Mechanical metamaterials

Mechanical metamaterials

An important field of activity of NEWMATT consists of the design, prototyping, testing and patent of innovative lattice metamaterials that show tunable compression and shear moduli, as a function of the size of the lattice members (or rods), and the mechanical properties of the employed materials. On using theoretical and numerical approaches in association with rapid prototyping techniques and laboratory tests, NEWMATT develops layered “metamaterials” formed by optimized lattice structures confined between stiffening plates.

A first application of such metamaterials regards the base isolation of seismic-resistant buildings through confined pentamode lattices. Pentamode lattices are network structures with unit cell showing four rods meeting at a point. Such “extreme” metamaterials exhibit five soft modes of deformation, and are known to exhibit very low shear moduli (theoretically equal to zero), being able to stop or dramatically attenuate shear waves. One of the most promising application of pentamode metamaterials is the field of protection of structures from dynamic excitations, either mechanically as well as naturally induced. Over recent years, the structural engineering community has recognized the importance of techniques that can reduce or even eliminate the damage typically sustained during severe seismic events. Seismic isolation and energy dissipation technologies are receiving increased attention due to their effectiveness and ease of implementation on both existing and new structures.

EVENTUALE TITOLO

Unit cell geometry and simulation of the mechanical response under shear excitations

Other lattice metamaterials of interest to NEWMATT are nanoscale cellular materials with closed or open pore structures, and cell size of the order of few dozens of nanometers. Such nano-insulation-materials (NIMs) exhibit an overall thermal conductivity lower than 10 mW/(mK), which stems from the Knudsen effect where the mean free path of the gas molecules is larger than the pore diameter. It is worth noting that current thermo-insulation materials have thermal conductivity in air significantly larger than NIMs, typically around 30-50 mW/(mK). NEWMATT employs 3D/4D printing techniques for the optimal design and rapid prototyping of nanoscale cellular materials.

NEWMATT uses pentamode lattices confined between stiffening plates as next-generation seismic isolators, whose isolation properties may be finely adjusted to the structure being isolated. Intensive research conducted by NEWMATT has demonstrated that confined pentamode lattices feature soft shear and twisting modes, and simultaneously exhibit noticeably high elastic rigidities against both vertical and bending loads. The response of currently available seismic isolators greatly depends on the properties of the materials used, while the stiffness properties of confined pentamode lattices depends mostly on their geometry. This implies that the response of “pentamode bearings” can be easily tuned by altering the geometry to control the vertical and horizontal stiffness for each application. It is also worth noting that pentamode lattices can bear both compression and tension vertical loads during seismic excitations, due to the nonzero tensile strength of their rods. This differs from the behavior of rubber bearings that are not fastened with dowels connecting the rubber layers and steel shims, and is useful in preventing the uplift of the isolated structure. Moreover, pentamode bearings can be manufactured on employing rapid prototyping techniques that make use of single or multiple materials (metals, polymers, etc.), and space grid technologies employing ball-joint systems.

Physical samples obtained through 3D printing.

Nano-Insulation Materials with open or closed cell structure.

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