Universal properties of creep flow in amorphous solids

Amorphous solids, such as atomic glasses, colloidal suspensions, granular matter or foams, begin to deform plastically when exposed to external stress Σ. Steady state shear flow of these materials, in absence of thermal fluctuations, is usually described as dγ/dt ∼ (Σ − Σ_c)^β for stresses above critical stress Σ_c and vanishes below it, while in presence of thermal fluctuations flow persists below Σ_c. The transient plastic deformation, called creep flow, is much less understood despite its importance in practical applications. Creep flow often displays a power-law decay in time dγ/dt ∼ t^−ν after which it can either arrest or eventually yield at fluidisation time τ_f . In recent years various numerical values and laws have been suggested for the exponent ν and fluidisation time τ_f in particular experimental or numerical studies. We propose that scaling properties of the creep flow are determined by its the steady state flow. This allows us to predict ν and τ_f characterising the creep flow in terms of the steady state flow parameters, both in athermal and thermally activated systems. We successfully test our predictions using mesoscopic elasto-plastic models of amorphous solids and find them to be consistent with published experimental results.