Two-dimensional mechanical metamaterials with bending-induced expansion behavior

A conventional thin homogeneous elastic plate shows no net lateral strain when subjected to a pure bending load. Here, a two-dimensional (2D) metamaterial exhibiting an exotic bending-induced expansion behavior is designed based on the structure unit with a non-symmetric contact under tensile and compressive loads. Expansion behavior was demonstrated in the fabricated 2D metamaterial structures in four-point bending, tension, and compression tests and corresponding simulations. The bending-expansion ratio, defined as the lateral strain times the curvature radius divided by the length of the unit cell, is a non-dimensional parameter depending on the geometry of the structure.