Portail HAL IMT Mines Albi
Not a member yet
5440 research outputs found
Sort by
Stabilité des matrices thermostables et conséquences sur la consolidation des préformes composites comêlées
No full textThe use of carbon/PAEK preforms for the elaboration of composites with high performance thermoplastic matrix allows to overcome the difficulty of impregnation of fibrous reinforcements. Nevertheless, the preform consolidation requires high processing temperatures that can activate degradation mechanisms by chain scissions and crosslinking. Thus, this PhD thesis work focuses on the influence of the degradation of PAEK matrices, and more particularly PEEK, on the consolidation of structural composites from commingled preforms. Such preforms consist of a homogeneous assembly of polymeric multi-filaments distributed within the reinforcing yarns. The stability of the PEEK matrix was analyzed at different manufacturing steps, from the raw product to the preform, in order to establish the relationship between the successive transformations in the processes, the integrity of the matrix and the behavior during consolidation. The consolidation by thermocompression of semi-finished products made of carbon/PEEK commingled yarns was first studied. Various characterization techniques were used to determine the modifications of the preform matrix. The impact of these modifications on PEEK degradation kinetics in the molten state were characterized and allowed to highlight a strong influence of the melt-spinning operation required for the preparation of the commingled preforms. PEEK yarns were thus manufactured by melt-spinning in order to study the influence of the different key steps of the process on the integrity of PEEK during its transformation in the molten state. The analysis of yarns taken at different steps of the process revealed the major effect of the additives added during processing on the matrices stability. In order to account for the effect of degradation on the consolidation of carbon/PEEK preforms, an impregnation model integrating a thermo-kinetic viscous constitutive law was then developed. This model allows to predict the evolution of the porosity rate during the consolidation of commingled-based preforms, while integrating the degradation of the PEEK matrix. Finally, a preliminary study of the relationship between oxygen diffusion and the crosslinking reaction of PEEK in a rheometer has been initiated. This analysis discusses the impact of the form factor of the PEEK matrix in the molten state on the degradation kinetics.L’utilisation de préformes carbone/PAEK pour l’élaboration de composites à matrice thermostable permet de pallier la difficulté d’imprégnation des renforts fibreux. Néanmoins, la mise en œuvre de ces préformes nécessite d’appliquer des températures élevées pouvant activer des mécanismes de dégradation par scissions de chaînes et réticulations. Ainsi, ces travaux de thèse portent sur l’influence de la dégradation des matrices PAEK, et plus particulièrement PEEK, sur la consolidation de composites structuraux à partir de préformes comêlées. Ces préformes sont constituées d’un assemblage homogène de multi filaments polymères distribués au sein des mèches de renfort. La stabilité du PEEK a été analysée aux différents stades de fabrication, du produit brut jusqu’à la préforme, afin d’établir la relation entre les transformations successives dans les procédés, l’intégrité de la matrice et le comportement durant la consolidation. Tout d’abord, la consolidation par thermocompression de semi-produits constitués de fils comêlés carbone/PEEK a été étudiée. Diverses techniques de caractérisation ont été utilisées afin de déterminer les modifications subies par la matrice des préformes. L’impact de ces modifications sur sa cinétique de dégradation à l’état fondu ont été caractérisées et ont permis de mettre en évidence une forte influence de l’étape de filage nécessaire à la préparation des préformes comêlées. Des fils de PEEK ont alors été fabriqués afin d’étudier l’influence des différentes étapes clés du procédé sur l’intégrité du PEEK lors de sa transformation à l’état fondu. L’analyse de fils prélevés à différents stades du procédé a permis de révéler l’effet majeur des additifs ajoutés lors de la transformation sur la stabilité des matrices. Afin de rendre compte de l’effet de la dégradation sur la consolidation des préformes carbone/PEEK, un modèle d’imprégnation intégrant une loi de comportement visqueuse thermo-cinétique a ensuite été développé. Ce modèle permet de prédire l’évolution du taux de porosités durant la consolidation des préformes faites de fils comêlés, tout en intégrant la dégradation de la matrice PEEK. Enfin, une étude préliminaire du couplage entre la diffusion d’oxygène et la réaction de réticulation du PEEK dans un rhéomètre a été initiée. Cette analyse discute l’impact du facteur de forme de la matrice PEEK à l’état fondu sur la cinétique de dégradation
Twenty Years of Configuration Knowledge Modeling Research. Main Works, What To Do Next?
No full textInternational audienceA configuration software (configurator) associates a knowledge base (KB) with a knowledge processing unit (PU). The KB describes all possible combinations of components while the PU overlays this knowledge with the customer requirements. Our work deals with the KB and the approaches, models, or tools for modeling configuration knowledge. Our goal is to present a small quantitative literature survey highlighting two work streams: the first one gathers modeling works dealing with constraint-based approaches while the second deals with ontologies, description logic, or object-oriented modeling approach. We will also consider hybrid approaches. We will present a quantitative analysis of published materials in Web of science over the last twenty years. The keywords occurrence versus time will also be studied in detail to identify tendencies in configuration knowledge modeling
How accurate was Bronze Age weighing in Western Europe ?
No full textInternational audienceThis paper aims to bring new insights about weighing practices and instruments during Late Bronze Age in Western Europe. Northern France and Southern England share the particularity of providing tiny balance beams and weights dedicated to weigh small quantities. It is traditionally accepted that most of the Bronze Age weights found in Western Europe correspond roughly to a same practice built around one metrological system. Nevertheless, the deviations observed between several weights which should correspond to the same values in the metrological system raise questions about the accuracy of the Bronze Age balances.This paper synthetizes the general categories of weights and beams used during the Bronze Age in Northern France and Southern England and their main characteristics. Using new mathematical and digital protocols – sensitivity analysis, 3D modelling and simulation, and finite element analysis – we highlight the main mechanical features of the Bronze Age balances, the accuracy that should be expected with them and their resistance to use.Our results show than ancient balances were way more accurate that what is generally estimated. They show that most of them should probably allow to see differences between the loading of the two pans less than 0.5 g in most of cases. These results also raise new interpretations about the use of metrological systems during the Bronze Age considering that certain weights, generally interpreted as the same value, would appear as completely different if they were put on each pan of such a balance. The resistance simulations also show that the bone beams were very robust and could support loading much heavier than the weights identified for the same period
Co-pyrolysis of biomass and plastics from waste in an induction heated reactor
No full textInternational audienc
Synthesis of Biologically Relevant 1,2,3-and 1,3,4-Triazoles: From Classical Pathway to Green Chemistry: Review
No full textInternational audienceGreen Chemistry has become in the last two decades an increasing part of research interest. Nonconventional «green» sources for chemical reactions include micro-wave, mechanical mixing, visible light and ultrasound. 1,2,3-triazoles have important applications in pharmaceutical chemistry while their 1,2,4 counterparts are developed to a lesser extent. In the review presented here we will focus on synthesis of 1,2,3 and 1,2,4-triazole systems by means of classical and « green chemistry » conditions involving ultrasound chemistry and mechanochemistry. The focus will be on compounds/scaffolds that possess biological/pharmacophoric properties. Finally, we will also present the formal cycloreversion of 1,2,3-triazole compounds under mechanical forces and its potential use in biological systems
Slow and intermittent stress relaxation of biomass granular media
No full textInternational audienceIn the present work, the relaxation of several wood powders has been investigated in an annular shear cell. It is found that the slow logarithmic relaxation commonly observed for various materials including granular materials is interrupted by large events. Their frequency and amplitude are investigated with respect to particle size and stress-history by measuring stresses and strain. These large events during the relaxation appear to be controlled by the deformation. The coarser the particles are, the bigger is the deformation of the powder bed between two fast relaxation events and during the event
Robustness, Resilience: typology of definitions through a multidisciplinary structured analysis of the literature
No full textInternational audienceThe concepts of robustness and resilience are used with increasing frequency from different sectors. The literature review reveals several meanings for each of these terms due probably to specific use in each of the sectors and a progressive adjustment of the definitions across the time. The aims of this article are to identify these definitions and the main similarities and difference between the concepts of resilience and robustness and to propose a classification of them in order to avoid confusions, bad meaning and to provide a better understanding of the subtleties under these concepts. Based on a structured analysis of the literature published in journals of different sectors this paper conceptualizes and comprehensively presents a systematic review of the recent literature on robustness and resilience definitions. Decision-makers and researchers can benefit from our survey since it introduces a structured analysis and recommendations as to which definitions can be used
An Improved Decision Support Method for Resilience Assessment Based on Multi-Viewpoint Modeling and Functional Analysis of Interconnected Systems
No full textInternational audienceCritical infrastructures provide services that are essential to the functioning and well-being of society. Failure to provide these services is unacceptable. This is a problem when considering the unpredictable nature of the environment (leading to crisis, natural disasters, terrorist attacks) and internal failures. The concern is even greater due to the interconnected and interdependent nature of critical infrastructures, which might lead to failure propagation, causing domino and cascade effects. The resilience of a system is the ability to reduce the magnitude and/or duration of disruptive events or their consequences, allowing a satisfactory level of performance and quality of services. Improving critical infrastructures' resilience before any disruption occurs can reassure society's vital needs. The goal of the paper is to define an improved decision support method for resilience by combining resilience assessment and multi-viewpoint modeling methods
Introduction to the Digital Government and Business Process Management (BPM) minitrack HICSS’54
No full textInternational audienceDigital Government (traditionally known as e-Government) focuses on value delivery to citizens through information and communication technology (ICT) support for processes, activities and resources. Digital government’s collaborative processes involve organizations (employees, technologies), partners (providers, consumers), and users (citizens, foreigners), leading to complex interactions within different e-Government models and available technologies.Business Process Management (BPM)constitutes a real asset for enhancing the services of an organization and their coordination, as well as the products that each actor of a virtual network delivers to meet clients’ expectations (citizens, patients, etc.). Successful inter-organizational process management within e-Government collaborative organizations will lead to better conceptual and technological integration, not only with each other but also with citizens and users in general. To this end, it is necessary to devise new ways to deal with the complexity of e-Government collaborative process definition, modeling, analysis, enactment and monitoring from various dimensions and points of view including theory, engineering, interoperability, agility, social aspects, etc