Journal Published Online: 12 February 2008
Volume 36, Issue 3

Thickness Gaging of Thin Plates by Multi-Peak Frequency Decomposition of Lamb Wave Signals

CODEN: JTEVAB

Abstract

In the present work ultrasonic Lamb wave testing has been applied for thickness gaging of thin aluminum plates with 2, 3, and 4-mm thickness. Angle probes operated in pulse-echo arrangement with 0.98 MHz central frequency and 7°, 12°, and 20° incident angles were utilized for investigations. High order modes (A1, S1, A2, and S2) were selected and evaluated for measurements and a fast Fourier transform was utilized for frequency decomposition. The variation with thickness and frequency of the phase velocity was the basis of measurement. Two methods were proposed for thickness gaging: (1) a probe with 6000–8000 m/s phase velocity and one or two other probes with higher than 10 000 m/s phase velocity were utilized simultaneously to inspect each test area and the peak frequency with the highest amplitude excited by each probe was evaluated, and (2) a single probe was utilized and all visible peak frequencies were evaluated. These methods overcome the limitations of the previous research, which applied a peak frequency shift method for corrosion monitoring of plates only for a known mode and known initial thickness and low thickness reductions. The second method is more practical and accurate and has potential for on-line automatic thickness gaging of rolled plates.

Author Information

Edalati, K.
Department of NDT and Inspection, Radiation Protection Technological Center of Iran, Tehran, Iran
Edalati, A.
Kankash Parto Technical Inspection Company, Tehran, Iran
Kermani, A.
Department of NDT and Inspection, Radiation Protection Technological Center of Iran, Tehran, Iran
Pages: 9
Price: $25.00
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Details
Stock #: JTE100662
ISSN: 0090-3973
DOI: 10.1520/JTE100662