Modélisation des propriétés mécaniques de tubes composites tressés SiCf/SiC

International audienceAfin d'améliorer la sécurité et l'optimisation des ressources en uranium, le CEA développe les réacteurs de fission de IVème génération. Ils proposent alors plusieurs modèles pour confiner le matériau fissible dont le concept aiguille utilisant des tubes CMC SiCf/SiC. Le dimensionnement de structures tubulaires en CMC de faible diamètre et de faible épaisseur n'est pas une chose aisée puisque peu d'études à travers le monde portent sur ce sujet. Notre travail est divisé en deux parties i) mettre au point une méthode permettant de faire des essais de traction et de pression interne sur de tels tubes ii) créer un modèle numérique pour simuler le comportement de ces tubes et permettre leur dimensionnement. Cet article traite principalement de l'adaptation de la géométrie à partir du logiciel Gentools développé au laboratoire et qui permet le maillage de composites tissés multicouches

Oxidation of Silicon Carbide Composites for Nuclear Applications at Very High Temperatures in Steam

Single-rod oxidation and quench experiments at very high temperatures in steam atmosphere were conducted with advanced, nuclear grade SiCf/SiC CMC cladding tube segments. A transient experiment was performed until severe local degradation of the sample at maximum temperature of approximately 1845 °C. The degradation was caused by complete consumption of the external CVD-SiC sealcoat, resulting in steam access to the fiber–matrix composite with less corrosion resistance. Approaching these very high temperatures was accompanied by accelerated gas release mainly of H2 and CO2, the formation of surface bubbles and white smoke. Three one-hour isothermal tests at 1700 °C in steam with final water flooding and one three-hour experiment with fast cool-down in Ar atmosphere were run under nominally identical conditions. All isothermally tested samples survived the tests without any macroscopic degradation. The mechanical performance of these quenched clad segments was not significantly affected, while maintaining a high capability to tolerate damages. Despite these harsh exposure conditions, load transfer between SiC fibers and matrix remained efficient, allowing the composites to accommodate deformation

A Finite Fracture Approach for Determining the Fracture Onset of a Brazed SiC Specimen

AbstractThe failure initiation of a brazed sample made of silicon carbide substrates and submitted to bending is analyzed with the help of a criterion which combines a maximum incremental energy release rate and a maximum tensile stress conditions. Two different modes of cracking are considered to develop in the vicinity of the free edge between the brazed layer and the ceramic substrate: edge debonding and substrate cracking. The comparison of the predictions with the experimental results allows estimating the fracture properties of the bonding

Estimation de la diffusivité thermique de composites C/SiC sous chargement mécanique

L'accès aux propriétés thermiques des matériaux composites thermostructuraux destinés aux applications nucléaires est un enjeu important pour prévoir leur comportement en condition d'utilisation. Dans un objectif prévisionnel mais également de compréhension des transferts de chaleur, ce travail s'intéresse à l'évaluation des diffusivités thermiques transverses de composites Cf/SiC soumis à un chargement mécanique de type traction. La démarche mise en place s'appuie sur l'utilisation de la méthode flash associée à une analyse du signal par thermographie IR permettant de générer des cartographies de propriétés

Use of a temporary immersion bioreactor system for the sustainable production of thapsigargin in shoot cultures of <i>Thapsia garganica</i>

Abstract Background Thapsigargin and nortrilobolide are sesquiterpene lactones found in the Mediterranean plant Thapsia garganica L. Thapsigargin is a potent inhibitor of the sarco/endoplasmic reticulum calcium ATPase pump, inducing apoptosis in mammalian cells. This mechanism has been used to develop a thapsigargin-based cancer drug first by GenSpera and later Inspyr Therapeutics (Westlake Village, California). However, a stable production of thapsigargin is not established. Results In vitro regeneration from leaf explants, shoot multiplication and rooting of T. garganica was obtained along with the production of thapsigargins in temporary immersion bioreactors (TIBs). Thapsigargin production was enhanced using reduced nutrient supply in combination with methyl jasmonate elicitation treatments. Shoots grown in vitro were able to produce 0.34% and 2.1% dry weight of thapsigargin and nortrilobolide, respectively, while leaves and stems of wild T. garganica plants contain only between 0.1 and 0.5% of thapsigargin and below detectable levels of nortrilobolide. In addition, a real-time reverse transcription PCR (qRT-PCR) study was performed to study the regulatory role of the biosynthetic genes HMG-CoA reductase (HMGR), farnesyl diphosphate synthase (FPPS), epikunzeaol synthase (TgTPS2) and the cytochrome P450 (TgCYP76AE2) of stem, leaf and callus tissues. Nadi staining showed that the thapsigargins are located in secretory ducts within these tissues. Conclusions Shoot regeneration, rooting and biomass growth from leaf explants of T. garganica were achieved, together with a high yield in vitro production of thapsigargin in TIBs

Case Reports1. A Late Presentation of Loeys-Dietz Syndrome: Beware of TGFβ Receptor Mutations in Benign Joint Hypermobility

Background: Thoracic aortic aneurysms (TAA) and dissections are not uncommon causes of sudden death in young adults. Loeys-Dietz syndrome (LDS) is a rare, recently described, autosomal dominant, connective tissue disease characterized by aggressive arterial aneurysms, resulting from mutations in the transforming growth factor beta (TGFβ) receptor genes TGFBR1 and TGFBR2. Mean age at death is 26.1 years, most often due to aortic dissection. We report an unusually late presentation of LDS, diagnosed following elective surgery in a female with a long history of joint hypermobility. Methods: A 51-year-old Caucasian lady complained of chest pain and headache following a dural leak from spinal anaesthesia for an elective ankle arthroscopy. CT scan and echocardiography demonstrated a dilated aortic root and significant aortic regurgitation. MRA demonstrated aortic tortuosity, an infrarenal aortic aneurysm and aneurysms in the left renal and right internal mammary arteries. She underwent aortic root repair and aortic valve replacement. She had a background of long-standing joint pains secondary to hypermobility, easy bruising, unusual fracture susceptibility and mild bronchiectasis. She had one healthy child age 32, after which she suffered a uterine prolapse. Examination revealed mild Marfanoid features. Uvula, skin and ophthalmological examination was normal. Results: Fibrillin-1 testing for Marfan syndrome (MFS) was negative. Detection of a c.1270G > C (p.Gly424Arg) TGFBR2 mutation confirmed the diagnosis of LDS. Losartan was started for vascular protection. Conclusions: LDS is a severe inherited vasculopathy that usually presents in childhood. It is characterized by aortic root dilatation and ascending aneurysms. There is a higher risk of aortic dissection compared with MFS. Clinical features overlap with MFS and Ehlers Danlos syndrome Type IV, but differentiating dysmorphogenic features include ocular hypertelorism, bifid uvula and cleft palate. Echocardiography and MRA or CT scanning from head to pelvis is recommended to establish the extent of vascular involvement. Management involves early surgical intervention, including early valve-sparing aortic root replacement, genetic counselling and close monitoring in pregnancy. Despite being caused by loss of function mutations in either TGFβ receptor, paradoxical activation of TGFβ signalling is seen, suggesting that TGFβ antagonism may confer disease modifying effects similar to those observed in MFS. TGFβ antagonism can be achieved with angiotensin antagonists, such as Losartan, which is able to delay aortic aneurysm development in preclinical models and in patients with MFS. Our case emphasizes the importance of timely recognition of vasculopathy syndromes in patients with hypermobility and the need for early surgical intervention. It also highlights their heterogeneity and the potential for late presentation. Disclosures: The authors have declared no conflicts of interes

Outils de caractérisation thermophysique et modèles numériques pour les composites thermostructuraux à haute température

This work is an original contribution to the study of the thermostructural composite materials thermal behaviour. It aims to develop a methodology with a new experimental device for thermal characterization adapted to this type of material and to model the heat transfer by conduction within these heterogeneous media. The first part deals with prediction of the thermal effective conductivity of stratified composite materials in the three space directions. For that, a multiscale model using a rigorous morphology analysis of the structure and the elementary properties is proposed and implemented. The second part deals with the thermal characterization at high temperature. It shows how to estimate simultaneously the thermal effusivity and the thermal conductivity. The present method is based on the observation of the heating from a plane sample submitted to a continuous excitation generated by Joule effect. Heat transfer is modelled with the quadripole formalism, temperature is here measured on two sides of the sample. The development of both resistive probes for excitation and linear probes for temperature measurements enables the thermal properties measured up to 1000°C. Finally, some experimental and numerical application examples lead to review the obtained results.Ce travail apporte une contribution originale à l'étude du comportement thermique des composites thermostructuraux à haute température. Il se consacre à la fois au développement d'une méthodologie et d'un nouveau dispositif expérimental de caractérisation thermique par contact adapté pour ce type de matériau ainsi qu'à la modélisation des transferts de chaleur par conduction au sein de ces milieux hétérogènes. La première partie du document traite de la prédiction de la conductivité thermique effective de composites stratifiés 2D dans les trois directions de l'espace. Pour cela, une stratégie de modélisation multiéchelle, s'appuyant sur une analyse morphologique précise des matériaux étudiés et sur la connaissance de leurs propriétés élémentaires, est proposée puis appliquée. La seconde partie du document aborde la caractérisation thermique en température et démontre comment identifier simultanément l'effusivité et la conductivité thermique. La méthode développée est fondée sur l'observation de l'échauffement d'un échantillon plan soumis à un créneau de flux généré par Effet Joule. L'écriture du modèle direct (1-D) fait appel au formalisme des quadripôles thermiques, les observables sont les températures en face avant et en face arrière de l'échantillon. La mise au point de sondes résistives et de capteurs de température linéiques, revêtus de faible épaisseur de céramique isolante permet la réalisation de mesures jusqu'à 1000°C. Enfin, divers exemples d'applications expérimentales et numériques conduisent à une analyse critique de l'ensemble des résultat

Outils de caractérisation thermophysique et modèles numériques pour les composites thermostructuraux à haute température

Ce travail apporte une contribution originale à l'étude du comportement thermique des composites thermostructuraux à haute température. Il se consacre à la fois au développement d'une méthodologie et d'un nouveau dispositif expérimental de caractérisation thermique par contact adapté pour ce type de matériau ainsi qu'à la modélisation des transferts de chaleur par conduction au sein de ces milieux hétérogènes. La première partie du document traite de la prédiction de la conductivité thermique effective de composites stratifiés 2D dans les trois directions de léspace. Pour cela, une stratégie de modélisation multiéchelle, s'appuyant sur une analyse morphologique précise des matériaux étudiés et sur la connaissance de leurs propriétés élémentaires, est proposée puis appliquée. La seconde partie du document aborde la caractérisation thermique en température et démontre comment identifier simultanément léffusivité et la conductivité thermique. La méthode développée est fondée sur l'observation de l'échauffement d'un échantillon plan soumis à un créneau de flux généré par effet Joule. L'écriture du modèle direct (1-D) fait appel au formalisme des quadripôles thermiques, les observables sont les températures en face avant et en face arrière de l'échantillon. La mise au point de sondes résistives et de capteurs de température linéiques, revêtus de faible épaisseur de céramique isolante permet la réalisation de mesures jusqu'à 1000°C. Enfin, divers exemples d'applications expérimentales et numériques conduisent à une analyse critique de lénsemble des résultats.This work is an original contribution to the study of the thermostructural composite materials thermal behaviour. It aims to develop a methodology with a new experimental device for thermal characterization adapted to this type of material and to model the heat transfer by conduction within these heterogeneous media. The first part deals with prediction of the thermal effective conductivity of stratified composite materials in the three space directions. For that, a multiscale model using a rigorous morphology analysis of the structure and the elementary properties is proposed and implemented. The second part deals with the thermal characterization at high temperature. It shows how to estimate simultaneously the thermal effusivity and the thermal conductivity. The present method is based on the observation of the heating from a plane sample submitted to a continuous excitation generated by Joule Effect. Heat transfer is modelled with the quadripole formalism, temperature is here measured on two sides of the sample. The development of both resistive probes for excitation and linear probes for temperature measurements enables the thermal properties measured up to 1000°C. Finally, some experimental and numerical application examples lead to review the obtained results

New lipid sources in the insect industry, regulatory aspects and applications

Edible insects constitute a sustainable and alternative source of nutrients: they have potential to become a valuable protein source for addressing animal and human markets addressing part of the global food demand. After protein, the second largest fraction of the insect is constituted of lipids. Lipids can represent 10 to 15% of the insect in dry matter, making this fraction one of the major co-products of insect industry. The composition of the insect fat may change in terms of quantity and composition of fatty acids profile. Insect species, stage of growth, extraction technologies are some parameters that can impact the fat quality. Many applications of insect fat are naturally focusing on animal nutrition to replace vegetal or fish oil in poultry or aqua feed. Health or human food applications are also envisaged to replace vegetal oil or butter in processed foods, and some technical and sensory tests are reported in this review. However, these last applications, concerning food are submitted to the regulation and especially to the Novel Food EU regulation. For these reasons, it is important to have more data about safety and innocuity of insect fats: a first study is dealing with this aspect, showing an absence of toxicity. Finally, some energy or surfactant applications can also be considered

Investigation of the neutron irradiation effects on the SIC/SIC composites at high temperature

International audienceSiC/SiC composites have aroused interest for fusion and fission nuclear applications due to their thermomechanical properties at high temperature and behavior under irradiation (low swelling, neutron transparency, …), essentially as core materials. In this aim, the CEA has been working on the manufacture and the development of tubular SiC/SiC composites cladding elements for more than a decade. During this period, an optimization of the mechanical properties and the mastering of the manufacturing process have been conducted. Third generation SiC fibers, Hi-Nicalon S and Tyranno SA3, and high-purity CVI pyrocarbon interphase and SiC matrix have been employed for their expected behavior under irradiation. However, the latter consequences have to be properly evaluated. Different types of materials have then been produced for several irradiations. Firstly, the manufacturing process and the materials characterization will be described as the irradiations conditions. The CROCUS irradiation was aimed to determine the mechanical behavior of SiC/SiC minicomposites and of various brazing fillers while the CEDRIC irradiation had as objective to follow their creep at high temperature (600 – 1000°C). The TIRAMISU purpose was to evaluate the effect of high-doses (> 100 dpa) at the Sodium Fast Reactor temperature (550°C). The aftermath of these irradiations on the materials dimensions (swelling) as well as on its structure (fibers, interphase) and mechanical properties will then be evaluated