HOT HARDNESS MEASUREMENTS ON MATERIALS UP TO 600 °C DURING THE FIRST HOUR OF USING

In the aeronautical field, materials are used in severe environmental conditions (temperature, atmosphere, exposure time ...), particularly for engine applications. In order to characterize the use of these materials in the evaluation of their properties, it is necessary to carry out tests in conditions close to their operating environment. Hot hardness is a simple method which can be applied on many different materials such as oxidized layers, coatings, composite materials, brazing cords, additive manufacturing materials. ONERA is developing micromechanical characterization means to carry out Vickers microhardness tests from room temperature up to 600 °C. In principle, a pyramidal punch is applied on the surface of a material and the applied load is continuously measured during indenter’s moving in the material. The material is tested locally under conditions close to the actual conditions of employment. The goal of this research is to improve microindentation in order to achieve temperature test campaigns up to 600 °C under a controlled atmosphere of argon and to validate a method to produce a series of results during the first hour of using up to 600 °C. Stainless material is studied to compare the evolution of its hot hardness properties versus different parameters such as load, holding time at the maximum load, atmosphere, and thermal duration. A discussion about these measurements and the technical limits of hot hardness technology is presented

Caractérisation du vieillissement d’une résine époxy par nanoindentation à haute température

International audienceThis article aims to understand better the mechanical properties and behavior of organic matrix composite materials under elevated temperature conditions. Two specific specimens of cured RTM6 epoxy resin are tested with DMA analysis: one being unaged and the other one aged for 5000 h at 130 °C under ambient air. Anti-plasticization effects seem to occur on aged resin. Series of nano-indentation tests are carried out from the surface to the core of the sample so as to measure gradient properties of the resin, at temperatures up to 150 °C using a high temperature indentation machine prototype. Thermo-oxidation phenomena involve oxidized layer formation during thermal ageing of the epoxy resin which is characterized through measurements of indentation Young’s modulus. After aged treatment, the variation of Young’s modulus of the oxidized layer at the surface of the sample is not clearly affected by the increasing test temperature whereas Young’s modulus of the core of the sample is decreasing significantly with the temperature test as on unaged epoxy resin. Thus, asymptotic growing of the oxidized layer is then confirmed.Cet article a pour but de mieux comprendre l’évolution des propriétés mécaniques des matrices organiques utilisées dans les matériaux composites à des températures élevées. Deux résines époxy RTM6 sont testées en DMA : l’une non vieillie et l’autre ayant subi un vieillissement de 5000 h à 130 °C sous air ambiant. Des effets dus à l’anti-plastification de la résine sont remarqués sur la résine vieillie. Des séries de tests de nanoindentation sont menées de la surface jusqu’au cœur de l’échantillon pour mesurer les gradients de propriétés de la résine, jusqu’à une température de test de 150 °C en utilisant un moyen prototype de nanoindentation à haute température. Des phénomènes de thermo-oxydation entraînent la formation d’une couche oxydée durant le vieillissement thermique de la résine époxy, qui est caractérisée en mesurant le module d’Young. Après vieillissement, la variation du module d’Young de la couche oxydée n’est pas clairement affectée par l’accroissement de la température alors que le module d’Young du cœur de l’échantillon décroît significativement avec la température comme sur la résine non vieillie. La croissance asymptotique de la couche oxydée est ainsi confirmée

Non-destructive testing of composite plates by holographic vibrometry

We report on a wide-field optical monitoring method for revealing local delaminations in sandwich-type composite plates at video-rate by holographic vibrometry. Non-contact measurements of low frequency flexural waves is performed with time-averaged heterodyne holography. It enables narrowband imaging of local out-of-plane nanometric vibration amplitudes under sinusoidal excitation, and reveals delamination defects, which cause local resonances of flexural waves. The size of the defect can be estimated from the first resonance frequency of the flexural wave and the mechanical parameters of the observed layer of the composite plate

Characterization of Cs vapor cell coated with octadecyltrichlorosilane using coherent population trapping spectroscopy

We report the realization and characterization using coherent population trapping (CPT) spectroscopy of an octadecyltrichlorosilane (OTS)-coated centimeter-scale Cs vapor cell. The dual-structure of the resonance lineshape, with presence of a narrow structure line at the top of a Doppler-broadened structure, is clearly observed. The linewidth of the narrow resonance is compared to the linewidth of an evacuated Cs cell and of a buffer gas Cs cell of similar size. The Cs-OTS adsorption energy is measured to be (0.42 $\pm$ 0.03) eV, leading to a clock frequency shift rate of $2.7\times10^{-9}/$K in fractional unit. A hyperfine population lifetime, $T_1$, and a microwave coherence lifetime, $T_2$, of 1.6 and 0.5 ms are reported, corresponding to about 37 and 12 useful bounces, respectively. Atomic-motion induced Ramsey narrowing of dark resonances is observed in Cs-OTS cells by reducing the optical beam diameter. Ramsey CPT fringes are detected using a pulsed CPT interrogation scheme. Potential applications of the Cs-OTS cell to the development of a vapor cell atomic clock are discussed.Comment: 33 pages, 13 figure

Cylindrical vector beams for rapid polarization-dependent measurements in atomic systems

We demonstrate the use of cylindrical vector beams - beams with spatially varying polarization - for detecting and preparing the spin of a warm rubidium vapor in a spatially dependent manner. We show that a modified probe vector beam can serve as an atomic spin analyzer for an optically pumped medium, which spatially modulates absorption of the beam. We also demonstrate space-variant atomic spin by optical pumping with the vector beams. The beams are thus beneficial for making singleshot polarization-dependent measurements, as well as for providing a means of preparing samples with position-dependent spin.Comment: 8 pages, 5 figures. Accepted in Optics Expres

Sub-Doppler spectroscopy of the near-UV Cs atom 6S1/2_{1/2}-7P1/2_{1/2} transition in a microfabricated vapor cell

We report on the characterization of sub-Doppler resonances detected by probing the 6S$_{1/2}$-7P$_{1/2}$ transition of Cs atom at 459 nm in a microfabricated vapor cell. The dependence of the sub-Doppler resonance (linewidth, amplitude) on some key experimental parameters, including the laser intensity and the cell temperature, is investigated. These narrow atomic resonances are of interest for high-resolution spectroscopy, instrumentation, and may constitute the basis of a near-UV microcell optical standard

IR thermography for lightning-strike damage monitoring in composite materials

International audienceThe increasing tendency to substitute metallic parts of aircrafts by lighter composite structures comes with other issues. One of them is the resistance of composite materials to lightning strike. The present paper illustrates how the use of infrared thermography can improve the understanding of lightning-strike induced damage and assess its severity. It is based on an experimental campaign carried out in ONERA: several carbon/epoxy composite samples, with or without specific protection, were impacted by lightning arcs of various current levels. An infrared camera was used during and after those tests to monitor and analyze the resulting damage inside the samples

Investigations for a Miniature Optical Frequency Reference Based on High-Contrast Sub-Doppler Resonance in a MEMS Cesium Vapor Cell

International audienceMany of modern quantum technologies require the development of high-performance and low-power consumption miniaturized devices such as laser systems, atomic clocks, magnetometers and other quantum sensors. These instruments are to date often based on the use of chip-size diode lasers and microfabricated (MEMS) cells filled with alkali atoms [1]. An interesting challenge concerns the development of miniaturized optical frequency references (OFR). Different approaches have been engaged in this direction. One of the most successful example is a rubidium microcell-based OFR, involving the two-photon spectroscopy technique. This approach has recently demonstrated a remarkable frequency stability level of 4.4×10–12 at 1 s [2]. The present study is focused on a simple alternative approach based on sub-Doppler spectroscopy (SDS) with counter-propagating light beams. We propose to use dual-frequency light beams with orthogonal linear polarizations and frequency difference w1–w2 = Dhfs, with Dhfs the frequency of the atom ground-state hyper-fine splitting. First dual-frequency sub-Doppler spectroscopy (DF SDS) experiments have been performed with cmscale cells [3,4]. In the present study, we present preliminary spectroscopy and frequency stability results of alaser stabilized using DF SDS with a Cs vapor microfabricated cell [5] (Fig.1a). An extended-cavity diode laser (ECDL) source and a Mach-Zehnder intensity EOM are used to obtain the dual-frequency light field. A forward beam goes through the cell and is then reflected by a mirror to create the backward beam

Impact de l'obésité sur la détection oro-sensorielle des lipides alimentaires chez la souris et chez l'Homme

La gustation est une composante essentielle de la détection oro-sensorielle des lipides alimentaires. La liaison des AGLC sur le récepteur CD36 joue un rôle prépondérant dans cette lipido-détection orale chez la souris et très probablement chez l Homme. En effet, elle intervient dans le choix alimentaire (sensibilité aux lipides) ainsi que dans la préparation de l organisme à l arrivée de lipides. Ce sensing oral des lipides est fortement régulé. Comme l obésité semble être responsable d une altération de la détection des saveurs primaires, l objectif de cette thèse a été d explorer si l obésité peut également être à l origine de perturbations de la détection orale des lipides à la fois chez l Homme et chez la souris. Nos résultats chez l Homme indiquent qu il existe une altération de la lipido-détection orale chez certains sujets obèses. Nous avons montré que ces derniers présentaient une consommation accrue en lipides. De plus, la sécrétion précoce de triglycérides plasmatiques induite par une stimulation orale observée chez les sujets minces n est plus reproduite chez les sujets obèses. Chez la souris, il a été montré que l obésité provoque une diminution de la sensibilité gustative aux lipides alimentaires. Ce phénomène est la conséquence d une dérégulation de la signalisation calcique CD36-dépendante au niveau des cellules gustatives. Chez ces animaux, la stimulation orale lipidique entraîne, comme chez l Homme, une augmentation transitoire de la triglycéridémie qui pourrait être responsable d une réduction de la taille du repas (rassasiement). En conclusion, l obésité affecte la lipido-détection orale chez l Homme et la souris. Le défaut de détection des lipides alimentaires associé à l abolition de la sécrétion précoce de triglycérides plasmatiques chez les sujets obèses pourrait être à l origine d une perturbation de la régulation de la prise alimentaire, entraînant une surconsommation d aliments riches en lipides et renforçant ainsi l obésitéGustation is an essential parameter in the oro-sensory detection of dietary lipids. In mice and most likely in humans, the binding of long-chain fatty acids to the CD36 receptor plays a major role in this oral fat detection. Gustation is involved in the food choice (fat sensitivity) as well as in the preparation of the body to the fat inflow. This oral lipid sensing is highly regulated. As obesity seems to be responsible for an alteration of the basic tastes detection, the aim of this thesis was to investigate whether obesity can impair the oral lipid detection in both mice and humans. In humans, our data show that there is an alteration of the oral fat detection in some obese subjects who have a higher lipid consumption than the other subjects. Besides, an early secretion of plasma triglycerides induced by an oral fat stimulation was observed in lean subjects but not in obese ones. In mice, a decrease in the dietary lipids taste sensitivity was shown to be caused by obesity. This is the consequence of a deregulation of the CD36-dependent calcium signalling in taste cells. In these mice, as in humans, the oral fat stimulation leads to a temporary increase in the blood triglyceride level which might be responsible for a reduced meal size (satiety). To conclude, obesity impairs oral lipid detection in both mice and humans. An altered dietary fat detection associated with an abolition of the early secretion of plasma triglycerides in obese people might induce an impaired regulation of the food intake, leading to an overconsumption of lipid-rich foods, and so a reinforcement of obesityDIJON-BU Doc.électronique (212319901) / SudocSudocFranceF

The oral lipid sensor GPR120 is not indispensable for the orosensory detectionof dietary lipids in the mouse

International audienceImplication of the long-chain fatty acid (LCFA) receptor GPR120, also termed free fatty acid receptor 4 (FFAR4), in the taste-guided preference for lipids is a matter of debate. To further unravel the role of GPR120 in the "taste of fat", the present study was conducted on GPR120-null mice and their wild-type littermates. Using a combination of morphological (i.e. immunohistochemical staining of circumvallate papillae - CVP), behavioral (i.e. two-bottle preference tests, licking tests and conditioned taste aversion) and functional studies (i.e. calcium imaging in freshly isolated taste bud cells - TBC), we show that absence of GPR120 in oral cavity was not associated with changes in i) the gross anatomy of CVP, ii) the LCFA-mediated increases in [Ca2+]i, iii) the preference for oily and LCFA solutions and iv) the conditioned avoidance of LCFA solutions. In contrast, the rise in [Ca2+]i triggered by grifolic acid (GA), a specific GPR120 agonist, was dramatically curtailed when GPR120 gene was lacking. Taken together these data demonstrate that activation of lingual GPR120 and preference for fat are disconnected, suggesting that GPR120 expressed in TBC is not absolutely required for the oral fat detection in the mouse