Application of resonant ultrasound spectroscopy to geomaterials

Abstract

Our objective is to apply resonant ultrasound spectroscopy (RUS) for obtaining the full elastic tensor of geomaterials. To our knowledge, RUS has never been successfully applied to complex materials such as rock: materials that are anisotropic and often inhomogeneous, and that contain grain-to-grain contacts, microcracks, etc. The fundamental problem with applying RUS to rock is high dissipation in the material, and the problem of coupling into all possible modes. The high dissipation limits the frequency band, and coupling into all modes controls the outcome of whether or not the full elastic tensor can be obtained. Our current experiment is operable in the frequency band of 3–30 kHz. Numerous sensor positions were tested in order to excite and detect different resonant modes. To date, the method has been applied to a rectangular brick sample. The comparison with theoretical calculation demonstrates that all modes (eigenfrequencies) of the sample were detected with high accuracy. Preliminary testing on cylindrical sandstone samples was also carried out. Duplicating the result from the brick in the rock sample is in progress. [This work is supported by the United States Industry Coalition, with the US DOE Contract W-7405-ENG-36, through the University of California.]