1,721,001 research outputs found
Scienza delle Costruzioni
No full textNunziante L., Gambarotta L. and Tralli A. (2003). Scienza delle costruzioni. McGraw-Hill-Italy-ISBN-88-386-6100-6
Dynamic homogenization of multi-layered lattice-like metamaterials with alternate chiral microstructure
No full textThis paper presents a dynamic continualization technique for a multi-layer beam-lattice metamaterial with an alternating chiral microstructure, where each layer is reciprocally interconnected through the insertion of pins. The study analyzes the dispersive properties of the system and its potential applications as a meta-filter, highlighting how the enhanced continualization technique introduced can capture the dispersive properties of stratified systems with chiral geometry. This approach makes it possible to derive higher-order gradient-type continuum models that yield dispersion spectra close to those obtained through a discrete Lagrangian treatment, without encountering dynamic instability effects due to thermodynamic inconsistency. These aspects are further investigated through the presentation of application examples, specifically concerning a stratified tetrachiral waveguide. A key finding of the studied examples is related to the passive/active tunability of the system, specifically in relation to the stiffness of the pin which determines significant influences on the dispersion spectra. To complete the analysis, a further example is finally proposed in which the waveguide is subjected to harmonic excitation, revealing how variations in the parameters can affect wave polarizations
Thermodynamically consistent non-local continualization for masonry-like systems
No full textMasonry-like systems composed by modular stiff units bonded by soft connections represent an efficient, versatile and ultimately successful strategy for natural and artificial macro-scale architectures. The static and dynamic behavior of masonry-like materials characterized by a running bond periodic pattern of rigid rectangular blocks and elastic interfaces is described by formulating equivalent nonlocal continuum models. The paper discusses the thermodynamic restrictions limiting the consistency of the standard continualization strategies. The inherent pathologies recognized in the macroscopic quasi-static response and/or in the dynamic dispersion properties of different continuum models motivate the original proposal of an enhanced continualization strategy. Based on the series expansion of the pseudo-differential functions accounting for shift operators and proper downscaling laws, the enhanced continualization scheme allows formulating homogeneous non-local continuum models of increasing orders, analytically featured by characteristic non-local constitutive and inertial terms. The enhanced continualization shows thermodynamic consistency in the definition of the overall elastic moduli, as well as qualitative agreement and convergent matching of the frequency dispersion functions. The theoretical findings are successfully verified though the solution of representative static and dynamic benchmark problems
Resilient multi-layered lattices with alternating chirality for self-recovering energy absorption
No full textThis research focuses on the development of a high-performance metamaterial that combines dissipation and resilience, a subject of growing actual interest in vibration and impact mechanics as part of the quest for avantgarde self-recovering materials. In this context, a high-performance resilient layered metamaterial with alternating chiral topology is conceived and analyzed. Specifically, the single layer is realized via the periodic assembly of rigid disks connected by elastic ligaments and stacked using passing pins. The metadevice is formed by stacking layers with alternating chirality. This configuration induces relative rotations between the aligned discs in contact when in-plane forces are applied. Frictional dilating interfaces between adjacent disks produce a dissipative and resilient mechanical response, returning to the initial configuration at the end of the unloading phase. Specifically, the dissipative mechanism is designed to significantly attenuate vibratory motions and/or absorb energy during impact processes, while being reusable after the dynamic actions have acted on the metamaterial. This cutting-edge metamaterial offers several advantages over current technologies: i) hysteretic response with maximum dissipation of mechanical energy and high stiffness; ii) reuse of the device without external interventions, restoring the initial configuration at the end of the dynamic process; iii) multi-directional dissipative response; and iv) bilateral response, providing equal performance under both traction and compression
Thermodinamically-consistent dynamic continualization of block-lattice materials
No full textLattice-like materials featuring periodic planar tessellation of regular rigid blocks connected by linear elastic
interfaces and chiral or achiral properties are considered. The chirality results from a uniform rotation of the
blocks with respect to their centroidal joining line and leads to interesting auxetic and dispersive acoustic
behaviors. The governing equations of the discrete Lagrangian model are properly manipulated via the novel
enhanced continualization scheme in such a way to obtain equivalent non-local integral and gradient-type
higher-order continua. Based on the formal Taylor series expansion of the integral kernels or the corresponding
pseudo-differential functions accounting for shift operators and proper pseudo-differential downscaling laws,
the proposed enhanced continualization technique allows formulating homogeneous non-local continuum
models of increasing orders, analytically featured by characteristic non-local constitutive and inertial terms.
The enhanced continualization shows thermodynamic consistency in the definition of the overall non-local
constitutive tensors, as well as qualitative agreement and quantitative convergent matching of the actual
complex frequency band structure. The theoretical findings are successfully verified though the study of wave
dispersion and attenuation properties as referred to a representative tetrachiral geometry
Dynamic continualization of masonry-like structured materials
No full textBlock-lattice materials featuring periodic planar running-bond tessellation of regular rigid blocks and linear elastic homogeneous isotropic interfaces are considered. The governing equations of the discrete masonry-like Lagrangian model are properly manipulated via the novel enhanced continualization scheme, in such a way as to obtain equivalent integral type non-local continua, whose band structure turns out to be coincident with that of the corresponding discrete models. The formal Taylor series expansion of the integral kernels allows deriving homogeneous generalized micropolar higher-order continuum models, characterized by non-local constitutive and inertial terms. The enhanced continualization exhibits thermodynamic consistency in the definition of the overall non-local constitutive tensors, as well as qualitative agreement and quantitative convergent matching of the complex frequency band structure in the regime of both homogeneous and non-homogeneous Bloch waves. The theoretical findings are effectively validated by studying the dispersion relations and the spatial attenuation properties, as referred to realistic representative cases of masonry-like block-lattice micro-structures
Computational design of innovative mechanical metafilters via adaptive surrogate-based optimization
No full textArchitected materials and metamaterials are a challenging frontier for the development of optimal design strategies targeted at the active and passive control of elastic wave propagation. Within this research field, the microstructural optimization of mechanical metamaterials for achieving desired spectral functionalities may require considerable computational resources. Based on this motivating framework, the present paper illustrates a machine learning methodology to attack the inverse design problem concerning the optimization of the dispersion properties characterizing a novel layered mechanical metamaterial, conceived starting from the bi-tetrachiral periodic topology. Specifically, an adaptive technique is adopted to surrogate and maximize the objective function purposely defined to determine the optimal beam lattice microstructure characterized by the largest stop bandwidth at the lowest centerfrequency (low-cutting mechanical metafilter). The technique is computationally efficient in identifying the existing optimal solution in the physically admissible parameter space. The designed bi-tetrachiral metamaterial provides satisfying broadband low-frequency filtering performances, not achievable by the component tetrachiral layers
Anisotropic peridynamics for homogenized microstructured materials
No full textAn anisotropic continuum-molecular model based on pair potentials for describing the linear static and dynamic behavior of periodic heterogeneous Cauchy materials is derived in the framework of peridynamic theory. Non-central pairwise actions are assumed as work-conjugates to specific pairwise deformation variables. A pairwise constitutive law, depending trigonometrically on the material fiber direction and preserving the elastic symmetries of the material, is properly defined. Based on this theoretical ground, a bond-based type continuum model with oriented material points, governed by six independent material micro-moduli, is obtained. Considering microstructured materials featuring periodic rigid massive blocks connected by soft elastic interfaces, the elastic potential functions of the continuum-molecular model are consistently identified in terms of geometrical and constitutive parameters of the microstructure. The identification is based on the formal analogy with the overall constitutive tensors of a homogeneous continuum obtained through continualization schemes and equivalent to the microstructured material. Consequently, the macroscopic elastic properties of the continuum-molecular model are described in terms of pairwise material properties, but its micro-moduli are also explicitly related to the specific properties of the linear elastic interfaces of the microstructured material. The accuracy of the proposed model in the static and dynamic response is successfully verified by comparison with high-fidelity finite element models of an auxetic tetrachiral block lattice considering different periodic cell orientations and elastic interface properties, as well as by comparison with analytical solutions for fully anisotropic elasticity
Acoustic waveguide filters made up of rigid stacked materials with elastic joints
No full textThe acoustic dispersion properties of monodimensional waveguide filters can be assessed by means of the simple prototypical mechanical system made of an infinite stack of periodic massive blocks, connected to each other by elastic joints. The linear undamped dynamics of the periodic cell is governed by a two degree-of-freedom Lagrangian model. The eigenproblem governing the free propagation of shear and moment waves is solved analytically and the two dispersion relations are obtained in a suited closed form fashion. Therefore, the pass and stop bandwidths are conveniently determined in the minimal space of the independent mechanical parameters. Stop bands in the ultra-low frequency range are achieved by coupling the stacked material with an elastic half-space modelled as a Winkler support. A convenient fine approximation of the dispersion relations is pursued by formulating homogenised micropolar continuum models. An enhanced continualization approach, employing a proper Maclaurin approximation of pseudo-differential operators, is adopted to successfully approximate the acoustic and optical branches of the dispersion spectrum of the Lagrangian models, both in the absence and in the presence of the elastic support
Overall constitutive properties of stratified lattices with alternating chirality
No full textThe present research focuses on a continuum description of stratified metamaterials achieved through the superposition of layers with alternating chirality. Each layer is constructed as a periodic assembly of centre-symmetric periodic cells, formed by a recurring arrangement of rigid circular discs connected by elastic ligaments. The layers are interconnected through elastic pins passing through the centres of aligned discs, allowing for either restrained or free relative rotation. A micropolar continuum model is used to describe each individual layer. The overall response of the metamaterials to in-plane forces is derived using a multi-field non-local model, expressed in terms of the average and difference of displacement and rotational fields. The overall micropolar and standard (Cauchy) constitutive tensors have been determined in closed form. The validity of the equivalent generalized micropolar model has been confirmed through comparison with discrete Lagrangian solutions of representative examples. In addition, a detailed analysis of a pseudo-indentation test has been carried out.This article is part of the theme issue 'Current developments in elastic and acoustic metamaterials science (Part 2)'
- …
