Changing the jamming transition with auxetic metagrains

The collective behaviour of granular material has been a topic of intense research to accurately describe natural phenomena such as the liquid-like behaviour found in avalanches and hourglasses to the solid-like behaviour experienced when walking across the beach. The transition from liquid-like to solid-like behaviour can be ascribed to a critical packing fraction. Here, we study how this transition can be tweaked by introducing a four-bar-linkage in all grains in the packing. This metagranular packing can therefore adapt to a high external pressure by self-adjusting the packing fraction. We show that, upon shearing, the auxetic property facilitates yielding of individual grains. As a direct result, the dilatancy effect observed in the packing is also much less significant. This work provides a novel method to self-adjust a close packing into the shear-jammed regime, preventing jamming inside the packing.