The instantaneous out-of-plane displacement two-dimensional (2-D) maps associated to the scattering generated by the interaction of Rayleigh-Lamb waves with defects in plate structures can be measured using pulsed TV-holography (PTVH) and employed to characterize damage in non-destructive inspection applications. On the basis of visual comparisons we have shown previously that, except for the amplitude in the backscattering zone, a reasonable description of the measured experimental scattering patterns produced by holes both in harmonic and transient regimes can be obtained using the finite element method (FEM) combined with a 2-D model based on the scalar wave equation. In this work a systematic quantitative analysis of the agreement between FEM simulated maps and filtered experimental PTVH maps is developed considering both the spatial distribution of the local (pixel-wise) error in amplitude and phase and the corresponding global (averaged) errors over different areas in the 2-D image of the acoustic field. Changes produced in the experimental values by the speckle noise and variations introduced in the numerical values by the uncertainty in the characterization of the incident acoustic wave and the shape and position of the hole are characterized in order to obtain the net value of the error between theory and experiment.
Pulsed TV-holography (PTVH) can be used for obtaining two-dimensional maps of instantaneous out-of-plane displacements in plates. In particular, our group has demonstrated that scattering patterns generated by the interaction of elastic waves with defects can be measured with PTVH and employed for the characterization of damage in nondestructive inspection of plate structures. Recently, we have succeeded in obtaining a quantitative description of experimental scattering patterns of quasi-Rayleigh (qR) waves produced by holes in harmonic regime using a finite element method (FEM) combined with a two-dimensional scalar wave equation, avoiding the standard and more complex vector approaches based on the rigorous linear elasticity theory. This scheme has been extended here for characterizing equivalent scattering phenomena in transient regime. Simulated scattering patterns, obtained with the scalar FEM, and the corresponding experimental patterns associated to the interaction of qR waves with holes, measured with our specifically developed PTVH system, have been compared. Results have shown that, except for the evaluation of the backscattering coefficient, a reasonable agreement between theory and experiment is obtained in both amplitude and phase, which confirms the feasibility and potential of the proposed scalar approximation for the characterization of experimental transient scattering patterns measured with our PTVH technique.
Pulsed TV-holography (PTVH) can be used for obtaining two-dimensional maps of instantaneous out-of-plane
displacements in plates. In particular, our group has demonstrated that scattering patterns generated by the
interaction of elastic waves with defects can be measured with PTVH and employed for quantitative characterization
of damage in non-destructive inspection in plate structures. Recently, we have succeeded in obtaining
a quantitative description of experimental scattering patterns produced by holes in harmonic regime using a
finite element method (FEM) applied to a two-dimensional model based on the scalar wave equation, avoiding
the standard and more complex vector approach based on the rigorous linear elasticity theory. In this work, a
similar scheme is employed to characterize equivalent scattering phenomena but in transient regime. Simulated
propagation and scattering patterns are tried with the scalar FEM and the corresponding experimental propagation
and interaction of Rayleigh-Lamb waves with artificial defects in plates are measured using our specifically
developed PTVH system. On this basis, a comparison between experimental maps and FEM simulated maps is
developed.
Pulsed TV-holography (PTVH) can be used for obtaining two-dimensional maps of instantaneous out-of-plane
displacements in plates. In particular, scattering patterns generated by the interaction of elastic waves with
defects can be measured with PTVH and employed for non-destructive inspection and damage detection in plate
structures. 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 formulations
based on elasticity theory. In this work, a finite element method (FEM) applied to a two-dimensional scalar
model 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 are
obtained with the scalar FEM assuming harmonic regime and free-stress boundary conditions. The corresponding
experimental interaction of narrowband Rayleigh-Lamb waves with artificial defects in plates are measured using
our specifically developed PTVH system. In our case, the raw optical phase-difference values are processed by
employing a specially developed procedure, based on a two step spatial Fourier transform method, to derive
a high quality two-dimensional acoustic field map from which an important part of the noise component has
been filtered out. A comparison between filtered experimental maps and FEM simulated maps is developed,
considering defects with different sizes in relation to the acoustic wavelength.
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