Guided waves represent promising non-destructive evaluation (NDE) techniques. Their advantage of long distance propagation is however hampered by complex wave scattering at each discontinuity along the investigated structure. These scattered waves can be used to locate and size possible defects. Theoretical investigation is a prerequisite step in the development of a NDE technique. Planar metallic structures with localized thickness variation imposed by design represent possible new industrial structures that could be tested using guided waves. The waves scattered at the region of variable thickness must be theoretically predicted and experimentally measured before any defect could be detected. Very few authors have investigated waveguides with continuous variation of thickness. Our previous numerical and experimental studies have proven the complexity of the scattering phenomenon in such cases. Among other remarks is the curved shape of the wave front. The present work investigates properties of the waves in the linear thickness variation region of the waveguide. A plain strain model is theoretically investigated and numerically tested using specialized finite elements based algorithms. Specific properties such as stress and displacements fields are determined by numerical simulation at several frequencies and slope angles.
The aim of this work is to obtain the geometry profile of a waveguide of continuous varying section, by inversing the experimental data. This determination is based on the use of the adiabatic behavior of guided waves. The geometry profiles obtained are in good agreement with the exact ones.
This experimental and numerical work deals with the study of Lamb modes propagating in a plate with a linear variation of thickness. The varying section area exhibits a filtering phenomenon for Lamb modes having a frequency-thickness cutoff. If the incident Lamb wave, excited at a given frequency and propagating downslope, reaches its thickness cutoff in the varying section area, it is reflected and propagates upslope. Otherwise, it is transmitted outside the varying section domain with modes conversion. The S2 incident mode is a particular case : when it reaches its cutoff , it is converted into the S1 mode with negative groupe velocity and a downslope propagation; then the S1 Lamb wave is reflected at its cutoff. The experimental and numerical studies are in good agreements.
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