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Publication 14-CNA-030

Stable Disarrangement Phases Arising from Expansion/Contraction or from Simple Shearing of a Model Granular Medium

L. Deseri
Dept. of Civil, Environmental and Mechanical Engineering, University of Trento
via Mesiano 77
38123 Trento, Italy
and
The Methodist Hospital Research Institute
6565 Fannin St., MS B-490
Houston, TX 77030 USA
and
Depts of Civil and Env. Eng. and Mechanical Eng.
Carnegie Mellon University,
Porter Hall, 5000 Forbes Av.,
Pittsburgh PA, 15213 USA
deseri@andrew.cmu.edu

D. R. Owen
Center for Nonlinear Analysis
Department of Mathematical Sciences
Carnegie Mellon University
Pittsburgh, PA

Abstract: A principal challenge in modelling granular media is to connect the macroscopic deformation of the aggregate of grains with the average deformation of a small number of individual grains. We used in previous research the two-scale geometry of structured deformations ($g,G$) and the theory of elastic bodies undergoing disarrangements (non-smooth submacroscopic geometrical changes) to obtain an algebraic tensorial consistency relation between the macroscopic deformation $F = grad g$ and the grain deformation $G$, as well as an accommodation inequality $detF >= detG > 0$ that guarantees that the aggregate provides enough room at each point for the deformation of the grains. These two relations determine all of the disarrangement phases $G$ corresponding to a given $F$. We use the term stable disarrangement phase to denote a grain deformation $G$ thatminimizes the stored energy density for the aggregate among all the disarrangement phases G' corresponding to $F$. In this article we determine for a model aggregate and for two familiar families of macroscopic deformation - - simple shearing and uniform expansion/contraction - - all of the stable disarrangement phases of the model aggregate, as well as the corresponding connections between aggregate deformation and grain deformation. We showed in an earlier article that each stable disarrangement phase of this model aggregate cannot support tensile tractions, and our present results confirm the no-tension property for the two families of macroscopic deformation treated here.

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