20 - Contact fatigue

Abstract

Rolling contact fatigue (RCF) failures are frequently observed on the surfaces of machine elements, such as bearings, gears, steel making rolls, railway rails and wheels, etc. RCF is affected not only by loading conditions but also by material properties, lubricants, surface conditions, and nonmetallic inclusions contained in materials. These make it very difficult to understand the phenomenon quantitatively from a mechanical point of view. Even if the surface roughness of a contact surface is very much diminished by the most advanced mirror polishing techniques, only one fracture origin somewhere on or beneath the surface leads to final failure of the component, even though under an identical contact loading there should be many potential fracture origins. This phenomenon is evidence of the influence of surface asperities and nonmetallic inclusions as fracture origins when they are hidden on or beneath the contact surface by surface finishing. Therefore we cannot solve the problem of contact fatigue using only the classical contact mechanics and lubrication theory.