Nathan C. Keim, Paulo E. Arratia
The question of how a disordered material's microstructure translates into macroscopic mechanical response is central to the understanding and design of materials like pastes, foams and metallic glasses. Here, we examine a 2D soft jammed material under cyclic shear, imaging the structure of $\sim 5 \times 10^4$ particles. Below a certain strain amplitude, the structure becomes reversible and conserved at long times, while above, it continually rearranges. We identify the boundary between these regimes as a yield strain, defined without rheological measurement of bulk stress or strain. Its value is consistent with a simultaneous but independent measurement of yield strain by stress-controlled rheometry of the bulk material. While there are virtually no irreversible rearrangements in the steady state below yielding, we find that deformation activates a mostly stable population of plastic rearrangements that are reversed with each cycle. These results point to a microscopic view of mechanical properties under cyclic deformation.
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http://arxiv.org/abs/1304.2253
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