  The transition from static to dynamic friction when an elastic body is slid
over another is now known to result from the motion of interface rupture
fronts. These fronts may be either crack-like or pulse-like, with the latter
involving reattachment in the wake of the front. How and why these fronts occur
remains a subject of active theoretical and experimental investigation, given
its wide ranging implications for a range of problems in tribology. In this
work, we investigate this question using an elastic lattice-network
representation; bulk and interface bonds are simulated to deform and, in the
latter case, break and reform dynamically in response to an applied remote
displacement. We find that, contrary to the oft-cited rigid body scenario with
Coulomb-type friction laws, the type of rupture front observed depends
intimately on the location of the applied boundary condition. Depending on
whether the sliding solid is pulled, pushed or sheared -- all equivalent
applications in the rigid case -- distinct interface rupture modes can occur.
We quantify these rupture modes, evaluate the interface stresses that lead to
their formation, and and study their subsequent propagation dynamics. A strong
analogy between the sliding friction problem and mode II fracture emerges from
our results, with attendant wave speeds ranging from slow to Rayleigh. We
discuss how these fronts mediate interface motion and implications for the
general transition mechanism from static to dynamic friction.
