Lubrication state monitoring of sliding bearing based on triboelectric Stribeck curve

Maintaining an optimal lubrication state is essential for the efficient and safe operation of machinery. Classical tribology theory employs the Stribeck curve to describe lubrication states by measuring friction forces under varying loads and speeds, inevitably requiring external sensors to obtain the friction torque, which limits practical applications. In this study, we applied the triboelectric principle to a commercial sliding bearing to achieve self-powered lubrication state monitoring with minimal alterations to the original structure. Fluorine-doped diamond-like carbon (F-DLC) films were systematically studied for the first time and demonstrated to be promising electronegative materials with enhanced output and durability through optimal fluorine doping. The electrical current and coefficient of friction (COF) of the proposed triboelectric sliding bearing were tested simultaneously using a well-designed platform under different loads and rotational speeds with various lubricants, revealing opposite trends. Thus, the current signals can serve as a “triboelectric Stribeck curve” for monitoring the lubrication states. The mechanism underlying the output changes under different lubrication regimes was elucidated using the Debye length concept. This study interprets the Stribeck curve, a classic concept in tribology, from the triboelectric perspective. It not only holds great potential for application in self-powered and real-time lubrication state monitoring of mechanical systems but also plays an important guiding role in other fields of tribology, such as gear and bearing design, lubricant composition improvement, and engine structure optimization.