Influence of packing density and stress on the dynamic response of granular materials

• Published in: Granular matter Vol. 19; no. 3; p. 1
• Main Authors: Otsubo, Masahide, O’Sullivan, Catherine, Hanley, Kevin J., Sim, Way Way
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01-08-2017; Springer Nature B.V
• Subjects: Acoustic emission testing; Acoustic measurement; Acoustic propagation; Assembly; Complex Fluids and Microfluidics; Computer simulation; Cubic lattice; Discrete element method; Dynamic response; Dynamical systems; Engineering Fluid Dynamics; Engineering Thermodynamics; Foundations; Geoengineering; Geophysics; Granular materials; Heat and Mass Transfer; Hydraulics; Industrial Chemistry/Chemical Engineering; Information dissemination; Longitudinal waves; Materials Science; Matrices (mathematics); Original Paper; Packing density; Physics; Physics and Astronomy; Propagation; Soft and Granular Matter; Sound propagation; Sound waves; Stiffness; Stress propagation; Wave propagation; Elasticity; Filtering; Eigenmode analysis; Dynamics; Discrete-element modelling; Waves
• ISSN: 1434-5021; 1434-7636
• DOI: 10.1007/s10035-017-0729-2

Laboratory geophysics tests including bender elements and acoustic emission measure the speed of propagation of stress or sound waves in granular materials to derive elastic stiffness parameters. This contribution builds on earlier studies to assess whether the received signal characteristics can provide additional information about either the material’s behaviour or the nature of the material itself. Specifically it considers the maximum frequency that the material can transmit; it also assesses whether there is a simple link between the spectrum of the received signal and the natural frequencies of the sample. Discrete element method (DEM) simulations of planar compression wave propagation were performed to generate the data for the study. Restricting consideration to uniform (monodisperse) spheres, the material fabric was varied by considering face-centred cubic lattice packings as well as random configurations with different packing densities. Supplemental analyses, in addition to the DEM simulations, were used to develop a more comprehensive understanding of the system dynamics. The assembly stiffness and mass matrices were extracted from the DEM model and these data were used in an eigenmode analysis that provided significant insight into the observed overall dynamic response. The close agreement of the wave velocities estimated using eigenmode analysis with the DEM results confirms that DEM wave propagation simulations can reliably be used to extract material stiffness data. The data show that increasing either stress or density allows higher frequencies to propagate through the media, but the low-pass wavelength is a function of packing density rather than stress level. Prior research which had hypothesised that there is a simple link between the spectrum of the received signal and the natural sample frequencies was not substantiated.