Discrete Element Modeling of Acoustic Wave Propagation in Granular Media: Nonlinearity and Material Softening.
Degree: 2019, ETH Zürich
Granular media is one of the most common form of material which exists
in many geophysical phenomena such as landslides and earthquakes.
It is also present in the industry for transport, storage, and for mixing
processes. Constitutive equations are essential to predict and control
granular media behavior, but they are not fully developed yet. In particular,
the history of a granular packing has a determinant influence
on the arrangement of its particles and the organization and nature of
inter-particle contacts. The arrangement of particles and contacts in turn
affects the material response to external perturbations such as compression,
shear and wave propagation. This thesis studies the propagation
of acoustic waves through the contact network. The Effective Medium
Theory and continuum descriptions partially solve the constitutive equations
of dense packings of granular media but cannot fully describe the
phenomenon as the Effective Medium Theory models ensembles and
continuum descriptions neglect particle rearrangements. Dynamic testing
has shown a dependency of resonance frequency on strain at low strains
in confined granular packings (Johnson and Jia 2005; Inserra et al. 2008)
but this study has not been extended to high strains.
We present a detailed study of dynamic testing in confined random
packings of weakly polydisperse glass beads using the Discrete Element
Method to measure the resonance frequency over a range of strains. We
find a decrease in resonance frequency at high strain, called softening,
that only depends on the normal component of the contact force, the
coordination number and the average inter-particle overlap. The mean-field
assumption of the Effective Medium Theory successfully predicts
the dependency of softening on confining stress.
The Effective Contact Theory is a model developed in this thesis to
relate the breaking of contacts and decrease in coordination number to
softening by defining a granular temperature based on kinetic energy. For
the first time, granular temperature is used to model contact evolution
rather than particle motion. The Effective Contact Theory successfully
relate the probability of a contact breaking to softening in granular media.
Simulations of wave propagation in static packings show an excellent
agreement between wave velocity measured from direct wave propagation,
dynamic testing and bulk and shear compression tests. Wave
damping and distortion increases with amplitude and frequency and, at
high frequency, waves are propagated through scattering and rapidly
Advisors/Committee Members: Herrmann, Hans J., Jia, Xiaoping.
Subjects/Keywords: Granular media; Condensed Matter Physics; wave propagation; Nonlinear phenomena; Effective field theories; effective contact theory; granular temperature; softening; Weakening; discrete element method; granular material; granular matter; Condensed matter; info:eu-repo/classification/ddc/530; Physics
to Zotero / EndNote / Reference
APA (6th Edition):
Lemrich, L. (2019). Discrete Element Modeling of Acoustic Wave Propagation in Granular Media: Nonlinearity and Material Softening. (Doctoral Dissertation). ETH Zürich. Retrieved from http://hdl.handle.net/20.500.11850/342965
Chicago Manual of Style (16th Edition):
Lemrich, Laure. “Discrete Element Modeling of Acoustic Wave Propagation in Granular Media: Nonlinearity and Material Softening.” 2019. Doctoral Dissertation, ETH Zürich. Accessed April 17, 2021.
MLA Handbook (7th Edition):
Lemrich, Laure. “Discrete Element Modeling of Acoustic Wave Propagation in Granular Media: Nonlinearity and Material Softening.” 2019. Web. 17 Apr 2021.
Lemrich L. Discrete Element Modeling of Acoustic Wave Propagation in Granular Media: Nonlinearity and Material Softening. [Internet] [Doctoral dissertation]. ETH Zürich; 2019. [cited 2021 Apr 17].
Available from: http://hdl.handle.net/20.500.11850/342965.
Council of Science Editors:
Lemrich L. Discrete Element Modeling of Acoustic Wave Propagation in Granular Media: Nonlinearity and Material Softening. [Doctoral Dissertation]. ETH Zürich; 2019. Available from: http://hdl.handle.net/20.500.11850/342965