Flexible printed circuit-based triboelectric film sensor for integrity monitoring of tensile bolted joints

Abstract This study presents an improved design of a triboelectric film sensor for integrity monitoring of tensile bolted joints, which is designed to capture the micro-scale relative motion due to the bolt’s looseness by utilizing the triboelectric effect of the polymer layer of the sensor in contact with the metal surface of the fastened objects. The key idea is twofold: First, we use the triboelectric effect between the polymer layer and the fastened object itself, instead of the triboelectric effect between two polymer layers. This allows the sensor to be a single sheet configuration instead of two-piece. The second idea is to make the sensor design fabricable as a standard flexible printed circuit. This makes it possible to produce sensors accurately and inexpensively. Experimental tests incorporating the proposed sensor into a tensile bolted joint have demonstrated that the sensor’s voltage output is inversely related to the bolt’s tightness. Additionally, a modeling study adopting Persson’s contact theory has been conducted to refine the understanding of the real contact area, triboelectric charging, and separation dynamics between the polymer and metal layers, which is crucial for the accurate modeling of sensor outputs under dynamic loading conditions. It has been concluded that the integrated mechanical and triboelectric model successfully aligns with the experimental findings, indicating the sensor’s potential for practical applications in bolt integrity monitoring.