Critical yielding rheology: from externally deformed glasses to active systems

TL;DR

This study uses simulations to explore the yielding transition in disordered materials and active systems, revealing differences in critical behavior and universality classes under various loading conditions.

Contribution

It provides the first detailed comparison of yielding behavior in passive and active disordered systems, highlighting different critical exponents and universality classes.

Findings

A Herschel-Bulkley law is observed in both scenarios.

Different critical exponents suggest different universality classes.

Active systems show a vanishing liquid regime near the jamming point.

Abstract

In the last decade many research efforts have been focused on understanding the rheology of disordered materials, and several theoretical predictions have been put forward regarding their yielding behavior. Nevertheless, not many experiments nor molecular dynamics simulations were dedicated to testing those theoretical predictions. Here we use computer simulations to study the yielding transition under two different loading schemes: standard simple shear dynamics, and self-propelled, dense active systems. In the active systems a yielding transition is observed as expected, when the self-propulsion is increased. However, the range of self-propulsions in which a pure liquid regime exist appears to vanish upon approaching the so-called "jamming point" at which solidity of soft-sphere packings is lost. Such an "active yielding" transition shares similarities with the generic yielding transition for shear flows. A Herschel-Bulkley law is observed in both loading scenarios, with a clear difference in the critical scaling exponents between the two, suggesting the existent of different universality classes for the yielding transition under different driving conditions. In addition, we present direct measurements of length and time scales for both driving scenarios. A comparison with theoretical predictions from recent literature reveals poor agreement with our numerical results.