Estimation of Ti-17 beta-phase Single-Crystal Elasticity Constants using X-Ray Diffraction measurements and inverse scale transition modelling

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Properties and Microstructure of Thermo-Pressed Wheat Gluten Films: a comparison with Cast Films

International audienceWheat gluten films were prepared by thermo-pressing, and their mechanical properties were compared to those of cast films. The stress−strain relationship was established for films with various amounts of glycerol. Both relationships were quite different, revealing a different network organization. Thermo-pressed films presented higher stress values than cast films, but the effect of the glycerol amount was similar in both cases, an increase of the glycerol amount leading to a decrease of both films stress. The glycerol influence on the strain at break of thermo-pressed films was very limited, with strain values reaching a maximum around 200%. The role of disulfide bridges on themomoulded films mechanical properties was investigated, and it was shown that some rearrangements and a significative protein insolubilization occurred during the process. The effective flow porosity of the protein network for thermo-pressed films was estimated by water capillary rise measurements to about 7%. Scanning electron microscopy was used to obtain some information about the microstructure of both cast and thermo-pressed films

Identification à l'aide de capteurs optiques à réseaux de Bragg des coefficients de dilatation hygroscopiques d'un composite à matrice organique

Cette étude porte sur l'identification des coefficients de dilatation hygroscopique de matériaux composites au moyen d'une nouvelle technique de mesure. Celle-ci repose sur l'insertion de capteurs optiques à réseaux de Bragg au coeur de la structure composite. Cette méthode est dédiée à la mesure de la déformation hygroscopique induite par la diffusion d'humidité dans un composite. L'évolution de la déformation, due à l'absorption d'humidité, a été représentée en fonction de la teneur en eau, afin de caractériser le coefficient de dilatation hygroscopique

Hydration and mechanical properties of arabinoxylans and β-D-glucans films.

Article WOS:000320486000005Arabinoxylans (AX) and (1 -> 3)(1 -> 4)-beta-D-glucans (BG) are the main components of the cell walls in the endosperm of wheat grain. The relative occurrence of these two polysaccharides and the fine structure of the AX are highly variable within the endosperm. Films of AX and BG were used as models of the cell wall to study the impact of polymer structure on the hydration and mechanical properties of the cell walls. Effective moisture diffusivities (D-eff) of AX and BG films were determined from 0 to 95% relative humidity (RH) at 20 degrees C. D-eff was influenced by the water content, and the structure of polysaccharides. Higher D-eff was obtained for films made with highly substituted AX compared to values obtained for films made with BG or lowly substituted AX. Proton dipolar second moments M-2 and water T-2 relaxation times measured by TD-NMR, indicated that the highly branched AX films exhibited a higher nano-porosity, favoring water motions within films. Results from! traction tests showed significant different mechanical properties between the AX and BG films. BG films exhibited much higher extensibility than AX films. Strength and extensibility of AX films decreased with increasing arabinose to xylose ratio. Our results show that the water motions and the mechanical properties of AX and BG films can be linked to the polysaccharide chains interactions that modulate the nanostructure of films

Numerical end experimental investigation of hygro mechanical states of glass fiber reinforced polyester composites experienced by FBG sensors

International audienceThis study is focused on the finite element analysis of the hygro-elastic stresses experienced by unidirectional composite structures instrumented by Fiber Bragg Grating (FBG) sensors. One of the significant advantages of this method is that by taking into account the complex geometry of elaborated specimen and their different constituents with heterogeneous hygroscopic and mechanical properties. In the first time, the obtained results were compared with the results obtained owing to an analytical solution deduced from the simplified concentric cylinders approach. This comparison allows us to evaluate the reliability of the concentric cylinders approach which cannot account for every aspects of the actual geometry of the studied samples. Besides the numerical results were compared to the experimental characterization of the mechanical states deduced from the Fiber Bragg Grating measurements

Durabilité des matériaux composites sous sollicitations hygrothermomécaniques

International audienceThe scope of the paper is to present the key points to be addressed in a durability study in the case composite materials in hygrothermomechanical environments. The experimental aging tests allowing the identificat ion of the diffusive behavior are presented. The induced effects on the mechanical behavior and the hygrothermomechanical coupling phenomenon are also examined.L’objectif de cet article est de présenter les points-clés d’une étude de durabilité pour des matériaux composites soumis à un environnement hygrothermomécanique. La démarche permettant de réaliser des essais de vieillissement afin d’identifier le comportement diffusif est présentée. Les effets induits sur le comportement mécanique et les phénomènes de couplages hygrothermomécaniques sont ensuite examinés

Food contact material for baking: a review on associated chemical risks and technological issues

This article presents an overview on product contact surfaces (PCS) used for baking supports, with a focus on associated neoformed and exogenous contaminants related to these PCSs in the case of baking. Exogenous contaminants are usually brought into the product from the surface contact material of the baking support, and in particular, from antistick coatings (ASC). Due to multiple thermal treatments, the performance of ASCs evolve during ageing, resulting in sticking problems. In addition, there is no European regulation in force to track associated chemical risks. Two main types of ASC material are used: perfluorinated and silicone based ASC. Sticking of bakery products during baking is linked to various aspects such as recipe, baking temperature, the use (or not) of antistick fluids, etc. For instance, silicone coatings are preferred to perfluorinated coatings for yellow dough. Some products, such as biscuits, can be baked directly on steel. A limited amount of literature exists on the risk of chemical transfer from either fluorinated or silicone based coatings to the food. Highly sensitive measurement methods based on liquid chromatograpy coupled to tandem mass spectometry (LC-MS/MS) and/or liquid chromatography-high resolution mass spectrometry (LC-HRMS) have been used for the determination of 13 perfluorinated compounds (including perfluorooctane sulfonate anion (PFOS) and perfluorooctanoic acid (PFOA) in water and pancakes cooked in contact with ASC. Preliminary results (not shown) indicated that contamination was below the regulation threshold when using new cookware equipment (frying pan). Two other PCSs used in baking, aluminium and baking paper, and their associated chemical risks are discussed. Neoformed contaminants are usually due to reactions between inoffensive precursors, which result from the interaction between these precursors and the matrix. The impact of the thermal treatment combined with the evolution of other physical parameters (e.g., moisture, pH, etc.) may result in the formation of neoformed contaminants. The case of the Maillard reaction compounds (MRCs) and of the 3-chloro-1,2-propanediol (3-MCPD) esters and the impact of the pH on those contaminants is discussed. Finally, the technological problem of sticking seems to be closely linked to the condition of the product contact surface, and thus indirectly linked to a higher risk of transfer of exogenous contaminants into the product. Therefore, it appears advisible to develop tools and protocols to assess the condition of baking support undergoing multiple thermal cycles for the benefit of the industry and of the health of consumers.JRC.I.1-Chemical Assessment and Testin