Torsional pump wave in a Dynamic Acousto-Elasticity Experiment

Martin Lott*, Marcel C. Remillieux**, Pierre-Yves Le Bas**, T.J. Ulrich**, Vincent Garnier*, Cédric Payan*

Dynamic acousto-elasticity testing is well known for its high sensitivity to dynamic changes in the mechanical properties of a body. Usually, it involves two waves : a high amplitude, low frequency ‘pump wave’, which changes the state of the body, and a low amplitude, high frequency ‘probe wave’, which monitors the condition of the body by velocity and amplitude shifting. Usually the ‘pump wave’ is a longitudinal wave. Here we present results where the pump wave is a torsional wave.
A slender bar of Berea sandstone is used for experiments. Effects produced by a torsional strain field are compared to those produced by longitudinal one, as used in traditional experiments. The symmetry of the strain field along the path of the probe wave removes the instantaneous strain effects. Only the coupling between higher order elastic constant and hysteresis phenomena remains.

Spectrum of time of flight shifting for :
a) longitudinal pump and
b) torsional one.





* Aix Marseille Univ, CNRS, Centrale Marseille, LMA, Marseille, France
** Geophysics Group (EES-17), Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA