  Packings of macroscopic granular chains capture some of the essential aspects
of molecular polymer systems and have been suggested as a paradigm to
understand the physics on a molecular scale. However, here we demonstrate that
the interparticle friction $\mu$ in granular chain packings, which has no
counterpart in polymer systems, leads to a nontrivial yielding and rheological
response. Based on discrete element simulations we study the nonlinear rheology
of random packings of granular chains under large amplitude oscillatory shear.
We find that the maximum stress and the penetration depth of the shear
deformation into the material bulk are nonmonotonic functions of friction with
extrema at intermediate values of $\mu$. We also show that the regularly
repeated gaps between the adjacent grains, which are special to commercial
granular chains, broaden the shear zone and enhance the entanglements in the
system by promoting the interlocking events between chains. These topological
constraints can significantly increase the degree of strain stiffening. Our
findings highlight the differences between the physics of granular chain
packings and molecular polymer systems.
