  We study granular suspensions under a variety of extensional deformations and
simple shear using numerical simulations. The viscosity and Trouton's ratio
(the ratio of extensional to shear viscosity) are computed as functions of
solids volume fraction $\phi$ close to the limit of zero inertia. Suspensions
of frictionless particles follow a Newtonian Trouton's ratio for $\phi$ all the
way up to $\phi_0$, a universal jamming point that is independent of
deformation type. In contrast, frictional particles lead to a
deformation-type-dependent jamming fraction $\phi_m$, which is largest for
shear flows. Trouton's ratio consequently starts off Newtonian but diverges as
$\phi\to\phi_m$. We explain this discrepancy in suspensions of frictional
particles by considering the particle arrangements at jamming. While
frictionless particle suspensions have a nearly isotropic microstructure at
jamming, friction permits more anisotropic contact chains that allow jamming at
lower $\phi$ but introduce protocol dependence. Finally, we provide evidence
that viscous number rheology can be extended from shear to extensional
deformations, with a particularly successful collapse for frictionless
particles. Extensional deformations are an important class of rheometric flow
in suspensions, relevant to paste processing, granulation and high performance
materials.
