Shear and compression wave velocities are examined in assemblages of spherical glass beads in isotropic, triaxial and multiaxial stress states in the Cubical Cell Apparatus (CCA). The CCA enables application of non-rotational stress-states to a cube-shaped sample with independent control of the three principal stresses. Waves are transmitted using bender/extender elements (Lings & Greening 2001), the performance of which are assessed by laser vibrometry. Uncertainties in the analysis of wave velocities are examined in relation to the method of travel time assessment, extending to frequency and shape of the transmitted pulse waveform. Results suggest that uncertainties over wave travel time result largely from the mismatching of the transmitted waveform and the method by which its arrival is analysed. Methods based on cross-correlation are the most universally applicable and can be semi automated but still rely on the operator to correctly identify the wave arrival. Results for velocities in isotropic stress states are curve-fitted to a power law; the coefficients and exponents of these best fit curves appear to be related by an inverse power law, which is backed up by published data. How this may relate to material properties remains unclear. Additional laser vibrometry results from targets on the outside of a cubical sample enable examination of the propagation of the wavefront through the sample. The received traces for S-wave transmissions support the theory that the operation of the bender element produces sideways propagating P-wave 'lobes' (Lee and Santamarina 2005). The trend of their arrivals with distance between the bender and laser target supports the accepted use tip-to-tip travel distance for S-wave transmissions but suggests it may be too short for P-waves; this latter requires further experimental work.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:683560 |
| Date | January 2014 |
| Creators | Hamlin, Simon Mark |
| Publisher | University of Bristol |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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