Remote, volumetric ultrasonic imaging of defects using two-dimensional laser induced phased arrays

Manufacturing processes, such as welding and additive manufacturing, take place at high temperatures and extreme environments that offer significant challenges to conventional nondestructive testing methods. Laser Induced Phased Arrays (LIPAs) have evolved as a promising testing method for the aforesaid applications due to its remote and couplant free operation. Contrary to transducer-based phased arrays, LIPAs are synthesized in post-processing by scanning the generation and detection lasers. 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, thus providing more information on defect characterization. In this work, two-dimensional (2D) LIPAs are synthesized in the non-destructive thermoelastic regime using lasers for ultrasonic generation and detection, in order to image defects at different depths inside an aluminum sample. The acquired data is processed using the Total Focusing Method (TFM) algorithm to obtain volumetric images representing the interior of the sample. A 3D finite element (FE) model is also developed to support the experiments.