  We report on the strongly nonlinear dynamics of an array of weakly coupled,
non-compressed, parallel granular chains subject to a local initial impulse.
The motion of the granules in each chain is constrained to be in one direction
which coincides with the orientation of the chain. We show that in spite of the
fact that the applied impulse is applied to a one of the granular chains, the
resulting pulse that initially propagating only in the excited chain gets
gradually equi-partitioned between its neighboring chains, and eventually in
all chains of the array. In particular, the initially strongly localized state
of energy distribution evolves towards a final stationary state of formation of
identical solitary waves that propagate in each one of the chains. These
solitary waves are synchronized and have identical speeds. We show that the
phenomenon of primary pulse equi-partition between the weakly coupled granular
chains can be fully reproduced in coupled binary models which constitute a
significantly simpler model that captures the main qualitative features of the
dynamics of the granular array. The results reported herein are of major
practical significance, since it indicates that the weakly coupled array of
granular chains is a medium in which an initially localized excitation gets
gradually defocused, resulting in drastic reduction of propagating pulses as
they are equi-partitioned among all chains.
