipping ratio, rotational speed, lubricant viscosity and load sequence, with each of them varying between two values. The first step was an investigation of the Coefficient of Traction (COT) under different testing conditions, followed by a set of RSTs to investigate surface damage initiation. It was found that the COT increased significantly under certain conditions of opposite rotational direction. The RST results showed that cracks and spalls on the surface were severer when higher slip ratio, higher contact pressure and higher rotational speed were applied first than that when lower levels of these parameters were applied first.