  Resonance ultrasound spectroscopy (RUS) is a non-destructive technique for
evaluating elastic and an-elastic material properties. The frequencies of free
vibrations for a carefully crafted sample are measured, and material properties
can be extracted from this. In one popular application, the determination of
monocrystal elasticity, the results are not always reliable. In some cases, the
resonant frequencies are insensitive to changes in certain elastic constants or
their linear combinations. Previous work has been done to characterize these
sensitivity issues in materials with isotropic and cubic symmetry. This work
examines the sensitivity of elastic constant measurements by the RUS method for
materials with hexagonal symmetry, such as titanium-diboride. We investigate
the reliability of RUS data and explore supplemental measurements to obtain an
accurate and complete set of elastic constants.
