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Apport des méthodes vibro-acoustiques non linéaires à la détection et à la localisation d’endommagements dans les structures aéronautiques en matériaux composites
No full textThe aeronautical industry is undergoing a transition from traditional materials to composite materials, which offer lower mass for an equivalent mechanical strength, thereby enabling a significant reduction in fuel consumption. However, these materials are susceptible to complex forms of damage, in particular impact-induced defects known as BVID (Barely Visible Impact Damage), which are often not detectable on the surface and therefore represent a major concern. Caused by low-energy impacts (hail, debris, or dropped tools during maintenance), such defects may evolve into critical states under repeated mechanical loading. As safety remains a permanent priority in the aeronautical sector, it relies in particular on monitoring the structural integrity of aircraft. Conventional non-destructive testing (NDT) techniques are based on scheduled, punctual, and costly inspections, which limit the achievable inspection frequency. Structural Health Monitoring (SHM) has been developed to overcome these limitations by providing continuous surveillance of the structure through sensors embedded in the aircraft. Among existing SHM approaches, those exploiting guided elastic waves are naturally sensitive to this type of defect. However, traditional baseline-dependent methods are not well suited for structures operating in harsh and evolving environments. The present work therefore aims to develop a baseline-free method for the detection and localization of BVID, using a pump–probe method based on vibro-acoustic modulation, in which a low-frequency vibration (pump) modifies the contact state of the defect and this perturbation is subsequently detected by a high-frequency ultrasonic wave (probe). Since the signatures provided by this class of methods are typically one order of magnitude weaker than those obtained with a baseline, a coherent imaging algorithm was first developed for highly anisotropic structures. This approach accounts for guided-wave focusing effects and the resulting phase skewing, enabling the localization of a BVID using a baseline even in the presence of very high noise levels. An artificial contact defect was then designed and modelled in order to enable the implementation of baseline-free imaging methods. It was shown that this defect imposes a variable force on the vibrating plate, thereby generating a varying contact interface. The modulation of a guided elastic wave crossing this defect was observed by means of piezoelectric sensors and confirmed through measurements of the ultrasonic field. The third stage focused on the localization of the artificial defect using SHM-compatible multi-emitter instrumentation. Several strategies were investigated, ranging from incoherent approaches that do not require the phase information of the ultrasonic signatures to coherent approaches that offer higher performance but also impose stricter constraints. The case of a monochromatic pump was first examined, followed by that of a random pump, using a method based on the singular value decomposition of differential matrices. A second matrix-based approach, founded on independent component analysis, made it possible to extract weak modulations from noise. Finally, the proposed methods were applied to a real BVID. The multimodal nature of guided elastic waves and the presence of modulations concurrent with the damage-related modulation make the interpretation of the results challenging. The modulations observed on the A0 and S0 modes were analyzed, as well as the modulation of the mode conversions between them, using multimodal imaging algorithms. An alternative approach, based on the frequency mixing of two ultrasonic waves, made it possible to reveal a nonlinear interaction in the BVID region through ultrasonic field measurements.L’industrie aéronautique opère une transition des matériaux traditionnels vers les matériaux composites, plus légers pour une résistance mécanique équivalente, permettant ainsi une réduction significative de la consommation de carburant. Cependant, ces matériaux subissent des endommagements complexes, notamment à la suite d’impacts générant des défauts appelés BVID (Barely Visible Impact Damage), souvent invisibles en surface, et qui constituent un enjeu majeur. Provoqués par des chocs légers (grêle, débris ou chutes d’outils lors de la maintenance), ils peuvent évoluer vers des états critiques suite à des sollicitations mécaniques répétées. La sécurité étant une préoccupation constante dans l’industrie aéronautique, elle s’appuie notamment sur le suivi de l’intégrité des structures. Les techniques traditionnelles de contrôle non destructif (CND) reposent sur des inspections ponctuelles programmées et coûteuses, limitant alors la fréquence des inspections. Le contrôle de santé intégré (SHM, pour Structural Health Monitoring) vise à pallier ces limites en assurant une surveillance continue de la structure à l’aide de capteurs embarqués sur l’appareil. Parmi les méthodes de SHM existantes, celles exploitant les ondes élastiques guidées sont naturellement sensibles à ces défauts. Cependant, les approches traditionnelles reposant sur un état de référence sont peu adaptées à des structures évoluant dans des environnements sévères. Ce travail vise alors à développer une méthode de détection et de localisation de BVID sans état de référence, via une méthode pompe-sonde reposant sur le principe de modulation vibro-acoustique, où une vibration basse fréquence (pompe) modifie l’état de contact du défaut, perturbation ensuite détectée par une onde ultrasonore (sonde). Comme les signatures obtenues avec cette famille de méthodes sont d’un ordre de grandeur plus faible que les signatures obtenues avec un état de référence, une méthode d’imagerie cohérente a d’abord été développée, pour des structures très anisotropes. Elle tient compte des effets de focalisation induisant une déviation de phase, et a permis de localiser un BVID avec état de référence en présence de bruit très élevé. Un défaut de contact artificiel a ensuite été conçu et modélisé, pour la mise en place de méthodes d’imagerie sans état de référence. Il a été montré que ce défaut impose une force variable sur la plaque en vibration, générant alors une interface de contact variable. La modulation d’une onde élastique guidée traversant ce défaut a été observée par des capteurs piézoélectriques et confirmée par une observation du champ ultrasonore. La troisième étape a porté sur la localisation du défaut artificiel avec une instrumentation multi-émetteurs compatible SHM. Plusieurs stratégies ont été explorées, des approches incohérentes, ne nécessitant pas l’information de phase des signatures ultrasonores, à des approches cohérentes plus performantes mais aussi plus contraignantes. Le cas d’une pompe monochromatique a été étudié, puis celui d’une pompe aléatoire grâce à une méthode basée sur la décomposition en valeurs singulières des matrices différentielles. Une seconde approche matricielle, fondée sur la décomposition en composantes indépendantes, a permis de détecter des modulations faibles noyées dans le bruit. Enfin, les méthodes développées ont été appliquées à un cas réel sur un BVID. La nature multimodale des ondes élastiques guidées et la présence de modulations concurrentes à celle du défaut rendent l’interprétation des résultats délicate. Les modulations observées sur les modes A0 et S0 ont été étudiées ainsi que la modulation des conversions entre ces modes à l’aide d’algorithmes d’imagerie multimodale. Une approche alternative, basée sur le mixage fréquentiel de deux ondes ultrasonores, a permis de mettre en évidence une interaction non linéaire dans la zone du BVID via une mesure du champ ultrasonore, et donne des pistes d’améliorations futures de la méthode
Enhancing support vector clustering labeling efficiency with scalable heuristics
No full textInternational audienceSupport Vector Clustering (SVC) is a powerful unsupervised learning method for detecting arbitrarily shaped clusters, making it highly relevant for complex pattern analysis tasks. However, its widespread use has been constrained by the high computational cost associated with its labeling phase. This paper presents three novel methods that enhance the scalability and efficiency of SVC, making it more suitable for large-scale pattern recognition applications. We first propose the Inheritance Support Vector Graph (InSVG), an optimized graph construction strategy that reduces redundant connectivity checks through transitive inference. We then introduce two intelligent labeling heuristics: Most Similar Test First (MSTF), which prioritizes similarity-based evaluations, and Most Similar Label First (MSLF), a fast approximation that eliminates connection tests by leveraging kernel-based proximity. These methods are evaluated on 15 diverse datasets, demonstrating labeling time reductions of up to 97% while preserving clustering quality, as measured by standard internal and external metrics. The proposed framework contributes to the field of pattern analysis by enabling the practical deployment of SVC in real-time or large-scale scenarios involving high-dimensional data
Aesthetics of Boundless Insight: On the Scalar Ideology of the Data Imaginary
No full textInternational audienceThis article explores the ways in which popular cinema contributes to the data imaginary. We engage in a close reading of key data-related scenes in Minority Report (2002), Moneyball (2011), and Snowden (2016), and we examine their extensive reliance on formal means that are deeply entangled with cinema’s capacity for scalar distortion. Using critical scholarship on the concept of scale as our interpretative lens, we argue that the distinct aesthetic construction of filmic engagements with data-driven issues is politically performative: The sequences that contribute to the data imaginary evoke what we term the “aesthetics of boundless insight,” eminently aligned with the discourse that presents big data as the key to unlimited potential and as a powerful technology without a predetermined agenda
Integrated assessment of the toxicological, ecotoxicological and ecological effects of all phytopharmaceutical treatments used during a whole crop season: the example of potato crop in North of France
No full textPlant protection products used in agriculture contain molecules specifically designed to be toxic to target organisms. However, their use can also have unintended effects, posing potential risks to ecosystems and non-target organisms, including humans. Research has deepened our understanding of the links between exposure to these substances and the effects observed in the environment. In particular, studies have highlighted how even low levels of exposure can cause chronic effects on non-target organisms and disrupt ecosystems. These findings underscore the importance of quantifying and characterising these exposures in order to better assess their potential impacts on human health and the environment.International audienceThis project enabled a retrospective assessment of the effects related to the use of plant protection products (PPP) during a whole potato crop season. In the field, cultivated soils presented multi-residual contamination by low doses of PPP, which may be old, consecutive to the culture or treatments of nearby plots; concerning tubers, few residues have been found, and at very low concentrations. In the laboratory, following oral exposure of mice, a transient, significant effect of PPP used for the culture and storage of harvested tubers on gene expression was observed, with a much lower effect on the intestinal microbiota. For exposures carried out in microcosms with cultivated soils, ecotoxicology models (earthworms, plants) expressed different responses, but few effects overall
Compréhension du dépistage prénatal de la trisomie 21 chez les femmes enceintes en France : une étude transversale à la lumière des recommandations de 2019
No full textInternational audienc
Edmond Fleg : d’un « homme de bonne volonté » à un « homme de dialogue ».: Sa contribution à la conciliation entre Juifs et chrétiens
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Observing object circulation as movement using participants’ visual ethnography: theoretical relevance and research protocol
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