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Effet hygrothermique sur la cinétique d’humidité, le comportement mécanique et les propriétés interfaciales des composites fibre d’alpha/polypropylène
No full textInternational audienceThe mechanical performance, hygrothermal aging behavior, and morphological stability of polyolefin composite materials reinforced with natural lignocellulosic fibers are significantly influenced by the interphase strength between the matrix and the reinforcements. This study focuses on analyzing the interfacial properties between the polypropylene (PP) matrix and alfa fiber reinforcements. The alfa fibers were classified into two groups: untreated and treated with a 3% (w/v) sodium hydroxide (NaOH) solution. Additionally, 5 wt% maleic anhydride (MAPP) was incorporated into the PP matrix as a compatibilizer. The composites, containing 30 wt% fibers, were fabricated using a single-screw extruder and subsequently injection molded. Hygrothermal aging was conducted by immersing the samples in distilled water at temperatures for up to 2 months. The tensile properties of unaged samples of PP/alfa fiber composites were evaluated and compared with those of aged composites. The findings indicated that the 65PP-A30T-5 MA composite, subjected to combined treatment, exhibited superior tensile properties both before and after hygrothermal aging compared to the other composites. The moisture absorption behavior of the composites at different temperatures showed good agreement with Fick’s law. Moreover, results from the modified Kelly-Tyson model demonstrated that the interfacial shear strength (τ) of the composites with combined treatment was higher than that of untreated composites. SEM analysis further confirmed that composites treated with 3% (w/v) NaOH and 5 wt% MAPP exhibited enhanced interfacial bonding and fewer voids
Digital Twin-based Bearing Fault Diagnosis Using a 4-DOF Model and Hybrid Deep Learning
No full textInternational audienc
Enseignements tirés des démarches de Schémas Directeurs Immobiliers et Énergétiques dans les collectivités locales accompagnées par l’ADEME
No full textRapport produit pour l'ADEM
Density-based isolation forest
No full textInternational audienceThis work addresses the problem of outlier detection and studies isolation forest algorithms, originally introduced by Liu et al. (2008). We propose a new algorithm, which we call the density-based isolation forest (dbiForest). A dbiForest consists of a large number of density-based isolation trees (dbiTrees). Each dbiTree aims to identify outliers through recursive binary splits based on multivariate density estimates. This original approach integrates density estimation into the structure of the isolation tree. Based on the assumption that outliers are both rare and different from normal values, this algorithm identifies outliers as points that lie in regions of low density. Through several numerical experiments, we empirically show that this new method can overcome some of the limitations of existing isolation forest algorithms.</div
Motifs justifiant un refus de titularisation
No full textInternational audienceNote sous CE, 21 mars 2025, no 488366 (Lebon T.), M. B. c/ Préfet de la Seine-Saint-Deni
Towards a methodological framework for early qualitative assessment of the ecological and economic costs of digital twins in industrial maintenance
No full textInternational audienceOver the last decade, the use of digital twins (DTs) has expanded significantly across a variety of sectors. They often take various forms, with an emphasis on the underlying technologies (IoT, Cloud Computing, AI, virtual reality, etc.). However, one question remains: once deployed, will these digital twins be utilized in a manner that is both cost-effective and sustainable? Digital twins originated in maintenance applications, which is where these technologies are currently the most mature. Previous work shows that in the literature, most articles concern predictive maintenance applications, which implies the frequent use of artificial intelligence and therefore the management of large volumes of data. However, in recent years, we have seen the emergence of virtual reality technologies for training and augmented reality for intervention assistance, which require both significant hardware and software resources.The aim of this article is to propose a qualitative methodology for classifying industrial maintenance digital twins. This methodology will enable the assessment of the economic and environmental costs of DTs, making it possible for decision makers to ask the right questions even at the earliest stages of the DT's conception. This is especially helpful since, at those early stages, designers often lack quantitative information. This approach offers a more accessible starting point for eco-design, unlike more quantitative methods, such as Life Cycle Assessment (LCA), which require higher precision in data collection and a significant amount of time. This qualitative methodology will be applied to recent literature, providing a preliminary analysis of the digital twins currently in operatio
Penalization and Necessary Optimality Conditions for a Class of Nonsmooth Sweeping Processes
No full textInternational audienceAbstract In this paper we derive necessary optimality conditions for a Mayer problem involving a controlled sweeping process characterized by a moving set which is merely locally prox-regular (not necessarily smooth) and satisfies a constraint qualification condition formulated exclusively in terms of its normal vectors. We employ a penalization method based on the distance from the moving constraint, which allows convergence estimates that are uniform with respect to the control and, moreover, the strong W 1 , 2 -convergence of the approximating solutions. An example of nonsmooth mechanics with finite degrees of freedom is presented
Conductive and thermoactivated flax yarns developed by in situ polypyrrole polymerizations: Interactions with carbohydrate polymers
No full textInternational audienceThis study investigated the functionalization of flax yarn via in situ chemical polymerization of conductive polypyrrole (FY-PPy) and polypyrrole-silver (FY-PPy-Ag). Voltage-controlled experiments were conducted to assess the electrothermal properties of the modified yarns, with a focus on the Joule effect. FY-PPy exhibited significantly higher electrical conductivity (826 S.m- 1) and thermal conductivity (8583 J.S- 1 m- 1.degrees C- 1) than FYPPy-Ag did, which had values of 505 S.m- 1 and 5616 J.S- 1 m- 1.degrees C- 1, respectively. This enhanced conductivity resulted in a greater temperature increase during Joule heating, with the superior electrothermal performance of FY-PPy linked to the coated material formed during polymerization. Quantitative assessments of the coated conductive material were performed, revealing 25.5 wt% of PPy in the FY-PPy sample and 16.5 wt% of PPy and 26.1 wt% of silver in the FY-PPy-Ag sample. Gas chromatography tests revealed that the cellulosic content of the initial yarn remained unchanged after both functionalization methods were applied; however, the non-cellulosic polysaccharide content decreased significantly due to acidic treatment. Longitudinal tensile tests and sorption-desorption characterizations indicated that FY-PPy retained properties closer to those of the unfunctionalized yarn, whereas FY-PPy-Ag exhibited greater property loss. Our findings provide essential insights into the enhanced characteristics of functionalized flax yarns, highlighting their potential applications in the advanced electronics and composite industries
