Mechanical modeling of innovative metamaterials alternating pentamode lattices and confinement plates

Abstract

This study examines the mechanical behavior of a novel class of mechanical metamaterials\ud alternating pentamode lattices and stiffening plates. The unit cell of such lattices consists of a\ud sub-lattice of the face cubic-centered unit cell typically analyzed in the current literature on\ud pentamode materials. The studied systems exhibit only three soft deformation modes in the\ud infinitesimal stretch-dominated regime, as opposed to the five zero-energy modes of unconfined\ud pentamode lattices. We develop analytical formulae for the vertical and bending stiffness\ud properties and study the dependence of such quantities on the main design parameters: the\ud lattice constant, the solid volume fraction, the cross-section area of the rods, and the layer\ud thickness. A noteworthy result is that the effective compression modulus of the analyzed\ud structures is equal to two thirds of the Young modulus of the stiffest isotropic elastic networks\ud currently available in the literature, being accompanied by zero-rigidity against infinitesimal\ud shear and twisting mechanisms. The use of the proposed metamaterials as novel seismicisolation\ud devices and impact-protection equipment is discussed by drawing comparisons with\ud the response of alternative devices already available or under development

Numerical and Analytical Approaches to the Self-Equilibrium Problem of Class θ = 1 Tensegrity Metamaterials

“…The remarkable influence of infinitesimal mechanisms on the geometrically nonlinear constitutive response and wave dynamics of tensegrity metamaterials has been highlighted in Fraternali et al (2012Fraternali et al ( , 2014. Analytic, numerical, and experimental studies on the implementation of the units studied in the present work within novel tensegrity metamaterials, including, e.g., impact protection gear and vibration isolation devices (Fraternali and Amendola, 2017), are addressed to future work.…”

Mechanical modeling of superelastic tensegrity braces for earthquake-proof structures

“…The currently accepted definition of seismic metamaterials refers to discrete structures forming shields that protect buildings from seismic waves, or lattice structures serving as unconventional seismic isolation devices [12,13]. We here propose structural uses of SMAD braces that allows us to stretch such a definition, with the aim of including bracing systems which make use of SMAD building blocks, and exhibit displacement amplification capacity and energy dissipation properties surpassing those of conventional anti-seismic braces.…”

On the Computational Design of Innovative Seismic Isolation Devices Based on Lattice Materials

“…The analytic study presented in Ref. [9] has obtained analytic formulae for the vertical stiffness Kv and bending stiffness Kφ coefficient of a laminated sfcc structure formed by an arbitrary number of layers. Such formulae read as follows (1) where and are the vertical stiffness and the bending stiffness (about either the or the axis) of the generic layer.…”

“…For critical structures, like power plants, solutions of devices with isolation capabilities in both horizontal and vertical directions are still under development. The literature results reviewed by the present study highlight that PMBs can be designed to behave as tension-capable and performance-based isolation devices, whose properties mainly depend on the geometry of the members forming the unit cell of the lattice, the nature of the connections joining the strut one another, and the struts and the stiffening plates, as well as the mechanical properties and sizes of the component materials [9], [10], [12], [13]. The response of such devices can be easily adjusted to that of the structure to be protected, and their fabrication does not necessarily require heavy industry, and expensive materials, being possible with ordinary 3-D printers.…”

“…A novel feature of layered structures formed by pentamode lattices and stiffening plates, hereafter referred to as "pentamode bearings" (PMBs), has been recently recognized in the literature, through the discovery that such systems exhibit a three-mode response characterized by stiff response against vertical compression and bending modes, and soft response in shear and torsion [9], [10], [11], [12], [13], [14]. It is known that unconfined pentamode lattices exhibit (theoretically) zero stiffness against compression loads in the stretch-dominated limit [2], [3].…”