Metamaterials are materials that are designed to exhibit a specific set of mechanical and physical properties. One class of metamaterials are the ultralight, ultrastiff mechanical metamaterials. For ordinary materials, the mechanical properties often rapidly decrease as their density is reduced. However, advancements in novel micro- and nanofabrication techniques, such as 3D printing enable the fabrication of microarchitected cellular materials (or cellular solids) with nearly constant stiffness per unit mass density. Typically there are two types of cellular materials that are classified based on their mechanical behavior into stretch- and bending-dominated structures. For stretch dominated structures, the goal is to create a lightweight and stiff material. The aim of these materials is to maximize the modulus (slope in the force vs. deformation curve in the initial elastic regime) as well as the initial collapsing strength. These materials are often referred to as microtruss lattice structures. On the other hand, for bending-dominated structures the goal is to create a compliant structure that can absorb large amounts of energy for e.g. damping applications.
Application Example: Stable Compression Testing of Micro-Scale Metamaterials
In the depicted work by Draper (Massachusetts, USA), the FT-NMT03 Nanomechanical Testing System is used for the stable compression testing of a unit cell of a microtruss lattice structure. As the structure is compressed, the applied stress is transferred into an elastic stretching and compression of the individual struts. When the elastic limit of one of the struts is reached, it plastically yields, leading to buckling and a complete collapse of the microstructure. Furthermore, due to the position controlled compression testing, the post-yield behavior of the materiel can be quantified.