  Frictional interfaces exhibits a very rich dynamical behavior due to
frictional interactions. This work focuses on the transition between spatially
localized and propagating stick-slip motion. To overcome the difficulties
related to the non-smoothness of the friction law we have studied two models:
(model I) a friction-excited chain of weakly coupled oscillators excited by a
frictional moving belt and (model II) a chain of Van der Pol oscillators. The
two models show very similar dynamical features. Both exhibit discrete
breathers (i.e. spatially localized periodic solutions) solutions for low
coupling and show propagation along the chain of high amplitude limit cycles
for stronger elastic coupling between the unit cells. In both models the
transition from discrete breathers to propagating limit cycles happens through
a nucleation process and, above a certain critical coupling, the velocity of
propagation scales linearly with the elastic coupling coefficient. We suggest
that dynamical features similar to what was demonstrated in this work are
expected for models that are different quantitatively but preserve the same
single-unit topology.
