<p>Ultrasonic phased arrays have seen a dramatic increase in their use for non-destructive testing. The data from one-dimensional (1D) phased arrays are used to produce two-dimensional (2D), cross-sectional images, whereas the data from two-dimensional phased arrays generate three-dimensional (3D) images (volumetric imaging), thus providing more information on defects. However, transducer-based phased arrays fail to operate at the high temperatures and harsh environments offered by methods such as welding and additive manufacturing. Laser Induced Phased Arrays (LIPAs) can be used in such hostile environments due to the remote mode of operation associated with laser ultrasonics. Contrary to transducer-based phased arrays, LIPAs are synthesized in post-processing. LIPAs implement one laser to generate ultrasound and another laser to detect the surface displacements. The generation and detection laser beams are scanned on the surface of the sample to capture the full matrix (FMC). In this work, 2D LIPAs are synthesized in the non-destructive thermoelastic regime using a 7 ns pulsed Nd:YAG laser and a 532 nm continuous wave laser to image defects of varying sizes at different depths inside an aluminium and a steel sample. The acquired data is processed using the Total Focusing Method (TFM) algorithm to obtain a volumetric image representing the interior of the sample. A 3D finite element (FE) model is also developed to support the experiments.</p>

Remote, Volumetric Ultrasonic Imaging of Defects Using Two-Dimensional Laser Induced Phased Arrays

Paper Proceedings: https://asmedigitalcollection.asme.org/qnde/QNDE2021/volume/85529

ASME 2021 48th Annual Review of Progress in Quantitative Nondestructive Evaluation (QNDE2021)

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