Laser ultrasound and simulated time reversal on bulk waves for non destructive control

3rd International Symposium on Laser Ultrasonics and Advanced Sensing

Diot, G.^1 ; Walaszek, H.^2 ; Kouadri-David, A.^3 ; Guégan, S.^3 ; Flifla, J.^4

Institut Maupertuis, Contour St-Exupéry, Campus de Ker Lann, 35170 Bruz, France^1

CETIM de Senlis, 52 Avenue Félix-Louat, 80067-60304 Senlis cedex, France^2

Université Européenne de Bretagne, INSA-LGCGM-EA 3913, avenue des Buttes de Coesmes 20, 35043 Rennes Cedex, France^3

ECAM Rennes-Louis de Broglie, Campus de Ker Lann, 35170 Bruz CS 29128, France^4

关键词: Compression waves;    Defect detection;    Laser ultrasound;    Non-destructive control;    Nondestructive inspection;    Ultrasound signal;    Wave identification;    Welding defects;   

Others  :  https://iopscience.iop.org/article/10.1088/1742-6596/520/1/012018/pdf
DOI  :  10.1088/1742-6596/520/1/012018

来源: IOP

【 摘 要 】

Laser welding of aluminium generally creates embedded welding defects, such as porosities or cracks. Non Destructive Inspection (NDI) after processing may ensure an acceptable weld quality by defect detection. Nowadays, NDI techniques used to control the inside of a weld are mainly limited to X-Rays or ultrasonics. The current paper describes the use of a Laser Ultrasound (LU) technique to inspect porosities in 2 and 4-mm thick sheet lap welds. First experimentations resulted in the detection of 0.5-mm drilled holes in bulk aluminium sheets. The measurement of the depth of these defects is demonstrated too. Further experimentations shows the applicability of the LU technique to detect porosities in aluminium laser welds. However, as the interpretation of raw measures is limiting the detection capacity of this technique, we developed a signal processing using Time-Reversal capabilities to enhance detection capacities. Furthermore, the signal processing output is a geometrical image of the material's inner state, increasing the ease of interpretation. It is based on a mass-spring simulation which enables the back-propagation of the acquired ultrasound signal. The spring-mass simulation allows the natural generation of all the different sound waves and thus enables the back-propagation of a raw signal without any need of filtering or wave identification and extraction. Therefore the signal processing uses the information contained in the compression wave as well as in the shear wave.