Development of methods for characterizing defects based on TFM multimode imaging
Résumé
In the field of ultrasonic non-destructive testing of materials, a method of imaging so-called TFM imaging (Total Focusing Method) is developing in the last few years. TFM is an advanced post-processing imaging algorithm of ultrasonic array data that shows great potential in defect detection and characterization. Based on ray tracing model, TFM imaging takes into account a multitude of paths by using several propagation modes (direct or over skip imaging) and several types of waves (longitudinal or transverse) allowing the imaging of extended defects of complex geometry. Yet the number of resulting images might become very high, and those could be affected by various reconstruction artifacts due to the coexistence of several contributions involving several mode of propagation and interactions with possible defects and / or the geometry of the part. The interpretation of those images becomes then complicated and the time of calculations important. The present work allows methods to optimize control configuration and determines pertinent modes depending on the parameters of the control known. It also improves on the quality of images via filtering artifacts and then to be able to characterize a defect (nature, position, size, orientation) in more unambiguous fashion. The performances achieved are compared to those of conventional TFM on simulated and experimental data.