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International audience; Phononic Crystals (PCs) are artificial materials with extensive application in the aerospace and aeronautical industries since they introduce frequency stop-bands (frequency ranges where wave cannot freely propagates). In this investigation 2D periodic and quasi-periodic pattern: instead of strictly repeating a pattern, a certain degree of irregularity is introduced. Quasi-periodic PCs in this paper are defined as assemblies of two different elements in two direction by using Thue-Morse and semi-Sierpinski carpet which results in asymmetry in both directions. Numerical studies on periodic and quasi-periodic lattices are performed. The spectral analysis in periodic waveguide is validated with the dispersion diagram of a reference model and vibration transmission of the lattices are studied. The wave characteristics in quasi-periodic super-cell configuration increases the wide of band-gaps about 22% compared to the reference model. Nevertheless, the associated level of vibration in the forced response of quasi-periodic lattices are predicted.

International audience; Mechanical structures are subjected to ambient vibrations or acoustic pressures which can be used to produce energy using adequate transducers that convert mechanical loadings into electrical polarization. The use of smart materials such as EAP (electro-active polymer) to harvest energy from the mechanical vibrations of the surrounding environment is a recent and promising concept. This study focuses on the characterization and identification of mechanical properties for an elastomer material (3M R VHB 4910) which can be functionalized such as an EAP material for acoustic energy control. Mechanical tests have been carried out using tensile testing machine equipped with a thermo-conditioning device to control the environmental conditions (temperature and humidity). Tensile test have been performed with an imposed loading–unloading strain rate for various temperatures. The measured force–displacement data have been filtered by moving mean.The force–displacement response exhibits an energy storage within the material and a dependence on temperature. Assuming incompressibility, three hyperelastic models have been considered : the Neo-Hookean model with one parameter, the Mooney-Rivlin model with two parameters and the Ogden model with two parameters. Each set of material parameters has been identified by using a non-linear inverse method based on non-linear least squares. It has been observed that, not only the Neo-Hookean model does not fit well with experimental data, , but also the Mooney-Rivlin model is more precise than the Ogden model. Thus, it has been found that the Mooney-Rivlin model is the best compromise between complexity and suitability. The relationship between initial shear modulus and temperature has been approximated by a linear relationship with a sufficiently small residual error.

International audience; The vast majority of structures introduce symmetry in one or two dimensions, which can be a periodicity in the case of constructing several identical unit cells. Periodic structures have found a big interest in engineering applications because they introduce frequency band effects, due to the impedance mismatch generated by periodic discontinuity in the geometry, which can improve the vibroacoustic performances.However, the presence of imperfections i.e. (defects, irregularity) in the structure, leads to a partial lost of regular periodicity (called quasi-periodic structure) that can have a noticeable impact on the vibrational and/or acoustic behaviour of the elastic system. The tailored irregularity, which is a designed loss of periodicity, can be used, therefore, to improve the dynamic behaviour of structures. In the present paper numerical studies on the vibrational analysis of two-dimensional non-planar periodic and quasi-periodic structures have been performed. The content deals with finite and infinite systems. The finite element models of solid structures focused on the band diagram analysis of the infinite systems andthe forced responses of the finite structures. The quasi-periodicity is defined by invoking the Thue-Morse sequence for building the assigned variations (geometry) along the domain of finite element model. The wave characteristics in quasi-periodic panels, present some elements of novelty and could be considered for designing structural filters and controlling the properties of elastic waves.

A nonlinear vibration energy harvester (VEH) based on electromagnetic transduction in a quasi-periodic system is proposed. The quasi-periodic system is obtained by varying the mass of one of the moving magnets which leads to the vibration energy localization. The mechanical nonlinearity is introduced by considering large displacements of the beams. It is shown that the introduction of the nonlinearity and the functionalization of the energy localization phenomenon lead to the enlargement of the bandwidth and the increase of the vibration amplitudes.

International audience; The severe dynamic environment of take-off and flight of launchers presents risks of damage and life cycle limitation of the payload. To improve the dynamic comfort of the payload, damping treatments are employed at the final stage of the launcher assemble. One well-known solution is the limitation of the vibration amplitudes by dissipating the energy at the bolted joints between the stages. To our knowledge, there is not a simple and effective method that allows an accurate damping prediction at the full structure level from the knowledge of localized dissipation between the components. Indeed, to model the damping of an assembled structure made up of several components, one carries out a 3D modeling of the interfaces [1] to have a good representation of the dissipation. The result is a damping model identified by interface, which is difficult to exploit in the prediction of the dynamic behavior of the full model. Moreover, for uniformly distributed dissipation, it is common to use the Rayleigh damping assumption to represent the damping matrix in the equivalent viscous model. In general, common methods [2] identify this matrix at a single interface. In this work, we propose a method of modeling the multi-interface Rayleigh damping which consists of the following steps: (i) calculation of the modal damping of each interface taken separately by using the modal effort method [3] or the modal displacement method developed in PERMAS finite element software; (ii) identification of the proportional damping matrix of each interface (proportionality coefficients of stiffness and mass matrices); (iii) assembly of the identified damping matrices; (iv) prediction of the dynamic response of the complete structure from the global model. The proposed method was validated on a reduced model of the ARIANE 5 launcher to calculate the dynamic responses taking into account the different types of dissipation in the interfaces for the asymmetric load case and successfully compared to the reference results. The main advantages of the proposed method are the simplicity of the numerical implementation, the reduction of the CPU, the quality of prediction and the perspective of integration in an optimization procedure of interfaces design with high damping performances.

International audience; Developing techniques for vibration energy harvesting (VEH) based on various energy conversion mechanisms is being a focus of interest. In this context, a multimodal approach in a quasiperiodic system for vibration energy harvesting is investigated . The basic idea to enhance the system performances consists in introducing imperfections. Thus, mistuning is achieved by varying the mass of few cells . These imperfections will lead to the vibration energy localization in regions close to the imperfections which will be exploited to maximize the harvested energy.