Full text loading...
Schematic layout of the experimental system and the object under investigation.
Layout of the sample structure. An artificial delamination was created by introducing a thin circular Teflon film (indicated by the dashed circle) between the second and third ply of a composite plate. A piezoelectric transducer was used to generate a standing wave pattern.
Stroboscopically obtained shearographic images of speckle correlation fringes and difference images obtained for a sinusoidal excitation signal applied on the piezoelectric transducer . (a) Images obtained with a low excitation amplitude. The first two rows show the intensity images at 90° and 270° temporal phase (with regard to the excitation signal), respectively. The third row shows their difference. The fourth row shows the improved result after asymmetry averaging over the displacement cycle. (b) Images obtained with the same approach, but the excitation amplitude was increased by a factor of 4. The shearing distance was different for the two experiments to allow for optimal fringe visibility. The gray scale was kept the same for the subtracted and asymmetry averaged images. To guide the eye of the reader, the defect is indicated by a circle.
Article metrics loading...