Nonlinear targeted energy transfer of two coupled cantilever beams coupled to a bistable light attachment

International audienceIn order to control the sound radiation by a structure, one aims to control vibration of radiating modes of vibration using " Energy Pumping " also named " Targeted Energy Transfer ". This principle is here applied to a simplified model of a double leaf panel. This model is made of two beams coupled by a spring. One of the beams is connected to a nonlinear absorber. This nonlinear absorber is made of a 3D-printed support on which is clamped a buckled thin small beam with a small mass fixed at its center having two equilibrium positions. The experiments showed that, once attached onto a vibrating system to be controlled, under forced excitation of the primary system, the light bistable oscillator allows a reduction of structural vibration up to 10 dB for significant amplitude and frequency range around the first two vibration modes of the system

Development of novel chitosan / guar gum inks for extrusion-based 3D bioprinting: process, printability and properties

The major limitation of 3D bioprinting is the availability of inks. In order to develop new ink formulations, both their rheological behavior to obtain the best printability and the target bio-printed objects conformities must be studied. In this paper, for the first time in our knowledge, the preparation and the characterization of novel ink formulations based on two natural biocompatible polysaccharides, chitosan (CH) and guar gum (GG), are presented. Five ink formulations containing different proportions of CH and GG were prepared and characterized in terms of rheological properties and solvent evaporation. Their printability was assessed (by varying the nozzle diameter, pressure and speed) using an extrusion-based 3D bioprinting process performed directly in air at 37 °C. Results showed that the incorporation of GG improved both the printability of the pure chitosan ink by increasing the viscosity of the solution and the shape fidelity by accelerating the solvent evaporation. We showed that the ink containing 15% (w/w) of GG and 85% (w/w) of CH had the best printability. This formulation was therefore used for the preparation of membranes that were characterized by infrared spectroscopy (FTIR) and X-Ray Diffraction (XRD) before and after gelation as well as for their mechanical properties (Young modulus, strength and strain at break). The optimal process printing parameters were determined to be: 27 G micronozzle, extrusion pressure below 2 bars and robot head speed between 20 and 25 mm/s. This novel ink formulation is a guideline for developing 2D scaffolds (such as auto-supported membranes) or 3D scaffolds for biomedical applications.publishe

Raman correlation spectroscopy: A method studying physical properties of polystyrene by the means of multivariate analysis

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Étude numérique et expérimentale du pompage énergétique des premiers modes vibratoires d'un système mécanique : Modélisation et étude paramétrique simplifiée

National audienceLa réduction des bruits et des vibrations reste un thème de recherche très porteur et de nombreux dispositifs actifs et passifs ont été développés pour améliorer le comportement vibroacoustique des ensembles mécaniques. L’absorbeur dynamique non-linéaire offre une meilleure robustesse en fréquence par rapport aux dispositifs existants actuellement. Ce système à raideur non-linéaire ne possède pas de fréquence propre et peut osciller librement à n’importe quelle fréquence. Une fois accroché sur un système vibrant, on peut obtenir (sous certaines conditions) des régimes de fonctionnement très particuliers où les échanges d’énergie se font dans un seul sens : du système vibrant vers l‘étouffeur non linéaire. On parle alors de « pompage d’énergie ». Plus récemment, nous avons cherché à étendre ce principe au domaine de le Vibroacoustique. Nous développons un nouveau type d’absorbeur dynamique non linéaire basé sur des lames minces bistables légères. Les résultats, tant expérimentaux que numériques, montrent qu’une réduction de plus de 10 dB du niveau vibratoire de poutres et de plaques peut être obtenue sur une large gamme de configurations

GHz Micro-modulator for telecommunication based on SBN and KTN bulk crystals

International audienceIn this paper, we report the development of micro-modulator technology using bulk SBN and KTN crystals, materials which exhibit giant electro-optical coefficients r33

NUMERICAL AND EXPERIMENTAL STUDY OF THE ENERGY PUMPING OF THE FIRST VIBRATION MODES OF A MECHANICAL SYSTEM USING BI-STABLE ATTACHMENT

International audienceIn order to control the sound radiation by a structure, one aims to control vibration of radiating modes of vibration using " Energy Pumping " also named " Targeted Energy Transfer ". This principle is here applied to a simplified model of a double leaf panel. This model is made of two beams coupled by a spring. One of the beams is connected to a non-linear absorber. This non-linear absorber is made of a 3D-printing support on which is clamped a buckled thin small beam with a small mass fixed at its center having two equilibrium positions. Once attached onto a vibrating system to control, a one direction energy exchange from the primary vibrating system to the non-linear absorber can be achieved under special operation. Our experimentations have shown that this simple bi-stable device leads up to more than 10 dB attenuation for the first two vibration modes of the system

A review on thermal degradation of polylactic acid (PLA)/polyhydroxybutyrate (PHB) blends

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