A VORONOI FINITE ELEMENT/DAMAGE MODEL FOR LIFE SCATTER IN ROLLING CONTACT FATIGUE

摘要

It has been widely accepted that the microstructure of bearing materials can significantly affect their rolling contact fatigue (RCF) lives. Hence, micro-level topological features of materials will be of significant importance to RCF investigation. The two most dominant RCF mechanisms are subsurface originated spalling and surface originated pitting. Subsurface originated spalling occurs when microcracks originate below the surface at material inhomogeneities like non-metallic inclusions and propagate towards the surface to form a surface spall. Surface originated pitting on the other hand, occurs in cases where surface irregularities in the form of dents or scratches are present. Miller showed that the scatter in fatigue lives needs to be studied by considering the effect of material microstructure on early crack growth. Bearing materials are polycrystalline in nature and consist of grains with various crystallographic orientations, shapes, and sizes. Ito and Fuller showed that grains of a polycrystalline material can be represented to a good degree of accuracy by using the Voronoi tessellation process. In this investigation, a Voronoi finite element fatigue damage model was developed to investigate the rolling contact fatigue of bearing elements and effects of topological randomness of material microstructure. For this purpose, damage mechanics approach developed by Kachanov, Chaboche, and Raje et al. is incorporated into the Voronoi finite element model (VFFM) developed by Jalalahmadi and Sadeghi. Contrary to most of the life models existing in the literature for estimating the RCF lives, the current model considers micro-crack initiation, coalescence and propagation stages.