Shear and crystallization in deformable granular packings: why don't auxetics order?

Shear of three-dimensional, highly compressed granular packings is simulated using a bonded particle approach that explicitly resolves elastic deformation. Varying Poisson’s ratio $\nu$ produces significant changes in rheology, packing structure, and grain morphology. During flow, conventional systems ($\nu >0$) readily crystallize while auxetics ($\nu <0$) resist ordering. This duality reflects the fact that conventional grains develop polyhedral-like facets but conserve volume while auxetics behave oppositely, demonstrating an unexpected interaction between elasticity, geometry, and crystallization.