Characterization of defects in plates by two-dimensional ultrasonic displacement maps: comparison between pulsed TV-holography measurements and finite element method predictions

Pulsed TV-holography (PTVH) can be used for obtaining two-dimensional maps of instantaneous out-of-planedisplacements in plates. In particular, scattering patterns generated by the interaction of elastic waves withdefects can be measured with PTVH and employed for non-destructive inspection and damage detection in platestructures. For quantitative characterization of damage (position, dimensions, orientation, etc.) on this basis,modeling of elastic wave scattering is usually performed in terms of full-vector three-dimensional formulationsbased on elasticity theory. In this work, a finite element method (FEM) applied to a two-dimensional scalarmodel based on Helmholtz equation is employed for obtaining a quantitative description of the scattering patterns,avoiding the aforementioned more complex and rigorous standard approach. Simulated scattering patterns areobtained with the scalar FEM assuming harmonic regime and free-stress boundary conditions. The correspondingexperimental interaction of narrowband Rayleigh-Lamb waves with artificial defects in plates are measured usingour specifically developed PTVH system. In our case, the raw optical phase-difference values are processed byemploying a specially developed procedure, based on a two step spatial Fourier transform method, to derivea high quality two-dimensional acoustic field map from which an important part of the noise component hasbeen filtered out. A comparison between filtered experimental maps and FEM simulated maps is developed,considering defects with different sizesin relation to the acoustic wavelength.Ministerio de Ciencia e Innovación y Comisión Europea (FEDER) | Ref. DPI2008-02709Dirección Xeral de Investigación, Desenvolvemento e Innovación, Xunta de Galicia | Ref. INCITE08PXIB303252PRUniversidad de Vigo | Ref. 09VIA0