P5E-7 Multi Resonances of the S0 Adiabatic Mode Propagating in a Linearly Varying Cross Section Waveguide, Experimental and Numerical Results

The aim of this work is to analyse the behavior of a Lamb wave propagating in duraluminum elastic waveguides whose section is varying linearly from 2 mm to 5 mm thickness. These waveguides are differing only by the slope of their varying section domain. The case of the S₀ mode propagating upslope is studied experimentally and numerically. The goal of this paper is to analyse the behavior of the adiabatic S₀ mode inside the area of varying section for these different waveguides. The experimental study is based on the use of a contact transducer placed on a Plexiglas wedge and of a laser velocimeter that measures the time dependent normal displacement on the plan surface, for several positions in the propagation direction. The signal processing is achieved using space and time FFT and also spatial sliding window FFT at fixed frequency. The numerical study is based on the Finite Elements Method, developed in 2-D transient analysis, using the Comsol software. Experimental and numerical results are in good agreement and show the well-expected adiabatic behavior during the propagation of the guided wave in the area of varying section. Moreover, this adiabatic mode exhibits some local resonances corresponding to maximum amplitudes in the varying section domain. The number and the positions of these amplitude peaks are strongly depending on the slope of the varying section domain: when the slope is decreasing, the number of resonances is increasing and their position is shifted to the increasing thickness, while the distance between two successive peaks decreases.