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Selection of pultruded composite materials for new, low-carbon emission, lightweight railways tracks, with a focus on mechanics, economics and sustainability
No full textInternational audienceIn the context of decarbonizing transport, the selection of materials for lightweight pultruded composite railway tracks adapted for light trains has been achieved. The candidates are made of thermoplastic PA6 and of acrylic-based resin, as well as thermoset epoxy resin with carbon, glass, basalt and flax fibres. A comparison of the economic cost and carbon emissions of each configuration is presented. 175 tensile, compression and off-axis tests were performed. The elastic properties and sizing allowances are provided. An initial estimate of the ecological cost of materials combinations was assessed using a cradle-to-gate approach on raw materials with the Global Warming Potential (GWP) criterion only. The mechanical properties of composites made of acrylic resin are affected by the nature of the fibres due to poor impregnation and the presence of porosity. Compared to acrylic resin, PA6 resin achieves higher strength values. This suggests that the pultrusion process for PA6 resin is less challenging, as it minimizes the occurrence of porosity. As expected, better properties were obtained with carbon fibres, albeit at a significantly higher ecological cost. Configurations involving basalt fibres offer the best ecological cost/performance ratio. Therefore, basalt fibres open up new possibilities for designing and sizing the next generation of composite railways
Reversible Strong Metal‐Support Interactions in Co/TiO 2 Catalysts Driven by CO 2
No full textInternational audienceStrong metal–support interactions can significantly influence catalytic performance. On titania supports, these interactions often involve the formation of a substoichiometric TiO X overlayer during high‐temperature reduction, which can be reversed by treatments under dioxygen. Under CO 2 hydrogenation conditions, where water is produced, complete removal of the TiO X overlayer has been reported, raising questions about its stability in the presence of a mild oxidant such as CO 2 . In this study, in situ and operando techniques were employed to examine the effect of varying conditions on both the titania overlayer and cobalt species in a Co/TiO 2 catalyst. After reduction at 350 °C, the overlayer consisted of stoichiometric anatase TiO 2 , while cobalt remained partially reduced. Exposure to CO 2 /H 2 at 220 °C enabled complete cobalt reduction without affecting the TiO 2 overlayer. In contrast, pure CO 2 at 220 °C caused overlayer removal and full cobalt oxidation. The impact of this CO 2 ‐mediated reversibility on CO 2 hydrogenation was also evaluated. Although steady‐state activity was largely unaffected, the transient regime showed substantial changes in selectivity and behavior. These results demonstrate that different treatments can strongly influence both the stability and reactivity of Co/TiO 2 catalysts, highlighting the importance of dynamic SMSI effects in CO 2 hydrogenation
Hydrolytic aging-induced embrittlement in short-fiber reinforced polyamide: A micromechanical approach using numerical homogenization
No full textInternational audienceThis work introduces a simulation framework for predicting the durability of 30 wt.% glass fiber reinforced polyamide-66 (PA66-GF30) composites under hydrolytic aging by directly coupling a chemical aging descriptor, the number-average molar mass (Mn), with a local mechanical failure indicator at the matrix level. Unlike prior studies that correlates Mn with global composite properties such as strain-at-break or maximum stress, the proposed approach targets the polyamide matrix, which is primarily affected by hydrolysis, enabling a more physical description of embrittlement. The identification of a local failure indicator was performed using FFT-based numerical homogenization on a representative three-dimensional microstructure, which was reconstructed from high-resolution micro-computed tomography (μCT) data. Accumulated plastic strain (APS) was found as a robust, orientation-independent criterion of failure initiation that correlates linearly with the drop of the Mn. The model predicts a critical Mn of approximately 18kgmol-1 for full embrittlement in PA66, consistent with values of the literature. Failure modeling was validated at the macroscale using FE-based simulations of hydrolyzed injection-molded components loaded in tension mode. This modeling approach is applicable to different hygro-thermal conditions and constitutes one of the first integrated chemo-mechanical simulation methods for fiber-reinforced polyamides. This framework provides a promising route for mechanistic-based lifetime assessment of polymer-based engineering components in hydrolytic environments
A crystal plasticity approach for understanding the effect of microstructure and crystallographic texture on mechanisms of low cycle fatigue
No full textInternational audienceThis study analyzes the effect of crystallographic orientations on fatigue nucleation in Ti alloys. Uniaxial low cycle fatigue tests were performed on additively manufactured Ti–6Al–4V specimens at various strain amplitudes. Slip system activity and orientations were examined using a crystal plasticity model implemented in the Massively Parallel Object Oriented Simulation Environment (MOOSE). Gumbel distributions of Fatigue Indicator Parameters (FIPs) increase proportionally with strain amplitude, while FIPs strongly correlate with cycles to failure. Interestingly, the contribution of shear on basal and prismatic slip systems is strain-dependent, verified through FIP projections on Inverse Pole Figure (IPF) maps. Our analyses show that evolution of backstress and threshold stress on prismatic slips plays the key role. Incorporating [removed] pyramidal slips captured tension–compression asymmetry under cyclic loading, enabling accurate representation of slip competition. Finally, idealized microstructures demonstrate design strategies for fatigue-resistant Ti alloys
A novel application of discrete event simulation as a digital twin for monitoring patient pathways in a hospital in real time
No full textInternational audienceIn this paper, we present a new application of Discrete Event Simulation (DES) as a Digital Twin (DT) for real-time monitoring of patient pathways (PPs) in a hospital. This application, which we call HospiT'Win, enables hospital managers and decision-makers to monitor and manage PPs in real time, supporting informed decision-making. Our approach relies on real-time synchronization between the DT and the PPs at each detected event in the hospital. This approach requires that the initial state of the simulation reflects the current state of the PPs in the hospital. For consistency, in the remainder of this paper, we refer to our approach as the DT of PPs. In this paper, we propose a real-time synchronization mechanism, based on DES, to synchronize the DT of PPs in a hospital with real PPs. This synchronization mechanism was tested using an emulator that mimics the stochastic processes of an outpatient clinic. The use of the proposed synchronization mechanism resulted in a dynamic DT that can track real PPs in hospitals in real time for each detected event. Moreover, this synchronization mechanism allowed for deeper analysis of the behavior of the emulated clinic through the DT and facilitated the detection of unexpected events. Quantitative evaluation showed an average synchronization latency of 0.73 s and an accuracy of 97.7% in tracking patient locations and activities. Based on two facts illustrated in the state of the art: (1) PPs are considered to be one of the tools used to improve and manage health care resources, and (2) DES tools have been used to study and improve these pathways through offline approaches and historical data, we have developed a dynamic virtual representation based on DES that is synchronized to track PPs in the hospital in real time. This approach enables the study of pathway behavior in real time, ultimately supporting hospital managers and decision-makers in improving hospital services and managing resources according to the required level of service and efficiency
Levelized cost of hydrogen: A dynamic simulation-based methodology for heavy-duty refuelling stations
No full textInternational audienceHeavy-duty vehicles generate over 25% of EU road transport greenhouse gas emissions (~6% of total emissions). Achieving the 2050 carbon neutrality target requires large-scale deployment of hydrogen fuel cell vehicles and cost-efficient refuelling infrastructure. This work introduces a novel methodology for assessing the levelized cost of hydrogen (LCOH) in heavy-duty refuelling stations by integrating thermodynamic simulations of station operation with techno-economic cost analysis. The thermodynamic model, HyFill, partially validated, predicts gas temperature in the tank within ±3 °C during refuelling and defueling. Capital cost estimates benchmarked against four vendor quotes achieve ±10% accuracy. Sensitivity analyses on model parameters and operational scenarios identify the discount rate and station utilization as dominant cost drivers. Additionally, a randomized operational scenario effectively approximates daily station behaviour, enabling robust LCOH evaluation where detailed data are unavailable. This integrated approach provides a more rigorous and practical framework for optimizing heavy-duty hydrogen refuelling station design and investment decisions
DESIGN AND MODELLING OF KNUDSEN MICROPUMPS FABRICATED VIA ADVANCED LASER MANUFACTURING
No full textInternational audienceKnudsen pumps are promising candidates for gas pumping in a variety of scientific and industrial applications involving MEMS devices for hydrogen transfer, gas chromatography, aerosol sampling, heat pumps, biomedical systems and sensors etc. These pumps exploit the phenomenon of thermal transpiration, where gas under rarefied conditions flows along a channel due to temperature gradient. This enables gas transport without moving parts, resulting in vibration-free operation, an important feature for miniaturized applications [1].For applications operating at atmospheric pressure, creating optimal rarefied conditions requires submicron-diameter channels, which is technically challenging. Only a few Knudsen pump prototypes have been reported in the literature, most of which are fabricated using Deep Reactive Ion Etching (DRIE) [2], wet etching [3], or porous materials [4]. DRIE enables the fabrication of channels with dimensions down to 1 μm, but with low aspect ratios (length/diameter ≈ 20) which impose constraints on thermal management. Porous materials contain natural defects that can restrict gas flow and reduce efficiency.In this work, two Knudsen pumps for over-and sub-atmospheric applications were modeled and designed, taking into consideration the manufacturing capabilities of advanced laser fabrication techniques based on Bessel beams [5] and Selective Laser-Induced Etching (SLE) [6]. Bessel beams enables fabrication of high length-to-radius ratio (>100) nanochannels with diameters down to few nanometers and high writing speeds up to 1000 channels per second. SLE enables the fabrication of precise 3D structures and channels with length-to-radius ratios greater than 50 and diameters down to 3 μm.</div
Comparison of the Physicochemical Properties of Coated and Intercalated Chitosan–Clay Systems: an Inverse Gas Chromatography Approach
No full textInternational audienceThis study aims to investigate the surface and interfacial physicochemical properties of chitosan (CS)‐coated bentonite (CSBt) and CS‐intercalated Na + ‐montmorillonite biocomposites (CSMMT). The structural and surface characteristics of these two CS‐based biocomposites were analyzed using thermogravimetric analysis (TGA), Fourier transform infrared (FTIR) spectroscopy, nitrogen adsorption, X‐ray diffraction (XRD), X‐ray photoelectron spectroscopy (XPS), and inverse gas chromatography at infinite dilution (IGC‐ID) as well as finite concentration conditions (IGC‐FC). XRD analysis revealed that CS was intercalated into the nanostructure of CSMMT biocomposites, a phenomenon not observed in CSBt biocomposites. XPS indicated that the CSMMT biocomposites possessed MMT‐rich surface, whereas CSBt biocomposites exhibited CS‐rich surface. IGC‐ID measurements showed that the dispersive components of the surface energy, , was higher for CSMMT biocomposites compared with CSBt. This increase is attributed to the preserved interlayered structure and the availability of high‐energy surface sites on CSMMT surface, while the CS coating on CSBt biocomposites masked these high‐energy adsorption sites. IGC‐FC analysis using isopropanol as a probe revealed that the distribution function remained bimodal for CSMMT biocomposites but became monomodal and symmetrical for CSBt biocomposites. This observation suggests the disappearance of high‐energy sites and confirms the coating of the clay by CS in the latter case
Framework for real-time multimodal container transport risk management
No full textInternational audienceIn the current context of globalization, multimodal container transport plays an important role in the efficiency and effectiveness of the supply chain. Indeed, containerization induces high productivity during port handling and a reduction of transport costs thanks to groupage. It also ensures the integrity and security of the goods transported. Nevertheless, the large number of stakeholders involved in the container transport process makes it extremely complex and leads to a loss of visibility and traceability during the transit of goods. In addition, the transit process is very often subject to random events that lead to delivery delays and increased transport costs. Considering all these difficulties, this work proposes a system for real-time detection of random events that may disrupt the multimodal transport of containers. In this paper we show how by relying on container traceability/visibility data, textual data and on natural language processing techniques, our system can detect in real time random events that may disrupt the transport flow. We describe the different modules and models that make up our system and then show its performance through a real use case. This work focuses on decision support for the activities of the stakeholders involved in the multimodal transport chain (exporters, consignees, carriers, shipping companies, etc.). The research is conducted in collaboration with an industrial partner (Traxens), who develops a real-time tracking solution for containers
Heat transfer modelling of radiant flux from a halogen lamp for enhancing Infrared thermography simulation
No full textInternational audienceInfraRed Thermography (IRT) is widely used in Non-Destructive Evaluation (NDE) for its ability to provide real-time, two-dimensional, non-contact measurements of heat distribution. Enhancing the analysis of thermal results requires a comprehensive understanding of the entire measurement chain from the heat source, through propagation, to detection, signal processing and data interpretation, which demands an effective combination of simulation and experimental approaches. This study presents the modelling of heat transfer, with particular emphasis on accurately characterising the radiant heat flux emitted by a halogen lamp. A fluxmeter sensor was employed to measure the radiant heat flux at different distances and spatial locations. Subsequently, 3D heat transfer models incorporating these heat sources were established and applied to an Acrylonitrile Butadiene Styrene plate to investigate thermal behaviour and the influence of factors within the measurement chain. Critical parameters were also considered, including thermal conductivity, convective heat transfer coefficients, fluxmeter sensor sensitivity, heat flux characteristics and measurement methods. Simulation results were validated against experimental data using both an infrared camera and a pyrometer and demonstrated strong agreement. Relative errors were below 4.2 % for pyrometer measurements, whereas slightly higher errors, up to 5.9 % for IRT method, which is mainly attributed the influence of environmental factors on this technique. These findings confirm the accuracy and reliability of the calibrated heat source and modelling parameters. Integrating experimental data into the thermal simulation enhances both accuracy and consistency, thereby establishing a more robust framework for the application of numerical methods throughout the IRT measurement chain in NDE applications