Karen Daniels, North Carolina State University

Granular materials such as those found near the Earth's surface are inherently heterogeneous, and continuum models of properties such as the shear modulus and sound speed often fail. One promising alternative is to build an understanding of bulk behaviors 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 both these methods, and the heterogeneous network of forces that they reveal. Through our experiments, I will talk about several frameworks capable of connecting the internal structure of disordered materials to their rigidity and/or failure under loading, and describe how we apply these ideas.

Short Biography
Karen Daniels is a Distinguished Professor of Physics at NC State University. She received her BA in Physics from Dartmouth College in 1994, taught school for a few years, and then pursued a PhD in Physics at Cornell University. After receiving her doctorate in 2002, she moved to North Carolina to do research at Duke University and then joined the faculty at NC State in 2005. Her lab at NC State investigates a number of problems in the deformation and failure of materials, from fluid flows, to piles of sand, to fracturing gels. 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 and ecological systems. In 2011-2012, she received an Alexander von Humboldt fellowship which allowed her to spend the year conducting research in Göttingen, Germany, and will be going to Bengaluru, India on a Fulbright fellowship this fall. She is a Fellow of the American Physical Society and the American Association for the Advancement of Science.