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Rolere S.,IRT Jules Verne | Rolere S.,CNRS Le Mans Institute of Molecules and Materials | Coulon J.-F.,ECAM Rennes Louis de Broglie | Poncin-Epaillard F.,CNRS Le Mans Institute of Molecules and Materials
European Polymer Journal | Year: 2017

Perfluorononanoic acid (F17) was grafted to an epoxy resin. The virgin epoxy resin and the fluorinated epoxy resin were cured at various temperatures. Both air-resin and substrate-resin interfaces of the cured materials were characterized in terms of: (i) free surface energy, (ii) surface composition, evaluated using angle-resolved X-ray photoelectron spectroscopy (AR-XPS). Fluorine proportion was quantified at probing depths of about 4.5 and 9 nm. The curing temperature highly influenced the diffusion of the perfluorinated chains towards both interfaces. Depending on the curing conditions, very low free surface energies (17 mJ/m2) due to high fluorine concentrations (fluorine/carbon ratio = 0.6) were measured at the air-resin interface. However, the F17 diffusion towards the substrate was also observed and led to important fluorine concentrations (F/C up to 0.4). Finally, a two-step curing procedure was used for monitoring the F17 diffusion during the curing, illustrated by an accumulation of fluorine atoms at both interfaces. A non-linear relation was highlighted between the surface energy drop and the fluorine content measured by AR-XPS. © 2017


Glaris P.,Thales Alenia | Glaris P.,CNRS Le Mans Institute of Molecules and Materials | Coulon J.-F.,ECAM RENNES Louis de Broglie | Dorget M.,Thales Alenia | Poncin-Epaillard F.,CNRS Le Mans Institute of Molecules and Materials
Composites Part B: Engineering | Year: 2015

Two routes for the grafting of fluorinated molecules to an epoxy resin were studied. The first one deals with the grafting of the liquid-state resin whereas the second one is focused on the grafting onto the solid-state resin. These grafting reactions were shown to be similar as studied through FTIR and XPS spectroscopies. However, it appears that the grafting onto the solid-state resin is limited by the curing advancement. N2 plasma-activation was used to solve this drawback and enhanced the grafting yield. This grafting improvement was mainly explained in terms of the surface wetting improvement and the attachment of nitrogen containing groups at the surface of the treated resin. © 2014 Elsevier Ltd. All rights reserved.


Glaris P.,Thales Alenia | Glaris P.,CNRS Le Mans Institute of Molecules and Materials | Coulon J.F.,ECAM RENNES Louis de Broglie | Dorget M.,Thales Alenia | Poncin-Epaillard F.,CNRS Le Mans Institute of Molecules and Materials
Composites Part B: Engineering | Year: 2015

Driving forces, responsible for the migration of a fluorinated additive added to a thermoset resin, toward the air/solid interface, were investigated. On this subject, the surface chemistry as characterized by XPS analyses was compared to theoretical models based on the rheological properties of the blend. It appears that the migration of the fluorinated molecules toward the surface cannot be described by a conventional diffusion model. A second model derived from the latter suits better to the experimental data and should be presented as another proof that additional motion forces drive the fluorine molecules migration in curing epoxy resin. ©2014 Elsevier Ltd. All rights reserved.


Glaris P.,Thales Alenia | Glaris P.,CNRS Le Mans Institute of Molecules and Materials | Coulon J.-F.,ECAM Rennes Louis de Broglie | Dorget M.,Thales Alenia | Poncin-Epaillard F.,CNRS Le Mans Institute of Molecules and Materials
Composites Part B: Engineering | Year: 2014

The aim of this work is to decrease the adhesion between a cured modified epoxy-based substrate and an in situ cured virgin epoxy-based piece. The effect of perfluorinated additives on the non-adhesion output is investigated through an adapted pull-off test. It appears that additive migration initiates the surface fluorination. Longer the fluorinated chain is, higher the surface fluorination is and weaker the adhesion strength is. The weak chemical affinity between these two epoxy resins is shown to be mainly responsible for these results leading to an adhesive rupture. © 2014 Elsevier Ltd. All rights reserved.


Jean-Baptiste D.,University of Technology of Belfort - Montbéliard | Hanlin L.,University of Technology of Belfort - Montbéliard | Christian C.,University of Technology of Belfort - Montbéliard | Jean-Marie M.,ECAM Rennes Louis de Broglie
Proceedings of the International Thermal Spray Conference | Year: 2015

Internal coating of cylinders has always been a challenge for cars engineers. Driven for more than two decades now by the ecological and economical constrains applied to the automotive industry, it constitutes a dynamic way of research and development for industrial applications. One of the most economical processes for this kind of coatings is the rotating twin-wire arc spray (TWAS) system. Meanwhile the actual quality and the performances of the corresponding coatings still leave place for some improvements. Therefore, in the work presented here, attention was paid to the second atomization phenomena in a TWAS system considering the influence of the gas flow parameters on the particles' morphology and deposition behavior. Numerical modeling of the plume and comparisons between several designs of the second atomizing units were also considered. © Copyright (2015) by ASM International All rights reserved.


Coulon J.F.,ECAM RENNES Louis de Broglie | Tournerie N.,ECAM RENNES Louis de Broglie | Maillard H.,ECAM RENNES Louis de Broglie
Applied Surface Science | Year: 2013

Adhesion strengths between aluminium thin film coatings and manufactured carbon/epoxy composite surfaces were measured by assessing fracture tensile strengths using pull-off tests. The effect of the substrate roughness (nm to μm) of these composite surfaces on adhesion was studied by examining the surface free energies and adhesion strengths. The adhesion strengths of the coatings varied significantly. To improve the coating adhesion, each composite surface was treated with atmospheric plasma prior to deposition, which resulted in an increase in the surface free energy from approximately 40 mJ/m2 to 70 mJ/m2 because the plasma pretreatment led to the formation of hydrophilic CO and CO bonds on the composite surfaces, as demonstrated by X-ray photoelectron spectroscopy analyses. The adhesion strengths of the coatings were enhanced for all surface roughnesses studied. In our study, the effect of mechanical adhesion due to roughness was separated from the effect of modifying the chemical bonds with plasma activation. The adhesion ability of the pure resin was relatively weak. Increasing the surface roughness largely improved the adhesion of the resin surface. Plasma treatment of the pure resin also increased the surface adhesion. Our study shows that plasma activation effectively enhances the adhesion of manufactured composites, even when the surface roughness is on the order of microns. The ageing of the surface activation was also investigated, and the results demonstrate that atmospheric plasma has potential for use in the pretreatment of composite materials. © 2013 Elsevier B.V. All rights reserved.


Diot G.,Institute Maupertuis | Koudri-David A.,CNRS Civil and Mechanical Engineering Laboratory | Walaszek H.,CETIM de Senlis | Guegan S.,CNRS Civil and Mechanical Engineering Laboratory | Flifla J.,ECAM Rennes Louis de Broglie
Journal of Nondestructive Evaluation | Year: 2013

Embedded welding defects, such as porosities and cracks, are generally formed during aluminium laser welding. It is challenging to test these defects with current non-destructive evaluation (NDE) methods. This work features the creation of defects and their study with the help of NDE methods. The chosen method should be able to detect porosities in lap-welded sheets of 5754 aluminium alloys. The welding process is described and the samples were first characterised with X-ray techniques to choose those containing defects of various sizes and densities. Secondly, these welds were tested with the Laser Ultrasonic Technique (LUT). The first results show that LUT gives defect signatures. Based on raw measurements only, our results show that it is difficult to give any precise description of the defects' size or position. To aid in the interpretation of the results, a frequency-bandwidth analysis has been performed because of the broadband nature of laser ultrasonic signals. © 2013 Springer Science+Business Media New York.


Savaux V.,Supelec | Djoko-Kouam M.,ECAM Rennes Louis de Broglie | Louet Y.,Supelec | Skrzypczak A.,Zodiac Data Systems
IET Signal Processing | Year: 2014

In this article, the authors study the convergence of an iterative algorithm for the joint estimation of the signal-to-noise ratio (SNR) and the transmission channel in orthogonal frequency division multiplexing context. At each step of the algorithm, the authors use the minimum-mean-square error (MMSE)-based SNR estimation, which feeds the linear MMSE channel estimation. Reciprocally, this efficient channel estimation is used to perform the SNR estimation. The authors provide a proof of convergence of the algorithm to a single value. Furthermore, we derive an accurate approximation of the bias of the estimation. Simulations show that the algorithm converges quickly and verifies the theoretical results. They also show the efficiency of both SNR and channel estimation. By comparing with the existing methods, the authors show that the tradeoff between the number of required pilots in the preamble and the performance of the SNR estimation were improved. Furthermore, for a fixed bit error rate, the SNR gap between the proposed channel estimation and the perfect one is <0.5 dB. © 2014 The Institution of Engineering and Technology.


Savaux V.,ECAM Rennes Louis de Broglie | Savaux V.,Supelec | Louet Y.,Supelec | Djoko-Kouam M.,ECAM Rennes Louis de Broglie | Skrzypczak A.,Zodiac Data Systems
Eurasip Journal on Advances in Signal Processing | Year: 2013

This article presents an iterative minimum mean square error- (MMSE-) based method for the joint estimation of signal-to-noise ratio (SNR) and frequency-selective channel in an orthogonal frequency division multiplexing (OFDM) context. We estimate the SNR thanks to the MMSE criterion and the channel frequency response by means of the linear MMSE (LMMSE). As each estimation requires the other one to be performed, the proposed algorithm is iterative. In this article, a realistic case is considered; i.e., the channel covariance matrix used in LMMSE is supposed to be totally unknown at the receiver and must be estimated. We will theoretically prove that the algorithm converges for a relevantly chosen initialization value. Furthermore simulations show that the algorithm quickly converges to a solution that is close to the one in which the covariance matrix is perfectly known. Compared to existing SNR estimation methods, the algorithm improves the trade-off between the number of required pilots and the SNR estimation quality. © 2013 Savaux et al.; licensee Springer.


Savaux V.,ECAM Rennes Louis de Broglie | Savaux V.,Supelec | Louet Y.,Supelec | Djoko-Kouam M.,ECAM Rennes Louis de Broglie | Skrzypczak A.,Zodiac Data Systems
Signal Processing | Year: 2013

This paper proposes a linear minimum mean square error-based (LMMSE) channel estimation method, which allows avoiding the necessary knowledge of the channel covariance matrix or its estimation. To do so, a perfectly tunable filter acting like an artificial channel is added at the receiver side. We show that an LMMSE estimation of the sum of this artificial channel and the physical channel only needs the covariance matrix of the artificial channel, and the channel estimation is finally obtained by subtracting the frequency coefficients of the added filter. We call this method artificial channel aided-LMMSE (ACA-LMMSE). Theoretical developments and simulations prove that its performance is close to theoretical LMMSE, and we show that this method reduces the computational complexity, compared to usual LMMSE, due to the covariance matrix used for ACA-LMMSE is computed only once throughout the transmission duration. We put the conditions on the artificial channel parameters to get the expected mask effect. Simulations display the performance of the proposed method, in terms of MMSE and bit error rate (BER). Indeed, the difference of BER between our method and the theoretical LMMSE is less than 2 dB. © 2013 Elsevier B.V. All rights reserved.

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