Amplitude correction for reduced axis scanning of layered materials

Abstract

This dissertation explores an amplitude correction method for reduced axis scanning of a layered structure. The technique is applicable to inspection of a component with complicated contours. Reduced axis scanning technique decreases the number of required degrees of freedom in the scanning system. The reduced axis scanning can provide a more reliable automated inspection method. Gain correction is required to accommodate the non-normal incident wave that is used when scanning with a reduced axis system. Models based on matrix solutions of the wave transmission in the component are used for gain correction. The exploration of the applicability of these methods to wave transmission in a layered elastomeric or polymeric matrix composite plate are shown. Samples of layered elastomeric or polymeric matrix composite plates are considered both theoretically and experimentally. The transmission coefficient of multilayered material structure at an arbitrary incident angle is considered using the transfer matrix method. The model is incrementally increased in complexity from an elastic material model to a visco-elastic material model. All of the modeling assumes an orthotropic material, although calculation is for an arbitrary incidence which reduces material symmetry. In the theoretical derivations of the transfer matrix, the use of the second rank and third rank determinant simplifies the expressions of the transfer matrix and the resulting algorithm. The experimental method uses water immersion and a through transmission configuration. Theoretical transmission curves are reconstructed by convolving the calculated transmission coefficient with a reference signal. Experimental results for a carbon fiber/epoxy composite plate are shown which compare favorably to theoretical results for the simple lamina lay-up used for the testing.