Publications

The effect of increased productivity in L-PBF manufacturing on the metal dusting resistance of Inconel 625 was studied at 610 ◦C. Two sets of processing parameters were tested: the standard parameters given by the machine manufacturer and degraded parameters with increased scan speed and hatching distance. The materials obtained with degraded parameters presented numerous lacks of fusion at the surface and exhibited significantly shorter incubation times before corrosion. Carburisation was preferentially localised around the defects where the oxide scale was less protective and where the confinement of the atmosphere could result in an increase of the local carbon activity.

The Proper Generalized Decomposition (PGD) is a Model Order Reduction framework that has been proposed to be able to do parametric analysis of physical problems. These parameters may include material properties, boundary conditions, etc. With this framework most of the computation may done in an off-line stage allowing to perform real time simulation in a variety of situations. Nevertheless, this scheme may lose its efficiency where the domain itself is also considered as “a parameter”. Optimal transport techniques, on the other hand, have demonstrated exceptional performance in interpolating different types of fields described over geometrical domains with varying shapes. Hence trying allying both techniques is quite natural. The core idea is that PGD handles the parametric solution, while the optimal transport-based methodology transports the solution for a family of domains defined by geometrical parameters such as lengths, radii, thicknesses, etc. In this first attempt the associated methodology is proposed and apply in simple 1D and 2D cases showing interesting performances.

Monitoring a deep geological repository for radioactive waste during the operational phases relies on a combination of fit-for-purpose numerical simulations and online sensor measurements, both producing complementary massive data, which can then be compared to predict reliable and integrated information (e.g., in a digital twin) reflecting the actual physical evolution of the installation over the long term (i.e., a century), the ultimate objective being to assess that the repository components/processes are effectively following the expected trajectory towards the closure phase. Data prediction involves using historical data and statistical methods to forecast future outcomes, but it faces challenges such as data quality issues, the complexity of real-world data, and the difficulty in balancing model complexity. Feature selection, overfitting, and the interpretability of complex models further contribute to the complexity. Data reconciliation involves aligning model with in situ data, but a major challenge is to create models capturing all the complexity of the real world, encompassing dynamic variables, as well as the residual and complex near-field effects on measurements (e.g., sensors coupling). This difficulty can result in residual discrepancies between simulated and real data, highlighting the challenge of accurately estimating real-world intricacies within predictive models during the reconciliation process. The paper delves into these challenges for complex and instrumented systems (multi-scale, multi-physics, and multi-media), discussing practical applications of machine and deep learning methods in the case study of thermal loading monitoring of a high-level waste (HLW) cell demonstrator (called ALC1605) implemented at Andra’s underground research laboratory.

Une grande quantité de chêne est actuellement considérée de faible qualité, ces bois étant souvent utilisés pour des applications à faible valeur ajoutée comme le bois de chauffage. Le projet TreCEffiQuaS cherche à offrir de meilleurs débouchés aux bois de chêne de qualité secondaire en les transformant en matériaux de construction. Pour cela, les défis à relever étaient de garantir leur résistance par des méthodes non-destructives et de développer des procédés de transformation performants et abordables pour les petites entreprises françaises. De nombreux essais ont été réalisés sur un échantillon représentatif de la ressource française de chêne sessile et pédonculé de qualité secondaire, permettant d’en évaluer les propriétés mécaniques et révélant que 90 % de ces bois peuvent théoriquement être utilisés pour la construction. Des classes de résistance adaptées aux applications de type lamellé-collé ont été proposées, et un algorithme de classement par machine a été développé, basé sur l’orientation des fibres du bois mesurée par scanner industriel. Ce classement par machine s’est révélé beaucoup plus efficace que le classement visuel traditionnel, atteignant un rendement de 83 % pour la classe de résistance DT11, la première utilisable en construction. Une méthode de tronçonnage optimisé pour la transformation de ces bois en lamelles aboutées a aussi été proposée, permettant d’obtenir des rendements matière élevés et des résistances mécaniques satisfaisantes. Ces avancées permettent d’envisager une plus grande valorisation économique des bois de chêne de qualité secondaire, tout en respectant les normes et répondant aux besoins du marché de la construction en produits techniques bois.

New supercritical carbon dioxide (scCO2)-based cutting fluids combining the cooling from scCO2 and lubrication from various additives are investigated in this study. Selected components, including ionic liquids, vegetable and mineral oils, water, and PEG, were introduced into supercritical CO2, and tribological tests were performed on a CNC lathe to analyze their influence on Ti6Al4V/WC-Co contact. Forces and temperatures were recorded to compare the perfomances of the scCO2-lubricant mixtures for future use in machining. The analysis of the apparent friction coefficient and sticking zone showed a noticeable decrease by ionic liquids when combined with scCO2 at a speed of 100 m/min and 4 mL/min delivery flow rate. The other lubricants (water and PEG vegetable oils) performed similarly to standard mineral oil and are less expensive, which could help in developing future low-cost yet effective cooling and lubrication methods for the machining industry.

This study focuses on the elaboration of duplex stainless steels (DSS) from powder mixtures using spark plasma sintering (SPS). Different mass fractions of an austenitic 316L powder and a ferritic 410L one were blended and then sintered by SPS. Microstructural characterizations of the sintered samples obtained from different powder mixtures were performed. They were coupled with marking experiments of the powder particles’ surface. The results showed the formation of martensite within the ferritic powder and at the austenite/ferrite interfaces, following two different mechanisms. In addition, it was found that the width of the martensitic regions is mainly influenced by the diffusion of Cr and Ni from the austenitic to the ferritic powder during sintering. The characterizations revealed that the originality of this approach lies in the particular microstructure obtained after sintering. The characteristic size of the ferritic and austenitic domains in the final material is that of the initial powder particles (up to some hundred microns). Moreover, each domain is formed by equiaxed and isotropic grains, having a size ranging from some microns to some tens of microns. This particular microstructure justifies the use of the term “composite duplex stainless steels” (COMPLEX) for this kind of new DSS.

The study develops an oxidative kinetic model of acrylic‐urethane network during photo‐aging. The kinetic model can track chemical reaction dynamics well and also enables to estimate the network lifetime by counting scission/crosslinking events. Estimated network lifetime is semiquantitively coincided with the one derived from different statistical approach.

This paper aims to assess the effect of layer thickness on the elastoplastic properties of the constituent materials of multilayer coating systems, as well as on the stress and strain fields in the vicinity of the coating/substrate interface. A methodology based on a trust-region reflective optimization algorithm, integrated with finite element analysis of the nanoindentation process, is employed to extract the elastoplastic properties of the distinct layers, constituting multilayer coating. This approach is validated on a CrN/CrAlN multilayer coating systems with varying layer thicknesses from 1 to 0.35 µm, by which Young's modulus (E), yield stress (σy), and work hardening exponent (n) of each individual coating material layer were obtained. The results revealed a reduction in the hardness and Young's modulus of either CrN, or CrAlN coating layer as the layer thickness decreased. Finite element analysis of the nanoindentation process demonstrated that decreasing the coating layer thickness leads to an increase in the plastic deformation within the coatings, which reduces the stress concentration in this area. The simulation results suggest that an optimum thickness of 0.5 μm of CrAlN and CrN monolayer materials would improve the adhesion properties of CrN/CrAlN multilayer coatings.

AbstractPoly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) (PHBV) is a biodegradable polymer with significant potential for use in food packaging. However, its limited melt strength poses a challenge when employing film‐blowing techniques to produce flexible packaging. To overcome this obstacle, we developed blends consisting of 70 wt% PHBV and 30 wt% poly(butylene‐co‐succinate‐co‐adipate) (PBSA). Organic peroxides such as dicumyl peroxide and 2,5‐dimethyl‐2,5‐di‐(tert‐butylperoxy)hexane, were utilized as reactive compatibilizers to enhance the interfacial adhesion between the polymers. Additionally, acetyl tributyl citrate (ATBC) was employed as a plasticizer to improve processability and ductility. The inclusion of organic peroxides resulted in the formation of long‐branched structures, as confirmed by the van‐Gurp‐Palmen plot. The melt flow index decreased from 30 to 9.8 g/10 min without ATBC and 15.5 g/10 min with ATBC. Successful production of blown PHBV/PBSA films was achieved on a pilot scale (bubble height 180 cm). These films exhibited heat‐sealing capability and increased impact strength (7.7 kJ/m2). Moreover, the films maintained a maximum elongation at break of 4% during a 3‐month storage experiment with frozen food. Food safety was assessed through overall migration experiments, and the non‐plasticized films received approval. In conclusion, the compatibilized PHBV/PBSA blends demonstrate great potential as materials for manufacturing film‐blown flexible packaging.

AbstractCarbon fiber (CF)/polyetherketoneketone (PEKK) composites are exposed to Skydrol, a hydraulic fluid made of phosphate esters widely used in the aviation field. The present study investigates Skydrol absorption of CF/PEKK composite layups and the associated PEKK matrix. A significant unexpected increase of Skydrol uptake is observed for cross‐ply composites (0.50%) compared to unidirectional ones (0.06%), independently of ply number. The use of ‘model’ fluids like water and ethanol allows to identify the origin of this anomalous Skydrol absorption in the case of cross‐ply layup. We propose that the latter involves an imbibition process governed by the fluid surface tension and the presence of submicronic cavities. SEM imaging of composite cross‐section after ion beam polishing confirms fiber‐matrix submicronic debonding in the interlaminar region in the cross‐ply composite. SEM–EDX confirms the presence of Skydrol into the submicronic cavities. Despite this anomalous absorption, off‐axis tensile testing as well as ILSS testing show no significant impact of Skydrol on CF/PEKK mechanical properties with less than 10% difference compared to the initial values. Highlights Absorption by diffusion of Skydrol in neat PEKK and CF/PEKK composites, Link between fluid surface tension and anomalous Skydrol absorption, Evidence of submicronic cavities in CF/PEKK composites by means of SEM–EDX, Low impact of Skydrol on CF/PEKK mechanical properties.