Quantitative flaw reconstruction from ultrasonic surface wavefieldsmeasured by electronic speckle pattern interferometry

摘要

A new method for imaging flaws in plate and shell structures isnpresented. The method employs two-dimensional ultrasonic surface wavendata obtained by optical electronic speckle pattern interferometryn(ESPI) techniques. In the imaging method, the measured out-of-planendisplacement field associated with an externally excited ultrasonic Lambnwave is processed to obtain the spatial frequency domain spectrum of thenwavefield. A free space Green's function is then deconvolved from thenwavefield to obtain quantitative images of effective scattering sources.nBecause the strength of these effective sources is directly dependent onnlocal variations in sample thickness and material properties, thesenimages provide a direct map of internal inhomogeneities. Simulationnresults show that the method accurately images flaws for a wide range ofnsizes and material contrast ratios. These results also demonstrate thatnflaw features much smaller than an acoustic wavelength can be imaged,nconsistent with the theoretical capability of the imaging method tonemploy scattered evanescent waves. Reconstructions are also obtainednfrom ultrasonic Lamb wave displacement fields recorded by ESPI in anflawed aluminum plate. These reconstructions indicate that the presentnmethod has potential for imaging flaws in complex structures for whichnESPI wavefield measurements cannot be straightforwardlyninterpreted