  We study the rheology of dense granular flows for frictionless
spherocylinders by means of 3D numerical simulations. As in the case of
spherical particles, the effective friction $\mu$ is an increasing function of
the inertial number $I$, and we systematically investigate the dependence of
$\mu$ on the particle aspect ratio $Q$, as well as that of the normal stress
differences, the volume fraction and the coordination number. We show in
particular that the quasi-static friction coefficient is non-monotonic with
$Q$: from the spherical case $Q=1$, it first sharply increases, reaches a
maximum around $Q \simeq 1.05$, and then gently decreases, reaching back its
initial value for $Q \simeq 2$. We provide a microscopic interpretation for
this unexpected behavior through the analysis of the distribution of
dissipative contacts around the particles: as compared to spheres, slightly
elongated grains enhance contacts in their central cylindrical band, whereas at
larger aspect ratios particles tend to align and dissipate by preferential
contacts at their hemispherical caps.
