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Rigidity and Failure in Granular Materials: From the Particle to the Bulk Scale

Professor Karen Daniels, North Carolina State University
Room S105

Granular materials, including those found in geophysical contexts and
engineered to specific purposes throughout our built world, are inherently
heterogeneous: continuum models of bulk properties often fail to capture
the full range of behaviors. One promising alternative is to build an
understanding of material properties from measurements at the particle
scale. Our lab's experiments make use of idealized, optically birefringent
materials to quantify the interparticle forces -- and thereby directly
measure the stress tensor at the particle scale -- within compressed or
sheared granular materials. I will describe these experimental techniques,
the heterogeneous network of forces that they reveal, and what we learn
from analyzing systems at the mesoscale. Through our experiments, I will
talk about several frameworks (network science, rigidity percolation,
phonon modes, stress-force-fabric) capable of connecting the internal
structure of disordered materials to their rigidity and/or failure under
loading, and describe how we are beginning to apply these results to more
realistic systems.

About the speaker
Karen Daniels is a Distinguished Professor of Physics at NC State
University, where her research group investigates a number of problems
in the deformation and failure of materials, from fluid flows, to piles of
sand, to fractures in amorphous materials. When not working with her
students on experiments in the lab, she likes to spend time in the
outdoors, which has led her to contemplate the implications of her
research for geological systems. Through support from the Alexander von
Humboldt Foundation and the Fulbright-Nehru program, she has spent
sabbaticals at the Max Planck Institute for Dynamics and Self-
Organization in Göttingen, Germany, and in the departments of Civil and
Chemical Engineering at IISc Bangalore. She is a Fellow of the American
Physical Society and the American Association for the Advancement of Science.