Interplay of softness and rearrangements during avalanche propagation*

Disordered solids yield at a common shear strain of about 3%, but the behavior beyond yield is different for different systems and for systems with different histories. Foams can deform indefinitely without fracturing, many systems exhibit crackling noise or avalanche behavior, and still others exhibit shear banding and brittle fracture. Here we study an athermal, jammed packing of Hertzian particles that are sheared quasistatically. We identify the stress drops associated with rearrangements and then use steepest descent dynamics to study the evolution of the avalanches. We find that the avalanches consist of localized events that appear sequentially in well-separated locations of the sample. To understand this behavior, we exploit a machine-learning approach that has been developed to correlate local structure with dynamics in glassy systems. Following earlier work, we define a quantity softness that correlates with dynamical events during the avalanche process. We study the interplay of softness and dynamics: particles with higher softness are more likely to shift, while dynamical events affect local structure and hence softness. This interplay gives insight into the avalanche process.