Creep of interfaces#
The physical properties of a material are often controlled by embedded interfaces (e.g. for dislocations in crystals, crack fronts, frictional interfaces, or magnetic domain walls). Pinned by impurities, they dramatically increase the material’s strength, toughness, or hysteresis. Often, the interfaces undergo a depinning transition at the critical force (or stress, or magnetic field). At a finite temperature, the depinning transition is rounded: the interface creeps at any finite force.
Even if the creep rate is small and difficult to observe directly, its effect can have a dramatic impact on the material’s properties. For example, at the frictional interface, the static friction coefficient grows logarithmically with time, even though the interface is seemingly at rest. In layered systems this can lead to an erratic stick-slip response .
On a fundamental level, creep is due to thermal activations. Due to elastic coupling the activations are spatially correlated: thermal avalanches occur, see animation. In depinning-like systems, these avalanches are characterized by the same exponents as the depinning transition itself .