1,721,010 research outputs found
Mechanical modeling of innovative metamaterials alternating pentamode lattices and confinement plates
Full text linkThis study examines the mechanical behavior of a novel class of mechanical metamaterials alternating pentamode lattices and stiffening plates. The unit cell of such lattices consists of a sub-lattice of the face cubic-centered unit cell typically analyzed in the current literature on pentamode materials. The studied systems exhibit only three soft deformation modes in the infinitesimal stretch-dominated regime, as opposed to the five zero-energy modes of unconfined pentamode lattices. We develop analytical formulae for the vertical and bending stiffness properties and study the dependence of such quantities on the main design parameters: the lattice constant, the solid volume fraction, the cross-section area of the rods, and the layer thickness. A noteworthy result is that the effective compression modulus of the analyzed structures is equal to two thirds of the Young modulus of the stiffest isotropic elastic networks currently available in the literature, being accompanied by zero-rigidity against infinitesimal shear and twisting mechanisms. The use of the proposed metamaterials as novel seismicisolation devices and impact-protection equipment is discussed by drawing comparisons with the response of alternative devices already available or under development
Discrete-to-continuum approaches to the mechanics of pentamode bearings
No full textThis work deals with the multiscale modeling of the mechanical response of pentamode lattices, and a preliminary study on engineering applications of structural bearings formed by pentamode lattices confined between stiffening plates. Numerical and experimental results show that the confinement effect played by the stiffening plates, the geometry and mechanical properties of the junctions strongly influence the overall stiffness properties of such structures. As a result, the mechanics of confined pentamode lattices significantly differs from that of unconfined lattices, being able to accommodate compression and tension vertical loads, and featuring performance-based response under shear loading. Their application for use in anti-seismic system development and/or as shear-wave band gap systems awaits attention
Non-linear elastic response of layered structures, alternating pentamode lattices and confinement plates
No full textWe study the mechanical response under large elastic strains of pentamode layers confined between stiffening plates, and the potential use of such systems as novel seismic isolation and impact protection devices. We analyze pentamode materials that exhibit three soft deformation modes in the infinitesimal stretching regime that follow by the presence of perfectly hinged connections between the rods. The response of these metamaterials under large elastic strains is characterized by an elastic-stiffening effect in terms of the lateral force-displacement response, which increases in the presence of rigid connections and decreases by increasing the number of layers. Our results lead us to conclude that the analyzed pentamode metamaterials can be effectively employed as novel, performance-based devices for seismic and mechanical vibration protection, by designing the lattice geometry, the stiffness properties of the joints, and the lamination scheme in a suitable manner and as a function of the operating conditions
On the mechanical modeling of the extreme softening/stiffening response of axially loaded tensegrity prisms
Full text linkWe study the geometrically nonlinear behavior of uniformly compressed tensegrity prisms through fully elastic and rigid--elastic models. The given models predict a variety of mechanical behaviors in the regime of large displacements, including an extreme stiffening-type response, already known in the literature, and a newly discovered, extreme softening behavior. The latter may lead to a snap buckling event producing an axial collapse of the structure. The switching from one mechanical regime to another depends on the aspect ratio of the structure, the magnitude of the applied prestress, and the material properties of the constituent elements. We discuss potential mechanical and acoustic applications of such behaviors, which are related to the design and manufacture of tensegrity lattices and innovative metamaterials
Bending dominated response of layered mechanical metamaterials alternating pentamode lattices and confinement plates.
Full text linkA numerical study on the elastic response of single- and multi-layer systems formed by alternating pentamode lattices and stiffening plates is presented. Finite element simulations are conducted to analyze the dependence of the effective elastic moduli of such structures upon suitable aspect ratios, which characterize the geometry of the generic pentamode layer at the micro- and macro-scale, and the lamination scheme of the layered structure. The given numerical results highlight that the examined structures exhibit bending-dominated response, and are able to achieve low values of the effective shear modulus and, contemporarily, high values of the effective compression modulus. We are lead to conclude that confined pentamode lattices can be regarded as novel metamaterials that are well suited for seismic isolation and impact protection purposes. Their elastic response can be finely tuned by playing with several geometrical and mechanical design variables
Effective stiffness properties of multi-layered pentamode lattices in the stretching-dominated regime
No full textWe study the mechanics of pentamode metamaterials consisting of multi-layered pentamode lattices alternated with rigid plates. The examined systems respond in the stretching-dominated regime induced by the presence of perfectly hinged connections between the rods and the stiffening plates. We anakyze the variation of the effective stiffness properties of the examined systems with the lattice constant, the solid volume fraction, the cross-section area of the rods, and the number of layers
On the solitary wave dynamics of tensegrity lattices with stiffening response: A numerical study
No full textWe present some peculiar results about the solitary-wave dynamics of novel tensegrity-based metamaterials. It has been previously shown that one-dimensional chains of triangular tensegrity prisms with stiffening behavior support the propagation of compressive solitary waves. We show that such result can be generalized to two-dimensional and three-dimensional modular tensegrity lattices composed of polygonal and polyhedral units. Differently from the one-dimensional case, the stiffening response of these lattices originates at the interface between adjacent units, not from the unit themselves. We present numerical results on the response to impulsive loads of slender assemblies composed by square units in two-dimensions, and cubic units in three-dimensions. We observed compact compressive waves forming at impact locations, together with localized thermalization effects. Such compact waves propagate with nearly constant speed and energy, while maintaining their shape, and emerge from collision with other compact waves almost unaltered, losing a small fraction of their energy. These results suggest the investigation of the dynamics of regular and quasi-regular tessellations formed by other types of polygonal and polyhedral units
In-situ identification techniques for layered structures based on carbon nano tube arrays
No full textSeismic application of pentamode lattices
No full textLa categoria dei “metamateriali estremi” è stata introdotta in letteratura per definire materiali che esibiscano, contemporaneamente, modi di deformazione molto “soffici” e modi “rigidi” (materiali unimode, bimode, trimode, quadramode e pentamode, a seconda del numero di modi soffici). Questa definizione può essere applicata a classi speciali di metamateriali meccanici, quali, ad esempio, materiali compositi, schiume strutturali, materiali cellulari, ecc., che siano dotati di proprietà meccaniche speciali, non rinvenibili nei materiali ordinari. Sistemi pentamode sono stati proposti per realizzare l’isolamento dalle onde meccaniche dei corpi (“elasto-mechanical cloak”), mediante avvolgimento del corpo da
isolare con membrane elastiche a struttura reticolare pentamode. Tuttavia, il potenziale ingegneristico di tali materiali è stato sinora solo parzialmente esplorato. Il presente lavoro presenta nuove versioni di materiali pentamode, ossia cristalli strutturali artificiali che
esibiscano moduli di elasticità tangenziale marcatamente più bassi dei moduli di comprimibilità uniassiale e volumetrica. Architetture tensegrity sono impiegate per controllare i modi soffici e le proprietà meccaniche dei reticoli pentamode, attraverso l'inserimento di attuatori e cavi precompressi all'interno delle celle unitarie. Tali strutture sono proposte come dispositivi di isolamento sismico di tipo innovativo, che presentino proprietà di isolamento regolabili in base alle proprietà dinamiche struttura da isolare.The category of “extremal materials” has been introduced in the literature to define materials that simultaneously show very soft and very stiff deformation modes (unimode, bimode, trimode, quadramode and pentamode materials, depending on the number of soft modes). This definition applies to a special class of mechanical metamaterial – composite materials, structural foams, cellular materials, etc. – which feature special mechanical properties. Pentamode materials have been proposed for transformation acoustics and elasto-mechanical cloak, but their potential in different engineering fields is still only partially explored. We here present novel versions of pentamode materials: artificial structural crystals showing shear moduli markedly smaller than the bulk modulus. Novel pentamode lattices with tensegrity architecture are designed, through the insertion of actuated struts and/or prestressed cables within basic pentamode lattices. Such systems are proposed as tunable seismic base-isolation devices, profiting from their low and adjustable shear moduli, which can be easily adapted to the dynamic properties of the structure to be isolated
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