Ada Amendola

Multiscale tunability of solitary wave dynamics in tensegrity metamaterials

A class of strongly nonlinear metamaterials based on tensegrity concepts is proposed, and the solitary wave dynamics under impact loading is investigated. Such systems can be tuned into elastic hardening or elastic softening regimes by adjusting local and global prestress. In the softening regime these metamaterials are able to transform initially compression pulse into a solitary rarefaction wave followed by oscillatory tail with progressively decreasing amplitude. Interaction of a compression solitary pulse with an interface between elastically hardening and softening materials having correspondingly low-high acoustic impedances demonstrates anomalous behavior: a train of reflected compression solitary waves in the low impedance material; and a transmitted solitary rarefaction wave with oscillatory tail in high impedance material. The interaction of a rarefaction solitary wave with an interface between elastically softening and elastically hardening materials with high-low impedances also demonstrates anomalous behavior: a reflected solitary rarefaction wave with oscillatory tail in the high impedance branch; and a delayed train of transmitted compression solitary pulses in the low impedance branch. These anomalous impact transformation properties may allow for the design of ultimate impact mitigation devices without relying on energy dissipation.

On the mechanical modeling of the extreme softening/stiffening response of axially loaded tensegrity prisms

Abstract We 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.

OPTIMAL DESIGN AND ADDITIVE MANUFACTURING OF NOVEL REINFORCING ELEMENTS FOR COMPOSITE MATERIALS

We experimentally investigate on the use of additive manufacturing technologies for the design and fabrication of innovative reinforcing elements of novel composite materials. We perform short-beam shear tests on cement mortar specimens reinforced with additively manufactured reinforcing fibers made of photopolymers or a titanium alloy. The fracture toughness, shear capacity and first crack strength of the examined materials are estimated based on the provisions of different international standards for construction materials. We also characterize the surface morphology of the examined fibers through microscopy analyses before and after testing. The given results highlight that the microscopic or macroscopic nature of the surface roughness of the analyzed fibers greatly influences the energy absorption capacity of the final materials, while the nature of the fibers’ material (metallic/polymeric) is of central importance in terms of strength properties. The present study represents a first step in the direction of designing reinforcing elements with hierarchical structure to form fabrics, fibers and coatings of groundbreaking reinforcements for next generation composites, profiting from the rapid prototyping capabilities of additive manufacturing technologies at different scales. Fabbrocino, I. Farina, A. Amendola, L Feo, F.Fraternali

On the Mechanical Modeling of Tensegrity Columns Subject to Impact Loading

A physical model of a tensegrity columns is additively manufactured in a titanium alloy. After removing sacrificial supports, such a model is post-tensioned through suitable insertion of Spectra cables. The wave dynamics of the examined system is first experimentally investigated by recording the motion through high-speed cameras assisted by a digital image correlation algorithm, which returns time-histories of the axial displacements of the bases of each prism of the column. Next, the experimental response is mechanically simulated by means of two different models: a stick-and-spring model accounting for the presence of bending-stiff connections between the 3D-printed elements (mixed bending-stretching response), and a tensegrity model accounting for a purely stretching response. The comparison of theory and experiment reveals that the presence of bending-stiff connections weakens the nonlinearity of the wave dynamics of the system. A stretching-dominated response instead supports highly compact solitary waves in the presence of small prestress and negligible bending stiffness of connections.

A Finite Element Analysis of the Stability of Composite Beams With Arbitrary Curvature

A finite element approximation of a theory recently proposed for the geometrically nonlinear analysis of laminated curved beams is developed. The application of the given finite element model to the computation of stability points and post-buckling behavior of beams with arbitrary curvature is also carried out, on taking into account the influences of shear deformation and warping effects on the in-plane and out-plane responses of the beam. The stability analysis is performed through a path-following procedure and a bordering algorithm. Several numerical results are given and comparisons with classical beam theories and other theories available in the relevant literature are established. The given results highlight that the proposed finite element model is well suited to study the stability of structures that incorporate laminated composite beams, such as, e.g., light-weight roof structures and arch bridges.

ACCURATE NUMERICAL METHODS FOR STUDYING THE NONLINEAR WAVE-DYNAMICS OF TENSEGRITY METAMATERIALS

This paper presents presents an effective numerical approach to the nonlinear dynamics of columns of tensegrity prisms subject to impulsive compressive loading. The equations of motions of the analyzed structures are formulated in vector form, by modeling the cables as deformable members and the bars as rigid bodies. The given numerical results investigate the wave dynamics of tensegrity columns, with focus on the propagation of compression solitary waves with variable size and amplitude throughout the system, as a function of the applied impact velocity and the state of prestress of the structure. The engineering potential of the examined structures as tunable acoustic actuators is discussed. 3911 Available online at www.eccomasproceedia.org Eccomas Proceedia COMPDYN (2017) 3911-3922

2D LATTICE STRUCTURES - A PARAMETRIC ANALYSIS

As discussed in a number of papers, both the static and the dynamic response of square lattice materials are strongly affected by the inner microstructure. It is worth noting that results obtained without considering this influence are totally misleading, especially if non-uniform changes in terms of stresses and strains are concerned at the local scale. Within this context, the present work focuses on a parametric analysis aimed at evaluating the influence of the main mechanical properties of RUC on the dynamic response of a 2D square lattice, thus extending previous results towards the condition of a possible different nonuniform mass density distribution over the RUC configuration. The existence of the band gaps within the low frequency region is searched as well as the position and width of the existing gaps are evaluated by means of a numerical strategy already developed and tested. 4986 Available online at www.eccomasproceedia.org Eccomas Proceedia COMPDYN (2017) 4986-4999