Key differences in the mechanical response of granular versus continuum solids

Granular materials are composed of discrete, macroscopic particles that interact via dissipative, contact interactions. When granular materials are compressed, they undergo a jamming transition from a liquid- to a solid-like state. In this presentation, I will describe the key differences between the mechanical properties of granular solids compared to continuum solids. First, continuum solids (e.g. modeled using Lennard-Jones interactions) can store a significant amount of potential energy during isotropic compression and thus their elastic moduli typically increase with pressure. In contrast, granular solids undergo frequent particle rearrangements during compression, which prevents them from storing significant elastic energy. We find that along elastic segments where granular solids do not undergo particle rearrangements during compression, their shear moduli actually decrease with increasing pressure. Second, granular solids are always anisotropic at jamming onset, even in the large-system limit. In contrast, compressed Lennard-Jones glasses are isotropic in the large-system limit. Finally, we show that jammed solids possess a large number of structural “defects" that are activated duirng applied shear and are the source of the collective, non-affine displacement fields in granular solids.