Crossover in the dynamics of jerky flow in Al - Mg polycrystals

Jerky flow in Al-Mg alloys is investigated through the statistics of the stress drops size, and through a dynamic analysis of the stress vs. time records. At low applied strain rate levels, peaked distributions are associated with chaotic dynamics, while at higher strain rates, the unstable behavior is characterized by power law distributions reminiscent of a critical dynamics. In addition, the bands of localized plastic deformation shift from stationary to propagating. This crossover is discussed in terms of a nonlocal model of jerky flow, with a range of negative strain rate sensitivity and spatial interactions of varying strength.