Determination of water uptake in organic coatings deposited on 2024 aluminium alloy: Comparison between impedance measurements and gravimetry

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.

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

This study aims to increase effectivity of the overmolding approach for thermoset/thermoplastics hybrid composites. The samples were prepared by overmolding of polyamide-6 (PA6) onto fully cured continuous carbon fiber-reinforced epoxy composites with the aid of hot melt adhesives. Specifically, the influence of hot melt adhesive application at the interface between the thermoset and thermoplastic parts of hybrid composites was investigated. The experimental scheme highlights the effects of hot melt type and adhesive layer thickness (ALT) on the performance of these hybrid joints. Thermoplastic polyurethane (TPU) based hot melt adhesive performed better adhesion characteristics among others (copolyesters, polyolefin) according to findings from lap shear test and DMA analysis. The fracture surfaces observed with optical microscopy and SEM also confirmed the synergistic effect of these parameters.

Effects of hot melt adhesives on the interfacial properties of overmolded hybrid structures of polyamide-6 on continuous carbon fiber/epoxy composites

The effective mechanical properties of a polyurethane adhesive (oligoetherdiol, -triol, MDI) in gold joints (bond line thickness, dP = 35–550 µm) are studied in the linear deformation range by dynamic mechanical analysis in shear mode. These properties depend on dP: thin ones possess a higher dynamic glass transition temperature and show a narrower glass transition than the thick ones. The storage modulus rises with decreasing dP for the rubbery plateau. The results attest mechanical interphases in the polyurethane with increased crosslink density and reduced cooperative mobility than in bulk. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42058.

Dynamic mechanical properties of very thin adhesive joints

Thermal cycling in space environment can cause physical aging of polymers used in structural adhesive bonded joint. Later, they can initiate failure. A methodology to follow physical aging effects on their thermal, mechanical and dielectric properties is applied to a commercial epoxy adhesive. The analytic description, using Tool, Narayanaswamy and Moynihan model gives a good description of the enthalpy relaxation. It is completed by a phenomenological analysis of the evolution of the adhesive thermal transitions, mechanical properties and molecular mobility. Tested samples with bonded assembly are representative of in service configurations. The influence of physical aging on the adhesive and the associated bonded assemblies is analyzed.

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Enthalpy relaxation phenomena of epoxy adhesive in operational configuration: Thermal, mechanical and dielectric analyses

https://hal.archives-ouvertes.fr/hal-00840784/document

New bonded assembly configuration for dynamic mechanical analysis of adhesives

In this paper, a passive vibration damping concept based on multifunctional materials was studied for thermoplastic composite structures. The synergy between piezoelectric and conductive particles brings a new contribution of energy dissipation based on the local transduction-dissipation phenomenon. While piezoelectric fillers ensure the conversion of mechanical energy into electrical energy (transduction), conductive particles locally dissipate the electric charges created avoiding saturation in the vicinity of piezoelectric particles. Here, the concept has been studied at material and structure scales for laboratory and preindustrial samples in order to bring solid proof of the damping concept. For this purpose, piezoelectric and electrically conductive particles were dispersed into engineering thermoplastics polyamide 12 and poly ether ketone ketone. Damping films were obtained by hot press and embedded in a composite sandwich beam and carbon fiber reinforced polymer (CFRP)-aluminum panels. Dynamic mechanical analysis and vibration tests were performed on bulk nanocomposite samples and in composite sandwich beams. The study of hysteresis loops and frequency response function showed strong nonlinear effects and vibration amplitude decrease up to 50%. Tests on CFRP-aluminum panels highlighted the structural damping increase demonstrating the potential capacity of this multifunctional material for energy dissipation in typical aerospace structures.

L. Quiroga Cortes

Papers

New bonded assembly configuration for dynamic mechanical analysis of adhesives

Improving damping capabilities of composites structures by electroactive films containing piezoelectric and conductive fillers