Micro-scale frictional behavior of a bearing steel (JIS SUJ2) in cyclic sliding motion

Abstract Application of fracture mechanics has recently been emphasized to establish the mechanics-based evaluation of the rolling contact fatigue strength for designing mechanical elements such as bearing, rail/wheel, gear, etc. Flaking that is a typical rolling contact failure mode is intimately related to the shear-mode (modes II and III) fatigue crack growth, which is significantly affected by the interaction of opposing crack faces. Understanding the tribological properties on the crack faces being in the reciprocating sliding contact is therefore essential for the material design as well as the mechanical design of many components associated with rolling contact fatigue. The present study carried out a ring-on-ring test by making use of a combined axial-torsional fatigue testing machine to investigate the micro-scale frictional phenomena under the non-lubricated condition. The material investigated was a heat-treated high-carbon-chromium bearing steel (JIS SUJ2) with a Vickers hardness of 753. The tests were conducted up to 104 cycles under the various conditions of mean contact pressures of 10-100 MPa, relative displacement amplitudes of about 10-100 μm, sinusoidal frequencies of 0.1-10Hz, and initial surface roughness values, Ra, of 0.2-1.7. The time variations of the tangential force, contact load and the relative displacement between contact surfaces were periodically monitored at a predetermined number of cycles during testing.