Noncontact and remote NDE systems and methods are highly desired in a broad range of engineering applications such as material property characterization. This paper aims to develop such a noncontact/remote NDE system based on laser ultrasonic guided waves and establish its fundamental capability for material thickness evaluation. The noncontact system employs pulsed laser (PL) for guided wave actuation and scanning laser Doppler vibrometer (SLDV) for guided wave wavefield sensing. A cylindrical planoconvex lens is adopted to focus the pulsed laser beam to a line source in order to excite broad band signals in the target plate. Aluminum plates with different thicknesses are evaluated through SLDV line scans and 2D time-space wavefields are acquired. Frequency-wavenumber (f-k) spectra are obtained through 2D Fourier transform, and the A 0 dispersion curve for each plate is extracted. Through Comparing the extracted A 0 curve with the theoretical A 0 dispersion curves, the thicknesses of the tested plates are identified. Reflective tape effect on the plates are also studied: the reflective tape attached for SLDV enhancement affects the guided waves in the target plate significantly when the plate is relatively thin.

Stress corrosion cracking (SCC) has been observed in the high-level nuclear waste tanks that were constructed by welding carbon steel plates. This paper aims to establish an ultrasonic inspection system and its fundamental ability for SCC inspection and quantification on thick welded steel plates. A welded steel plate was fabricated without heat treatment by joining two carbon steel plates through gas metal arc welding (GMAW) procedure. SCC growth, which was initiated with starter cracks across the weld, were observed in a few weeks after submerging the plate in 5 molar (5M) sodium nitrate (NaNO 3 ) solution at about 90 °C. The SCC is inspected with an ultrasonic guided wave system, which employs a piezoelectric transducer for guided wave actuation and a scanning laser Doppler vibrometer (SLDV) for wavefield sensing. The measured wavefield can immediately show wave interactions with the crack. Wavefield images are further generated for the crack length quantification. To demonstrate the crack sizing capability of using the piezoelectric transducer and SLDV, the previous results from the magnetic particle test (MT) are compared. Reasonable agreement in crack length measurement is obtained with the ultrasonic test imaging technique.