Corrosion damage detection and characterization using non-destructive evaluation techniques.

摘要

The objective of this thesis is to detect and characterize localized corrosion in 2024T3 Aluminum alloy using non-destructive evaluation (NDE) techniques. Ultrasonic lamb wave inspection and fractal geometry are the two NDE techniques considered to detect and characterize corroded surfaces in aluminum plates respectively. Lamb wave scanning approach requires generation of ultrasonic So mode Lamb wave using an incident transducer with a tone burst centered at a near non-dispersive frequency. A receiving transducer scans the sections of the thin plate along a line parallel to the propagating lamb wave on the face of plate free from defect. Corrosion damage is localized by comparing relative normalized wave energy the propagating wave in a plate with damage with that of relative normalized energy variation of propagating wave in a plate without any damage. To demonstrate Lamb wave approach experiments were performed on 1.6 mm-thick Al plates with corrosion induced artificially using FeCl3 solution. Fractal geometry is a NDE technique to characterize corroded surfaces with a parameter called the fractal dimension. Image analysis was performed by obtaining microscopic and macroscopic digitized images of the corroded aluminum alloy surface. Box-counting algorithm was implemented on binary images to obtain fractal dimension, a parameter used to characterize corrosion. Attempt was made to quantify the extent of corrosion in Al plates using this non-contact NDE approach.