Utilisation de méthodes de champ pour étudier les lois de comportement des polymères fondus

Colloque avec actes et comité de lecture. Internationale.On utilise la vélocimétrie laser et la biréfringence d'écoulement pour mesurer les champs de vitesse et de contraintes dans des écoulements de polymères fondus dans des géométries convergentes. La démarche choisie pour valider des lois de comportement rhéologiques consiste à, (a) calculer les vitesses de déformations à partir des mesures de la vitesse, (b) déduire les contraintes en utilisant une loi de comportement basée sur des théories macromoléculaires (Marrucci et Ianniruberto [1]), (c) confronter les contraintes calculées à celles mesurées par biréfringence d'écoulement, (d) itérer sur les valeurs des paramètres non linéaires de la loi choisie jusqu'à réaliser un accord satisfaisant. Dans un premier temps nous nous sommes intéressés aux phénomènes sur l'axe de l'écoulement

Evaluation of a tube-based constitutive equation using conventional and planar elongation flow optical rheometers

The original publication is available at http://www.springerlink.comInternational audienceThe predictions of the Marrucci and Ianniruberto model (2003) have been studied in various rheometric flows as well as a planar elongation flow using the 'optical elongational rheometer' technique proposed by Schuberth and Münstedt (Rheol Acta 47:111-119, 2008). This combination of techniques extended the range of pertinence of the model to high-extensional rates. Relevance of the identified parameters with respect to tube theory was then discussed

Soft Listeria: actin-based propulsion of liquid drops

We study the motion of oil drops propelled by actin polymerization in cell extracts. Drops deform and acquire a pear-like shape under the action of the elastic stresses exerted by the actin comet. We solve this free boundary problem and calculate the drop shape taking into account the elasticity of the actin gel and the variation of the polymerization velocity with normal stress. The pressure balance on the liquid drop imposes a zero propulsive force if gradients in surface tension or internal pressure are not taken into account. Quantitative parameters of actin polymerization are obtained by fitting theory to experiment.Comment: 5 pages, 4 figure

Mesures de champ dans des écoulements complexes pour l'identification du comportement d'un polyéthylène basse densité

http://hdl.handle.net/2042/16620International audienceIn this study, we present preliminary experimental results for the evaluation and identification of constitutive equations for viscoelastic polymer melts using flow field measurements such as Laser-Doppler velocimetry and flow-induced birefringence. We focus on the influence of temperature and flow rate on the vortex size of a secondary flow of a low density polyethylene which strongly depends on balance between shear and extensional rheological properties of the material. Further work will show that this method, coupled with numerical simulations, can be applied to identify non-linear parameters of a Pom-pom like constitutive equation by using an inverse analysis procedure = On présente les premiers résultats d'une étude dont le contexte est l'évaluation et l'identification de lois de comportement par l'utilisation de méthodes de mesures de champ telles que la vélocimétrie Laser-Doppler et la biréfringence d'écoulement. On s'intéresse à l'influence de la température et du débit sur la taille de recirculations dans l'écoulement d'un polyéthylène basse densité. La taille de ces recirculations est fortement dépendante des propriétés mécaniques relatives du matériau en cisaillement et élongation. Ces mesures seront utilisées pour l'identification d'un modèle de type pom-pom par une méthode d'identification inverse

Investigation of LDPE converging flows using fieldwise measurements techniques

International audienceThis study is devoted to the analysis of the secondary flow of a low-density polyethylene melt occurring in the entrance region of extrusion dies. From a processing point of view, the appearance of secondary flows can lead to flow instabilities (as observed for helical defect in circular channels) and polymer degradation (due to long residence times). The flow is investigated in the entrance region of a flow channel by means of both Laser Doppler Velocimetry (LDV) and Flow Induced Birefringence (FIB) using a transparent slit die with a planar contraction of 14:1. We focus on the influence of temperature T and flow rate Q on the vortex size of the secondary flow, which strongly depends on balance between shear and extensional rheological properties of the material, as previously observed by means of LDV. The same dependence with T and Q is also observed on FIB patterns, in which one can identify a boundary line which exhibits a strong contrast in the birefringence pattern. This contrast could be related to the fact that molecular conformations (and consequently the birefringence pattern) change locally due to a different thermomechanical history, which indeed would occur close to the vortex boundary

Dynamics of a deformable self-propelled particle under external forcing

We investigate dynamics of a self-propelled deformable particle under external field in two dimensions based on the model equations for the center of mass and a tensor variable characterizing deformations. We consider two kinds of external force. One is a gravitational-like force which enters additively in the time-evolution equation for the center of mass. The other is an electric-like force supposing that a dipole moment is induced in the particle. This force is added to the equation for the deformation tensor. It is shown that a rich variety of dynamics appears by changing the strength of the forces and the migration velocity of self-propelled particle

Contribution à la mise en place d’un microscope à force Atomique métrologique (mAFM) : Conception d’une tête AFM métrologique et caractérisation métrologique de l’instrument.

Scanning probe microscopes are very well used for characterization at the manometer scale. To ensure the measurement coherency and the accuracy of the results, those microscopes need to be periodically calibrated. It’s done thanks to reference standards whose dimensional characteristics are measured by a metrological atomic force microscope (mAFM) for example.The aim of this thesis work is the improvement of the metrological AFM of the LNE in order to reduce the measurement uncertainty. To reach this goal, a thermally passive AFM head has been developed and integrated on the instrument. It contains an original system to measure the cantilever deflexion and thus detect the force acting between the sample and the tip. This system is based on the optical beam deflection method but allow deporting the heat sources outside the instrument. To reach this goal, a new specific sensor has been developed. It is based on a four quadrant optic fibre bundle that contains 40 000 micro-fibre and which is ideal to replace the existing four quadrant photodiode and its conditioning electronic circuit with the bundle and its conditioning electronic circuit placed outside the instrument. This sensor has been modelled, and experimentally validated.The Developed AFM head which integrates the deflection measurement system is then thermally passive. Its design is based on the complete dissociation of the metrological loop and the structural loop. The metrological loop is made of Zerodur® in other to acquire an excellent mechanical and thermal stability and thus reduce the thermal dilatation. For the same reason, the AFM head support frame is fully made of Invar. The AFM head is placed on a motorized frame based on three piezo-leg motors (tripod) to make the tip/sample approach but also to set the interferometer signal quality. The interferometer signal is improved by combining the linear displacements of the three motors to generate small rotations. This allows setting the parallelism of the mirrors linked to the head with those linked to the translation stage.Once the AFM head integrated on the instrument, the assembly is characterized in order to establish the uncertainty budget. Different uncertainty components have been experimentally evaluated as for example: the interferometer non linearity, the drift of the XYZ position, the parasitic rotations of the translation stage, the Abbe error, the roughness and the flatness of the mirrors and the dead path errors. The impact of the each component has been quantified and listed in the uncertainty budget. This allowed getting a first estimation of the combined uncertainty of the instrument.Les microscopes en champ proche sont très largement utilisés pour caractériser des propriétés physiques à l’échelle du nanomètre. Afin d’assurer la cohérence et l’exactitude des mesures dimensionnelles qu’ils retournent, ces microscopes ont besoin d’être étalonnés périodiquement. Le raccordement à la définition du mètre SI est assuré par le biais d’étalons de transfert dont les caractéristiques dimensionnelles sont étalonnées à l’aide d’un Microscope à Force Atomique métrologique (mAFM).Les travaux de thèse portent sur la contribution à la mise en place du Microscope à Force Atomique métrologique du LNE dans le but de caractériser et réduire l’incertitude de mesure. Une tête AFM passive thermiquement et spécifiquement conçue pour des applications de nanométrologie dimensionnelle a été développée et intégrée au mAFM. Elle comporte un système original pour mesurer les déflexions du levier nécessaire à la détection des forces s’exerçant à l’extrémité de la pointe. Il utilise une évolution de la méthode du levier optique qui permet de déporter les sources de chaleurs à l’extérieur de l’instrument. Pour cela, un nouveau capteur a été développé. Il est basé sur l’utilisation d’un bundle composé de 40 000 microfibres optiques structurées en quatre quadrants. Il remplace avantageusement une photodiode quatre quadrants et permet de transporter le signal lumineux jusqu’à des photodiodes placées à l’extérieur de l’instrument. Ce système a été modélisé, caractérisé et validé expérimentalement. La tête AFM ainsi développée est passive thermiquement. Sa conception repose sur la dissociation complète de la chaine métrologique, constituée en Zerodur, afin de lui conférer une excellente stabilité thermique et mécanique. Pour les mêmes raisons, le châssis de la tête qui supporte l’ensemble des composants et notamment le système de mesure des déflexions du levier est entièrement conçu en Invar. Cette tête repose sur une structure motorisée constituée de trois moteurs à reptation permettant l’approche de pointe mais également le réglage des interféromètres. Après intégration de la tête dans le mAFM, l’ensemble de l’instrument a été caractérisé afin d’établir son bilan d’incertitude. Plusieurs composantes ont ainsi été évaluées expérimentalement comme la non-linéarité et la stabilité de la mesure de position par interférométrie, les rotations parasites du scanner, les erreurs d’Abbe, les défauts de rugosité et de planéité des miroirs ainsi que les erreurs de bras mort. L’impact de chaque composante a été quantifié et listé dans le bilan d’incertitude. Ces travaux ont permis d’avoir une première estimation de l’incertitude de mesure du mAFM

Grain growth competition and formation of grain boundaries during solidification of hcp alloys

Grain growth competition during directional solidification of a polycrystal with hexagonal (hcp) symmetry (Mg-1wt%Gd alloy) is studied by phase-field modeling, exploring the effect of the temperature gradient G on the resulting grain boundary (GB) orientation selection. Results show that selection mechanisms and scaling laws derived for cubic (fcc, bcc) crystals also apply to hcp materials (within their basal plane), provided a re-estimation of fitting parameters and re-scaling to account for the sixfold symmetry. While grain growth competition remains stochastic with rare events of unexpected elimination or side-branching along the developing GBs, we also confirm an overall transition from a geometrical limit to a favorably oriented grain limit behavior with an increase of thermal gradient within the dendritic regime, and the progressive alignment of dendrites and GBs toward the temperature gradient direction with an increase of G during the dendritic-to-cellular morphological transition. Comparisons with original thin-sample directional solidification experiments show a qualitative agreement with PF results, yet with notable discrepancies, which nonetheless can be explained based on the stochastic variability of selected GB orientations, and the statistically limited experimental sample size. Overall, our results extend the understanding of GB formation and grain growth competition during solidification of hcp materials, and the effect of thermal conditions, nonetheless concluding on the challenges of extending the current studies to three dimensions, and the need for much broader (statistically significant) data sets of GB orientation selected under well-identified solidification conditions

Marketing and Innovation Process in Agri-Food Companies: Analysis via the Stage-Gate Model

The uncertainty that characterises the development of new products has become one of the major concerns of management professionals and researchers. A new marketing approach focusing on the synergy between creativity, innovation, and marketing skills has underlined the importance of marketing efforts in the success of new products throughout the innovation process. In this article, we highlight the innovation process adopted by agri-food companies by examining the deployment of marketing activities in their innovation process. For this purpose, we adopted the „Stage-Gate System” (SGS) model developed by Cooper et al. (2016), a proven method for managing product development projects in the manufacturing sector. In addition, by mobilising dependency and influence matrices, we situate the place given to marketing in the new product development process while emphasising the importance of cross-functional collaboration. To carry out this research, we opted for a qualitative exploratory method at six companies, and we used a triangulation of analysis methods: content analysis, cognitive content analysis, and processual analysis. For the modelling of process mapping, we drew inspiration from the Stage-Gate System innovation process model. The stages of the innovation process and the theoretical links identified in the SGS model are confirmed by the findings of the empirical study, except that economic profitability and cost optimisation take precedence over the needs of target customers, which may restrict the success of the new product launch