Scaling of relaxation and excess entropy in plastically deformed amorphous solids

Abstract

When stressed sufficiently, solid materials yield and deform plastically via reorganization of microscopic constituents. Indeed, it is possible to alter the microstructure of materials by judicious application of stress, an empirical process utilized in practice to enhance the mechanical properties of metals. Understanding the interdependence of plastic flow and microscopic structure in these nonequilibrium states, however, remains a major challenge. Here, we experimentally investigate this relationship, between the relaxation dynamics and microscopic structure of disordered colloidal solids during plastic deformation. We apply oscillatory shear to solid colloidal monolayers and study their particle trajectories as a function of shear rate in the plastic regime. Under these circumstances, the strain rate, the relaxation rate associated with plastic flow, and the sample microscopic structure oscillate together, but with different phases. Interestingly, the experiments reveal that the relaxation rate associated with plastic flow at time t is correlated with the strain rate and sample microscopic structure measured at earlier and later times, respectively. The relaxation rate, in this nonstationary condition, exhibits power-law, shear-thinning behavior and scales exponentially with sample excess entropy. Thus, measurement of sample static structure (excess entropy) provides insight about both strain rate and constituent rearrangement dynamics in the sample at earlier times.

Mechanical annealing and memories in a disordered solid

“…Intuitively, the condition b = c should correspond to mechanical equilibrium, with no imposed shear stress in either direction. However, Galloway et al (39,40) found that an elliptical signature could be detected even at equilibrium and that it survived further shear deformations below the yielding transition, so that its disappearance was a proxy for yielding. They identified it as the memory of an earlier large plastic deformation, consistent with scattering results from bulk metallic glasses that were previously deformed (4,41,42).…”

Mechanical annealing and memories in a disordered solid

“…Intuitively, the condition b = c should correspond to mechanical equilibrium, with no imposed shear stress in either direction. However Galloway et al (39,40) found that an elliptical signature could be detected even at equilibrium, and that it survived further shear deformations below the yielding transition. They identified it as the memory of an earlier large plastic deformation-consistent with scattering results from bulk metallic glasses that were previously deformed (5,41,42).…”

Correlation between plastic rearrangements and local structure in a cyclically driven glass

“…Even though S 2 has been introduced long ago 54,55 , it is a useful concept that continues to be widely used 17,[56][57][58] . As a matter of fact, recently, scaling relations have been reported between S 2 and diffusivity in glassy systems 59 and relaxation rates in cyclic sheared systems 60 . In order to look at this quantity on a single-particle level, the two-body entropy of particle i can be defined as:…”