Polar Characteristics of the Group and Phase Velocities as Well as the Frequency Dependence of Lamb Waves in Graphite/Epoxy Composites
The anisotropy of graphite/epoxy composite plates was studied using measurements of phase and group velocities of Lamb waves. Three types of composite structures were used: unidirectional, two-directional with orthogonal fibers, and quasi-isotropic. Two experimental methods were developed. For single mode, the phase and group velocities and the angle of deviation between them were measured using angle variable contact ultrasonic transducers which were situated on the surface of the plates. For multimodes, a new broadband single transducer immersion technique was used to examine the dispersion behavior for the phase velocity as propagation direction was varied relative to the fibers. The experimental data for an So mode was compared with calculations of the angular dependence of the phase and group velocities of bulk waves in the graphite/epoxy composite material. The advantage of the Lamb wave technique over bulk waves is the ability to measure the in-plane anisotropic properties of thin composite plates such as those used in actual aircraft applications.
KeywordsPhase Velocity Group Velocity Composite Plate Fiber Direction Lamb Wave
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