Morvan Ouisse

Patch Transfer Functions as a Tool to Couple Linear Acoustic Problems

A method to couple acoustic linear problems is presented in this paper. It allows one to consider several acoustic subsystems, coupled through surfaces divided in elementary areas called patches. These subsystems have to be studied independently with any available method, in order to build a database of transfer functions called patch transfer functions, which are defined using mean values on patches, and rigid boundary conditions on the coupling area. A final assembly, using continuity relations, leads to a very quick resolution of the problem. The basic equations are developed, and the acoustic behavior of a cavity separated in two parts is presented, in order to show the ability of the method to study a strong-coupling case. Optimal meshing size of the coupling area is then discussed, some comparisons with experiments are shown, and finally a complex automotive industrial case is presented.

Structural energy flow optimization through adaptive shunted piezoelectric metacomposites

In this article, a numerical approach for modeling and optimizing two-dimensional smart metacomposites is presented. The proposed methodology is based on the Floquet–Bloch theorem in the context of elastodynamics including distributed shunted piezoelectric patches. The dedicated numerical technique is able to cope with the multimodal wave dispersion behavior over the whole first Brillouin zone for periodically distributed two-dimensional shunted piezomechanical systems. Some indicators allowing the optimization of the shunt impedance for specific performance objectives are presented and applied for illustration purposes on the design of an adaptive metacomposite with specific functionalities. In order to validate the strategy, the designed metacomposite is integrated in a support structure, and a full three-dimensional model is derived to illustrate the efficiency of the approach.

Kirigami Auxetic Pyramidal Core: Mechanical Properties and Wave Propagation Analysis in Damped Lattice

The work describes the manufacturing, mechanical properties, and wave propagation characteristics of a pyramidal lattice made exhibiting an auxetic (negative Poissons ratio) behavior. Contrary to similar lattice tessellations produced using metal cores, the pyramidal lattice described in this work is manufactured using a kirigami (origami pluscutting pattern) technique, which can be applied to a large variety of thermoset and thermoplastic composites. Due to the particular geometry created through this manufacturing technique, the kirigami pyramidal lattice shows an inversion between in-plane and out-of-plane mechanical properties compared to classical honeycomb configurations. Long wavelength approximations are used to calculate the slowness curves, showing unusual zero-curvature phononic properties in the transverse plane. A novel 2D wave propagation technique based on Bloch waves for damped structures is also applied to evaluate the dispersion behavior of composite (Kevlar/epoxy) lattices with intrinsic hysteretic loss. The 2D wave propagation analysis shows evanescence directivity at different frequency bandwidths and complex modal behavior due to unusual deformation mechanism of the lattice.

Experimental characterization of a bi-dimensional array of negative capacitance piezo-patches for vibroacoustic control

This study presents an experimental investigation of the application of a periodic array of shunted piezoelectric patches with negative capacitance for the broadband control of waves propagating on a flexible plate. A 15 × 5 array of piezoelectric patches is bonded onto the top surface of a freely supported rectangular plate. The patch array is intended to serve as an active interface between two regions of the plate, where one region has an input disturbance force and the other does not. Each patch is shunted through a single circuit, reproducing a resistance in series with a negative capacitance. The magnitude of the reactive part of the negative shunting impedance is tuned close to the intrinsic capacitance of the piezoelectric patch. The real part is adjusted for either light damping so as to induce a reactive (reflective) response, or with heavy damping to induce greater absorption. The experimental responses of the system equipped with this active interface display a strong attenuation or reflection of vibrations, depending on the shunt resistance, over a large frequency range, including the mid-frequency regime. In an effort to control vibroacoustic phenomena, this study represents the first attempt to implement an integrated smart metacomposite active interface on a plate structure.

Impact of the irregular microgeometry of polyurethane foam on the macroscopic acoustic behavior predicted by a unit-cell model

This paper deals with the prediction of the macroscopic sound absorption behavior of highly porous polyurethane foams using two unit-cell microstructure-based models recently developed by Doutres, Atalla, and Dong [J. Appl. Phys. 110, 064901 (2011); J. Appl. Phys. 113, 054901 (2013)]. In these models, the porous material is idealized as a packing of a tetrakaidecahedra unit-cell representative of the disordered network that constitutes the porous frame. The non-acoustic parameters involved in the classical Johnson-Champoux-Allard model (i.e., porosity, airflow resistivity, tortuosity, etc.) are derived from characteristic properties of the unit-cell and semi-empirical relationships. A global sensitivity analysis is performed on these two models in order to investigate how the variability associated with the measured unit-cell characteristics affects the models outputs. This allows identification of the possible limitations of a unit-cell micro-macro approach due to microstructure irregularity. The sensitivity analysis mainly shows that for moderately and highly reticulated polyurethane foams, the strut length parameter is the key parameter since it greatly impacts three important non-acoustic parameters and causes large uncertainty on the sound absorption coefficient even if its measurement variability is moderate. For foams with a slight inhomogeneity and anisotropy, a micro-macro model associated to cell size measurements should be preferred.

Design variables for optimizing adaptive metacomposite made of shunted piezoelectric patches distribution

A two-dimensional array of a piezoelectric transducer shunted on a negative capacitance circuit is designed and applied to achieve broadband vibration reduction of a flexible plate over tunable frequency bands. Each surface-bonded patch is connected to a single independent negative capacitance synthetic circuit. A finite-element-based design methodology is used to predict and optimize the attenuation properties of the smart structure. The predictions are then experimentally validated by measuring the harmonic response of the plate and evaluating some derived quantity such as the loss factor and the kinetic energy ratio. The validated model is finally used to explore different configurations with the aim of defining some useful design criteria. The results obtained clearly show how the proposed strategy represents a robust and effective solution for the control of vibrations in complex structures.

A piezo-shunted kirigami auxetic lattice for adaptive elastic wave filtering

Tailoring the dynamical behavior of wave-guide structures can provide an efficient and physically elegant approach for optimizing mechanical components with regards to vibroacoustic propagation. Architectured materials as pyramidal core kirigami cells combined with smart systems may represent a promising way to improve the vibroacoustic quality of structural components. This paper describes the design and modeling of a pyramidal core with auxetic (negative Poissons ratio) characteristics and distributed shunted piezoelectric patches that allow for wave propagation control. The core is produced using a kirigami technique, inspired by the cutting/folding processes of the ancient Japanese art. The kirigami structure has a pyramidal unit cell shape that creates an in-plane negative Poissons ratio macroscopic behavior. This structure exhibits in-plane elastic properties (Youngs and shear modulus) which are higher than the out-of-plane ones, and hence this lattice has very specific properties in terms of wave propagation that are investigated in this work. The short-circuited configuration is first analyzed, before using negative capacitance and resistance as a shunt which provides impressive band gaps in the low frequency range. All configurations are investigated by using a full analysis of the Brillouin zone, rendering possible the deep understanding of the dynamical properties of the smart lattice. The results are presented in terms of dispersion and directivity diagrams, and the smart lattice shows quite interesting properties for the adaptive filtering of elastic waves at low frequencies bandwidths.

Experimental Investigations on Viscoelastic Properties of a Shape Memory Polymer

The shape memory polymers (SMPs) are polymeric smart materials which have the remarkable ability to recover their primary shape from a temporary one under an external stimulus. The study deals with the synthesis and the thermo-mechanical characterization of a thermally-actuated SMP, the tBA/PEGDMA, with a special focus on viscoelastic properties. The mechanical characterization is performed using three kinds of tests: quasi-static tensile tests, dynamic mechanical analysis (DMA) and modal tests. The first one allows the identification of the Youngs modulus and the Poisson’s ratio at ambient temperature. Modal analyses are done for various temperature values, and resonance frequencies are measured. In order to validate the time-temperature equivalence on this SMP, a DMA is performed under harmonic loading for different temperatures and a master curve highlights a complementarity of the results. Finally a suitable model for the viscoelastic behavior of the SMP is identified.Copyright

Adaptive metacomposites for vibroacoustic control applications

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, and so forth. In order to realize such a multiobjective design, new methods are now available, which allow active transducers and their driving electronics to be directly integrated into otherwise passive structures. This new concept could allow fine control of the material physical behavior to induce new functional properties that do not exist in nature and that cannot be introduced by passive approaches. In this sense, we can speak of integrated distributed adaptive metacomposites that merge with the notion of programmable material. Through two different examples dealing with active acoustical impedance and elastodynamical interface, this paper presents theoretical tools and validations for designing specific applications of this new technology.

Isothermal and anisothermal implementations of 2D shape memory alloy modeling for transient impact response calculation

A numerical implementation of the Raniecki Lexcellent (RL)?(Raniecki et al 1992 Arc. Mech. 44 261?284, Raniecki and Lexcellent 1994 Eur. J. Mech. A 13 21?50, Raniecki and Lexcellent 1998 Eur. J. Mech. A 17 185?205) models for shape memory alloys (SMA) coupled with the heat equation is presented in this paper, adapted to high strain rate loading. The objective is to predict the time response of a 2D SMA structure subjected to an impulse force and induced free vibration with a decreasing amplitude for isothermal and anisothermal conditions. The choice of material mechanical properties has been done in order to have phase transformations during the oscillations. The apparent damping and stiffness effects due to these phase changes is clearly identified when the results are compared with a linear model without induced martensite. The thermomechanical constitutive relation of the SMA has been fulfilled to be able to take into account the time reaction when the strain rate is very high. The full model has been implemented in a finite element code and tested on a 2D sample.