Lamb wave based identification and parameter estimation of corrosion in metallic plate structure using a circular PWAS array
A circular array of Piezoelectric Wafer Active Sensor (PWAS) has been employed to detect surface damages like
corrosion using lamb waves. The array consists of a number of small PWASs of 10 mm diameter and 1 mm thickness.
The advantage of a circular array is its compact arrangement and large area of coverage for monitoring with small area of
physical access. Growth of corrosion is monitored in a laboratory-scale set-up using the PWAS array and the nature of
reflected and transmitted Lamb wave patterns due to corrosion is investigated. The wavelet time-frequency maps of the
sensor signals are employed and a damage index is plotted against the damage parameters and varying frequency of the
actuation signal (a windowed sine signal). The variation of wavelet coefficient for different growth of corrosion is
studied. Wavelet coefficient as function of time gives an insight into the effect of corrosion in time-frequency scale. We
present here a method to eliminate the time scale effect which helps in identifying easily the signature of damage in the
measured signals. The proposed method becomes useful in determining the approximate location of the corrosion with
respect to the location of three neighboring sensors in the circular array. A cumulative damage index is computed for
varying damage sizes and the results appear promising.
This paper was published in SPIE Proceedings Vol. 7295
Health Monitoring of Structural and Biological Systems 2009, Tribikram Kundu, Editors, 72951C