Nonlinear Mechanical Metamaterials: from Statics to Dynamics

Abstract

Metamaterials have emerged in the last 20 years as promising candidates to engineer material parameters and properties that transcend those of the constitutive elements. Research on metamaterials spans multiple fields of physics and engineering ranging from electromagnetism to optics and from acoustic to mechanics. Despite the many applications they are used for, all metamaterials share a common leitmotif since they are all created by assembling relatively simple elements (also called building blocks) to realize complex and structured materials. During my PhD, I used a combination of analyses and experiments to investigate the nonlinear response of mechanical metamaterials. More specifically, I used finite element analyses to demonstrate that a palette of symmetry breakings can be realized in substrate-attached liquid crystal elastomer cellular structures by independently programming the anisotropy at the molecular and structural scales. Secondly, I investigated experimentally and numerically the response of hinged shallow arches subjected to a transverse midpoint displacement. I found that this simple system supports a rich set of responses, which, to date, have received relatively little attention. I observed not only the snapping of the arches to their inverted equilibrium configuration, but also an earlier dynamic transition from a symmetric to an asymmetric shape that results in a sudden strength loss. Lastly, I demonstrated that such hinged shallow arches enable realization of a multistable mechanical metamaterial for which nonreciprocity and reversibility can be independently programmed.