Percussion-based vibration and audio signal analysis for structural health monitoring of bolted joints

Bolted joints are critical to engineering structures and their integrity is essential for safety and functionality. Traditional monitoring methods are often expensive and intrusive, necessitating the development of more efficient approaches. Preload loss in pretensioned bolts is inevitable in practice, making the reliable detection of loosening vital for structural reliability. This study presents a novel structural health monitoring (SHM) method based on vibration and percussive audio-emission signals generated during controlled percussion. A single bolted lap joint was subjected to percussion, and the resulting audio and vibration signals were recorded and analyzed in both the time and frequency domains to assess bolt tightness. As the bolt torque increased from 0 Nm to 25 Nm, significant variations were observed in signal characteristics. For the vibration signals, the Signal Energy, Peak-to-RMS ratio, and kurtosis changed by 48.84%, 61.02%, and 90.15%, respectively. For audio signals, the corresponding variations were 39.53%, 44.77% and 80.79%. Fast Fourier Transform (FFT) analysis showed a correlation between bolt tightening levels and frequency amplitudes, with slight frequency increases in both signal types with an increase in bolt torque. The results demonstrate that percussion-induced signals effectively reflect bolt tightness. Comparative analysis of vibration and audio responses highlights the potential of this multi-modal approach to enhance the reliability of bolted joint SHM applications.