| Laser-generated ultrasound in carbon epoxy composites provides an ultrasonic signature, which is difficult to interpret owing to the elastic anisotropic and inhomogeneous nature of these materials. In this manuscript, both a line source and a point source representation of laser-generated ultrasound in materials exhibiting transverse isotropy is presented. The bounding plane of the half space is assumed to be the plane of isotropy. Neglecting thermal diffusion, it is shown that in the limit of strong optical absorption, a laser source can be modeled as shear stress dipole applied at the bounding surface. A formal solution is found using double (Fourier-Laplace) transforms. The Cagniard-de Hoop technique is used to analytically invert the transform for the epicentral case as well as the surface wave case. Solutions for a sub-surface source and for observation points that are off the epicental axis are obtained numerically.; Experimental validation of the theory is performed using single crystal zinc and a unidirectional carbon epoxy sample. For the carbon fiber epoxy sample, the plane of isotropy was found to be perpendicular to the fiber direction. For zinc, the experimentally obtained epicentral and surface wave displacements agree well with theoretical predictions. The carbon epoxy sample exhibits homogeneous behavior when the wave vector is perpendicular to the fiber direction. When the wave vector is aligned with the fiber direction, the waveform appears to be influenced by the inhomogeneous nature of the composite. |
