Reference-free impedance-based crack detection in plate-like structures

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.