Emergent disorder and mechanical memory in periodic metamaterials.

Ordered mechanical systems typically have one or only a few stable rest configurations, and hence are not considered useful for encoding memory. Multistable and history-dependent responses usually emerge from quenched disorder, for example in amorphous solids or crumpled sheets. In contrast, due to geometric frustration, periodic magnetic systems can create their own disorder and espouse an extensive manifold of quasi-degenerate configurations.

Dissipation Indicates Memory Formation in Driven Disordered Systems.

Disordered and amorphous materials often retain memories of perturbations they have experienced since preparation. Studying such memories is a gateway to understanding this challenging class of systems. However, it often requires the ability to measure local structural changes in response to external drives.

Discontinuous Tension-Controlled Transition between Collective Actuations in Active Solids.

The recent finding of collective actuation in active solids-solids embedded with active units-is a new promise for the design of multifunctional materials with genuine autonomy, and a better understanding of dense biological systems. Here, we combine the experimental study of centimetric model active solids, the numerical study of an agent-based model, and theoretical arguments to reveal a new form of collective actuation and how mechanical tension can serve as a general mechanism for transitioning between different collective actuation regimes. The presence of hysteresis when varying tension back and forth highlights the nontrivial selectivity of collective actuations.

Memory from coupled instabilities in unfolded crumpled sheets.

Crumpling an ordinary thin sheet transforms it into a structure with unusual mechanical behaviors, such as enhanced rigidity, emission of crackling noise, slow relaxations, and memory retention. A central challenge in explaining these behaviors lies in understanding the contribution of the complex geometry of the sheet. Here we combine cyclic driving protocols and three-dimensional (3D) imaging to correlate the global mechanical response and the underlying geometric transformations in unfolded crumpled sheets.