  We analyze the contact and force networks in a dense confined packing of
pentagonal particles simulated by means of the contact dynamics method. The
particle shape effect is evidenced by comparing the data from pentagon packing
and from a packing with identical characteristics except for the circular shape
of the particles. A surprising observation is that the pentagon packing
develops a lower structural anisotropy than the disk packing. We show in this
work that this weakness is compensated by a higher force anisotropy that leads
to enhanced shear strength of the pentagon packing. With the polygonal shape of
the particles, the strong force chains are mostly composed of edge-to-edge
contacts with a marked zig-zag aspect.
