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Publication 14-CNA-005

Stable Disarrangement Phases of Granular Media I:
Classification of the Disarrangement Phases of a Model Aggregate

Luca Deseri
Group of Solid and Structural Mechanics-DICAM
University of Trento, Trento Italy

Visiting Professor
Mechanics, Materials and Computing Center
CEE & ME-CIT
Carnegie Mellon University
Pittsburgh PA 15213-3890 USA
deseri@andrew.cmu.edu

David R. Owen
Department of Mathematical Sciences
Carnegie Mellon University, Pittsburgh, PA 15213, USA
do04@andrew.cmu.edu

Abstract: We model granular media as continuous bodies that are aggregates of many small elastic bodies (elastic aggregates). Our model rests on the multiscale geometry of structured deformations through the field theory "elasticity with disarrangements". This setting provides a tensorial consistency relation $D\Psi (G)(F^{T}-G^{T})=0$ and an accommodation inequality $0< \det G\leq \det F $ that relate, through the free energy response $\Psi $ of the individual pieces of the aggregate, the deformation gradient $F$ of the aggregate and the average deformation $G$ of the pieces of the aggregate. The solutions $G$ of these two relations are called disarrangement phases corresponding to $F$. In Part I we classify all of the disarrangement phases for a model elastic aggregate. The compact phase $G=F$, in which the pieces of the aggregate all deform in the same way as the aggregate, itself, forms one category in the classification, while the non-compact phases $G\neq F$ are categorized as to whether the stress $(\det F)^{-1}D\Psi (G)F^{T}$ is planar, uniaxial, or zero. Our classification will form the basis for the solution of boundary value problems for the model aggregate as well as for a broader class of aggregates. In Part II we use the classification to obtain an unexpected connection between elastic aggregates and materials with no-tension response.

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