Andrade creep revisited
Résumé
Transient creep of many materials at high temperatures obeys Andrade's law, in which creep strain is proportional to the cube root of time. The present paper aims at revisiting in terms of criticality the different explanations proposed so far. In agreement with Mott's statistical theory, and using the concept of load shedding and mechanical cascades introduced in Cottrell's microscopic model, we show that Andrade creep is obtained assuming only long range back stresses and delayed obstacle overcoming, both of them involving a large number of interacting sites responsible for stress fluctuations. The time exponent is 1/3 if work hardening is linear, and larger otherwise. Andrade's creep appears as a power law approach of the linear (or χ) creep regime.