Acoustic detection of bolt detorquing in structures

Recent interest in structural health of bridges and large buildings has lent new urgency to the development and enhancement of theories and methods in the field of Non- Destructive Testing (NDT). We demonstrate a simple technique for acquiring data from an impact test using a basic electronic stethoscope. The Continuous Wavelet Transform (CWT) is used to process and display the transient responses of a bolted joint in a structure before and after each bolt is detorqued. We enhance the interpretation of results using speaker-driven audio output. Preliminary results indicate that bolted joints in large structures might be quickly and inexpensively evaluated for looseness using signals in the audible range, with minimal post processing.