Interferences in the re-emission field of multimodal leaky Lamb waves propagating in an immersed plate analytical modelling, simulation and experimentation

International audienceThe use of leaky Lamb waves is of great interest to achieve Non Destructive Testing (NDT) on nuclear power plant vessel and through the vessel. The transmission and re-emission of energy by leaky Lamb waves from an immersed plate is studied in case of multi-modal propagation. Parameters influencing the generation of leaky Lamb waves with an incident bounded beam are studied. When more than two Lamb modes are propagating together, interferences can be generated in the re-emitted field, and directions taken by these interferences are predicted and observed. The field transmitted by a plate is computed using the Bertoni and Tamir model adapted to the transducer used, Finite Elements simulation with COMSOL Multiphysics software, and is experimentally observed with C-scan visualisation. Comparison between the analytical model, Finite Element simulations and experimentation proves that side lobes generated by a transducer can generate a different leaky Lamb mode than the one targeted. A good agreement is observed between these three approaches. Thus, to avoid multi-modal generation with an incident beam, the best way is to use the leaky Lamb mode that has the highest leaky attenuation coefficient at the frequency of work