Date of Award
Level of Access
Master of Science (MS)
Second Committee Member
Third Committee Member
In this work, characterizing a flaw in a plate means sizing and localizing it. Rapid and accurate inspection of anisotropic plates using guided waves (known as Lamb waves) has been limited by the complex nature of these waves: they contain many modes and exhibit dispersion, i.e. their shape changes as they travel. Current practice typically simplifies the signals by restricting either the type of mode generated and/or detected and/or its frequency range. The objective of this work is to use broadband, multi-mode signals to characterize flaws in anisotropic plates. The plates of interest here are unidirectional Graphite-Epoxy slabs. The signals are obtained numerically, using the finite element software ABAQUS/Explicit; therefore, the signals are synthetic.
The theoretical dispersion curves pertaining to the plates of interest here are first calculated. Then two digital signal-processing techniques, the 2DFFT and the reassigned spectrogram, are used for, respectively, sizing and locating the flaw. Both techniques are applied to the synthetic Lamb waves propagating through the graphite- epoxy plate. The 2DFFT output is compared to the theoretical dispersion curves. After agreement is obtained for a pristine plate, an energy coefficient can be calculated for a plate with a given notch and related to the depth of the flaw. Finally, the reassigned spectrogram is used to characterize the modal and frequency content of the synthetic signals as a function of time. The reassigned spectrogram can then be related to the analytical dispersion curves. This correlation enables the location of notches in the composite specimen.
de Smirnoff, Severine Imbert, "Nondestructive Flaw Characterization in a Unidirectional Composite Plate" (2002). Electronic Theses and Dissertations. 2581.
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