ULTRASONIC SPECTROSCOPY IN CROSS-PLY FIBER REINFORCED COMPOSITES APPLIED TO DISPERSION EFFECTS CHARACTERIZATION OF ELASTIC SHEAR WAVE

Abstract

The theoretical and experimental studies of the dispersion effects, for the propagation of elastic shear waves, in two cross-ply fiber reinforced composites are presented. They exhibit, in the long wavelength limit, a fourfold and an eightfold axis of rotation, respectively. When the elastic wavelength becomes comparable to the composite period, spatial dispersion effects are expected : departure from the linearity of the curves, stop bands and, in the eigthfold axis material, an acoustical activity induced by the helical stacking of the elementary layers