Banding and polarization in driven multistable materials

We study a disordered network of bistable bonds subjected to periodic strain. The model is inspired by experiments on crumpled sheets, and it features behaviors associated with glasses, including a complex energy landscape, memories, and large avalanches. At small strain amplitudes, the system quickly converges to a limit cycle where it repeatedly cycles between a set of states. At large amplitudes, motion is erratic and does not converge to a limit cycle. The transition appears to be continuous, with diverging time scales. The nature of instabilities is different on both sides of the transition. At small strain amplitudes, instabilities are correlated only over a finite distance. Above the transition, instabilities are localized along diagonal bands. The distance between bands grows near the transition and appears to diverge. We propose a simple model that explains these observations. Below the transition, we propose a new "order parameter"-the polarization of the instabilities along the driving direction.