Study of the fundamental Lamb modes interaction with asymmetrical discontinuities

The interaction of the fundamental Lamb modes with asymmetrical discontinuities in isotropic plates is studied numerically and experimentally. Three kinds of discontinuities that enable mode conversions are considered: steps down, steps up and asymmetrical notches. The anti-symmetrical and symmetrical Lamb modes contributions are separated by means of the simple arithmetic operations of addition and subtraction. The power reflection and transmission coefficients are then computed with the well-known average power flow equation described in a previous work. Furthermore, the asymmetrical notch is reconstructed from the superposition of a step down and a step up. It is shown that it allows directly the determination of all power coefficients of the reflected, the transmitted and the multiple converted Lamb modes contrarily to the finite element model. Finally, an experimental device is realized to test aluminum plates with different notch depths. Good agreement is found between experimental and numerical results. (c) 2008 Elsevier Ltd. All rights reserved.