Planar defects characterization by selective TFM imaging for weld inspection Kombossé Sy, Olivier Roy


Ultrasonic detection and characterization of crack-like planar defects is highly dependent on the expertise of the operator. In conventional inspection, this type of defect is represented by a set of echoes produced at its tips, and the presence of other echoes related to the geometry of the piece is an additional complication for interpretation of inspection results. Welds inspection is well representative of these difficulties.

Advanced methods using Total Focusing Method (TFM) imaging applied to non-destructive testing presents a real interest because it directly produces realistic images, thus facilitating the analysis of results and providing new perspectives for defects characterization.
TFM imaging is based on a calculation of travel time between the elements of the phased arrays transducer and each point of the image to be formed. Depending on the kind of path that we consider, with or without rebounds on the backwall, with or without wave conversion, it is possible to consider a large number of reconstruction modes for the same acquisition. The images associated with these modes can then carry different information, sometimes complementary on the same defect. The complementarity and relevance of each of them may however vary depending on the inspection configuration and the characteristics of defect to be detected. It is therefore important to select the relevant modes before the inspection.

A method for predicting the relevant modes has been developed and validated on simulated and experimental data.