Towards the Application of 2D Elastic Full-Waveform Inversion to Ultrasonic Data for Non-Destructive Testing

Non-destructive testing (NDT) has been used over the last years to test materials in order to assure safety and improve product reliability. It usually makes use of ultrasonic waves. This study aims to evaluate if the 2D elastic full-waveform inversion (FWI) of ultrasonic waves can reconstruct the properties of materials in a pipe embedded in a concrete block. The data were acquired at the Fraunhofer Institute for Non-Destructive Testing (IZPF). Prior to the inversion of lab data, synthetic inversion tests on numerically modelled waves are conducted to investigate the feasibility of such a test. On one hand, full data content inversion only simulates the position and shape of the pipe. On the other hand, the inversion of tapered transmitted waves partly displays the characteristics of the material in the pipe. Improvement in result leads to perform a cross talk test, which shows that the high velocity contrast between the concrete and materials in the pipe may contribute to the bad resolution imaging. In the realistic application, only tapered transmitted waves are inverted due to the complexity of late arrivals coda. It was possible to either locate the pipe to an extend but not to size it correctly or designate the material in it. ... mehrComparison between modelled and lab data show that in addition to the high velocity contrast, the directivity feature of the transducers might strongly affect inversion. Further tests need to be carried on to assess the hypothesis.