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Proceedings Paper

Corrosion damage detection with piezoelectric wafer active sensors
Author(s): Dustin T. Thomas; John T. Welter; Victor Giurgiutiu
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Paper Abstract

Since today's aging fleet is intended to far exceed their proposed design life, monitoring the structural integrity of those aircraft has become a priority issue for today's Air Force. One of the most critical structural problems is corrosion. In fact the KC-135 now costs $1.2 billion a year to repair corrosion. In this paper, we plan to show the use of Lamb waves to detect material loss in thin plates representative of aircraft skins. To do this we will use embedded transducers called Piezoelectric Wafer Active Sensor (PWAS) in a pitch-catch configuration. The sensors were placed on a grid pattern. Material loss through corrosion was simulated by removing the material mechanically with an abrasive tool. Thus, simulated corrosion pits of various depths and area coverage were made. Three-count tone burst wave packets were used. The Lamb wave packets were sent in a pitch-catch mode from one transmitter PWAS to the other PWAS in the grid acting as receivers. The Lamb wave mode used in these experiments was A1, since this was found to be more sensitive to changes due to material loss. At the frequencies considered in our experiments, the A1 waves are highly dispersive. It was found that, as the Lamb wave travels through simulated corrosion damage, the signal changes. The observed changes were in the signal wavelength (due to change in the dispersive properties of the medium) and in signal amplitude (due to redistribution of energy in the wave packet). This change in signal can be correlated to the magnitude of damage. To achieve this, we have used several approaches: (a) direct correlation between the sent and the received signals; (b) wavelet transform of the signal followed by correlation of the wavelet coefficients time-frequency maps; (c) Hilbert transform of the signal to produce the signal envelope and comparison of the resulting envelope signals (d) neural network correlation between the sent and received signals. It was found that these methods work well together in a complementary way.

Paper Details

Date Published: 21 July 2004
PDF: 12 pages
Proc. SPIE 5394, Health Monitoring and Smart Nondestructive Evaluation of Structural and Biological Systems III, (21 July 2004); doi: 10.1117/12.541152
Show Author Affiliations
Dustin T. Thomas, Air Force Research Lab. (United States)
John T. Welter, Air Force Research Lab. (United States)
Victor Giurgiutiu, Univ. of South Carolina (United States)

Published in SPIE Proceedings Vol. 5394:
Health Monitoring and Smart Nondestructive Evaluation of Structural and Biological Systems III
Tribikram Kundu, Editor(s)

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