Development of the specular echoes estimator to predict relevant modes for Total Focusing Method imaging

Abstract

Total Focusing Method imaging is an ultrasonic testing method which has emerged in recent years as an alternative to standard phased array inspection methods in non-destructive testing, due to its high resolution and the realistic images of defects that it provides.In the case of crack-like defects, it provides images where the profile and the tips of the defects are reconstructed. TFM imaging is a procedure which yields the spatial position of the reflectors from which the main transient signals observed in the data are originated from. Thereby, diffraction echoes are located at the tips of the defect, and specular echoes appear along the profile of the defect. This signature allows the characterization of the planar nature of the defect.However, a correct reconstruction requires the use of the relevant ultrasonic path to produce the echoes wanted among a large number of possible paths between the array transducer and the reflector.In this paper, we have developed a method based on physical considerations, for predicting relevant paths. The tool is applied in several inspection configurations involving notches nearby welds. Validation is achieved from a variety of synthetic and experimental results.