  The linear stability analysis of an uniform shear flow of granular materials
is revisited using several cases of a Navier-Stokes'-level constitutive model
in which we incorporate the global equation of states for pressure and thermal
conductivity (which are accurate up-to the maximum packing density $\nu_{m}$)
and the shear viscosity is allowed to diverge at a density $\nu_\mu$ ($<
\nu_{m}$), with all other transport coefficients diverging at $\nu_{m}$. It is
shown that the emergence of shear-banding instabilities (for perturbations
having no variation along the streamwise direction), that lead to shear-band
formation along the gradient direction, depends crucially on the choice of the
constitutive model. In the framework of a dense constitutive model that
incorporates only collisional transport mechanism, it is shown that an accurate
global equation of state for pressure or a viscosity divergence at a lower
density or a stronger viscosity divergence (with other transport coefficients
being given by respective Enskog values that diverge at $\nu_m$) can induce
shear-banding instabilities, even though the original dense Enskog model is
stable to such shear-banding instabilities. For any constitutive model, the
onset of this shear-banding instability is tied to a {\it universal} criterion
in terms of constitutive relations for viscosity and pressure, and the sheared
granular flow evolves toward a state of lower "dynamic" friction, leading to
the shear-induced band formation, as it cannot sustain increasing dynamic
friction with increasing density to stay in the homogeneous state. A similar
criterion of a lower viscosity or a lower viscous-dissipation is responsible
for the shear-banding state in many complex fluids.
