Guided and Leaking Interface Waves for NDI/NDE
Last year at this review one of us pointed out that it was theoretically possible to propagate guided elastic waves along the interface between an installed interference-fit fastener and the parts that it joins, and that these waves might be useful for nondestructive inspection and evaluationl. During discussion of that paper, the speaker was asked if experiments were planned, and another questioner wanted to know what would happen if elastic parameters of fastener and part didn't fall in the comparatively narrow ranges for which unattenuated guided waves can propagate.
The speaker replied that experiments were indeed planned, and that, hopefully, even when material parameters did not allow guided waves, attenuated interface waves might still propagate and be useful for inspection and evaluation.
This report can be viewed as an amplified answer to the two questions. We have carried out experiments. They confirm the existence of both true guided waves, and of "leaking" or attenuated waves, on interfaces between materials of engineering interest. The theory presented last year, with some extensions, is a useful guide to excitation and reception methods, propagation speeds, and for leaking modes, attenuation factors. Preliminary pulse-echo observations indicate that these waves can be used for indications of flaws in awkward places, such as on a fastener hole in an inner plate.