Degradation of high loaded oscillating bearings: Numerical analysis and comparison with experimental observations

Nowadays mechanical systems are expected to sustain extreme working conditions, due to the increase of the involved power and the optimized design. Moreover special applications like aeronautics, space engineering and robotics require the reduction of the contact area in the contact pairs, which allow the relative motion between components, by increasing the power transmitted per unit of contact area. As a consequence the joint degradations are between the main issues, resulting in possible failures or increase of consumption and maintenance costs. This paper addresses the analysis of the degradation mechanism of oscillating ball bearings subjected to high loads. These bearings, needed to assure the repetitive relative rotation between two members of the mechanical system (e.g. repetitive motions of assembling and manufacturing robots, ship helms, aircraft flaps, etc.), can reach extreme contact pressures at the ball-race contact surfaces; the oscillations of the bearings provide a fatigue loading of the contact area due to the repetitive rotation of the balls between the races. This work is aimed to calculate the contact stress distributions due to the specific boundary conditions, in order to relate them with the bearing degradation. A numerical model is presented to reproduce the loading conditions and calculate the contact stress and strain distributions in order to correlate them with the damages observed experimentally; results obtained by 2D modelling and 3D modelling, for both elastic and plastic properties of the bearing material, are reported and compared. The numerical results and the comparison with tribological observations of a degraded bearing, after cyclic load application, suggest a possible degradation scenario that brings to the failure of the bearing due to subsurface damages. © 2014 Elsevier B.V.