Early bolt looseness monitoring using the leading waves energy in piezoelectric active sensing

Abstract

Bolt monitoring plays a vital role in ensuring the safe operation of engineering structures. The utilization of piezoelectric (PZT) active sensing and analysis of ultrasonic energy transmitted through the interface of bolted connections has demonstrated high feasibility for monitoring bolt looseness. However, the ultrasonic energy saturation effect (i.e. the response signal energy changes slightly as the bolt preload variation) near the rated bolt preload restricts its applicability in early detection of bolt loosening. In this paper, for the energy saturation in the PZT active sensing method, a new bolt looseness indicator with the energy of leading waves (i.e. the first several wave packets) in the response signal is proposed for bolt loosening monitoring, especially for the early bolt loosening monitoring since the energy of the leading wave packets has the linear relationship with bolt preload. The experimental results show that the energy of the first several wave packets in the response signals can be as a looseness indicator of bolt preload. Within the entire range of bolt preload, the indicator exhibits a linear relationship with the bolt preload. Moreover, this method successfully resolves the challenge of energy saturation, providing an effective approach for monitoring bolt preload.