Nondestructive evaluation (NDE) plays a critical role in the safety and quality control of structures. Effective NDE inspection system and methods are highly desired in a broad range of engineering applications such as coating thickness evaluation. On one hand, laser generated ultrasound has been widely used for NDE in many engineering applications since the laser enables both contactless and remote ultrasound generation. On the other hand, noncontact laser vibrometry has been intensively adopted for NDE applications to measure ultrasound wavefield and proved effective for both material characterization and damage detection. The combination of laser ultrasound generation and sensing towards a fully remote and noncontact system will enable more flexible NDE applications.

This paper aims to develop a noncontact/remote ultrasonic guided wave NDE system and establish its fundamental capability for material thickness characterization. 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 same material properties and different thicknesses are inspected using the noncontact system for proof of concept study. The inspection is performed through SLDV line scans and 2D time-space wavefields are acquired for each plate. Through 2D Fourier transform, the acquired wavefields are transferred to frequency-wavenumber (f-k) domain, where broad band frequency components are observed. The frequency and wavenumber components in the acquired f-k spectrum for each certain thickness plate agree well with theoretical dispersion curves. Reflective tape effect on the plates are also studied: the reflective tape attached for SLDV enhancement affects the guides waves in the target plate significantly when the plate is thinner than 1 mm. The developed noncontact PL-SLDV system combined with effective material characterization capability will enable better safety and quality control of new structures during manufacturing process and intime monitoring and maintenance of the existing ones.


Noncontact/Remote Material Characterization Using Ultrasonic Guided Wave Methods

Division / Sponsors: 
Aerospace Division

Paper Proceedings: https://asmedigitalcollection.asme.org/SMASIS/SMASIS2020/volume/84027

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