Novel piezoresistive sensing approach for high-temperature monitoring and assessment of fault modes and structural integrity in bolt fasteners

In aerospace, energy, and transportation applications, engineering structures often operate at elevated temperatures, where the reliability of bolted fasteners is essential to maintaining structural integrity. However, current structural health monitoring (SHM) techniques exhibit limited thermal resistance and poor integration with bolted joints, thereby restricting their effectiveness in high-temperature environments. To address these challenges, an advanced piezoresistive sensor array with a nanocomposite sensing layer composed of graphene nanoplatelets, multi-walled carbon nanotubes, aluminum oxide, and polyimide was developed on a flexible printed circuit substrate. The optimized filler composition and thermal stabilization enhanced both high-temperature endurance and sensitivity. Stable repeatability and recoverability were experimentally verified, and the sensors maintained reliable performance at temperatures up to 400°C. The designed sensor array enabled synchronous monitoring of fastener loading conditions, precise detection of bolt loosening, and identification of out-of-plane deformation of the washer, thereby providing a comprehensive characterization of fastener state variations and fault modes. The proposed monitoring approach provides a basis for future research on monitoring other high-temperature failure mechanisms, such as fatigue and thermal degradation. These findings establish the proposed approach as an innovative and reliable SHM solution for bolted joint fasteners in high-temperature environments.