Stratified Contact Modeling and Stiffness Evolution Mechanism of Scraped Surfaces Under Mixed Lubrication

The scraping process is a key technique for enhancing lubrication and improving surface flatness in mechanical joint surfaces. However, the microscopic contact mechanism remains poorly understood due to the complexity and randomness of scraping. To overcome the limitations of traditional single-Gaussian rough surface models in mixed lubrication analysis, this study develops a novel bi-Gaussian stratified contact stiffness model. This model achieves a more accurate description of interface contact behavior by accurately characterizing the topography features of the scraped surface. Based on the probability density function (PDF) of bi-Gaussian surfaces, the modified Brake model is used to develop a solid contact stiffness model for the scraped surface. This model is then corrected by treating the lower Gaussian surface as a substrate. Subsequently, the average Reynolds equation is applied to model the liquid contact stiffness and solid–liquid coupling through the oil film thickness. Contact stiffness experiments conducted on scraped surfaces with three accuracy levels verify the proposed model. Finally, parametric studies are performed using the established model to evaluate the effects of both the proportion and roughness of the upper Gaussian surface on the resultant solid and liquid contact stiffness. The results indicate that under a 40 kN load, increasing the proportion of the upper Gaussian surface from 40 to 90% increased the total contact stiffness by approximately 21%, and reducing its roughness from 6 μm to 1 μm increased the total contact stiffness by approximately 52%.