The Effect of Anisotropic Focusing of Lamb Modes on a Carbon-Epoxy Plain Woven Fabric Composite Plate

Abstract

The medium anisotropy give rise to interesting effects in the physics of wave propagation: the angular dependence of the group velocity, the skew angle between pha se and group velocities, and the elastic focusing leading to the concentration of wave energy in dete rminated directions. All these effects are mode dependent and must be taken into account to choose the ad equate propagating mode in NDE or SHM applications. In this article the dispersion curves of p hase and group velocities, and the patterns of wave focusing for the A0 and S0 modes are theoretically obt ained and verified experimentally. The angular dependence of the group velocity and the effect of the anisotropic elastic focusing is studied in a 1.97 mm-thickness multilayer carbon-epoxy plain woven fab ric composite. The time traces are obtained by scanning the plate with the aid of a retro-reflective film st uck to the surface using a laser Doppler vibrometer. A good agreement between the theory and the expe rimental results was obtained. The Maris factor corresponding to the A0 mode shows smoother angular v ariation than that of the S0 mode which depends much more on the direction.