Filippo Casadei

Broadband Vibration Control Through Periodic Arrays of Resonant Shunts: Experimental Investigation on Plates

In this work, a periodic 4 × 4 lay-out of resistive inductive (RL) shunted piezoelectric transducer (PZT) patches is designed and applied to achieve broadband vibration reduction of a flexible isotropic plate over tunable frequency bands. Each surface-bonded PZT patch is connected to a single independent RL circuit and all shunt circuits are tuned at the same frequency. A finite element-based design methodology is used to predict the attenuation properties of the unit cell that characterize the periodic assembly. The predictions are experimentally validated by measuring the spatial average harmonic response of the plate. Significant broadband attenuation is obtained over frequency bands centered at the resonance frequency of the shunting circuit.

Vibration control of plates through hybrid configurations of periodic piezoelectric shunts

Periodic arrays of hybrid-shunted piezoelectric actuators are used to suppress vibrations of an aluminum plate over broad frequency bands. Commonly, piezoelectric-shunted networks are used for individual mode control, through tuned, resonant resistive/inductive circuits, and for broadband vibration attenuation, through negative impedance converters. Periodically placed resonant shunts allow for broadband reduction resulting from the attenuation of propagating waves in frequency bands which are defined by the spatial periodicity of the array and by the shunting parameters considered on the circuit. Such attenuation typically occurs at medium–high frequencies, while negative impedance converter networks are effective in reducing the vibration amplitudes of the lower modes of the structure. In this article, the combination of periodic resonant shunts and negative impedance converter networks on the same aluminum panel is studied to verify the possibility of combining the advantages of the two concepts. Both numerical and experimental investigations demonstrate that broadband attenuation is achieved in the mid–high frequency regimes due to the presence of resistive/inductive networks, while the combination with negative impedance converter circuits is responsible for amplitude reduction of the full frequency spectrum. Numerical simulations and frequency response measurements on a plate demonstrate that an attenuation region of about 1000 Hz is achieved with a maximum 8 dB vibration reduction.

Vibration control of plates featuring periodic arrays of hybrid shunted piezoelectric patches

Periodic arrays of hybrid shunted piezoelectric actuators are used to suppress vibrations in an aluminum plate. Commonly, piezoelectric shunted networks are used for individual mode control, through tuned, resonant RLC circuits, and for broad-band vibration attenuation, through negative impedance converters (NIC). Periodically placed resonant shunts allow broadband reduction resulting from the attenuation of propagating waves in frequency bands which are defined by the spatial periodicity of the array and by the shunting parameters considered on the circuit. Such attenuation typically occurs at high frequencies, while NICs are effective in reducing the vibration amplitudes of the first modes of the structure. The combination of an array resonant shunts and NICs on a two-dimensional (2D) panel allows combining the advantages of the two concepts, which provide broadband attenuation in the high frequency regimes and the reduction of the amplitudes of the low frequency modes. Numerical results are presented to illustrate the proposed approach, and frequency response measurements on a cantilever aluminum plate demonstrate that an attenuation region of about 1000Hz is achieved with a maximum 8 dB vibration reduction.

Harnessing fluid-structure interactions to design self-regulating acoustic metamaterials

The design of phononic crystals and acoustic metamaterials with tunable and adaptive wave properties remains one of the outstanding challenges for the development of next generation acoustic devices. We report on the numerical and experimental demonstration of a locally resonant acoustic metamaterial with dispersion characteristics, which autonomously adapt in response to changes of an incident aerodynamic flow. The metamaterial consists of a slender beam featuring a periodic array or airfoil-shaped masses supported by a linear and torsional springs. The resonance characteristics of the airfoils lead to strong attenuation at frequencies defined by the properties of the airfoils and the speed on the incident fluid. The proposed concept expands the ability of existing acoustic bandgap materials to autonomously adapt their dispersion properties through fluid-structure interactions, and has the potential to dramatically impact a variety of applications, such as robotics, civil infrastructures, and defense systems.

Vibroacoustic Energy Diffusion Optimization in Beams and Plates by Means of Distributed Shunted Piezoelectric Patches

This chapter proposes a synthesis of different new methodologies for developing a distributed, integrated shunted piezo composite for beams and plates applications able to modify the structural vibro acoustical impedance of the passive supporting structure so as to absorb or reflect incidental power flow. This design implements tailored structural responses, through integrated passive and active features, and offers the potential for higher levels of vibration isolation as compared to current designs. Novel active and passive shunting configurations will be investigated to reduce vibrations such as distributed Resistance Inductance and Resistance with negative Capacitance circuits.

Vibration Damping of Thermal Barrier Coatings Containing Ductile Metallic Layers

This paper explores the vibration damping properties of thermal barrier coatings (TBCs) containing thin plastically deformable metallic layers embedded in an elastic ceramic matrix. We develop an elastic–plastic dynamical model to study how work hardening, yield strain, and elastic modulus of the metal affect the macroscopic damping behavior of the coating. Finite element (FE) simulations validate the model and are used to estimate the damping capacity under axial and flexural vibration conditions. The model also provides an explanation for the widely observed nonlinear variation of the loss factor with strain in plasma-spayed TBCs. Furthermore, it facilitates the identification of multilayer configurations that maximize energy dissipation. [DOI: 10.1115/1.4028031]

Application of the multi-scale finite element method to wave propagation problems in damaged structures

This work illustrates the possibility to extend the field of application of the Multi-Scale Finite Element Method (MsFEM) to structural mechanics problems that involve localized geometrical discontinuities like cracks or notches. The main idea is to construct finite elements with an arbitrary number of edge nodes that describe the actual geometry of the damage with shape functions that are defined as local solutions of the differential operator of the specific problem according to the MsFEM approach. The small scale information are then brought to the large scale model through the coupling of the global system matrices that are assembled using classical finite element procedures. The efficiency of the method is demonstrated through selected numerical examples that constitute classical problems of great interest to the structural health monitoring community.

Multiscale analysis of wave-damage interaction in two and three dimensional isotropic plates

In this paper a geometric multiscale finite element method (GMsFEM), recently developed by the authors, is applied to the analysis of wave propagation in damaged plates. The proposed methodology is based on the formulation of both two- and three-dimensional multi-node (or multiscale) elements capable of describing small defects without resorting to excessive mesh refinements. Each multiscale element is equipped with a local mesh that is used to compute the interpolation functions of the element itself and to resolve the local fluctuations of the solution near the defect. The computed shape functions guarantee the continuity of the solution between multiscale and conventional elements. This allows using an undistorted discretization in the uniform portion of the domain while limiting the use of multiscale elements only in the vicinity of the defects. In this article the method is applied to evaluate the reflection coefficients due to cracks of different size and orientation in an otherwise homogeneous plate. Also, numerical simulations of wave-damage interaction are used to compute the scattering coefficients associated to three-dimensional defects in isotropic plates.

Beams and Plates Vibroacoustic Energy Diffusion Optimization by Mean of Distributed Shunted Piezoelectric Patches

Research activities in smart materials and structures are very important today and represent a significant potential for technological innovation in mechanics and electronics. The growing interest of our society in the problem of sustainable development motivates a broad research effort for optimizing mechanical structures in order to obtain new functional properties such as noise reduction, comfort enhancement, durability, decreased ecologic impact, etc. In order to realize such a multi-objective design, new methods are now available which allow active transducers and their driving electronics to be directly integrated into otherwise passive structures. The number of potential applications of these approaches is growing in many industrial fields such as civil engineering, aerospace, aeronautics, ground transportation, etc. The main research challenge today deals with the development of new multi-functional structures integrating electro-mechanical systems in order to optimize their intrinsic mechanical behavior to achieve desired goals.

Large-amplitude stress waves in nonlinear periodic structures

The ultimate goal of this research is to investigate the propagation of large-amplitude stress waves in nonlinear periodic structures. Sources of non-linearity are associated with large-strain kinematics, material non-linearity, and bifurcation paths. In this study, we use a numerical approach to investigate the propagation on large strain waves in periodic lattice structures of finite size. Insights on the dispersion properties of such systems, and their functional dependence on the strain levels, are obtained by post-processing the time-history results obtained through time-domain explicit simulations. In particular, we highlight the effects of nonlinear amplitude parameters on the bandgaps and wave directionality of the considered systems.