HAL Portal UBS (Université Bretagne Sud)
Not a member yet
14201 research outputs found
Sort by
Hierarchical Modeling of Archaeological and Modern Flax Fiber: From Micro- to Macroscale
No full textInternational audienceFlax fiber reinforcements weaken with aging and microstructural changes, limiting their applications. Here, we examine the effects of microstructure and aging on flax fiber elements' performance by using 4000-year-old and modern Egyptian flax as references through multi-scale numerical modeling. This study introduces a novel investigation into the tensile stress distribution behavior of archaeological and modern flax yarns. The finite element (FE) model is derived from 3D volumes obtained via X-ray microtomography and tensile testing in the elastic domain. At the microscale, fibers exhibit higher axial stress concentrations around surface defects and pores, particularly in regions with kink bands and lumens. At the mesoscale, fiber bundles show increased stress concentrations at inter-fiber voids and lumen, with larger bundles exhibiting greater stress heterogeneity, especially around pores and surface roughness. At the macroscale, yarns display significant stress heterogeneity, especially around microstructural defects like pores and fiber-fiber cohesion points. Aged fibers from ancient Egyptian cultural heritage in particular demonstrate large fiber discontinuities due to long-term degradation or aging. These numerical observations highlight how porosity, surface imperfections, and structural degradation increase stress concentration, leading to fiber rupture and mechanical failure. This insight reveals how aging and defects impact flax fiber performance and durability
Asymptotic properties of heteroscedastic asymmetric Laplace regression for longitudinal data
No full textInternational audienceLinear mixed-effects models are powerful tools for analyzing complex datasets with longitudinal data but any violation of model assumptions, such as heteroscedasticity, implies invalidity of the model. We develop a new estimator based on the asymmetric Laplace distribution, which explains the heteroscedasticity between different groups of data, establishing its asymptotic properties. Our model focuses on the determination of the data dispersion. Using the permissive formalism of the asymmetric Laplace distribution, we demonstrate the asymptotic properties of a class of estimators defined by a generalized optimization problem inspired by maximum likelihood. More generally, this article highlights the theoretical opportunities offered by the asymmetric Laplace distribution in the framework of linear mixed models and longitudinal data
De Macao à Faifo : les débuts de la mission jésuite en Cochinchine (première moitié du XVIIe siècle)
No full textInternational audienc
Étude numérique et expérimentale du cisaillement d’un acier doux en grandes déformation : anisotropie, effet d'histoire et effet de la vitesse de déformation
No full textWhile the propulsion mode of automobiles seems to be shifting from internal combustion to electric power, the manufacturing method for the vehicle body is still mainly based on the assembly of sheet metal formed by plastic deformation. Increased knowledge of the behavior of the sheet materials can help, through numerical forming and crash simulations, to optimize the quantity of material to be used for the vehicle body.To expand the database of experimental data on material behavior, 2 complementary experimental set-ups involving large shear strains have been developed.The first device is based on the in-plane torsion test, which enables shear kinematic to be applied under quasi- static and dynamic conditions. This test also enables all material directions to be loaded simultaneously, providing direct access to the material's anisotropy across the entire surface of the metal sheet.The second device is based on the simple shear test: 2 translating jaws and a rectangular specimen. The innovative idea is to sequentially machine the free edges of the rectangular specimen, where the limitations of the simple shear test are concentrated. The central zone of the specimen can therefore achieve large strains under simple shear kinematic, keeping the simple shear test’s simplicity and straightforward analysis.Linear load paths are useful for determining damage accumulation laws. However, during forming and further impact, a material element undergoes complex loading paths. To investigate the performance of the various damage indicators proposed in the literature, an experimental campaign was carried out up to fracture for differentcombinations of 2 proportional paths.Alors que la propulsion automobile évolue du thermique vers l'électrique, le procédé de fabrication de la caisse du véhicule repose toujours sur l’assemblage de tôles mises en forme par déformations plastiques. Une connaissance accrue du comportement de ces matériaux permet, grâce aux simulations numériques de mise en forme et de crash, d’optimiser la quantité de matière utilisée pour la réalisation de la structure.Afin d’élargir la base de données expérimentales sur ces matériaux, deux dispositifs expérimentaux complémentaires appliquant des sollicitations de cisaillement en grandes déformations sont présentés.Le premier repose sur l’essai de torsion plane, permettant d’appliquer un cisaillement dans des conditions quasi- statiques et dynamiques. Cet essai sollicite toutes les directions du matériau simultanément, permettant un accès direct à l’anisotropie du matériau dans le plan de la tôle métallique.Le second dispositif est basé sur l’essai de cisaillement simple : 2 mors en translation et une éprouvette rectangulaire. Cet essai est limité par des phénomènes locaux aux bords libres. L’innovation consiste à re-usiner ces bords de manière séquentielle, permettant ainsi d’atteindre de grandes déformations tout en conservant la simplicité de l’essai.Les trajets de chargements linéaires sont essentiels pour la calibration de modèles de cumul d’endommagement. Cependant, lors d’une phase de mise en forme ou d’un impact, le matériau subit des trajets complexes. Afin de qualifier les modèles de cumul d’endommagement proposés dans la littérature, une campagne expérimentale dedétermination de la déchirure pour différentes combinaisons de 2 trajets proportionnels a été réalisée
Non-parametric Multi-Partitions Clustering
No full textInternational audienceIn the framework of model-based clustering, a model, called multi-partitions clustering, allowing several latent class variables has been proposed.This model assumes that the distribution of the observed data can be factorized into several independent blocks of variables, each block following its own mixture model.In this presentation, we assume that each block follows a non-parametric latent class model, {\it i.e.} independence of the variables in each component of the mixture with no parametric assumption on their class conditional distribution. The purpose is to deduce, from the observation of a sample, the number of blocks, the partition of the variables into the blocks and the number of components in each block, which characterise the proposed model. By following recent literature on model and variable selection in non-parametric mixture models, we propose to discretize the data into bins. This permits to apply the classical multi-partition clustering procedure for parametric multinomials, which are based on a penalized likelihood method (e.g. BIC). The consistency of the procedure is obtained and an efficient optimization is proposed. The performances of the model are investigated on simulated data
L'égalité n'est pas l'unité : le Conseil d'État soumet les prestations des cantines pénitentiaires aux circonstances locales
No full textInternational audienc
Histoire de la psychothérapie institutionnelle des années 1950 à nos jours
No full textInternational audienc
Étude spatiale de l’Antiquité tardive: L'approche websig du projet Atlas
No full textInternational audienceCe chapitre traite des méthodologies et des approches utilisées pour créer le WebSIG et la collecte de données qui en découle dans le cadre du projet ATLAS. L’un des principaux défis de l’approche interdisciplinaire intégrée est la collecte et la combinaison de trois types de données différents : archéologiques, épigraphiques et littéraires. La disparité des types de données constitue un défi pour le développement d’un WebSIG véritablement intégré. Malgré ces défis, le WebSIG ATLAS a été en mesure de fournir un WebSIG en accès libre combinant les ensembles de données. La combinaison et l’analyse de ces trois sources de données au sein du WebSIG est une nouveauté et permet aux chercheurs de différents horizons de placer les découvertes dans leur contexte plus large et de développer de nouvelles idées sur la structure urbaine dans l'Antiquité tardive