Monitoring damage propagation using PZT impedance transducers

Lead Zirconate Titanate (PZT) transducers have been extensively used in the electromechanical impedance (EMI) based structural health monitoring (SHM). Many EMI models have been developed for damage assessment, mostly focusing on single damage identification. However, in real life, structures are frequently subjected to multiple or progressive damages. Specifically, structural components such as beams and columns are subjected to loading, vibration, wear and tear which could cause multiple damages. Once damages occur, they usually propagate along certain directions due to continuous usage or inadequate protection. Moreover the increase in severity of damages may lead to failure of the structural components or even the whole structure. The EMI technique which is based on the electromechanical interaction between the PZT transducer and its host structure has been found to be effective in damage detection. However, systematic study on monitoring the progressive of damage in multiple directions in the structures is still in need. In this paper, the EMI technique using surface bonded PZT transducers is employed to obtain the structural health signature. Experimental tests are carried out to study the damage propagation on aluminum plates, where damages are created along the length and width directions of the plates by drilling holes in sequence. Structural health signatures are obtained for each damage state and compared with the signature of non-damage state, followed by the discussion on the characteristics of damage propagation. In addition, for different damaged states, finite element modeling is carried out to verify the experimental signatures. The acquired numerical results are analyzed both qualitatively and quantitatively. Both experimental and numerical results demonstrate the capability of EMI technique for damage propagation monitoring.