In this paper, initial efforts on the characterization of the ultrasonic oblique incidence data to obtain the fiber orientation and ply Lay-up properties of orthotropic symmetry material systems, such as fiber reinforced composites, will be discussed. The acoustical data domain used was the plate wave dispersion curves. The influence of ply-Lay-up ordering in cross-ply symmetric graphite/epoxy laminates on leaky plate wave dispersion curves was studied. The Thomson-Haskell Method was implemented to model the reflection factor behavior of fluid-loaded laminated plates and compute the dispersion curves. Two different types of ply ordering — staggered and inverted — were examined. It was found that the all dispersion modes are sensitive to changes in lay-up sequence. Consequently, it was concluded that stacking sequence identification from leaky plate wave dispersion data is indeed possible, provided accurate experimental and robust combinatorial optimization techniques are used. It is further recommended that Genetic Algorithms can be used as the optimization tool for solving the inverse problem of nondestructively obtaining the ply-Lay-up from experimental oblique incidence ultrasonic data on composite materials.

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