Activity-induced annealing leads to a ductile-to-brittle transition in amorphous solids

Active glasses are dense and disordered systems consisting of motile particles that display phenomenology observed in many biological systems. Here we investigate motility-driven annealing and fluidization in these systems and establish a correspondence between the yielding behaviour of glassy systems under active dynamics and their yielding under oscillatory shear. The yielded region of the phase diagram correlates with tissue fluidization, whereas the annealing region explains age-related maturation and stiffening. This suggests that some mechanical changes observed in ageing tissues can partially stem from processes analogous to enhanced ageing observed in active glasses. In addition to showing similar yielding diagrams, we strengthen the correspondence to oscillatory shear by demonstrating diverging time scales to steady states, the possibility of memory encoding and reading, and the importance of stress reversals in the annealing process in both cases. Finally, we study yielding in active solids and demonstrate that given the correct geometry, one can either suppress or promote brittle failure via shear band formation by tuning activity.