Flexible Mechanical Metamaterials With Unusual Dual-Plateau Negative Poisson's Ratio Responses Under Large Deformation

Flexible mechanical metamaterials with stable negative Poisson's ratios hold great promise for applications in flexible electronics. Nevertheless, most existing stretchable auxetic designs rely on single or strongly coupled deformation modes, which confine their mechanical responses to only one stable state and restrict their functional versatility. A dual-plateau Poisson's ratio characteristic that enables strain-switchable and bi-stable Poisson's ratio states has rarely been reported in previous studies. This work introduces a new class of flexible mechanical metamaterials based on rotating soft network structures (RSNSs), where deformable network units replace the rigid plate units in traditional rotating rigid structures. Owing to a unique multi-stage deformation mechanism, the proposed RSNS metamaterials exhibit an unusual strain-switchable dual-plateau negative Poisson's ratio response under large tensile deformation. The dual-plateau Poisson's ratio characteristic is accurately captured by FEA simulations and can be systematically tuned through rational design of structural geometries. The RSNS metamaterials can be constructed by modular assembly of discrete rotating units using physical pin-based hinges or by one-step fabrication employing a living-hinge design. Finally, a class of RSNS-based stretchable luminescent devices is demonstrated, exhibiting strain-controlled optical information switching performance, with each stable working state sustained over a finite continuous strain range.