  We consider dense rapid shear flow of inelastically colliding hard disks.
Navier-Stokes granular hydrodynamics is applied accounting for the recent
finding \cite{Luding,Khain} that shear viscosity diverges at a lower density
than the rest of constitutive relations. New interpolation formulas for
constitutive relations between dilute and dense cases are proposed and
justified in molecular dynamics (MD) simulations. A linear stability analysis
of the uniform shear flow is performed and the full phase diagram is presented.
It is shown that when the inelasticity of particle collision becomes large
enough, the uniform sheared flow gives way to a two-phase flow, where a dense
"solid-like" striped cluster is surrounded by two fluid layers. The results of
the analysis are verified in event-driven MD simulations, and a good agreement
is observed.
