Contact Stress Modeling in Railway Bearings for Imperfect Contact Geometries

Abstract

The connection between bearing raceway condition and fatigue in tapered roller bearings utilized in the railroad environment is of interest. Roller bearings for railroad applications are typically precision ground to exact dimensions with crowned contact geometries for optimal loading of components. This normally results in completely elastic Hertzian contact stresses under standard railcar loads with original equipment manufacturer raceway contact geometries. However, with extremely uneven bogie load distributions, impact damage, corrosion and spall repair, imperfect stress distributions can occur on bearing raceways utilized in the railroad environment. Railroad bearing applications in North America have the added complexity that the life of the product is not defined in the same way as in other industries. For example, the definition of spalling remains consistent across all industries and is outlined in the Association of American Railroads (AAR) Manual of Standards and Recommended Practices. However, an inconsistency compared to other industries is that the fatigue life of the product in the rail industry is not always considered complete at the first evidence of fatigue spalling. Although some other industries allow for the remanufacture and restoration of bearing assemblies, the aggressive raceway fatigue regrinding practices allowed by the AAR are not commonly permissible in other industries. These remanufacturing practices adversely influence subsurface stress magnitudes below the raceway surface, as they reduce the effective length of the raceway and can create stress risers. Engineering tools like the novel modeling method presented in this paper can be used by bearing designers to evaluate the impact of surface discontinuities, at the center or edge of the raceway, on the overall stress state of bearing raceways. For the various types of raceway conditions detailed above, a new tool was developed using finite element methods to simulate the stress state of the bearing under complex raceway contact geometries or adverse load conditions. The finite element contact stress tool was successfully validated using proven Hertzian contact theory. Peak maximum shear and von Mises subsurface stress predictions between the finite element model and conventional contact theory agreed within .001 inches, with regards to peak stress depth below the surface, and 10,000 psi, with regards to peak stress magnitude. This newly developed methodology will be used in future studies to analyze other load conditions and raceway contact geometries that cannot be analyzed with basic Hertzian contact theory, in order to illustrate practical application of the tool. Specifically, overload conditions are analyzed in the work presented. Furthermore, a proposed methodology for future work related to the examination of the stress state created by current AAR bearing reconditioning acceptance standards related to raceway impact damage and spall repair will be introduced.