A novel active sensing method for robust multi-bolt monitoring and looseness detection via vibration features

Vibration is a leading cause of bolt loosening that threatens the integrity of bolted structures. Existing piezoelectric-based active sensing systems often suffer from weak vibration responses, structure-dependent frequency bands, and the need for many transducers and channels for multi-bolt monitoring. To overcome these challenges, this study presents a novel active impedance sensing device that mimics the distributed mechanoreception observed in biological systems. The device prototype is strategically designed to enhance sensitivity via amplifying local piezoelectric vibration responses, enabling a single PZT to detect and differentiate multiple bolt loosening events within a group of bolts. This compact system also eliminates the need for one transducer-to-one bolt deployment and frequency band pre-calibration, therefore overcoming the drawbacks of the existing systems. Furthermore, a bolt-looseness detection method is proposed, employing principal component analysis and k-nearest neighbor for automated localization. Through comprehensive numerical evaluations and experimental validations on bolted joints with varying looseness scenarios, the proposed method exhibits high accuracy to bolt looseness and robustness to noise. These characteristics render it well-suited for real-world applications, particularly in structural joints of numerous bolts.