Thermal elastohydrodynamic lubrication and subsurface stress in multilayer-coated angular contact ball bearings

Multilayer coatings are widely used in modern mechanical equipment to prevent the tribopairs from surface wear and improve the fatigue life. This study develops a mixed thermal elastohydrodynamic lubrication model for a coated angular contact ball bearing, incorporating multilayer coatings on the raceway surface. The influence coefficients associated with elastic deformation and stress components in the multilayer contact problem are determined through frequency response functions. The correctness of the model is verified by comparing its results with available numerical results from the literature. Based on the dynamic characteristics analysis of bearings, the influences of multilayered gradient structure, gradient thickness, and gradient layer number on the lubrication characteristics of the bearing are investigated. Results show that the non-uniformly decreasing gradient structure provides the best surface lubrication performance at low speed, whereas the uniformly increasing gradient structure gives better comprehensive performance at high speed when both lubrication behavior and subsurface maximum shear stress are considered. The change rule of lubrication performance with the gradient thickness of different gradient structures is basically the same, and the greater the gradient thickness, the greater the difference between them. An increase in the number of gradient layers leads to a smoother and more homogeneous subsurface stress distribution, while exerting only a minor influence on the film thickness, pressure, temperature, and the magnitude of the maximum subsurface shear stress.