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Évaluation dirigée par les données des risques et opportunités pour la planification industrielle et commerciale dans l’industrie automobile
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When, How, and Why Curing Conditions Change the Mechanical Properties of Silica-Free Silicone Elastomers
No full textInternational audienceCommercial RTV-2 silicones, such as Sylgard 184 or RTV 141, are widely utilized in various fast-growing academic fields (e.g., microfluidics, soft robotics, biomedical devices), thanks to their ease of processing, biocompatibility, good mechanical properties, and transparency. This study primarily investigates the structural origins of the significant enhancement in elastomer stiffness and large strain response observed in these silica-free but MD V Q resin-filled systems, as the curing temperature increases. We explicitly reveal the complex structural heterogeneity present within these elastomer networks. First, the evolution of mechanical and swelling behavior of commercial RTV-2 silicones, as a function of curing temperature and time, was monitored. High-resolution solid-state 29 Si NMR analysis revealed that hydrosilylation between cross-linkers and MD^VQ resins proceeds slowly at room temperature and requires a prolonged curing time for complete cross-linking, which contrasts with the typically prescribed 2 days curing time at 23 °C. Double-quantum NMR results stressed that cross-link density evolves over 4 months at room temperature, while no difference is detected among specimens cured at different T ≥ 60 °C. Additionally, low-field solid-state NMR also indicated an increase in the rigid phase fraction of the silicone as the curing temperature rises, matching the trends of stiffness and swelling responses. Furthermore, small-angle X-ray scattering measurements exhibited a significant scattering peak, indicating progressive aggregation with increasing curing temperature, which we attributed to the macroscopic self-structuring of MD^VQ resins. These findings demonstrate that variations in stiffness cannot be attributed to an enhanced cross-linking reaction in these RTV-2 systems but rather imply strengthening through nanostructuration at increasing curing temperature
Crystal structure of 4-(3,5-dimethyl-1,7-diphenyl-1,7-dihydrodipyrazolo[3,4- b :4′,3′- e ]pyridin-4-yl)phenol dimethyl sulfoxide disolvate
No full textInternational audienceA new bispyrazolylpyridine(BPP)-containing derivative, namely, 4-(3,5-dimethyl-1,7-diphenyl-1,7-dihydrodipyrazolo[3,4- b :4′,3′- e ]pyridin-4-yl)phenol ( 1 ), C 27 H 21 N 5 O·2C 2 H 6 OS, has been synthesized by a Hantzsch multicomponent reaction using acetic acid (AcOH) as solvent and copper(II) acetate monohydrate [Cu(OAc) 2 ·H 2 O] as mild oxidant. The structure of the compound was fully characterized by single-crystal X-ray diffraction. The crystallographic study shows that the molecule crystallizes in the triclinic system with space group P 1 , with one molecule per asymmetric unit. Whereas the phenolic substituent in the para position of the pyridine group is highly twisted from the planar bispyrazolopyridine core [56.19 (4)°], the two phenyl rings present on the nitrogen atoms are only slightly distorted [11.77 (5) and 29.17 (5)°]. The crystal structure is consolidated by intermolecular C—H...O hydrogen bonds and π–π stacking interactions
WAXD investigations on the effect of loading history on strain-induced crystallization for a fully formulated filled natural rubber
No full textInternational audienceModelling crystallization under stretch is a key topic for fatigue design of rubber-like antivibration parts. Nevertheless, most of the academic studies consider unfilled natural rubber while the industrial materials are fully formulated compounds filled with carbon blacks and exhibit a highly dissipative visco-elastic behavior. This behavior is very useful for antivibration systems but complicates the characterization and modelling of the phase change, as the addition of fillers and additives brings in numerous additional dissipation sources and intricates the time effects on the thermomechanical response and on crystallization. In this study, we use well resolved WAXD synchrotron measurements to perform in situ measurements under various mechanical protocols. The objective is to characterize the evolution of the triplet {strain, stress, crystallinity index}, and their derivatives, for various time and mechanical solicitations. First, classic load/unload tension tests over a range of strain rates leading to non-equilibrium cases are achieved, to serve as a reference database on the compound studied. Then, a multi-relaxation cyclic test combining static and monotonic steps is applied in order to describe the crystallization state and kinetics around a relaxed state (sometimes called "equilibrium hysteresis"). The results provide a precious database to identify or challenge the existing thermodynamic models, for conditions seldom met in the literature: fully formulated material and various mechanical loading time histories
First evaluation of color K-edge image quality using spectral photon-counting CT combined with two contrast agents: A phantom study
No full textInternational audiencePurpose: The purpose of this study was to assess the image quality of color K-edge imaging obtained with a spectral photon-counting CT (SPCCT) scanner using a spectral phantom with a mixture of iodine-based and gadolinium-based contrast agents. Materials and methods: A clinical SPCCT scanner prototype was used to scan a spectral phantom. Three dedicated cavities were filled with three contrast agents including iodine alone, gadolinium alone and a mixture of both. Two concentrations of 0.5 and 2 mg/mL were evaluated using nine helical PCCT scans at 120 kVp and 150 mAs. Conventional, color iodine and color K-edge gadolinium images were obtained through a material decomposition algorithm using three basis materials (water, iodine, gadolinium). Attenuation (in Hounsfield unit [HU]), iodine and gadolinium concentrations and task-based transfer function (TTF) were measured on each cavity and image. The noise power spectrum (NPS) was calculated on the phantom's background. Results: Color K-edge imaging differentiated iodine and gadolinium but underestimated their concentrations. Gadolinium concentrations were underestimated by 9.4 ± 2.2 (standard deviation [SD]) % and 9.2 ± 1.0 (SD) % for gadolinium alone, 14.9 ± 2.3 (SD) % and 11.4 ± 1.2 (SD) % for the mixture, at 0.5 and 2 mg/mL, respectively. Similar TTF values at 50 % were found for color iodine (0.43 ± 0.01 [SD] mm -1 ) and color K-edge gadolinium (0.45 ± 0.03 (SD) mm -1 ) images for respective cavities at 2 mg/mL but the lowest values were found for color K-edge gadolinium images (0.43 ± 0.01 [SD] mm -1 vs. 0.29 ± 0.01 [SD] mm -1 ) at 0.5 mg/mL. The value of noise magnitude was 24.75 HU, 0.06 mg/mL and 0.03 mg/mL for conventional, color iodine and color K-edge gadolinium images, respectively. Conclusion: Color K-edge imaging helps distinguish between contrast agents while being associated with lownoise magnitude, high-frequency spatial noise and high spatial resolution.</div
Végétalisons nos cours d’eau : les ripisylves, un habitat aux multiples bénéfices
No full textInternational audienceRiparian forests are all forest stands and linear woodlands located alongside watercourses, where the aquatic and terrestrial environments meet. In recent decades, an increasing number of scientific studies have emphasised the ecological, social and economic advantages of preserving and restoring riparian forests. The first part of this article summarises the associated benefits. The second part presents reasons for preserving and restoring riparian forests as a strategy for mitigating climate change and adapting to its effects on rivers, biodiversity and humans. These characteristics mean that the restoration of riparian vegetation is a management measure that should be developed within a well-thought-out, locally adapted framework.La ripisylve désigne l’ensemble des peuplements forestiers et boisements linéaires situés aux abords des cours d'eau, à l’interface entre les milieux aquatique et terrestre. Ces dernières décennies, un nombre croissant d’études scientifiques ont mis en lumière les intérêts écologiques, sociétaux et économiques de la préservation et de la restauration des ripisylves. Dans la première partie de cet article, nous synthétisons les bénéfices associés aux ripisylves. Nous présentons, dans une seconde partie, les éléments soutenant la préservation et la restauration des ripisylves comme des stratégies d’atténuation du changement climatique et d'adaptation à ses effets sur les rivières, la biodiversité et les humains. Ces caractéristiques font de la restauration de la végétation des berges des cours d’eau une mesure de gestion à développer dans les années à venir, dans un cadre réfléchi et adapté aux contraintes locales
Dynamic strain-aging in C-Mn steel welds for nuclear power plants: a multi-scale investigation
No full textInternational audienceCarbon-manganese (C-Mn) steel welds, commonly employed in the secondary circuits of nuclear power plants, are susceptible to Dynamic Strain Aging (DSA). This phenomenon, caused by interactions between interstitial atoms and dislocations during plastic deformation, may significantly affect mechanical properties by inducing hardening and embrittlement. Understanding these effects is critical for predicting long-term weld behavior and ensuring the reliability of nuclear power plant components. In this study, DSA mechanisms and their consequences are explored across various scales through macroscopic tensile testing, in-situ transmission electron microscopy (TEM) tensile experiments, and atom probe tomography (APT), offering a comprehensive understanding of its influence on weld performance.Macroscopic tensile tests conducted at 20°C and 300°C, analyzed using the Kocks-Mecking framework, yield two notable findings. First, despite its thermal activation, dynamic recovery is unexpectedly reduced at 300°C. This reduction enhances the work-hardening rate and mechanical strength, contrary to typical expectations of thermal softening. Second, uniform elongation improves concurrently with mechanical strength at 300°C, as evidenced by Considère’s criterion. TEM observations of tensile-fractured specimens support these results, revealing more elevated dislocation densities at 300°C than at 20°C. These findings confirm a direct correlation between suppressed dynamic recovery and the observed increase not only in strength but also in ductility.To further investigate DSA effects at the nanoscale, in-situ TEM tensile tests were conducted across a temperature range from room temperature to 600°C. The lattice-controlled dislocation motion observed at low temperature transitions progressively to the obstacle-controlled regime, near room temperature. Within the DSA-active range of 150–350°C, plastic deformation is dominated by dislocation bursts instead of continuous individual motion, a characteristic signature of DSA. This behavior aligns with macroscopic observations, linking reduced dynamic recovery to interstitial atom segregation, which hinders dislocation motion. Ex-situ measurements using atom probe tomography evidence the segregation of interstitial atoms to dislocations, in accordance with the in-situ TEM experiments. These results demonstrate how interstitial atoms interactions with dislocations tailor plastic deformation mechanisms at the nano-scale, leading to macroscopic changes in mechanical properties.Finally, a quantitative model based on the Kocks-Mecking framework captures the combined effects of temperature and interstitial atom segregation on dynamic recovery and work hardening. The model predicts a sharp decline in dynamic recovery with increasing nitrogen content, which saturates beyond a critical concentration. Experimental validation through heat-treated samples confirms these predictions: reducing nitrogen content significantly decreases DSA sensitivity, while higher nitrogen concentrations do not produce additional effects on tensile properties.This multi-scale characterization provides critical new insights into the mechanisms underlying DSA in C-Mn steel welds. Notably, under specific conditions, interstitial atoms can enhance tensile properties at 300°C by simultaneously increasing both strength and elongation. These findings challenge traditional assumptions about DSA as purely detrimental, revealing a nuanced understanding of its influence. This work enables more accurate predictions of weld performance over time, directly contributing to safer and more reliable operations of nuclear power plants.Les soudures en acier carbone-manganèse (C-Mn), couramment utilisées dans les circuits secondaires des centrales nucléaires, sont sensibles au vieillissement sous déformation (VSD). Ce phénomène, causé par les interactions entre les atomes interstitiels et les dislocations pendant la déformation plastique, peut affecter de manière significative les propriétés mécaniques des soudures en induisant un durcissement et une fragilisation. Il est essentiel de comprendre ces effets pour prédire le comportement à long terme des soudures et garantir la fiabilité des composants des centrales nucléaires. Dans cette étude, les mécanismes du VSD et leurs conséquences sont explorés à différentes échelles par le biais d'essais de traction macroscopiques, d'essais de traction in situ par microscopie électronique à transmission (MET) et d’analyses par sonde atomique tomographique (SAT), ce qui permet de comprendre l'influence de ces mécanismes sur les propriétés mécaniques des soudures.Des essais de traction macroscopiques réalisés à 20°C et 300°C, analysés à l'aide du modèle de Kocks-Mecking, ont permis de faire deux constatations notables. Premièrement, malgré l'activation thermique, la restauration dynamique est réduite de manière inattendue à 300 °C. Cette réduction augmente le taux d'écrouissage et la résistance mécanique, contrairement aux observations habituelles en matière d'adoucissement thermique. Deuxièmement, l'allongement uniforme augmente de manière concomitante à la résistance mécanique à 300°C, comme le montre le critère de Considère. Les observations MET d'éprouvettes rompues en traction confirment ces résultats, révélant des densités de dislocation plus élevées à 300°C qu'à 20°C. Ces résultats établissent une corrélation directe entre la diminution de la restauration dynamique et l'augmentation observée non seulement de la résistance mécanique mais aussi de la ductilité.Pour étudier plus en détail les effets du VSD à l'échelle nanométrique, des essais de traction in-situ au MET ont été réalisés dans une plage de températures allant de la température ambiante à 600°C. Aux basses températures, le mouvement des dislocations est contrôlé par la friction de réseau. Avec l’augmentation de la température, la friction de réseau devient négligeable à partir de la température ambiante. Le mouvement des dislocations est alors athermique, contrôlé par les obstacles de la microstructure. Dans la plage de 150 à 350°C où le VSD est actif, la déformation plastique repose majoritairement sur des avalanches de dislocations au lieu d'un mouvement individuel continu, ce qui est caractéristique du VSD. Ce comportement est cohérent avec les observations macroscopiques, liant la diminution de la restauration dynamique à la ségrégation des atomes interstitiels sur les dislocations, ce qui entrave leur mouvement. Cette ségrégation sur les dislocations est mise en évidence par des mesures ex-situ de sonde atomique tomographique. Ces résultats démontrent comment les interactions entre les atomes interstitiels et les dislocations modifient les mécanismes de déformation plastique à l'échelle nanométrique, entraînant des modifications macroscopiques des propriétés mécaniques.Enfin, un modèle quantitatif basé sur le modèle de Kocks-Mecking permet de décrire les effets combinés de la température et de la ségrégation des atomes interstitiels sur la restauration dynamique et l'écrouissage. Le modèle prédit une forte diminution de la restauration dynamique avec l'augmentation de la teneur en azote, mais une saturation au-delà d'une concentration critique. L’étude expérimentale d’échantillons traités thermiquement confirme ces prévisions : la réduction de la teneur en azote diminue de manière significative la sensibilité au VSD, tandis que des concentrations d'azote plus élevées ne produisent pas d'effets supplémentaires sur les propriétés de résistance à la traction.Cette caractérisation multi-échelle fournit de nouvelles informations cruciales sur les mécanismes qui contrôlent le VSD dans les soudures en acier C-Mn. Notamment, dans des conditions spécifiques, les atomes interstitiels peuvent améliorer les propriétés de traction à 300°C en augmentant simultanément la résistance et l'allongement. Ces résultats remettent en question les hypothèses traditionnelles selon lesquelles le VSD est purement délétère et révèlent une compréhension plus nuancée de son influence. Ce travail permet des prévisions plus précises du comportement mécanique des soudures dans le temps, contribuant directement à une exploitation plus sûre et plus fiable des centrales nucléaires
Photonic bandgap properties of hyperuniform systems self-assembled in a microfluidic channel
No full textTraditional self-assembly methods often rely on densely packed colloidal crystalline structures and have inherent limitations in generating materials with isotropic photonic bandgaps (PBG). This study explores the photonic properties of materials structured according to hyperuniform disordered patterns (HUDS) generated via a hydrodynamic process in a microchannel. This research employs simulations to characterize optical bandgaps and determine the minimum dielectric contrast required for PBG formation in structures based on the templates experimentally formed under various conditions during the hydrodynamic process. The optimal conditions in the hydrodynamic process for realizing PBG have been identified. The findings offer a promising avenue for the large-scale production of isotropic photonic bandgap materials
