Soft kirigami composites for form-finding of fully flexible deployables

Abstract: We introduce a new class of thin flexible structures that morph from a flat shape into prescribed 3D shapes without an external stimulus such as mechanical loads or heat. To achieve control over the target shape, two different concepts are coupled. First, motivated by biological growth, strain mismatch is applied between the flat composite layers to transform it into a 3D shape. Depending on the amount of the applied strain mismatch, the transformation involves buckling into one of the available finite number of mode shapes. Second, inspired by kirigami, portions of the material are removed from one of the layers according to a specific pattern. This dramatically increases the number of possible 3D shapes and allows us to attain specific topologies. We devise an experimental apparatus that allows precise control of the strain mismatch. An inverse problem is posed, where starting from a given target shape, the physical parameters that make these shapes possible are determined. To show how the concept works, we focus on circular composite plates and design a kirigami pattern that yields a hemispherical structure. Our analysis combines a theoretical approach with numerical simulations and physical experiments to understand and predict the transition from 2D to 3D shapes. The tools developed here can be extended to attain arbitrary 3D shapes. The initially flat shape suggests that conventional additive manufacturing techniques can be used to functionalize the soft kirigami composites to fabricate, for example, deployable 3D shapes, smart skins, and soft electromagnetic metasurfaces.