Abstract：We seek to understand the development of shear and normal stress anisotropies in frictionless granular packings undergoing athermal quasistatic simple and pure shear. We focus on packings of bidisperse disks and circulo-polygons in two spatial dimensions that interact via purely repulsive contact forces. We find that jammed disk packings form geometric families, for which the packing fraction varies approximately quadratically with strain with positive curvature, for packings that share the same interparticle contact network.  Packings of circulo-polygons also form geometric families during shear, but they can be either concave up or down.  We derive and confirm relations for the shear and normal stress anisotropies in terms of the derivative of the packing fraction with respect to strain for packings of disks and circulo-polygons.  We show that disk and circulo-polygons packings develop a nonzero shear stress (with a zero normal stress anisotropy) in the large-system limit when undergoing quasistatic simple shear. In contrast, static disk and circulo-polygon packings possess a nonzero normal stress anisotropy (with a zero shear stress) in the large-system limit when undergoing quasistatic pure shear. 

Brief Biography:

Professor Corey O’Hern joined the faculty of the School of Engineering and Applied Science at Yale with joint appointments in the Department of Mechanical Engineering & Materials Science (MEMS), Applied Physics, and Physics in July 2002 after postdoctoral fellowships in physics at the University of Chicago and the University of California, Los Angeles.  He received tenure at Yale in 2011 and became a full professor in 2018. The O’Hern research group tackles a broad range of fundamental questions in soft matter and biological physics using a combination of theoretical and computational techniques.  He has authored more than 100 manuscripts in peer-reviewed journals and given more than 150 seminars, colloquia, and presentations at universities and scientific meetings in the US and abroad. He has served in a number of leadership positions in the US soft matter research community, including the Chair of the Topical Group on Statistical and Nonlinear Physics of the American Physical Society.  In 2017, he was elected as a Fellow of the American Physical Society.