Longitudinal critically refracted wave for residual stress assessment on a welded plate using 3D laser vibrometry

Local residual stresses, remaining in a material without any external load, generally result from manufacturing processes and associated deformations. Their characterization is important, as they can weaken the mechanical performance of the structure. Previous works have shown that ultrasonic techniques using longitudinal critically refracted waves (LCR) are successful for residual stress assessment near the surface in welded joints. In order to optimize the residual stress measurement, this work proposes a 3D scanning laser vibrometric detection, allowing to measure the three components of the displacement field produced by a LCR transducer over relatively long distances and on curved surfaces. The experiments are conducted for validation on a welded plate sample for which the calibration results are available in the literature. The base metal (BM) is P460 fine grain steel and the welding (Melted Zone) is performed along an X-shaped groove using the same filler metal. The wave generation is achieved by an angle beam piezoelectric transducer placed on the edge of the rectified area. Post-processing of vibrational signals acquired on the sample surface enables to extract the LCR wave and to construct the residual stress profile across the weld line. The results are in good agreement with those from the literature.