Application of orthogonality-relation for the separation of Lamb modes at a plate edge: numerical and experimental predictions

M Ratassepp; A Klauson; F Chati; F Léon; D Décultot; G Maze; M Fritzsche

doi:10.1016/j.ultras.2014.10.022

Application of orthogonality-relation for the separation of Lamb modes at a plate edge: numerical and experimental predictions

Ultrasonics. 2015 Mar:57:90-5. doi: 10.1016/j.ultras.2014.10.022. Epub 2014 Nov 5.

Authors

M Ratassepp¹, A Klauson², F Chati³, F Léon³, D Décultot³, G Maze³, M Fritzsche⁴

Affiliations

¹ Department of Mechanics, Tallinn University of Technology, Ehitajate tee 5, Tallinn 19086, Estonia. Electronic address: madis.ratassepp@ttu.ee.
² Department of Mechanics, Tallinn University of Technology, Ehitajate tee 5, Tallinn 19086, Estonia.
³ Laboratoire Ondes et Milieux Complexes UMR CNRS 6294, Université Le Havre, 75 rue Bellot CS 50540, Le Havre, France.
⁴ Polytec GmbH, Sales International, Waldbronn, Germany.

PMID: 25465106
DOI: 10.1016/j.ultras.2014.10.022

Abstract

In this study the orthogonality relation-based method for post-processing finite element (FE) predictions and experimental measurements is applied in order to separate Lamb modes at a plate edge at normal incidence. The scattered wave field from the free edge is assumed to be a superposition of all the eigenmodes of an infinite plate. The eigenmode amplitudes of the reflected wave field are determined by implementing the orthogonality-based method on the measured plate edge displacements. Overlapping wavepackets of Lamb modes at a plate edge are simulated by using the FE model and the experiment in the case of an incident S0 mode in a plate with a notch. In the experiment a 3D Scanning Laser Doppler Vibrometer (3D SLDV) (Johansmann and Sauer, 2005) is used to measure 3 dimensional vibrations and thus the edge two-dimensional displacement components simultaneously. It is demonstrated that it is possible to extract signals of various propagating and non-propagating modes in time-domain. The influences of the errors in practical measurements on the extraction procedure have also been studied.

Keywords: 3D Scanning Laser Doppler Vibrometer; Lamb modes; Mode separation; Orthogonality.