ABSTRACT

When a disordered jammed solid is sheared for many cycles at constant strain amplitude, it can relax until the same particle rearrangements repeat in each cycle. I discuss two ways this simple form of mechanical annealing helps illuminate these materials’ complexity. First, experiments with a 2D colloidal solid show how annealing forms a memory of strain amplitude, and how disordered solids exemplify a generic behavior called return-point memory. This prompts the question of whether an annealed sample could instead be free of memories. Paradoxically, this can be done by storing as many memories as possible—which we can understand by measuring the population of rearranging regions within a sample. Second, I discuss another possible outcome of annealing: an orbit in which the period of particle motions is a multiple of the period of driving. Unlike return-point memory, this behavior can arise from frustrated interactions among the rearranging regions, and it suggests a way to reveal these elusive interactions in experiments.