A PHYSICAL MODEL STUDY OF SCATTERING OF WAVES BY ALIGNED CRACKS - COMPARISON BETWEEN EXPERIMENT AND THEORY

An approximation to plane-wave propagation through a composite materia l is examined using a physical model with oriented but randomly distri buted penny-shaped rubber inclusions within an isotropic epoxy resin m atrix. A pulse transmission method is used to determine velocities of shear and compressional waves as a function of angle of incidence and crack density. The experimental and theoretical results of Hudson were compared and limitations within the crack parameters used in this stu dy have been determined. Results from both polarized shear waves (S1, S2) compare favourably with the theory for a composite with up to 7% c rack density, but theory and experiment diverge at higher crack densit ies. On the other hand, compressional-wave velocities at low crack den sities (1% and 3%) compare favourably with the theory. It is also show n that the velocity ratio V(p)/V(s) for two extreme cases, i.e. propag ation normal and parallel to the cracks, as a function of crack densit y and porosity, has a strong directional dependence.