Uniaxial stretching mechanics of cellular flexible metamaterials

Cellular flexible metamaterials (CFMs) with alternating vertical and horizontal pores can exhibit nonlinear and tunable mechanical properties. While most of CFMs exhibit novel mechanical properties with elastic instabilities under compression, much less is known about their nonlinear responses under stretching. In this paper, we investigate the mechanics of CFMs under uniaxial stretching with combined experiments, numerical simulations, and analytical models. The internal structure design incorporates a so-called “soft mechanism”, where slender internal structures permit internal rotation of more rigid structures. The stress–strain responses and Poisson's ratio are programmed by controlling the pore pattern (i.e. pore shape and ligament thickness). A 2D plate-chain model, which reduces the CFM into chains of rigid square plates connected by the flexible beams, is developed to study the relation between the elastic modulus of CFMs and pore patterns. An analytical model without fitting parameters is constructed to predict stress–strain responses at small and large stretching deformations, showing good agreement between experiment and theory.