Statistical physics of elastoplastic steady states in amorphous solids: Finite temperatures and strain rates

The effect of finite temperature T and finite strain rate (gamma) over dot on the statistical physics of plastic deformations in amorphous solids made of N particles is investigated. We recognize three regimes of temperature where the statistics are qualitatively different. In the first regime the temperature is very low, T<T-cross(N), and the strain is quasistatic. In this regime the elastoplastic steady state exhibits highly correlated plastic events whose statistics are characterized by anomalous exponents. In the second regime T-cross(N)<T<T-max((gamma) over dot) the system-size dependence of the stress fluctuations becomes normal, but the variance depends on the strain rate. The physical mechanism of the crossover is different for increasing temperature and increasing strain rate, since the plastic events are still dominated by the mechanical instabilities (seen as an eigenvalue of the Hessian matrix going to zero), and the effect of temperature is only to facilitate the transition. A third regime occurs above the second crossover temperature T-max((gamma) over dot) where stress fluctuations become dominated by thermal noise. Throughout the paper we demonstrate that scaling concepts are highly relevant for the problem at hand, and finally we present a scaling theory that is able to collapse the data for all the values of temperatures and strain rates, providing us with a high degree of predictability.