Instabilities and Collective Phenomena in Plastic Flow of Crystalline Solids

Plastic flow of crystalline solids (as of granular media or colloids) is characterized by collective phenomena emerging on multiple scales. We discuss two examples: (i) In solution-hardened alloys, the interaction of solutes and lattice dislocations leads to a stress vs. deformation rate characteristics of the 'shear thinning' type. This gives rise to deformation instabilities on macroscopic scale, which manifest themselves through periodic, quasiperiodic or chaotic oscillations in the stress-strain curves and the emergence of coherent deformation modes (solitary waves and/or localized 'blobs'). (ii) In any crystalline system, the onset of plastic deformation corresponds to a non-equilibrium transition from a pinned to a moving phase in the defect (dislocation) arrangement ('yielding transition'). This leads to an intermittent flow dynamics with avalachelike strain bursts and long-range spatial correlations in the flow pattern. These fluctuation phenomena can be directly observed in mesoscopic systems (deformation of micron-sized samples).