Multi-Bolt Loosening Monitoring Using an Integrated Vibro-Acoustic Modulation Technique

This paper proposed an integrated vibro-acoustic modulation method (IVAM) for multi-bolt loosening monitoring. Numerical simulations and experiments of a single bolt model are initially conducted to illuminate the contact acoustic nonlinearity (CAN) and vibro-acoustic modulation (VAM) phenomenon. The finite element model considers the coupled field effects and the contact interface of the bolted joint. A pumping wave with a certain low frequency combined with a probing signal sweeping through the frequency range of 50 kHz to 100 kHz was implemented and verified to effectively trigger VAM on the bolted connection. A comprehensive damage index (CDI) associated with the linear energy and nonlinear CAN change due to the bolt looseness is then proposed to evaluate bolt looseness in a full life cycle. For further study, IVAM is applied on a complex multi-bolt connection part to locate and identify the loosened bolts. Several cases are investigated to analyze its performance. An intelligent self-verification mechanism is used to ensure the accuracy of the results. The proposed IVAM method with an outcome CDI matrix possesses great application potential for multi-bolt connection monitoring with high sensitivity and accuracy. This paper finishes with summary, concluding remarks, and suggestions for future work.