Estimation of wall thinning in mild steel using laser ultrasound Lamb waves and a non-steady-state photo-emf detector

A. S. Murfin, R. J. Dewhurst

    Research output: Contribution to journalArticlepeer-review

    Abstract

    In this work, a non-steady-state photo-emf receiver has been used to detect the lower frequency fundamental a0 Lamb waves in mild steel. Experimentally, the Lamb waves are laser-generated in the thermoelastic regime using a Q-switched, 20 ns, pulsed Nd:YAG laser and a line source. Typical Lamb waves had centre frequencies of 250 kHz but with frequency components that extended beyond 1 MHz. In mild steel, higher order Lamb wave modes were not considered to be significant below a frequency thickness product of 1.6 MHzmm. Below this level, associated velocity dispersion curve offered phase velocity changes that were sensitive to thickness change. Samples up to 5 mm in thickness were examined without significant interference from higher order modes. A non-steady-state photo-emf detector used as the ultrasonic detector had the advantage of a lower frequency cut-off at 100 kHz compared to a confocal Fabry-Pérot interferometer (CFPI) of about 2 MHz. Both schemes offered greater stand-off distance (>20 cm) than is possible with EMATs, which have a stand-off distance less than 1.0 mm. Progress made in detecting wall thinning in steel plate with thickness up to 5 mm is reported. © 2002 Elsevier Science B.V. All rights reserved.
    Original languageEnglish
    Pages (from-to)777-781
    Number of pages4
    JournalUltrasonics
    Volume40
    Issue number1-8
    DOIs
    Publication statusPublished - May 2002

    Keywords

    • Lamb waves
    • Laser-ultrasound
    • Photo-emf sensor
    • Thickness monitoring

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