The paper describes a theoretical study of adhesion at the contact between rough surfaces with small-scale surface asperities using an elastic-plastic model of contact deformation that is based on accurate finite element analysis (FEA) of an elastic-plastic single asperity contact. The model considers a large range of interference values from fully elastic through elastic-plastic to fully plastic regimes of contacting asperities. The well-established elastic and plastic adhesion indices are used to consider the different conditions that arise as a result of varying load and material parameters. The loading and unloading behaviour for different combinations of these adhesion indices are obtained as functions of mean separation between the surfaces. Comparison with a previous elastic-plastic model that was based on some arbitrary assumptions is made, showing significant differences.

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An experimental investigation was performed for investigating the tribological performance of micro-dimple surface texture patterns on a cylindrical surface in a realistic operating environment of starved lubrication. Micro-dimples were generated by a dual-frequency surface texturing method, in which a high-frequency (16.3 kHz) three-dimensional (3D) vibration and a low-frequency (230 Hz) one-dimensional (1D) vibration were applied at the tool tip simultaneously, resulting in the generation of the hierarchical micro-dimples in a single step. Rotating cylinder-on-pin tribological tests were conducted to compare the tribological performance of the non-textured reference specimen and micro-dimple samples. The effect of surface textures generated with various shape parameters (long drop and short drop), dimension parameters (length and surface texture density), and operation parameters (load and sliding velocity) on the tribological performance was evaluated. Stribeck curves indicate that the hierarchical micro-dimples exhibit a lower coefficient of friction than the reference specimen in the high contact-pressure regions. It is also observed that variation in the length of a micro-dimple, the shape effect, is the major factor affecting the friction response of the textured surfaces. The generation of additional hydrodynamic pressure and lift effect by hierarchical structures is the main reason for the improved performance of hierarchical micro-dimple surfaces.