1,721,119 research outputs found
Variable kinematics equivalent single layer theories for magneto-electro-elastic multilayered plates
No full textIn recent years, the employment of smart materials able to provide multi-functional capabilities, besides the traditional structural functions, has been gaining attention in several technological fields (automotive, aerospace, biomedical, robotics, etc.). This possibility of coupling different physical fields can be and it has been exploited in transducer applications, structural health monitoring, vibration control, energy harvesting and other applications.
In this framework, magneto-electro-elastic (MEE) materials are attracting increasing consideration from academic and industrial audiences: MEE materials have the ability to couple mechanical, electrical and magnetic fields and this makes them particularly suitable for smart applications. Generally, besides few exceptions, single-phase materials exhibit either piezoelectric or piezomagnetic behavior, but no direct magneto-electric coupling is observed.
The full magneto-electro-elastic coupling is actually obtained by employing composites with piezoelectric and piezomagnetic phases, that then provide the magneto-electric effect through the elastic field. MEE composites are obtained in the form of multi-phase materials, i.e. piezoelectric and piezomagnetic particles and/or fibers, or in the form of laminated structures, with piezoelectric and piezomagnetic layers stacked to achieve the desired coupling effects. Multilayered configurations appear to be more effective than bulk composites. Thus, reliable and efficient modeling tools are required for the analysis and design of smart magneto-electro-elastic laminated plates.
Actually, numerical solutions are needed and considering that fully-coupled 3D finite element solutions for multilayered plates and shells present very high computational costs, 2D efficient laminated plates theories and the corresponding finite element solutions have been developed with the aim of reducing the analysis effort while preserving a suitable level of accuracy. In the framework of 2D plate theories, finite elements solutions based on layer-wise modeling have been proposed. The layerwise approach enables high accuracy; however its computational cost grows as the number of layers increases. Additionally, layer-wise modeling of laminated plates requires the development of ad hoc procedures and elements which make somehow difficult to integrate them into finite element commercial codes.
On the other hand, equivalent single-layer plate theories do not present these drawbacks as their solution complexity is independent from the number of layers although they are generally less accurate than the layer-wise ones, especially for thick plates and first order through-the-thickness expansion. Recently, an equivalent single-layer approach for multilayered MEE plates and its finite element solution have been proposed by the authors, who developed an effective purely mechanical plate model as result of the condensation of the electro-magnetic state to the mechanical variables. It is worth noting that such a modeling strategy could take advantage of the solution tools available for the mechanics of classical multi-layered plates and could lead to the straightforward integration of MEE plate elements into available codes.
In the present work the proposed model is systematically extended to refined equivalent single layer plates theories approaching the problem through a suitable application of the Carrera Unified Formulation. Finite element solutions for magneto-electro-elastic multilayered plates obtained by theories with different expansion order are presented and compared to ascertain the effect of the employed theory on the plate response accuracy
Finite elements for nonlinear free vibrations analysis of smart laminates subjected to in-plane loadings
No full textAdvanced composites, able to provide multi-functional capabilities besides the traditional structural functions, has been gaining attention in many
technological fields. This inherent coupling of different physical fields can be exploited in transducer applications, structural health monitoring, vibration
control, energy harvesting and other applications. Magneto-electro-elastic (MEE) composite materials are attracting increasing consideration as they
couple mechanical, electrical and magnetic fields and this makes them particularly suitable for smart applications. Generally, single-phase materials
exhibit either piezoelectric or piezomagnetic behavior and no direct magneto-electric coupling is observed. However, the full magneto-electro-elastic
coupling can be obtained by using composites with both piezoelectric and piezomagnetic phases that provide the magneto-electric effect through the elastic field. These MEE composites are obtained in the form of multi-phase materials, i.e. piezoelectric and piezomagnetic particles and/or fibers, or in the
form of laminated structures, with piezoelectric and piezomagnetic layers stacked to achieve the desired coupling effects. Multilayered configurations
appear to be more effective than bulk composites.
For the analysis and design of MEE structures, reliable and efficient modeling tools are required. Analytical solutions are available for simple
configurations and, actually, numerical approaches need to be deployed for complex analyses. Fully-coupled 3D finite element solutions for multilayered
plates and shells present very high computational costs; 2D laminated plate theories and the corresponding finite element solutions have been developed
with the aim of reducing the analysis effort while preserving a suitable level of accuracy. In the framework of 2D plate theories, finite elements solutions
based on equivalent-single-layer or layer-wise modeling have been proposed implementing different order theories. Recently, an equivalent single-layer
approach for multilayered MEE plates and its finite element solution have been proposed by the author, who developed an effective purely mechanical
plate model as result of the condensation of the electro-magnetic state to the mechanical variables. This model was systematically extended to refined
equivalent-single-layer and layer-wise plates theories approaching the problem through a suitable application of the Carrera Unified Formulation (CUF).
Finite element solutions for magneto-electro-elastic multilayered plates obtained by theories with different expansion order have been presented.
In the present work, a unified framework based on CUF is presented to develop layer-wise and equivalent-single-layer plate models for the nonlinear free
vibrations analysis of MEE laminates. Variable kinematics with von Karman strains is assumed and approximated by standard isoparametric finite
elements. Under the assumption of quasi-static behavior of the electromagnetic fields, the electromagnetic state of each single layer is preliminary
determined by solving the corresponding governing equations coupled with the proper interface continuity and external boundary conditions. This allow
condensing the electromagnetic state into the plate kinematics and the layer governing equations are inferred by the principle of virtual displacements.
This approach identifies effective mechanical layers, which are kinematically equivalent to the original smart layers. These effective layers are
characterized by stiffness and inertia load properties, which consider the multifield coupling effects as their definitions involve the electromagnetic coupling
material properties. The layers equations are finally assembled enforcing the mechanical interface conditions. This allows obtaining the smart plate FE
resolving system, which involves mechanical nodal variables only. Numerical results are presented
Shadowing e Gis qualitativo: due strumenti per narrare la città
Full text linkQuesto breve articolo descrive la città attraverso due tecniche di ricerca qualitativa (lo shadowing e il Gis qualitativo). Partendo da alcuni esempi, tratti dall’esperienza sul campo, vengono valutati limiti e possibilità delle tecniche in oggetto. L’obiettivo è quello di argomentare la necessità di utilizzare e sviluppare nuovi strumenti metodologici per conoscere le configurazioni urbane. Gli autori sostengono il bisogno di muoversi all’interno di un orizzonte interdisciplinare e di utilizzare tecniche capaci di far emergere narrazioni polifoniche della città. Analizzando le potenzialità dialogiche dello shadowing e le potenzialità sovversive dei Gis qualitativi, una cartografia capace di rappresentare lo spazio mentale degli abitanti, viene affermata la necessità di continuare nella pratica di metodi ibridi, capaci di stimolare la creazione di nuove ri-descrizioni. La città, quindi, per essere compresa, pensata e trasformata ha bisogno di creatività e sperimentazione: nuovi strumenti che tentino modalità ibride di conoscenza, scardinando l’egemonia di rappresentazioni autoritarie incapaci di dare corpo e voce ai gruppi sociali meno potenti. L’obiettivo finale, dunque, diviene il bisogno di proiettare la ricerca urbana qualitativa in un orizzonte politico, inteso come spazio pubblico della discussione e dell’interazione.This brief paper describes the city through the use of two different techniques of qualitative research: shadowing and qualitative Gis. By discussing a few examples of field research, the paper assesses the limits and possibilities of these techniques. The aim is to prove the necessity of using and developing new methodologies to investigate the most recent urban phenomena. In order to achieve this goal, only an interdisciplinary approach can help the emergence of polyphonic narrations of the city. Through the analysis of the dialogic assets that shadowing possesses, and of the subversive potential of qualitative Gis (conceived as a sort of mapping that can represent the mind-space of citizens), the authors succor the use of mixed methodologies that enhance the creation of narrative re-descriptions of the urban forms. Understanding, conceiving and transforming the city implies creativity and experimentation: therefore, we need to conceive new instruments that use hybrid knowledge systems, and shatter the hegemony of those traditional, authoritative representations that cannot give voice to the most deprived social groups. The final goal of the paper is thus defined as the need to project qualitative urban research into a political horizon that becomes the public space of discussion and interaction
Gli itinerari della memoria. Il paesaggio della Sicilia nei racconti degli immigrati siciliani a Losanna
No full textLarge deflection analysis of magneto-electro-elastic laminates
No full textMagneto-electro-elastic (MEE) composites containing piezoelectric and piezo-magnetic phases have recently emerged for many application smart structures technology.
In this framework, the development of tools to analyze the MEE laminates is essential for their efficient design.
In the present work, a model for the large deflection analysis of MEE laminated plates is proposed. The first order shear deformation theory and the von Karman stress function approach are employed to model the mechanical behavior whereas quasi-static behavior is assumed for the electro-magnetic quantities. First, the magneto-electric problem is solved in terms of the plate mechanical primary variables. In turn, this result is employed into the equations of motion and large displacement plate compatibility equation leading to a system of coupled partial differential equations involving the plate transverse displacement, rotations and a stress function. In this resolving system, the stiffness coefficients of the pure mechanical case are modified by the effects of the magneto-electro-mechanical couplings and new stiffness coefficients arise. The external magneto-electric inputs are modeled as applied equivalent forces and moments. Once the mechanical problem is solved the electro-magnetic quantities can be recovered. The presented results show the influence of large deflections on the plate response and can be useful in the analysis and design of layered MEE composite plates
Analysis of piezoelectric active patches performances by boundary element techniques
No full textThis paper presents the analysis of active piezoelectric patches for cracked structures by
Boundary Element Method. A two dimensional boundary integral formulation based on the
multidomain technique is used to model cracks and to assemble the multi-layered piezoelectric
patches to the host damaged structures. The fracture mechanics behavior of the repaired structures
is analyzed for both perfect and imperfect interface between patches and host beams. The imperfect
interface, representing the adhesive between two different layers, is modeled by using a “Spring
Model” that involves linear relationships between the interface tractions, in normal and tangential
directions, and the respective discontinuity in displacements. Numerical analyses performed on a
cracked cantilever beam repaired by single and multilayered patches are presented. It is pointed out
that the adhesive deeply influences the performances of the repair as highlighted by an increasing of
the SIF’s values with respect to perfect bonding case
A boundary element model for piezoelectric dynamic strain sensing of cracked structures
No full textA piezoelectric sensor model is here presented for the Structural Health Monitoring (SHM) of damaged structures. A boundary element approach based on the Dual Reciprocity BEM is then used to model and analyze the transient response of a piezoelectric patch bonded on a cracked beam. The BE model is written for the piezoelectric problem employing generalized displacements. The multidomain boundary element technique is implemented to model non-homogeneous and cracked configuration, taking contact conditions into account. Analyses have been carried out for an isotropic beam with a piezoelectric strip attached on it and dynamical results for the undamaged structure have been compared with FE results showing good agreement. Parametric analysis is performed with the aim to characterize the sensitiveness of the piezoelectric patch by varying the crack positioning along the beam span. More particularly, seven electrodes are considered on the piezoelectric patch and the electrical response of the SHM piezoelectric sensor is characterized by means of a damage index in order to locate the crack
Boundary elements analysis of adhesively bonded piezoelectric active repair
No full textThis paper presents the analysis of active piezoelectric patches for cracked structures by the
Boundary Element Method. A two dimensional boundary integral formulation based on the multidomain
technique is used to model cracks and to assemble the multi-layered piezoelectric patches to the host
damaged structures. The fracture mechanics behavior of the repaired structures is analyzed for both perfect
and imperfect interface between patches and host beams. The imperfect interface, representing the
adhesive between two different layers, is modeled by using a "Spring Model" that involves linear
relationships between the interface tractions, in normal and tangential directions, and the respective
discontinuity in displacements. Numerical analyses performed on a cracked cantilever beam repaired by
single and multilayered patches are presented. It is pointed out that the adhesive deeply influences the
performances of the repair as highlighted by an increasing of the repairing voltage values with respect to
perfect bonding case
Analytical solution for the transient response of symmetric magnetoelectric laminated beams
No full textIn this paper an analytical solution is presented for the forced vibration problem of
magnetoelectric symmetric laminated beams. In deriving the mathematical model the
Timoshenko’s beam theory is used and the electric and magnetic fields are assumed to
be quasi-static. The model is written for a magnetoelectric sensing device by applying
proper magnetoelectric boundary conditions on the beam top and bottom surfaces.
The model highlights that the magneto-electro-mechanical couplings affect the bending
stiffness and that the magnetoelectric inputs can be treated as equivalent bending
moments. Forced vibration analyses are presented to assess the reliability of the solution
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