Cracks or pulses? Investigating slip nucleation at soft frictional interfaces

The transition from stationary to dynamic sliding between two contacting elastic bodies can occur via the propagation of unsteady interface rupture fronts. These fronts can broadly be manifest either as crack-like or pulse-like modes, depending on the local elastic fields, and can propagate with a wide range of velocities. Understanding the nucleation and propagation of these rupture modes at elastic contacts has attracted significant attention over the past two decades, especially given their consequences for systems as diverse as soft interfaces and crustal earthquakes. In this work, we focus on comprehending fundamental nucleation mechanisms for rupture fronts and link them to the remote boundary conditions applied while sliding an elastic block against a rigid substrate. We develop a two-dimensional elastic model comprised of bulk lattice-spring networks that dynamically break and readhere interface bonds via distance-based criteria. We closely investigate the characteristics of rupture modes for a homogeneous interface, tracing their evolution from nucleation up until complete traversal through the interface. We show that the selection of the rupture modes also depends intimately on the local stress fields at the interface.