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In this paper, we show that a two-field model for pantographic sheets generalized to include a more refined description of the deformation of interconnecting pivots and structural dissipation is capable of describing the sheets mechanical behavior for (1) cyclic extension tests in elastic regimes and (2) damage initiation. To this aim, we performed two kinds of experimental tests. In the first ones, we tested, remaining in the elastic regime, pantographic sheets under different cyclic loads. Second, we extended the specimens reaching the first rupture. The numerical model was calibrated in order to predict (1) the observed amplitude and shape of hysteretic cycles and (2) the observed localization of the first rupture. In this framework, (1) a simultaneous rupture of several pivots is observed and theoretically justified, (2) the primary dissipation mechanism and rupture initiation are attributed to pivots’ shear deformation.

The linear stability of a piezo-electro-mechanical (PEM) system subject to a follower force is here discussed. The mechanical subsystem is constituted by a linear visco-elastic cantilever beam, loaded by a follower force at the free end. It suffers from the Hopf bifurcation, whose critical load is strongly affected by damping, according to the well-known Ziegler’s paradox. On the other hand, the electrical subsystem consists of a distributed array of piezoelectric patches attached to the beam and connected to a properly designed second-order analog circuit, aiming at possibly enhancing the stability of the PEM system. The partial differential equations of motion of the PEM system are discretized by the Galerkin method. Linear stability analysis is then carried out by numerically solving the associated eigenvalue problem, for different significant values of the electrical parameters. A suitable perturbation method is also adopted to detect the role of the electrical parameters and discuss the effectiveness of the controller.

Buckling of uniformly and not uniformly compressed tower buildings, resting on Winkler type soil, is investigated. An equivalent beam is introduced, able to capture the essential behavior of the building. It is a 3D Timoshenko beam, modeled in the framework of a direct approach, whose constitutive law is derived via a homogenization procedure, which includes the effect of the column prestress. The continuous model is discretized via finite differences, and a linear bifurcation analysis is carried out by solving an algebraic eigenvalue problem. Numerical results are shown for sample problems, aimed at detecting the structural behavior, and illustrating the role of some mechanical parameters. Results supplied by the equivalent beam model are compared with those derived by finite element analyses, carried out on three-dimensional frames.

In this paper, the effects of linear damping on the post-critical behavior of the Ziegler’s column are discussed. To this end, the well-known double-pendulum, loaded at the free-end by a follower force, firstly introduced by Ziegler, is considered in regime of finite displacements. The multiple scale method is applied to the equations of motion expanded up to the cubic terms, to analyze the nonlinear behavior of a generically damped column, close to the simple-Hopf bifurcation triggered by the follower force. The obtained bifurcation equations are shown to be useful in providing qualitative information about the nonlinear mechanical response of the column in the whole damping plane. Validation of the asymptotic solution, carried out via numerical analyses of the exact equations of motion, points out the effectiveness of the proposed analysis also on the quantitative side.

The linear stability of a cantilever beam subject to a follower force is investigated. A system of distributed piezoelectric devices is attached to the beam with the purpose of improving the dynamic stability of the structure. They are connected to a second-order network and second-order analog electrical circuit. The assembly of the mechanical and piezoelectric subsystems constitutes a coupled Piezo-Electro-Mechanical (PEM) system, whose equations of motion, derived within a variational approach, are discretized via the Galerkin weighted residual method and the stability of the trivial equilibrium is addressed by numerically solving the associated eigenvalue problem. A sensitivity analysis, carried out on a numerical ground, is thus conducted on a wide range of the electrical parameters to investigate the effectiveness of the proposed controller.

In this paper, we aim to explore the mechanical potentialities of a material made of an orthogonal net of fibers arranged in logarithmic spirals. Therefore, an annular plate described with a second-gradient model is envisaged to evaluate the behavior of such material in a nonlinear elastic regime when large displacements and deformations occur. Several mechanical tests are performed numerically under the finite element method approximation obtained directly with a weak formulation based on the elastic energy that it is assumed to be predictive for this kind of network system of fibers. Plots reporting the mechanical characteristics in all the considered tests are provided to illustrate the overall mechanical behavior of the evaluated system.

Breast implant-associated anaplastic large cell lymphoma is an uncommon malignancy associated with textured breast implants, and since 2014 13 Danish cases have been identified. Early diagnosis is important to minimise morbidity. Most patients present with swelling of the breast due to seroma within the fibrous capsule, fewer with a tumour. The diagnosis is based on cytology/histology with finding of typical anaplastic large cells, positive for CD30 and negative for anaplastic lymphoma kinase. Staging includes bone marrow examination and PET-CT scan, and a minority need systemic treatment, as argued in this review.

In this paper, the proper modeling of a class of nonlinear periodic beam-like structures, behaving as shear beams in the 3D environment, is critically considered. Multi-story frame buildings are taken as an example of these structures and the suitability of the (unflexurable) shear-shear-torsional beam model in describing the behavior of the building, is investigated. In this context, the range of applicability of the equivalent beam model is detected through an order-of-magnitude analysis, which is developed in linear regime and corroborated by means of finite-element analyses. A new continuous shear-shear-torsional beam model, here referred to as ‘complete model’, is formulated in the framework of the direct one-dimensional approach, while its nonlinear hyperelastic constitutive law is obtained by identification with a three-dimensional body, through an energy equivalence. In addition, a ‘minimal model’ is derived from the complete one for which only the cubic terms generated by the stretch of the columns are retained, while the remaining cubic terms and all the quadratic terms, generated by the finite twist angle, are neglected. Perturbation solutions for both the complete and the minimal model are obtained. The limits of applicability of the minimal model are discussed in terms of nonlinear static responses of some structures taken as case-studies.

The cyclic behavior and dissipative properties of pantographic fabrics are analytically and experimentally investigated in this paper. To these purposes, a two-dimensional second-gradient continuum model, already developed in the literature, is taken as representative of the elastic behavior of the homogenized system. However, to take into account the dissipative phenomena, the model is enriched with a suitable Dahl-like phenomenological dissipation law, accounting for friction effects at the interconnecting pivots, that it is shown to be effective in describing the macroscopic hysteretic behavior under cyclic and quasi-static imposed displacement time-histories. Numerical results are compared against experimental ones, thus showing the effectiveness of the continuum model in reproducing the real behavior of pantographic fabrics.

A design framework is here presented for the development of an architected solid with targeted mechanical properties thanks to an optimized porosity distribution. A 2D lattice of regular hexagons is considered as core element of a sandwich panel and a Bloch-Floquet-based approach is adopted to derive homogenized equivalent properties. The density distribution of the equivalent continuum is taken as objective function to be minimized in the optimization process. To this end, suitable constraints are designed to avoid empty regions and ensure a minimized density where required by the mechanical actions. A de-homogenization process is carried out on the optimized equivalent continuum to derive the configuration of regular hexagons with optimally varying wall thickness. Static and buckling responses of the optimized architected solid are compared with that of a 2D continuum whose material density distribution is determined through a classical topology optimization. It is shown that the architected 2D solid can absorb higher strain energy, with respect to classically optimized structures, which suffer a buckling-driven collapse below the elasticity threshold. The architected solid is also shown to have an improved energy absorption capability, that may increase considerably its performance, depending on the ductility of the adopted material.

One-dimensional equivalent beam models, embedded in a two-dimensional space, are developed in this work for static analysis of beam-like structures, such as planar frames (fine models). Extensible shear and Timoshenko beam models (coarse models) are formulated in the framework of the direct one-dimensional approach, under the assumption of rigid cross-section, while their constitutive laws are determined through a homogenization procedure. A linear constitutive equation is obtained, also taking into account for the presence of bracing elements in the frame, with axial and shear forces coupled with bending. The warping of the cross-section, caused both by shear and bending, is taken into account, in an approximate way, by resorting to the concept of shear and flexural factors. These factors are introduced to correct the constitutive coefficients of the equivalent beam. They are determined by equating the elastic potential energy of the fine model and that of the coarse models, once the same macroscopic displacement is given. The limits of applicability of the corrected homogenized beam models are discussed with reference to the linear static response of some planar frames, taken as case-studies. Numerical results obtained by the homogenized models are compared with finite element analyses on planar frames, in order to show the effectiveness of the procedure.

In this paper, the static behavior of an elastic beam resting on a rigid substrate is investigated. The structure lies on a rigid substrate and exchanges with it tangential forces, in correspondence with a finite number of contact points. These actions entail extension of the beam in the longitudinal direction together with a negligible bending, owing to the small eccentricity between the beam’s axis line and the rigid substrate. The beam obeys a linear elastic law, while, at the interface, different nonlinear constitutive models are considered to account for stick-slip phenomena due to friction, as well as wear due to abrasion. It is assumed that the contact points are a-priori known, thus entailing that the structural system can be treated as naturally discrete. The static problem is accordingly shown to be governed by a system of nonlinear ordinary differential equations in time, which rules, in incremental form, the equilibrium at the contact points in the longitudinal direction. A numerical solution for the equilibrium equations is carried out, under different imposed time histories of the longitudinal displacement assigned at the boundary. Numerical results are presented to compare and discuss the in-time evolution of the contact interactions between the beam and the substrate.

In this paper, a Timoshenko beam model is formulated for buckling analysis of periodic micro-structured beams, uniformly compressed. These are planar grid beams, whose micro-structure consists of a square lattice of equal fibers, modeled as Timoshenko micro-beams. The equivalent beam model is derived in the framework of a direct one-dimensional approach and its constitutive law, including the effect of prestress of the longitudinal fibers, is deduced through a homogenization approach. Accordingly, micro&ndash, macro constitutive relations are obtained through an energy equivalence between a cell of the periodic model and a segment of the equivalent beam. The model also accounts for warping of the micro-structure, via the introduction of elastic and geometric corrective factors of the constitutive coefficients. A survey of the buckling behavior of sample grid beams is presented to validate the effectiveness and limits of the equivalent model. To this purpose, results supplied by the exact analyses of the equivalent beam are compared with those given by finite element models of bi-dimensional frames.

The linear dynamics of finite-dimensional viscoelastic structures is addressed in this paper. The equations of motion of a general, discrete or discretized, dynamical system, made of elements behaving as multiparameter viscoelastic solid models, are formulated in terms of internal variables, whose evolution is ruled by flow laws. The classical elastic-viscoelastic Principle of Correspondence is discussed in conjunction with the Fourier transform, and a new strategy, which leaves the system in the time-domain is proposed. By exploiting the fact that the spectrum of the system is well-separated if damping is small, a Center Manifold-like reduction is performed, which eliminates the internal variables, lowering the dimensions to those of the corresponding elastic system, thus filtering the fast dynamics. The order of magnitude of the error related to the reduction is investigated. A comparison with the popular Kelvin–Voigt model is performed for homogeneous structures. Examples on sample structures are worked out, namely the one degree-of-freedom viscoelastic system and the discretized elastic beam on viscoelastic soil. In all the examples the (3-Parameters) Standard Model is adopted.

In this paper, beam-like structures, macroscopically behaving as planar Timoshenko beams, are considered. Planar frames, made by periodic assemblies of micro-beams and columns, are taken as examples of these structures and the effectiveness of the equivalent beam model in describing their mechanical behavior, is investigated. The Timoshenko beam (coarse model) is formulated via the direct one-dimensional approach, by considering rigid cross-sections and flexible axis-line, while its constitutive laws is determined through a homogenization procedure. An identification algorithm for evaluation of the constitutive constants is illustrated, based on Finite Element analyses of the cell of the periodic system. The inertial properties of the equivalent model are instead analytically identified under the hypothesis the masses are lumped at the joints. The advantages in using the equivalent model are discussed with reference to the linear static and dynamic responses of some planar frames, taken as case-studies, for which both analytical and numerical tools are used. Numerical results, obtained by the equivalent model, are compared with Finite Element analyses on planar frames (fine models), considering both symmetric and not-symmetric layouts, in order to show to effectiveness of the proposed algorithm. A comparison with analytical results is carried out to validate the limits of applicability of the method.

Li-ion batteries have experienced a widespread deployment due to the strong interest in electrochemical devices capable of storing a large amount of energy in small volumes and supplying high powers when required. However, besides those advantages, this technology still presents several unsolved issues, especially regarding the safety aspects. These devices can, in fact, experience thermal runaway if the generated thermal power is not adequately dispersed, and this can occur when the cell / battery is subjected to abuse conditions (mechanical, electrical or thermal abuses). The experimental study was carried out using a full-scale hardware simulator, capable of simulating the thermal behavior of a battery pack, where electrically heated elements replaced real Li-ion cells. This expedient guarantees a high reproducibility of the working conditions and consequently a higher reliability of the measured data. The hardware simulator allows to reproduce the thermal behavior under normal operating conditions, and under abuse conditions which can lead to thermal runaway. The present work reports the results of the tests that have been carried out by reproducing the abuse conditions in one cell inside a battery module; the abused cell is heated with a high power (from 100 to 500 W for cells with a maximum heat loss of 30 W under normal operating conditions) and the efficiency of different cooling systems is checked both in limiting the temperature of the abused cell and in preventing the propagation of heat to the adjacent cells. In particular, different fluids, different fluid speeds and different mitigation methods have been tested.

Linear and nonlinear analyses of a piezoelectric-controlled Ziegler’s column, endowed with a Van der Pol-like nonlinear damping, are carried out in the present paper. The effects of three linear and passive piezoelectric controllers on the position and on the amplitude of the limit-cycle at the Hopf bifurcation, triggered by the follower force, are investigated. The controllers, previously introduced in the literature and here referred to as Non-Singular Resonant, Singular Non-Resonant, and Tuned Piezoelectric Damper, resemble well-known devices, adopted for controlling both linear and nonlinear oscillations, namely, a large-mass Tuned Mass Damper, a singular Energy Sink, and a classical small-mass Tuned Mass Damper. Numerical simulations on a linearly and uniformly damped column, under different nonlinear damping conditions, are carried out to show the effectiveness of the controllers in reducing the amplitude of the limit-cycle and their behavior with respect to the possible occurrence of the hard loss bifurcation.

This paper describes a set of experimental tests carried out to better understand the thermal behavior of Lithium-ion batteries under load and the capability of various cooling fluids in maintaining the working conditions within a safe range for the cells. Despite several theoretical models are available in the literature, very few experimental data are reported. Different types of cells have been analyzed. The generation of hot spots has sometimes been registered, their occurrence being independent of cell geometry and size; instead, the battery's history and age, appeared the main factors in determining the onset of hot spots on the surface of the cell. Two experimental rigs have been set up to test the capability of different cooling fluids in removing the surplus heat generated in a Li-ion battery module, where the cells of interest have been replaced with electrically heated elements with the same thermal characteristics of the cells. It was thus possible to safely investigate “extreme” operating conditions, where the occurrence of a thermal runaway is possible. Among the tested fluids, air was unable to adequately limit the surface temperature increase, while a perfluorinated polyether, allowed to work within the optimal temperature range, even under severe operating conditions.

International audience; Recently the exotic properties of pantographic metamaterials have been investigated, and various mathematical models (both discrete and continuous) have been introduced. However, the experimental evidence available up to now concerns only polyamide specimens. In this paper, we use specimens printed using metallic powder. We prove experimentally that the main qualitative and quantitative features of pantographic sheets in planar deformation are independent of the constituting materials, at least when they can be regarded as homogeneous and isotropic at micro-level. Of course, the absolute value of Young’s modulus of constituent material affects the overall reaction force needed to the hard device to impose a given displacement: A first investigation on this effect is also attempted.

International audience; In the last decade the exotic properties of pantographic metamaterials have been investigated and different mathematical models (both discreteor continuous) have been introduced. In a previous publication a large part of the already existing literature about pantographic metamaterials has been presented. In this paper we give some details about the next generation of research in this field. We present an organic scheme of the whole process of design, fabrication, experiments, models and image analyses.

Temperature control is one of the most significant factors to improve the performance and extend the cycle life of a battery. It is, therefore, important to design and implement an effective battery thermal management system (TMS). Phase change materials (PCMs) can be used as a cooling means for batteries. In the present paper, a preliminary analysis of the thermal behavior of PCMs used to cool down a heated metal surface was carried out. Tests have shown that pure PCMs are able to limit the temperature increase, but only for relatively low-heat fluxes. At higher values of the heat produced, the thermal conductivity of the PCM was increased by using solid foams characterized by higher thermal conductivity; it was, thus, possible to keep the surface temperature within safe limits for longer times. A computational fluid dynamics (CFD) model of the composite material (PCM + solid foam) was also developed, which allowed to predict the temperature trend within the system under different boundary conditions. However, the average thermal conductivity of the composite system that best fitted the experimental results was found to be much lower than that theoretically predicted by using common semiempirical correlations.

We report a case presenting with recurrent episodes of severe hypothermia preceding the diagnosis of Hodgkin lymphoma. The episodes of hypothermia were accompanied by other symptoms of autonomic dysfunction, mainly hypotension, which could be caused by autonomic neuropathy as part of a paraneoplastic syndrome. In comparison with previous reports describing an association between the presence of hypothermia and an adverse outcome, the present patient has responded well to lymphoma-specific treatment and is currently in an ongoing complete remission. Due to the peculiar cyclic pattern of the hypothermic episodes presented in this case, we hypothesize whether intermittent release of disease-related chemo- and cytokines could be a plausible pathogenetic explanation.