  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 a flow-arrest
state diagram 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
nonequilibrium 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 shear
jamming and discontinuous shear thickening.
