Generalized Lamb Müdes in Friction Welded Steel Layer On

The evaluation of bond quality between two dissimilar materials is one of the most difficult problems in NDE. Most previous work consisted of analysis of the spectral components of the normal incidence reflected spectrum. In this study, the quality of bond between steel layer and aluminum substrate is investigated using generalized Lamb waves. The dispersion curve for these waves, which has been studied for layer-substrate structures by Farneiland Adler [1], is extended for the fluid-loaded case in this paper. The combinations used in this study where the shear velocities of the two materials are close to each other show interesting behavior in the lowest mode. The slope of the lowest mode at very low values of frequency times layer thickness can be either positive or negative depending on the longitudinal velocities of the two materials followed by a turning point and a slope reversal. The objectives of this paper are: i) to experimentally verify the predicted dispersion curves (to our knowledge this is the first time), and ii) to utilize the dispersion curve as an NDE method for bond quality of such material combinations.