Numerical Methodology to Predict Subsurface Crack Initiation from Non-metallic Inclusions Due to Rolling Contact Fatigue

Abstract

Bearings used in the intermediate and high speed stages of offshore wind turbine gearboxes run in harsh working conditions and may fail prematurely due to rolling contact fatigue (RCF). The microstructural alterations linked with such premature bearing failures are often described as white etching crack failures (WEC). Understanding these white etching bearing failures requires the study of RCF phenomenon at multiple scales ranging from macroscopic to microscopic and at different stages such as crack initiation and propagation. This paper presents a 2D numerical framework to evaluate subsurface RCF crack initiation originating from non-metallic inclusions in bearings. The global finite element (FE) model simulates parts of the contact bodies such as roller elements and raceway to represent the contact zone. A submodel containing a non-metallic inclusion is derived from the global FE model of a rolling contact. The inclusion is elliptical in shape and its position, dimensions and orientation can be changed. A moving Hertzian pressure distribution is modeled to simulate the rolling pass and the stress history around the inclusion/matrix interface. A multi-axial critical plane approach is adopted to calculate fatigue initiation damage. After explaining the numerical framework, this paper highlights the functionalities based on a number of case studies, focusing on effects of normal load and surface traction between the roller and inner raceway, and on inclusion characteristics. The results give us an insight into the underlying physics behind the mechanism of subsurface initiated RCF. Investigation of the link between RCF and white etching cracking is ongoing.