A new concept of a reference-free impedance method, which does not require direct comparison with a baseline
impedance signal, is proposed for damage detection in a plate-like structure. A single pair of piezoelectric (PZT) wafers
collocated on both surfaces of a plate are utilized for extracting electro-mechanical signatures (EMS) associated with
mode conversion due to damage. A numerical simulation is conducted to investigate the EMS of collocated PZT wafers
in the frequency domain at the presence of damage through spectral element analysis. Then, the EMS due to mode conversion induced by damage are extracted using the signal decomposition technique based on the polarization characteristics of the collocated PZT wafers. The effects of the size and the location of damage on the decomposed EMS are investigated as well. Finally, the applicability of the decomposed EMS to the reference-free damage diagnosis is discussed.
Impedance-based structural health monitoring (SHM) has been of great interest to many researchers. In general,
conventional impedance-based damage detection techniques identify damage by comparing "current" impedance signals
with "baseline" ones obtained from the pristine condition of a structure. However, structures in field are often subject to
changing environmental and operational conditions that affect the measured impedance signals and these ambient
variations can often cause false-alarms. In this paper, a new reference-free impedance method, which does not require
direct comparison with baseline impedance signals, is employed for crack detection in a plate-like structure. This method
utilizes a single pair of PZTs collocated on the both surfaces of a structure to detect mode conversion caused by the
presence of crack damage. A new statistical damage classifier is developed for instantaneous damage classification based
on decomposed impedance signatures containing mode conversion information. Experimental tests, particularly under varying temperature and loading conditions are presented to demonstrate the applicability of the proposed method to crack detection.
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