Electromechanical Impedance Instrumented Wearable Piezoelectric Ring-Type Sensor for Bolted Connection Monitoring

Due to the loss of preload, structural failure caused by bolt loosening is common in engineering structures. Effective monitoring of bolted connections is of great importance in providing early warning to the structural maintenance department. In this study, a novel and reusable electromechanical impedance (EMI) instrumented wearable piezoelectric ring (WPR) was proposed to detect bolted connection loosening. In the experimental investigation, the EMI spectra of three identical WPRs during the bolt-loosening process were acquired and analyzed. It was concluded that bolt looseness changes can be qualitatively and quantitatively characterized by conductance spectra. Specifically, the resonance frequency and amplitude at certain frequencies were reduced correspondingly as bolts loosen. This was further validated by finite element model (FEM) simulation results. Moreover, two statistical metrics including mean absolute percentage deviation (MAPD) and root mean square deviation (RMSD) were adopted to evaluate different degrees of bolted connections quantitatively. Both metrics showed an increasing tendency during the bolt loosening process in three different frequency bands. It was found that both metrics demonstrated a significant linear correlation with bolt torque variations. Both of them serve as reliable indicators to detect loose bolts in the bolted connection. The present work verifies the feasibility and applicability of using EMI-instrumented WPR to monitor bolted connections.