Research
Design, manufacturing and testing of innovative seismic isolation devices
The nascent field of mechanical and acoustic metamaterials, defined as engineered lattice materials that feature unconventional behaviors mainly derived by the geometry of their microstructure, rather than from their chemical composition, is growing rapidly and attracting increasing attention from many research areas - including acoustics, aerospace and mechanical engineering, medical diagnosis and remote sensing, sound and heat control . Today, there is an urgent need for advanced studies exploring the engineering potential of such materials, and practical methods for their fabrication.
My research in this area aims at designing novel versions of pentamode materials: artificial structural crystals showing shear moduli markedly smaller than the bulk modulus. Novel systems will be designed to control the soft modes of these pentamode materials, through the tuning of the bending moduli of members and junctions, and/or the insertion of struts or prestressed cables within pentamode lattices.
Actuated pentamode metamaterials will be constructed and tested as seismic base-isolation devices, profiting from the low and adjustable shear moduli of such systems. In addition, pentamode materials will be experimentally used as components of new-generation seismic dampers
Physical models of such devices will be manufactured through novel additive manufacturing techniques (3D printing in polymeric and metallic materials). An experimental validation phase will investigate the mechanical response and the control of such models. It will lead to an evaluation of the scalability of the proposed solutions, and the associated economic benefits (in collaboration with Ferdinando Auricchio at the University of Pavia, link; Russell Goodall at the University of Sheffield, link; Gianmario Benzoni at the UCSD, link).
Multiscale design, modeling, manufacturing and testing of lattice structures
I am currently working on the computational design, maunfacturing and experimentation of a variety of periodic lattices, and foam-like structures at macro, micro, and nanoscales, such as, e.g., carbon nanotube (CNT) foams and multilayered CNT structures (CNT 1, CNT 2, CNT 3), and tensegrity materials and structures (TENSEGRITY 1, TENSEGRITY 2). I have carried out such studies at Unisa, Caltech and UCSD. My research interests are focused on periodic arrays of particles/units featuring a variety of special mechanical behaviors, which include: extreme values of mass/stiffness/strength parameters, mechanical waves control, wave steering and directional behaviors. In the near future, my research is aimed at deepening the fundamental understanding of lattice mechanics, and its application to the design, modeling, and manufacturing of innovative multiscale materials and structures. Lattice structures will be employed at different scales, to form cellular solids; devices; fibers and fabrics; and building-scale structures. An additional goal of this research consists of applying mechanical metamaterials in engineering fields where current knowledge of such systems is only partial, like, e.g., civil engineering and sustainable construction (ITALY-USA project).
A modeling research line of this researchwill study the effects of internal and external prestress on nonlinear lattice mechanics, with the aim of designing arbitrary lattice behaviors. Material-scale applications of multiscale lattices will deal with novel dynamic devices and hierarchical composite materials. A structure-scale application will exploit lattices with morphing abilities to design adaptable envelopes for energy efficient buildings The present research line will lead to the computational design, modeling, and fabrication of new materials and structures, using innovative concepts. Use will be made of 3D printing technologies such as multiscale additive manufacturing of tensegrity structures through electron beam melting, laser lithography and/or projection micro-stereolithography. Particularly interesting is the use of 3D micro-fabrication technologies for the manufacturing of miniaturized tensegrity structures. Such a technology could be used as a swellable material allowing selected elements to be pretensioned (cables), and a material without swelling for the compressive members (in collaboration with Ferdinando Auricchio at the University of Pavia, link;Chiara Daraio at the ETH, link; Vitali Nesterenko at the UCSD, link; Nicholas Boechler at the University of Washington, link; and Howon Lee at the Rutgers University, link).
Computer modeling and additive manufacturing via electron beam melting of physical models of tensegrity lattices in titanium alloy Ti6Al4V
(in collaboration with the Mercury Centre for Advanced Manufacturing Technology & Production, University of Sheffield, UK)
Solitary rarefaction wave in a softening tensegrity metamaterial
Force-displacement response of a hardening tensegrity prism
Force-displacement response of a softening tensegrity prism
Multiscale modelling of carbon nantotube structures
I have extensively studied the mechanical properties of dense, vertically aligned carbon nanotube (CNT) assemblies subject to compressive loading, starting with a mechanical model directly inspired by the micromechanical response reported experimentally for such structures. Infinitesimal portions of the tubes are represented by collections of bistable elastic springs. Under cyclic loading, the proposed model predicts switching between different elastic phases, hysteretic buckling, material densification, and fatigue damage. The continuum limit of the microscopic response leads to a mesoscopic dissipative element (micro-meso transition), which describes a finite portion of the structure. A series of mesoscopic units finally describes the macroscopic response of the CNT structure (CNT 1, CNT 3). In situ identification procedures have been proposed to quantify the material parameters corresponding to the microscopic and mesoscopic scales (CNT 2). The mechanical modeling of CNT assemblies is a necessary first step toward the construction of lightweight multilayer CNT-based laminar composites with tailored collapse and energy-dispersive properties. Additional future work in this area will include the study of the acoustic response CNT structures and their use of novel acoustic metamaterials.
(a) Schematic diagram of a vertically aligned CNT foam, uniformly loaded in compression. (b) SEM of the as-grown carbon nanotube film showing the alignment and the microstructural layering due to the growth process (Deck and Vecchio, 2005). (c) Modeling of a portion of a CNT foam as a collection of microscopic mass-spring elements.
