Unconventional rheological properties in systems of deformable particles*

We demonstrate in this work, the existence of an unconventional rheological and memory property in a Voronoi-based model of deformable particles such as foams, tissues, etc. whose energy depends upon their shape. These systems experience an unconventional "shear-weakening" transition when subjected to large shear strain, which is characterized by a sudden increase in the mechanical energy along with a drastic drop in the shear stress. This transition stems from the emergence of a short-ranged tetratic order in the system. In these shear weakened states, the contact network for the system evolves reversibly when subject to a reversal of applied strain, keeping the memory of its initial state, whereas the microscopic dynamics remain irreversible.