Programmable Kiri-Kirigami Metamaterials

A study was conducted to demonstrate that the design of kiri-kirigami (i.e., cuts on cuts)-based metamaterials that can be programmed to tilt into different orientations on demand, as well as potential applications in reflecting or transmitting sunlight as energy efficient building skins. oly(dimethylsiloxane) (PDMS) is chosen as the sheet material here because it is hyperelastic and thus allows for repetitive elastic loading and unloading without plastic deformation at a large strain. Upon stretching the kirigami structure, each cut unit undergoes out-of-plane buckling and tilts into a nearly vertical direction through both bending and twisting accompanied by the opening of a pore. Through building energy simulation, it is demonstrated that the potential application of kiri-krigami structures as building envelopes to reduce energy consumption. The engraving approach can be easily extended to other 3D kirigami and origami structures, where deterministic bending or folding can be precisely controlled and programmed by engineering notches or cuts. The spontaneous tilting and expanding of programmable kiri-kirigami structures via local actuation can be applied to other responsive materials such as light-responsive materials.