LONGITUDINAL CRACK INITIATION UNDER PURE ROLLING-CONTACT FATIGUE

Pure rolling contact fatigue tests were carried out on a two-disc machine. The longitudinal cracks were initiated on the specimen surface with pure rolling and rough driving disc conditions. Cracks were easily formed from the initial longitudinal finishing grooves on the surface. The crack distribution in the wear track depended on the elastohydrodynamic lubrication (EHL) condition. If the film thickness parameter LAMBDA was less than 0.1, most of the cracks were found at the center part of the wear track. With increasing LAMBDA, cracks were located towards the two sides of the wear track. When LAMBDA was greater than 0.5, the initiation of surface cracks was difficult except in the region near the surface defects. Three mechanisms of crack initiation under pure rolling conditions are postulated based on the micro-macro contact mechanics and micro-EHL theory.