Monitoring damage propagation using PZT impedance transducers

Structural health monitoring (SHM) is of great importance in preventing structural catastrophic failure which can lead to loss of life and property. Lead zirconate titanate (PZT) is one of the most effective types of piezoelectric material, and it has been widely used with the electromechanical impedance (EMI) based SHM technique. In the EMI technique, PZT transducers are surface bonded to a structure to be monitored, and, in the presence of electric fields, they interrogate the structure and record the admittance signatures. The existing EMI techniques have focused on single damage assessment. However, once damage occurs in a structure, it may propagate along a certain direction and eventually lead to failure or collapse of the structure. Therefore, effective monitoring of damage propagation is an important aspect in SHM. This paper presents a study on monitoring damage propagation in aluminium plates using the EMI technique. Experiments are carried out to study the damage propagation by drilling holes in sequence along the length and width directions of the plates. PZT admittance signatures are recorded for each damage state and compared with the signature of the pristine state. In addition, a semi-analytical EMI model is employed to predict the PZT admittance signatures and compare them with the experimental ones. Both experimental and predicted signatures are analysed qualitatively and quantitatively using a statistical method. The results demonstrate the capability of the EMI method for monitoring damage propagation.