Quantitative evaluation of bolt connection using a single piezoceramic transducer and ultrasonic coda wave energy with the consideration of the piezoceramic aging effect

In this paper, a method to quantitatively evaluate the status of bolted connection by using a single piezoceramic transducer and coda wave is proposed. The so-called coda wave was inherited from the seismological community to name the late part of a seismogram. Coda wave is a slowly decaying wave after being scattered multiple times due to medium heterogeneities or boundaries, and it is extremely sensitivity to small changes and highly repeatable. The bolt connection is good application of coda wave since the presence of the microscopically rough surfaces and the boundary along the bolt interface generate scattering events. Stress wave generated by a Lead Zirconate Titanate (PZT) transducer is often used to evaluate the status of bolted connection. However, with the aging of a PZT transducer, the amplitude of the excitation signal decreases, and the signal energy does not correctly reflect the real status of the bolt connection. In this paper, a single PZT transducer, acting as both an actuator and a sensor, is used to transmit and receive stress wave signal. The stress wave signal received by PZT sensor consists of two parts, one is the direct wave whose amplitude is related to the excitation signal, and the other part is the backscatter wave (coda wave) produced by microscopically rough surfaces and the boundary along the interface of a bolt connection. Coda wave amplitude is affected by both heterogeneity of microscopically rough surfaces and PZT performance. To eliminate the effects of PZT aging, coda wave is normalized through the amplitude of the direct wave, and the magnitude of coda wave energy (CWE) only reflects the change of connection states. The main innovation of this paper is to establish the quantitative relationship between the bolt connection status and the CWE with a single PZT transducer. An experiment on the evaluation of the bolt connection status was carried out in this research. The results indicate that quantitative evaluation on the bolt-connected structure can be achieved through CWE, thus verifying the proposed method.