PLATE MODE VELOCITIES IN GRAPHITE EPOXY PLATES/

Measurements of the velocities of the extensional and flexural plate m odes were made along three directions of propagation in four graphite/ epoxy composite plates. The acoustic signals were generated by simulat ed acoustic emission events (pencil lead breaks or Hsu-Neilsen sources ) and detected by broadband ultrasonic transducers. The first arrival of the extensional plate mode, which is nondispersive at low frequenci es, was measured at a number of different distances from the source al ong the propagation direction of interest. The velocity was determined by plotting the distance versus arrival time and computing its slope. Because of the large dispersion of the flexural mode, a Fourier phase velocity technique was used to characterize this mode. The velocity w as measured up to a frequency of 160 kHz. Theoretical predictions of t he velocities of these modes were also made and compared with experime ntal observations. classical plate theory yielded good agreement with the measured extensional velocities. For predictions of the dispersion of the flexural mode, Mindlin plate theory, which includes the effect s of shear deformation and rotatory inertia was shown to give better a greement with the experimental measurements.