Programmable composites

Multistable structures leave a fascinating impression as switchable states facilitate the programmability of materials, for instance, "if-then-else-behavior": if a certain load is reached (if-condition), the structure buckles and reacts returning a feedback force (then-consequence), otherwise it stays in its current state (else-state). This characteristic makes multistability attractive, for example, for energy harvesting or absorption as well as for permanent, but reversible deformation and shape morphing. In this chapter we present the design process for multistable composite materials exhibiting rate-dependent, unusual mechanical behavior starting from the CAD design of unit cells toward the simulation of cell arrays. The cells are composed of two materials with different mechanical properties. Their geometry is parametrized to control buckling that most solution schemes struggle to handle because of the occurrence of unstable phases. For this problem, we propose a surrogate-modeling technique to capture the complex transition between stable states and consider numerical damping to stabilize the computational procedure. To demonstrate the efficiency of the approach, we present numerical results for boundary value problems with arrays of multistable cells.