On the relation between the crossings and maxima of Lamb waves

In the presented paper surface displacements of Lamb waves are investigated. It is shown that at the crossings of symmetric and antisymmetric Lamb waves one component of the surface displacements vanishes for both modes leading to a pure longitudinal or pure transversal motion at the surface. This behavior is discussed by Mindlin´s approach using uncoupled dilatational and shear modes. Lamb wave dispersion relations and surface displacements are investigated with a semi-analytical finite element model. Experiments are carried out by a laser-ultrasonic setup and compared to the numerical results.