A Mixed Elasto-Hydrodynamic Lubrication Model for Studying Tribological Properties of Rough Surfaces

To investigate the influence of asperities on tribological properties in mixed elasto-hydrodynamic lubrication (EHL), a numerical model which can present the local contact state of the rough surface is developed. This model can produce a virtual rough surface in Gaussion distribution, and with the use of average flow Reynolds equation and the K-E elasto-plastic model, the hydrodynamic pressure and the contact pressure can be predicted, respectively. Fast Fourier transform (FFT) method is used to compute the elastic deformation of substrate. The influences of virtual asperities, nominal load, roughness and asperity curvature radius on the tribological properties of EHL are also discussed through plotting corresponding Stribeck curves and film thickness shapes. The results show that the contact of asperities induces the deformation of substrate, which subsequently increases the film thickness and reduces the hydrodynamic pressure. Thus, the load rate of oil film and the friction coefficient are increased accordingly. With the increase of nominal bearing load, the friction coefficient is decreased at low speed, implying that the transition point from boundary lubrication regime to mixed lubrication regime occurs at lower speeds. Smaller roughness implies the movement of the Stribeck curves towards left. The increase of asperity curvature radius accelerates the transformation from boundary lubrication to mixed lubrication. However, the transition from mixed lubrication to hydrodynamic lubrication seems not to be obviously influenced by the asperity curvature radius.