Amorphous solids plastically deform in response to mechanical stress. Plastic deformation consists of discrete plastic events that interact through the material elasticity and organise into avalanches. If the stress is sufficiently high amorphous solids yield and enter a flowing phase. The steady-state yielding transition separating the two phases is a dynamical phase transition, with a well-defined value of yield stress and diverging correlation length. Interestingly, due to the out-of-equilibrium nature of amorphous solids, their transient plastic deformation exhibits unusual phenomenology, dependent on preparation and deformation history. For example, when exposed to a constant stress transient plastic flow decays as a power-law in time, called creep flow, that is sometimes followed by a sudden fluidisation event during which the plastic flow rate increases by orders of magnitude.
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