A novel damage index integrating piezoelectric impedance and ultrasonic guided wave for damage monitoring of bolted joints

The structural safety of bolted joints, one of the typical connection techniques utilized in engineering applications, is threatened by the harsh service environment. Herein, a novel damage index (DI) integrating piezoelectric impedance and ultrasonic guided wave is proposed for satisfying the damage monitoring needs of bolted joints. By integrating the two sensing techniques, the shortcomings of a single sensing technique in terms of signal interpretation, stability, and structural adaptability are eliminated. The novel damage severity factor DI Z-V is formed by fusing the damage indices DI Z and DI V weighted by multi-class DIs of the two sensing techniques. Thanks to DI Z-V and a damage mode identification factor presented in this paper, the damage modes and damage severity of early-stage bolt loosening and crack damage are identified. Furthermore, a novel dynamic superposition model (DSM) based on a dynamic-update baseline is developed to address the deficiency that the static baseline method (SBM) has. SBM utilizes the undamaged state signal as the baseline and has the problem of being prone to failure in the later-stage of monitoring. Thus, the phenomenon of nonlinear variation of DI Z-V caused by damage deterioration was avoided via DSM optimization. The feasibility and effectiveness of the proposed method were verified by conducting a series of practical damage identification tests on aluminum bolted joints. And the results demonstrated that the proposed technique could not only identify the severity and mode of damage, but also has excellent reliability. Therefore, the novel damage monitoring technique for bolted joints is a good complement to the existing techniques, which can provide a new strategy for damage monitoring.