Caracterización térmica y mecánica del EVOH puro procesado por extrusión

Doble titulacióEl EVOH es un copolímero termoplástico etileno-alcohol vinílico. Tiene un gran interés industrial por sus buenas propiedades de barrera lo cual les hace especialmente útiles en los envases alimentarios. La última innovación es la adición de nanoarcilla para minimizar el efecto del agua que altera sus propiedades de barrera. El objetivo del presente estudio es analizar el comportamiento estructural del EVOH puro (Soarnol DC 32 03 F de Nipón Gohsei sin nanoarcilla) en las formas de granza prima extrudida tres veces en la extrusora doble husillo y de los films pasados en una extrusora multicapa. En efecto, ocurren problemas de degradación del polímero durante el procesamiento de mezcla y de conformación de las películas. El análisis de la degradación durante el procesamiento será realizado mediante: - una caracterización térmica de las granzas y de los films a través ensayos estándares de DSC, un fraccionamiento térmico (SSA) y un cálculo del índice de fluidez (MFI). - una caracterización mecánica clásica y a fractura de las películas a través ensayos de tracción y trabajo esencial de fractura (EWF) en DDENT. Los resultados térmicos y mecánicos han permitido identificar una posible reacción química durante el procesamiento de extrusión que tiene por consecuencia un alargamiento de las cadenas por creación de ramificaciones que actúan como defectos en los cristales. Además pueden ocurrir algunos entrecruzamientos puntuales (geles). La probabilidad de su presencia aumenta con los pases del proceso. Por lo tanto, a medida que aumentan los pases, observamos una disminución de la cristalinidad y de la perfección de los cristales, una aumentación de la rigidez y del trabajo necesario para iniciar la deformación plástica, así que una aumentación de la zona plástica en fractura. Finalmente, podemos asegurar de un cambio estructural del EVOH durante el procesamiento de mezcla que puede ser llamado degradación. La consecuencia es la alteración de las propiedades específicas del EVOH y sobre todo la de barrera

Variational assimilation for xenon dynamical forecasts in neutronic using advanced background error covariance matrix modelling

Data assimilation method consists in combining all available pieces of information about a system to obtain optimal estimates of initial states. The different sources of information are weighted according to their accuracy by the means of error covariance matrices. Our purpose here is to evaluate the efficiency of variational data assimilation for the xenon induced oscillations forecasts in nuclear cores. In this paper we focus on the comparison between 3DVAR schemes with optimised background error covariance matrix B and a 4DVAR scheme. Tests were made in twin experiments using a simulation code which implements a mono-dimensional coupled model of xenon dynamics, thermal, and thermal–hydraulic processes. We enlighten the very good efficiency of the 4DVAR scheme as well as good results with the 3DVAR one using a careful multivariate modelling of B

Differential influence of instruments in nuclear core activity evaluation by data assimilation

The global activity fields of a nuclear core can be reconstructed using data assimilation. Data assimilation allows to combine measurements from instruments, and information from a model, to evaluate the best possible activity within the core. We present and apply a specific procedure which evaluates this influence by adding or removing instruments in a given measurement network (possibly empty). The study of various network configurations of instruments in the nuclear core establishes that influence of the instruments depends both on the independant instrumentation location and on the chosen network

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

Assimilation de données pour la dynamique du xénon dans les cœurs de centrale nucléaire

Le calcul de la dynamique xénon requiert un modèle physico-numérique alimenté par des données ou paramètres et des conditions initiales. Les sources d’erreur de ce calcul peuvent provenir à la fois du modèle ainsi que des données. Dans cette thèse, nous proposons d'améliorer la prévision de la dynamique xénon par le recalage de l'état initial de cette dynamique en utilisant toutes les informations disponibles (modèle numérique, estimation a priori de l'état initial et mesures) complétées par le niveau de confiance dans chacune de ces informations. La méthode utilisée est un schéma d’assimilation de données de type 4DVAR. Des expériences jumelles nous permettent d’estimer la qualité des concentrations initiales ainsi recalées. Les résultats rencontrés permettent d'envisager la mise en place d’un outil d’aide au pilotage continuellement réajusté grâce aux mesures in-situ. ABSTRACT : Xenon-135 is a nuclear fission product which is known to be source of undesired roughly one day period density axial oscillations in pressurized water reactors. Xenon dynamics are non linearly coupled to another fission product the iodine-135. Such a coupling represents a challenge for the oscillation prediction. In order to improve xenon estimation, we investigate the feasibility of using variational data assimilation methods. The aim is to obtain a better estimation of initial 1D concentrations of xenon and iodine. Data assimilation techniques are widely used in meteorology and oceanography to improve initial states and forecasts. Such methods combine all kind of information about the system (model, a prior estimate of the true state and data). These information are weighted according to their accuracy expressed in error covariance matrices. The state resulting from the assimilation process is called analysis. 3DVAR and 4DVAR schemes for xenon dynamics are developed within the framework of twin experiments. This means that observations are obtained through numerical computation. Such a procedure allows an evaluation of produced analysis quality. The model developed for this purpose (CIREP1D) includes a monodimensional xenon dynamics linked to a monodimensional thermic and thermohydraulic model. Linear tangent and adjoint of this model are obtained through automatic differentiation. Observations are of three kinds : integrated powers over several nodes, power axial offset and boron concentration. This work figures out improvements on the estimation of iodine and xenon initial concentrations. Such encouraging results allow to set up tuning tool for an operator guiding syste

Robustness of nuclear core activity reconstruction by data assimilation

We apply a data assimilation techniques, inspired from meteorological applications, to perform an optimal reconstruction of the neutronic activity field in a nuclear core. Both measurements, and information coming from a numerical model, are used. We first study the robustness of the method when the amount of measured information decreases. We then study the influence of the nature of the instruments and their spatial repartition on the efficiency of the field reconstruction

Study of Na-Montmorillonite–Polyamide Fiber/Polypropylene Hybrid Composite Prepared by Reactive Melt Mixing

Hybrid composites of polypropylene (PP)/sodium montmorillonite (Na-MMT)/short polyamide fibers (PAfs) were prepared by reactive melt mixing in a Brabender plastograph. To enhance filler interactions within polypropylene, a functionalizing agent (FA) and a coupling agent were added to the Na-MMT and PAfs, respectively. An organic peroxide/sulfur mixture and tetramethylthiuram disulfide as an activator for sulfur were used to functionalize Na-MMT; on the other hand, the PAfs surface was treated using stearic acid. The aim of this study is to investigate how the morphology and the structural properties of 3, 5, and 7 wt% recycled functionalized sodium montmorillonite nanocomposites (f-Na-MMT) are affected by the presence of 5 wt% treated short polyamide fibers (t-PAfs). According to the obtained results, 5 wt% recycled f-Na-MMT/5 wt% t-PAfs/PP hybrid composite showed Na-MMT layers exfoliation. The nucleating effect of f-Na-MMT and t-PAfs was indicated by the differential scanning calorimetry (DSC) measurements. Morphological analysis of the hybrid composites was performed using scanning electron microscope (SEM) and optical polarized microscopy (POM), showing a good dispersion of the fibers with an interesting interfacial adhesion between the PP and t-PAfs phases. Hybrid composites of PP/f-Na-MMT/t-PAfs are considered for automotive industry