Strain and Strain rate-dependent Mechanical Metamaterials

Abstract

Generally, after the manufacturing process, the mechanical behaviors of a meta-structure or material are set and are hardly modified. Nevertheless, materials and structures with varying static or dynamical mechanical properties are attractive to many engineering fields. In this talk, I will introduce two types of mechanical metamaterials with tunable mechanical performances under large compressive deformations, one is strain-dependent mechanical metamaterial and another one is strain rate-dependent mechanical metamaterial. The tunable mechanical performances mean the tunable effective Young's modulus and Poisson's ratio (auxeticity), both of which are fundamental mechanical properties of materials. For the strain-dependent mechanical metamaterial, the corresponding theoretical model of their effective Young's modulus and Poisson's ratio were established, and the mechanism of their mechanical tunability has been explained. More importantly, simulation results demonstrate that the strain-dependent metamaterial has the potential for designing metamaterials exhibiting tunable phononic band gaps. For the strain rate-dependent mechanical metamaterial, we design a solid structure that displays unidirectional shock resistance, thus going beyond Newton’s second law in analogy to non-Newtonian fluids. We design the mechanical metamaterial with finite element analysis and fabricate it using three-dimensional printing at the centimetric scale (with fused deposition modeling) and at the micrometric scale (with two-photon lithography). The non-Newtonian elastic response is measured via dynamical velocity-dependent experiments. Reversing the direction of the impact, we further highlight the intrinsic non-reciprocal response.