Seminar: “Annealing Amorphous Solids using Oscillatory Shear and Active Dopants and Memory Formation” by Prof. Smarajit Karmakar

Prof. Smarajit Karmakar, Tata Institute of Fundamental Research, India

Title:
Annealing Amorphous Solids using Oscillatory Shear and Active Dopants and Memory Formation
 

Abstract:
Understanding the mechanical properties of amorphous solids has been a field of intense research not only for the zoo of interesting phenomena one observes once these solids are subjected to external deformations but also for their importance in industrial applications. Amorphous solids fail catastrophically via shear band formation, and tuning their mechanical yielding is important for designing better materials. I will focus on the annealing mechanisms in these solids as they are of practical importance. I will highlight the utilization of self-motility as another means to anneal glasses and use that as a means to fine-tune the failure mode of the system under uniaxial tensile deformation. I will demonstrate the annealing effects of activity and draw parallels with other well-known mechanical annealing processes, such as oscillatory shearing (both uni- and multi-directional).

We investigate motility-driven annealing and fluidization in these systems and establish a correspondence between the yielding behavior of glassy systems under active dynamics and their yielding under oscillatory shear. The yielded region of the phase diagram correlates with tissue fluidization, while 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. Finally, I will touch upon the memory effects in cyclically deformed amorphous solids through computer simulations. Applying oscillatory shear deformations in all orthogonal directions during encoding creates robust memories that are agnostic to the reading direction. Our extensive system size analysis shows that memory encoding is faster in small systems and becomes exceedingly challenging as systems approach the thermodynamic limit. Using tension-compression cycles on amorphous nanorods, we show that, indeed, memory encoding and reading are possible in the presence of free surfaces as well.

References:
•    Rishabh Sharma, Smarajit Karmakar, Nature Physics 21, 253-261 (2025).
•    Monoj Adhikari, Rishabh Sharma and Smarajit Karmakar, PRL 134, 018202 (2025)