[SY-L1] Flow and failure of (amorphous) materials - a nonequilibrium phase transition?
Invited
Amorphous materials show intriguing mechanical properties that are of fundamental interest and of great importance for applications. While the aging, deformation and failure have been longstanding research questions for conventional glasses, recent soft glasses including colloidal suspensions, foams and emulsions have spawned new interest and new perspectives on glassy flow. In these systems, flow is ubiquitous: it is easily induced by small applied stresses, and the underlying flow and failure mechanisms can be conveniently studied at the particle scale. Simulations and experiments on soft glassy systems have witnessed exciting scaling relations that are believed to underlie the flow of glasses under applied stress. In particular, colloidal and granular systems have been powerful models to directly visualize and measure internal strain fields and their hierarchical organization. The emerging picture is that flow and flow instabilities are related to non-equilibrium phase transitions from a reversible elastic-like to irreversible plastic response of the material. At yielding of the material, plastic regions percolate across the sample, mediating the flow in the otherwise elastic matrix. Flow is therefore neither strongly localized nor homogeneous across the material; instead, system-spanning correlations of plastic activity occur, revealing a novel kind of criticality of the slowly flowing material. Similar long-range correlated flow phenomena have been observed in the deformation of crystals, as bursts of dislocations. Also in these crystalline materials, the internal elastic strain field is believed to be responsible for the highly correlated dislocation activity. I will elucidate this underlying mechanism by detailed investigation of the strain field in colloidal crystals and glasses. Furthermore, I will show that the underlying general mechanism links our soft materials to a far wider range of materials and phenomena including conventional material plasticity, geological flow phenomena, and earth quakes.