Portail des publications scientifiques IMT Mines Alès
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Microstructure development in cellulose fibre reinforced PLA composites during processing: a thermal and rheological study
No full textInternational audienceThis work aims to determine the effect of cellulose fibre content and fibre size and shape on the crystallisation and solidification of polylactic acid (PLA) during cooling to better understand microstructure development in biocomposites. Hot melt twin-screw extrusion and injection moulding was used to prepare cellulose fibre reinforced PLA composites with different microstructures from the diluted to the concentrated regime. Differential scanning calorimetry, temperature-controlled optical microscopy and rheometry were used to study the non-isothermal and isothermal crystallisation and solidification of the composites. The non-isothermal analysis shows that cellulose fibres, regardless of their content, size and shape, did not affect either the PLA thermal characteristics (glass transition, cold crystallisation and melting temperatures), nor its degree of crystallinity. On the other hand, isothermal crystallisation kinetics of PLA is greatly influenced by the fibres, being accelerated when fibre content and length/aspect ratio are increased. Our results also reveal that crystallisation and related rheological behaviour during solidification of PLA can be tuned by modifying the fibre characteristics, thus contributing to better control PLA processing, especially when studying thermoplastic processes involving isothermal steps
Objectifs et réalités de l’économie circulaire
No full textInternational audienceL’économie circulaire (EC) peut être définie comme l’antonyme d’une économie linéaire qui convertit des ressources naturelles renouvelables et non renouvelables en déchets via différents processus de retransformation, et conduit à une détérioration de l’environnement en raison d’un prélèvement incontrôlé des ressources et d’une pollution généralisée par les déchets.L’émergence de l’économie circulaire découle des limites de la croissance dans les sociétés industrielles et traduit le fait que l’on ne peut consommer davantage que l'on ne remplace. L’économie circulaire ambitionne une minimisation des effets négatifs sur l’environnement, une limitation des déchets et une action restaurative vis-à-vis des dommages. Une symbiose industrielle est ainsi recherchée à travers les 4R (réduire, réutiliser, recycler, récupérer) afin de traduire la nécessité d’améliorer la productivité des ressources. Sa mise en œuvre s’effectue principalement dans trois domaines : l’offre des acteurs économiques, la demande et les comportements des consommateurs, ainsi que la gestion des déchets. Pour autant, il n’existe pas de définition précise, exhaustive et reconnue par tous de l’économie circulaire. Ceci s’explique par l’appropriation du concept par de nombreuses communautés d’acteurs qui l’analysent, la promeuvent ou la mettent en œuvre. De ce fait, la présentation de ses stratégies peut varier car l’ambition de l’économie circulaire de promouvoir un développement soutenable la place au cœur des débats économiques et des politiques publiques. Des interprétations diverses peuvent conduire à des critiques de diverses natures, notamment sur ses bases théoriques jugées hétérogènes, sur l’incapacité à assurer réellement la circularité, des objectifs parfois contradictoires, la prise en compte très limitée des aspects sociétaux et l’incapacité à maîtriser les effets rebond.L’économie circulaire se veut être un chantier clé de la transition écologique visant à sortir d’un modèle linéaire qui se heurte fatalement à l’épuisement des ressources de la planète. Les craintes relatives à la disponibilité des ressources dans un monde fini n’ont fait que croître depuis la publication en 1972 du rapport Meadows The Limits to Growth. Bien que le scénario de l’épuisement à court terme de ressources non renouvelables essentielles et stratégiques puisse être écarté, des risques majeurs sur leur approvisionnement sont réels, compte tenu d’une demande croissante et de tensions géopolitiques. En outre, les teneurs en minerais ne cessent de décroître pour des métaux courants et les impacts environnementaux et énergétiques de l’extraction minière sont de plus en plus significatifs. En conséquence, le recyclage des matériaux issus d’objets manufacturés en fin de vie est susceptible de permettre la récupération d’éléments critiques afin de relâcher les tensions sur l’approvisionnement. Cependant, les technologies de recyclage doivent s’améliorer afin de résoudre une partie des problèmes liés à la dispersion des éléments chimiques dans les produits manufacturés et limiter les contaminations dans les matériaux issus du recyclage. La maîtrise des microstructures des matériaux secondaires est également essentielle afin d’éviter des processus de décyclage.La mise en œuvre pratique de l’économie circulaire passe également par la réduction de l’empreinte écologique des produits tout au long de leur cycle de vie : extraction des matières premières, fabrication, distribution, utilisation et fin de vie. La réussite de cet objectif implique d’inclure la préservation de l’environnement dès la conception des biens et services. Il s’agit de développer une écoconception pilotée en intégrant pleinement la stratégie de fin de vie au moyen d’indicateurs appropriés. Cet article vise à décrire les caractéristiques majeures de l’économie circulaire et s’attache particulièrement à évoquer les problématiques de raréfaction de ressources non renouvelables en lien avec la faisabilité du recyclage de matériaux dont certains peuvent être considérés comme critiques. Une part importante de l’article est consacrée à l’écoconception, à même de représenter un outil majeur via des indicateurs appropriés afin de limiter l’usage de ressources non renouvelables et accroître le potentiel de valorisation des produits en fin de vie
Investigating overpressure BLEVE effects on 100 % liquid full vessel
No full textInternational audienceDespite extensive research done over several decades, BLEVE accidents persist and yet the complexity of this particular type of explosion poses ongoing challenges in the industry. Existing literature underscores the need to investigate BLEVE hazards to mitigate substantial threats to property and life, especially in populated areas. While previous studies have provided definitions and models for BLEVE, primarily concentrating on free field overpressure, the respective contributions of vapor and liquid phases in hazard formation remain unclear among various authors. This paper delves into the dynamics of a BLEVE emphasizing the critical role of liquid fill level in the overpressure hazard. This research is based on recent BLEVE experimental campaigns conducted in 2022 and 2024 on small-scale cylindrical aluminum vessels filled with pure propane. Cutting-edge scientific tools, including low and high-speed measurement instruments were employed to capture detailed data to extend the current understanding of a BLEVE. Particular attention was given to the fully liquid cases (100 %) as they represent a special case of a BLEVE. Valuable findings were obtained from experimental results regarding the relative contributions of vapor and liquid phases, addressing a critical gap in BLEVE comprehension. Key findings from experimental data indicate that the full liquid cases are characterized by two distinct types of failure pressures: the failure pressure and the saturation pressure at failing temperature. Additionally, it was observed that the full liquid cases exhibited the lowest peak overpressure and the longest lead overpressure duration relative to the failure pressure. A distinct trend line was identified in the full liquid experiments. If validated at large scale, the results of this investigation could serve as useful knowledge for industry and engineering by assisting in estimating the risks and consequences associated with BLEVE accidents, thus contributing to enhanced safety practices in industrial settings
Multi-Output Regression for the Prediction of World-Class Performances in Women’s Handball
No full textInternational audienceThe purpose of this study was to investigate the relationship between workload and in-game technical and athletic performance. To achieve this,A modeling approach that predicts multiple numerical output variables simultaneously, particularly useful when these outputs are correlated (multi-output regression) models were used to predict 7 performance indicators based on previous training and game athletic workloads measured by Inertial Measurement Units (IMU) indicators, previous in-game actions annotated by staff members and game contextual factors. We compared 4 single-output models (kNN, regression tree, random forest and(NN) Predictive models inspired by the human brain, used in this study for multi-output prediction in sports performance analysis (neural networks)), their multi-output counterparts and aA baseline model predicting future performance as the average of each player’s past performance, serving as a simple reference for comparison with more complex models (dummy baseline) (predicting the average performance of each player over the last month) in terms of average(Root Mean Squared Error) A measure of the quadratic difference between predicted and actual values in regression models (RMSE) (aRMSE) during aAn evaluation method where past training and game data are used sequentially to predict performance of the next game (chronological evaluation) where previous trainings and games data are used to train models to predict the next game performances. Overall, the use of multi-output regression models enabled a decrease of the average predictive error (A metric for prediction error that evaluates model accuracy in terms of average squared errors across multiple outputs in a multi-output models (aRMSE) = 4.23) in regards to their single-output counterparts (aRMSE = 4.35) while providing a significant decrease of average computation times (4.75 to 0.82 seconds). Among the 4 multi-output models, only the kNN (aRMSE = 3.852) and random forest (aRMSE = 3.888) performed better than the dummy regressor (aRMSE = 3.944). These results point towards that physical training may have a limited impact on game performance
Phosphate Low-Melting Glasses as Synergist in Flame-Retardant Cable Sheath Composition: Performance and Mode of Action
No full textInternational audienceNowadays, fiber optic cables are a strategic issue because of their importance in telecommunications. Due to the densification of optic cables and the reduction in polymeric layer thickness, the flammability of the external sheath has to be improved. Three novel flame-retardant compositions using phosphate low-melting glasses (LMGs) as aluminum trihydrate (ATH) synergist were assessed in a polyethylene–ethylene vinyl acetate (PE-EVA) matrix. It was highlighted that LMG at a 10 wt% content reduced the peak and mean value of heat release rate (HRR), respectively, to 142 and 90 kW/m2 corresponding to 52% and 42% reduction compared to ATH only. Potassium phosphate LMG was shown to perform better than sodium or zinc phosphate LMG. The improvement was assigned to the formation of an expanded mineral layer at the surface of the material during combustion that acts as a thermal shield slowing down the pyrolysis rate. The structural analysis revealed that the presence of alkaline cations in glasses led to short phosphate chains that resulted in low softening point and low-viscosity liquid. It was evidenced that under heat exposure the melted glass is likely to flow between the dehydrating ATH particles, creating a cohesive layer that expands. Additionally, interactions between ATH and LMG were also evidenced. The new crystalline species may also play a role in the cohesion of the layer
Flame retardancy of phosphorus-containing novolac epoxy-silsesquioxanes
No full textInternational audienceThe phosphorus-containing Novolac Epoxy modified with silsesquioxane (POSS) compounds to enhance flame retardancy and thermal behavior was investigated in this study. Two POSS compounds were used: octaphenyl polyhedral oligomeric silsesquioxane (OctaPOSS), and dodecaphenyl polyhedral oligomeric silsesquioxanes (DodecaPOSS). The results of DMA revealed an increase in the glass transition of the modified samples, with a significant shift in the Tan Delta peak (from 109.0 °C to 127.2 °C), indicating improved thermal stability. Thermogravimetric analysis confirmed enhanced thermal stability and charring effect, with modified samples exhibiting higher residue contents; such as OctaPOSS containing 2 wt% silicon and 1 wt% phosphorus, which produced nearly 6 wt% more residue than neat Novolac Epoxy. Flame-retardant tests, including vertical burning test and limiting oxygen index (LOI), demonstrated the effectiveness of the modified systems. OctaPOSS and DodecaPOSS containing 2 wt% silicon and 2 wt% phosphorus achieved a V0 rating and an LOI of 29.5 %, confirming self-extinguishing performance. Improved flame retardancy and reduced heat release were evidenced by cone calorimetry and microscale combustion calorimetry (MCC). OctaPOSS (2 wt% silicon and 2 wt% phosphorus) showed a 6 2% reduction in peak release rate (pHRR) from 1188 kW/m² for the neat Novolac Epoxy to 455 kW/m², and a heat release capacity (HRC) of 107 J/(g K), approximately 70 % lower than the neat sample. In addition, the fire growth rate reduction of 4.6 kW/(m² s), indicating improved flame retardancy. The combination of POSS and organophosphorus flame retardant also enhanced the charring effect, promoting a more cohesive layer and improving fire safety
Intrusion Pattern Recognition in DAS System Using Multi-Domain Features and Transformer Network
No full textInternational audienceDistributed Acoustic Sensing (DAS) offers a scalable and resilient solution for real-time perimeter security by transforming optical fibers into dense arrays of vibration sensors. However, its high-dimensional, noisy, and spatio-temporally complex data make accurate event recognition challenging. Conventional deep learning models, such as Convolutional Neural Networks (CNNs) and Long Short-Term Memory (LSTM) networks, often struggle to capture long-range dependencies and rely heavily on handcrafted or single-domain features, limiting their effectiveness in complex intrusion scenarios. Designing compact and discriminative feature representations remains a critical challenge. To address these issues, we propose DASViT1D, a novel intrusion detection framework that integrates a one-dimensional Vision Transformer (ViT1D) with fused multi-domain features. Specifically, we extract and combine Mel-Frequency Cepstral Coefficients (MFCC), Redundant Discrete Fourier Transform (RDFT), and Discrete Wavelet Transform (DWT) features to capture complementary spectral and temporal characteristics. ViT1D then leverages self-attention to model long-range dependencies across time. Evaluated on a public ϕ-OTDR DAS dataset with nine event classes, our approach achieves 93.5% accuracy, outperforming CNN-based baselines by nearly 8 points, with a false negative rate (FNR) of 0.009, a nuisance alarm rate (NAR) of 0.005, and fast inference (0.13s/sample), demonstrating its suitability for real-time DAS-based intrusion detection
Turn-taking fluency in free conversations with individuals diagnosed with schizophrenia
No full textInternational audienceDisruptions in language processing observed in Individuals diagnosed with schizophrenia (ISZ) are likely to impair turn-taking fluency and social functioning. While turn-taking research in ISZ is limited and mostly interview-based, this study examines fluency differences between ISZ and controls in free conversations and their links to social outcomes and symptoms. We recruited 20 ISZ, 20 healthy interacting partners (IP), and 20 matched controls (MAT). Each IP, unaware of the ISZ diagnosis, had a 6-min conversation with an ISZ and a MAT, and then rated their willingness to interact again. Voice recordings were analyzed for pauses, gaps, and overlaps. Results revealed that conversations with ISZ featured fewer overlaps, more and longer gaps, and extended pauses. Additionally, the gap duration influenced participants’ willingness to engage in future interactions. ISZ symptoms disrupted their speech and were linked to longer gaps and pauses in their partner’s speech. This study extends fluency research in ISZ by shedding light on natural conversational dynamics
Assessment of smoldering in biobased concretes
No full textInternational audienceThe building sector continues to seek solutions to reduce its carbon footprint, as this industry plays a crucialrole in the fight against global warming. Bi-obased concretes show great promise as a sustainable andenvironmentally friendly material for construction. They help lowering the carbon footprint while offeringthermal and acoustic performances. However, their use re-quires a comprehensive understanding of theirmechanical and physical properties to optimize their application in the construction industry. Despite theirpotential, limited data is available on their reaction to smoldering fire. In this study, the EN 16733 standardtest was conducted in FCBA laboratories on 34 different biobased concrete formulations to assess theirtendency to smolder. The results highlighted that the most influential factors are the den-sity of the biobasedconcretes and the binder nature. Lime appears to offer less protection against smoldering fire development.Several hypotheses were proposed to explain this observation. The basicity of calcareous binders promotesextensive charring of the bioresource at high temperatures, which is the driving force for smoldering
Stuck in Time and Space: Spatiotemporal disruption of reality in depersonalization
No full textInternational audienceSpace and time perception are fundamentally inescapable features of all our conscious perceptions. Depersonalization (DP) is a very common condition characterized by distressing feelings of estrangement from the self and the external world [1,2]. Previous work showed that peripersonal space perception is disrupted in schizophrenia but not in DP (3), on the other hand, time perception is disrupted both in DP and schizophrenia. Why this asymmetry? Is time perception more central to the sense of self than space perception? To better understand the specificities of DP, a comprehensive picture of time and space perception disruptions in this population is needed. To address this gap, we have conducted an online study (N = 1034) investigating the relation between HIGH DP traits measured by the Cambridge Depersonalization Scale (CDS > 50) [5] and altered subjective experiences of body, time, and space perception. The results demonstrated significant relationships between HIGH DP scores and distorted experiences of time, body and space. Looking at the shared variance between CDS facets “Anomalous Body Experience”, we found that altered body perception remains the most important predictor of spatiotemporal disruption experiences, with a slowing of subjective perception of time. Altogether, these results suggest that the distorted spatiotemporal experiences observed in DP may mainly come from experiences of estrangement from the bodily self. Thus, the body sets the pace of inner felt subjectivity. Our work calls for further investigations linking DP to disruption of internal/external clock and also in relation to active movements in the world