Shape optimization of cut-mediated soft mechanical metamaterials

Mechanical metamaterials are man-made design materials with unusual or auxetic mechanical properties. Elastomeric sheets with a set of cut patterns can exhibit giant stretchability, auxetic behavior, and programmable shape transformation. This type of cut-mediated soft mechanical metamaterial has attracted intensive attention recently because of its ease of material fabrication, diversity of cut patterns and cut hierarchies, and huge space for material design. Upon stretching, the cut lagaments of the metamaterial deform severely and much higher stress is induced around the cut tip due to stress concentration. This would limit the stretchability or even result in fracture of the cut-mediated metamaterials. Enhanced mechanical behaviors of soft metamaterials can be achieved through structural optimization. Research on optimization of cut-mediated mechanical matematerials is, however, really scarce, albeit of several demonstrations of perforated metamaterials. We present an optimization strategy and a platform based on commercial software to predict and optimize cut-mediated soft mechanical metamaterials. Optimization of the metamaterial is realized by modifying the boundary shape of cut liagments, which would reduce stress concentration, generate larger negative Poisson's ratio, and allow enhanced stretchability. Our optimization scheme of metamaterials would aid design and fabrication of mechanical metamaterials and transforming structures.