Composite hybride à matrice polymère pour l'amortissement de vibrations par transduction-dissipation locale

Ce travail de thèse a pour objectif l'élaboration d'un composite hybride à matrice polymère (polyamide 11) pour l'amortissement de vibrations par transduction-dissipation locale. Deux étapes préalables ont été abordées. Dans un premier temps, un composite conducteur a été réalisé. Les nanotubes de carbone, charges conductrices, ont permis d'atteindre un seuil de percolation électrique pour un faible taux de charge (0,55 % vol.). En parallèle, le polymère a acquis la propriété de piézoélectricité par l'incorporation de particules de PZT et après la polarisation du composite. Les propriétés mécaniques sont conservées jusqu'à 30 % vol. pour des particules submicroniques. Une augmentation de la partie conservative et dissipative du module mécanique du polyamide a été observée en analyse mécanique dynamique après dispersion simultanée de NTC et de PZT polarisé. Des essais vibratoires ont mis en évidence l'apport du phénomène de transduction-dissipation sur la capacité vibratoire de la matrice polymère, notamment par l'emploi d'une configuration sandwich. L'influence des différents paramètres inhérents à ce nouveau type d'amortissement a été discutée.This work deals with processing of a polymer based composite for vibration damping by transduction-local dissipation. Two preliminary steps have been performed. In a first time, a conductive composite has been elaborated. Carbon nanotubes, as conductive fillers, have allowed reaching an electrical percolation threshold for a low filler content (0,55 % vol.). In the same time, polyamide matrix became piezoelectric by dispersion of PZT particles and after a poling step. Mechanical properties are maintained until 30 % in volume for submicronic particles. An increase of the conservative and dissipative part of the mechanical modulus has been observed by dynamic mechanical analysis after a simultaneous dispersion of NTC and poled PZT. Vibration tests have highlighted the contribution of the transduction-local dissipation phenomenon to the damping factor of the polymer matrix, mainly through a sandwich configuration. The influence of various parameters on this new kind of damping has been discussed

High electrically conductive composites of Polyamide 11 filled with silver nanowires: Nanocomposites processing, mechanical and electrical analysis

Highly conductive composites of silver nanowires and semicrystalline polyamide 11 for different content were prepared. A newmethod was developed to introduce nanowires: a combination of solventway and an extrusion process. This technic provides pellets of composites directly suitable for sample molding. The silver nanowires poured in polyamide 11 were obtained by polyol process to reach large volume of nanowires. The dispersion of nanowires was evaluated by scanning electron microscopy and confirmed by a very lowpercolation threshold around 0.59 vol.%. The level of conductivity above the percolation threshold is about 102 S m−1. Differential scanning calorimetry and dynamic mechanical analyses have shown a stability of the composite physical structure and an optimization of the mechanical properties as a function of nanowires content until 3.6 vol.%. A simultaneous enhancement of the electrical conductivity of polyamide 11 was obtained

Evolution of dispersion of carbon nanotubes in Polyamide 11 matrix composites as determined by DC conductivity

Double-walled Carbon NanoTubes (DWCNTs) have been dispersed in a Polyamide 11 (PA11) matrix by two routes: in the solvent way, Polyamide 11 was first dissolved in its solvent to ensure a liquid state dispersion of carbon nanotubes by ultrasonic way; in the melt mixing way, an optimization of the extrusion parameters, such as mixing time, mixing speed, mixing temperature and screw rotation direction allow to reach satisfactory dispersion. Dispersion and percolation threshold have been compared thanks to the evolution of DC conductivity with carbon nanotubes weight fraction in Polyamide 11. An electrical percolation threshold of 1% in weight was found by the solvent way while the melt mixing way offers one of the lower percolation thresholds for a semi-crystalline matrix (0.93% in weight). An interpretation of the limitation of the electrical percolation threshold value in a semi-crystalline matrix will be proposed

Piezoelectric and mechanical properties of a high performance thermoplastic composite

To protect aircraft and satellite structures from mechanical solicitations such as vibrations, a piezoelectric-based passive damping concept is studied. Most of the time, the piezoelectric elements are surface bonded or embedded in the host structure that needs to be damped. There are integrated with an external shunted circuit. When the piezoelectric material is de-formed, it generates an electrical potential that is dissipated by Joule effect in a resistive ele-ment. More precisely, the purpose of this work is to integrate this passive macroscopic damping con-cept to the composite scale. For this, a hybrid piezoelectric composite based on high perfor-mance thermoplastic polymer as structural matrix is developed. This structural matrix belongs to the PAEK (Poly Aryl Ether Ketone) family. The high glass transition temperature of these thermostable polymers is a critical parameter in the choice of the piezoelectric ceramic. Its Cu-rie temperature has to be higher than the Tg of the composite. In addition, one of the main challenges is to ensure homogeneous particle dispersion with a sufficiently low content to maintain the matrix ductility. We propose to present the piezoelectric and mechanical proper-ties of a thermoplastic polymer / micronic piezoelectric particle composites as a function of their chemical composition

Discontinuity of physical properties of carbon nanotube/polymer composites at the percolation threshold

Evolution of DC conductivity with double-walled carbon nanotube concentration in a polyamide 11 matrix displays the electrical percolation phenomenon. The percolation threshold is observed for this composite at 0.85 wt.%. Thermal, mechanical and dielectric manifestations of the glass transition have been investigated as a function of carbon nanotube content. Thermal and mechanical analyses have shown a depression of the glass transition temperature or its mechanical manifestation at the percolation threshold. Regarding the dielectric modulus, three distinct behaviors (below, at, and above percolation threshold) have been observed. A discussion about the interactions between the polymer matrix and the conductive fillers will be proposed to further the understanding of the discontinuity of physical properties at the percolation threshold

New hybrid polymer nanocomposites for passive vibration damping by incorporation of carbon nanotubes and lead zirconate titanate particles

A new hybrid nanocomposite for vibration damping has been elaborated. Ferroelectric lead zirconate titanate particles and carbon nanotubes are dispersed simultaneously in an engineering semi-crystalline thermoplastic matrix by an extrusion processing. Ferroelectric particles have been made piezoelectric once incorporated into the polymer matrix through a poling step. The dynamic response of nanocomposites has been characterized by dynamic mechanical analysis and vibration test. The shear mechanical modulus exhibits an increase of the conservative and dissipative components after the poling step of nanocomposites. By vibration test, the first bending mode of the frequency response function has been followed and a significant damping inherent to poling is also recorded. These evolutions are heightened by the use of two constrained elastic layers. For the first time, a synergy between poled piezoelectric particles responsible for the transduction phenomena and conductive particles allowing a local dissipation of electric charges has been revealed by two complementary techniques for the improvement of the polymer damping

Polymerization study and rheological behavior of a RTM6 epoxy resin system during preprocessing step

Curing process and rheological behaviors of a monocomposant epoxy resin used in structural aeronautic applications are investigated. This study helped settle the basic parameters in order to optimize the infusion process of carbon fibers in an epoxy matrix. The effect of carbon nanotube dispersion during the preinjection step is also studied to improve electrical behavior of composite parts. The curing process has been analyzed at isothermal temperature using differential scanning calorimetry technique. Viscosity measurements were achieved with a Couette geometry, suitable for low viscosity resin. A shear-thinning effect caused by adding CNTs in the epoxy matrix is detected. It is more pronounced at high temperature for increasing CNT mass content

Integrated piezoelectric function in a high thermostable thermoplastic PZT/PEEK composite

A piezoelectric structural material has been developed. Lead Zirconate Titanate (PZT) submicronic nanoparticles have been dispersed in a thermostable high performance thermoplastic polymer Poly(Ether Ether Ketone) i.e. PEEK to ensure piezoelectric properties. The inorganic particles with a mean diameter of 900 nmare polycrystalline as highlighted by HRTEM with a grain diameter estimated at 15 nm. XRD patterns have shown that the crystalline structure is rhombohedral i.e. ferroelectric. The PZT/PEEK composites have been elaborated by extrusion which allows reaching a satisfactory dispersion of particles even at high volume fraction (30% in volume). One of the challenges was to find poling conditions compatible with the thermal stability of the matrix. Indeed, this composite must be poled above the polymer glass transition temperature to improve matching of dielectric permittivity between inorganic and organic phases. The influence of the poling electric field on the final piezoelectric activity of the composite has also been studied to better understand the role of the polymer matrix. Finally, after a poling step, the PZT/PEEK composite exhibits a piezoelectric strain coefficient which can be exploited over a wide temperature range

Composite hybride à matrice polymère pour l'amortissement de vibrations par transduction-dissipation locale

TOULOUSE3-BU Sciences (315552104) / SudocSudocFranceF