Experimental determination of the elastic coefficients of an orthorhombic material

In terms of elastic anisotropy, many rocks may be considered to have orthor hombic symmetry. Experimentally determining the nine independent elastic co efficients required for this case remains challenging. Elastic coefficients are most often found from measurements of the phase velocity in a variety of directions throughout a material, but finding this plane-wave velocity i s problematic. Here, quasi-P and quasi-S phase speeds are found using the t au -p transformation through a composite material of orthorhombic symmetry. Arrays of specially constructed transducers (0.65 MHz) with different mode s of vibration were placed on a rectangular prism of the material. More tha n 620 individual measures of phase speed were obtained at different directi ons and subsequently used in a generalized least-squares inversion that yie lds the required elastic coefficients. The analysis does not account for th e effects of wave-speed dispersion evident in the waveforms acquired in the composite material. This dispersion is particularly severe for the in-plan e, quasi-S polarization and is possibly a consequence of the fine layered s tructure of the material.