1,221 research outputs found
On the mechanical modeling of the extreme softening/stiffening response of axially loaded tensegrity prisms
We study the geometrically nonlinear behavior of uniformly compressed
tensegrity prisms, through fully elastic and rigid--elastic models. The
presented 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 acoustic
applications of such behaviors, which are related to the design and manufacture
of tensegrity lattices and innovative phononic crystals
Mechanical modeling of innovative metamaterials alternating pentamode lattices and confinement plates
This 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
Nonlinear acceleration wave propagation in the DKM theory
We study the evolutionary development of an acceleration wave propagating in a saturated porous material according to a Biot theory proposed by Donskoy, Khashanah and McKee. The theory is fully nonlinear, includes dissipation, and the analysis presented is exact. We derive sufficient conditions to show that two distinct waves propagate, a fast wave and a slower wave. A solution for the wave amplitude is presented for a wave moving into an equilibrium region
on the mechanical response of multilayered pentamode lattices equipped with hinged and rigid nodes
Purpose This paper aims to review recent literature results on the mechanical response of confined pentamode structures behaving either in the stretching-dominated or the bending-dominated regimes. Design/methodology/approach The analyzed structures consist of multilayer systems formed by pentamode lattices alternated with stiffening plates and are equipped with rigid or hinged connections. Findings It is shown that such structures are able to carry unidirectional compressive loads with sufficiently high stiffness, while showing markedly low stiffness against shear loads. In particular, their shear stiffness may approach zero in the stretching-dominated regime. Originality/value The presented results highlight the high engineering potential of laminated pentamode metamaterials as novel isolation devices to be used for the protection of buildings against shear waves
On the design, elastic modeling and experimental characterization of novel tensegrity units
Purpose This study aims to focus on a short review on recent results dealing with the mechanical modelling and experimental characterization of a novel class of tensegrity structures, named class θ = 1 tensegrity prisms. The examined structures exhibit six bars connected by two disjoint sets of strings. Design/methodology/approach First, the self-equilibrium problem of tensegrity θ = 1 prisms is numerically investigated for varying values of two aspect parameters and, next, their prestress stability is studied. The mechanical behavior of the examined structures in the large displacements regime under uniform compression loading is also numerically computed through a path-following procedure. Finally, the predicted constitutive response is validated through experimental tests. Findings The presented results highlight that the examined structures exhibit a large number of infinitesimal mechanisms from the freestanding configuration, and reveal that they exhibit tunable elastic response switching from stiffening to softening. Originality/value This multi-faceted elastic response is in agreement with previous literature results on the elastic response of minimal tensegrity prism, and suggests that such units can be usefully used as non-linear springs in next-generation tensegrity metamaterials
Experimental investigation of the softening-stiffening response of tensegrity prisms under compressive loading
The present paper is concerned with the formulation of new assembly methods
of bi-material tensegrity prisms, and the experimental characterization of the
compressive response of such structures. The presented assembly techniques are
easy to implement, including a string-first approach in the case of ordinary
tensegrity prisms, and a base-first approach in the case of systems equipped
with rigid bases. The experimental section shows that the compressive response
of tensegrity prisms switches from stiffening to softening under large
displacements, in dependence on the current values of suitable geometric and
prestress variables. Future research lines regarding the mechanical modeling of
tensegrity prisms and their use as building blocks of nonlinear periodic
lattices and acoustic metamaterials are discussed
The obstacle problem in masonry structures and cable nets
We consider the problem of finding a net that supports prescribed forces
applied at prescribed points, yet avoids certain obstacles, with all the
elements of the net under compression (strut net) or under tension (cable web).
In the case of masonry structures, for instance, this consists in finding a
strut net that supports the forces, is contained within the physical structure,
and avoids regions that may be not accessible due, for instance, to the
presence of holes. We solve such a problem in the two-dimensional case, where
the prescribed forces are applied at the vertices of a convex polygon, and we
treat the cases of both single and multiple obstacles. By approximating the
obstacles by polygonal regions, the task reduces to identifying the feasible
domain in a linear programming problem. For a single obstacle we show how the
region available to the obstacle can be enlarged as much as possible
in the sense that there is no other strut net, having a region
available to the obstacle with . The case where some of
the forces are reactive, unprescribed but reacting to the other prescribed
forces, is also treated. It again reduces to identifying the feasible domain in
a linear programming problem. Finally, one may allow a subset of the reactive
forces to each act not at a prescribed point, but rather at any point on a
prescribed line segment. Then the task reduces to identifying the feasible
domain in a quadratic programming problem.Comment: 22 pages, 12 figures, 3 supplemental video
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