Surface Mechanical Behavior and Surface Lubrication Properties of Bionic Foot

The surface mechanical behavior of metallic bionic foot exerts a decisive influence on their service life. A face-to-face friction test system was employed to simulate the surface tribological behavior of bionic foot during actuation. Cellulose coatings were in situ formed on the contact surfaces of three types of bionic foot to replicate practical operating conditions, followed by tribological testing and characterization analysis. This study investigated the effect of cellulose coating in retarding the wear of the three bionic feet and elucidated their surface lubrication properties. The results demonstrate that surface deformation of the bionic foot is primarily concentrated at the toe tips, as well as the edges and corners of the feet. Tribological test results indicate that after modification with cellulose coatings, the friction coefficient first decreases and then increases with increasing load; when the load reaches 20 N, the friction coefficient of the bionic foot surface drops to as low as 0.043, and the wear scar depth also reaches its minimum value. The underlying mechanism lies in the fact that friction-induced effects promote the formation of adsorbed tribofilms of cellulose on the surface of the bionic foot. These tribofilms effectively isolate the direct contact between the upper and lower friction pairs, thereby enhancing lubrication efficiency while significantly mitigating adhesive wear and abrasive wear. This study establishes mechanical models of the bionic foot to provide experimental validation and design guidelines aimed at enhancing its service life.