  Flowing granular materials often abruptly arrest if not driven by sufficient
applied stresses. Such abrupt cessation of motion can be economically expensive
in industrial materials handling and processing, and is significantly
consequential in intermittent geophysical phenomena such as landslides and
earthquakes. Using discrete element simulations, we calculate states of steady
flow and arrest for granular materials under the conditions of constant applied
pressure and shear stress, which are also most relevant in practice. Here the
material can dilate or compact, and flow or arrest, in response to the applied
stress. Our simulations highlight that under external stress, the intrinsic
response of granular materials is characterized by uniquely-defined steady
states of flow or arrest, which are highly sensitive to interparticle friction.
While the flowing states can be equivalently characterized by volume fraction,
coordination number or internal stress ratio, to characterize the states of
shear arrest, one needs to also consider the structural anisotropy in the
contact network. We highlight the role of dilation in the flow-arrest
transition, and discuss our findings in the context of rheological transitions
in granular materials.
