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Macromolecular and mechanical changes in aged silicones
No full textInternational audienceThree room temperature-vulcanized rubbers were thermally aged under air at 250°C or submitted to aminolysis at room temperature. Ageing was followed by uniaxial tensile testing, sol gel measurements in toluene, and Time Domain Double Quantum NMR characterization. Mechanical tests were exploited to identify the parameters of the Ogden model so as to describe the hyperelastic behavior of PDMS. Sol gel and Double Quantum NMR were used to track and quantify macromolecular changes within the samples. A multiscale correlation between the results of each technique was proposed to highlight the understanding of multiscale analysis in rubber ageing
Physics-informed deep homogenization approach for random nanoporous composites with energetic interfaces
No full textInternational audienceThis contribution presents a new physics-informed deep homogenization neural network model for identifying local displacement and stress fields, as well as homogenized moduli, of nanocomposites with periodic arrays of porosities under general loading conditions. Notably, it accounts for the surface elasticity effect, utilizing the Gurtin-Murdoch interface theory. First of all, a fully connected neural network model is established that maps the spatial coordinates, passing first through several sinusoidal functions, to the microscopic displacements. The loss function is formulated as the weighted sum of residuals of Navier-Cauchy equations in the bulk domains and the Young-Laplace equations on the energetic surfaces, evaluated on separate sets of collocation points. To more effectively predict stress concentrations inside the microstructures, we introduce fully trainable weights to each collocation point. The capacity and effectiveness of the new homogenization technique for capturing the size-dependent local and global response of nanocomposites with distinct pore sizes and shapes are verified upon extensive comparisons with the finite-element benchmark results, under various loading conditions. New results showcase the proposed theory’s ability to model random distributions of nano-porosities with a high degree of accuracy, a task not easily achievable with alternative techniques except for the specialized finite-element method
Coupled effects of hygrothermal degradation and fatigue damage of sheet molding compound (SMC) composite
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L’orientation des fibres du bois sous différents angles : de la caractérisation destructive ou non-destructive, par tomographie ou balayage de points lasers, à la prédiction des propriétés mécaniques locales de bois sciés
No full textOriginal experimental methodologies were developed to determine the 3D orientation of fibres of timber pieces by serial planing using optical measurements coupled with laser scanning. The use of the Gradient Structure Tensor (GST) accelerates this process, rapidly and robustly estimating the radial direction of the wood without prior segmentation of the growth rings. Its application to tomographic images confirmed the potential of this approach for non-destructive characterisation of the internal orientation and mechanical properties of sawn wood. The explicit integration of these orientation fields into finite element simulations (FEM) proved decisive in predicting local stiffness variations, validated by image correlation (DIC). The results also show that the local radial direction has a major influence, neglected in current approaches. These methodologies for determining fibre orientation provide access to experimental data for calibrating fibre deviation models and pave the way for improved mechanical grading tools based on a better understanding of the links between anatomical structure and mechanical behaviour.Des méthodes expérimentales originales ont été développées pour déterminer par rabotage sériel l’orientation 3D des fibres à partir de mesures optiques couplées à un balayage laser. L’exploitation du Gradient Structure Tensor (GST) a permis d’accélérer ce processus, en estimant la direction radiale du bois de manière rapide et robuste, sans segmentation préalable des cernes. Son application à des tomographies a confirmé le potentiel de cette approche pour une caractérisation non destructive de l’orientation interne et des propriétés mécaniques des bois sciés. L’intégration explicite de ces champs d’orientation dans des simulations éléments finis (FEM) s’est révélée déterminante pour la prédiction des variations de rigidité locale, validée par corrélation d'image (DIC). Les résultats montrent également que la direction radiale locale exerce une influence majeure, négligée dans les approches actuelles. Ces méthode de détermination de l'orientation des fibres offrent un accès à des données expérimentales de calibration des modèles de déviation des fibres et ouvrent la voie à une amélioration des outils de classement mécanique, fondée sur une meilleure compréhension des liens entre structure anatomique et comportement mécanique
Improving static workspace of a suspended cable-driven robot
No full textInternational audienceThis paper introduces optimization criteria to enhance the static equilibrium workspace of a suspended reconfigurable four cable-driven robot prototype. The proposed approach exploits the mobility of cable attachment points on the platform and extends their range using a new slider design offering two configurations: (i) cable attachment fixed at the slider center and (ii) cable attachment offset by 27 mm from slider center. The second configuration allows the platform to move and remain horizontal within 46 % of the reachable static equilibrium workspace. Simulation results demonstrate that positioning the cable attachment points as in configuration (ii), and moving them closer to the top of the platform, improve the platform's ability to correct its inclination. However, this configuration may reduce stability but expand the static workspace coverage. The prototype uses four cables and two embedded belts on the platform to control both position and orientation, unlike traditional cable-driven robots. Industrial applications include precision agriculture, such as hydroponics, as well as pick-and-place tasks and 3D printing. Future work will focus on experimentally validating these simulation results of the static equilibrium workspace with the new slider design for the two cable attachment configurations. Ce papier présente des critères d'optimisation pour améliorer l'espace de travail statique d'un robot parallèle suspendu à quatre câbles et reconfigurable. L'approche proposée exploite la mobilité des points de fixation des câbles sur la plateforme et étend leur portée en utilisant un nouveau design de curseur offrant deux configurations : (i) fixation des câbles au centre du curseur et (ii) fixation des câbles décalée de 27 mm par rapport au centre du curseur. La deuxième configuration permet à la plateforme de se déplacer et de rester horizontale dans 46 % du volume de l'espace de travail statique atteignable. Les résultats de simulation montrent que la position des points de fixation des câbles dans la configuration (ii), ainsi que leur déplacement plus près du sommet de la plateforme, améliorent la capacité de la plateforme à corriger son inclinaison. Cependant, cette configuration peut réduire la stabilité mais agrandit la couverture de l'espace de travail statique. Le prototype utilise quatre câbles et deux courroies intégrées à la plateforme pour contrôler à la fois la position et l'orientation, contrairement aux robots traditionnels à câbles. Les applications industrielles incluent l'agriculture de précision, comme l'hydroponie, ainsi que des tâches de pick-and-place et l'impression 3D. Les travaux futurs se concentreront sur la validation expérimentale des résultats de simulation de l'espace de travail statique avec le nouveau design du curseur et les deux configurations de fixation des câbles.</div
Influence of the process on water permeability of semi-crystalline PLA nanocomposites: solvent casting versus annealing of melt-blended films
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A penalization-based strong partitioned coupling with application to cavitation-induced damage
No full textInternational audienceA novel strong partitioned coupling strategy is developed in order to address Fluid–Structure Interaction (FSI) problems. The Brinkman penalization method is adopted to model the deformable fluid–solid interface on a fixed Cartesian grid. Originally designed for single-phase flows and rigid bodies, the penalization method is extended to compressible multiphase flows and deformable walls. This numerical model is applied to the analysis of cavitation-induced damage at the microscopic scale, focusing on the shock-induced collapse of a single bubble near an elastoplastic material. We examine the effect of initial bubble–wall distance on wall pressure, material damage and permanent wall deformation (i.e., cavitation pit). This parametric study is conducted for different material yield strengths. Both pit depth and area increase rapidly as the bubble–wall distance and yield strength decrease. Whereas closer bubbles generate a deep, circular pit, more distant bubbles can produce a shallower, annular pit. The effect of FSI coupling is thoroughly analyzed across all parametric configurations. Wall deformation results in the damping of wall pressure, leading to differences in material damage between weakly and strongly coupled simulations. At the moment of impact, the damping of wall pressure is initially governed by the ratio of the acoustic impedances of the fluid and solid media. It is then further amplified locally by plasticity or, more generally, in regions of higher deformation. A small reduction in wall pressure leads to a much more significant damping in both pit depth and pit area. While the decrease in wall pressure is locally affected by material deformation, the change in pit size remains approximately constant for all configurations
Geometric error compensation through position feedback modification and comparison of correction strategies in 3- axis machine-tool
No full textInternational audienceIn machine-tools, geometrical defects are unavoidable. They can greatly affect the dimensional accuracy of the final workpiece if not corrected. Software compensation strategies are less expensive than mechanical adjustments and they provide great improvement in volumetric accuracy. In this study, different compensation methods are compared in a 3-axis milling applications: Numerical Controller (NC) internal compensation tables, modification of the programmed tool-path (G code) and modification of position feedback signals. The latter is the main purpose of this work, because it shows great potential and is not linked to one particular type of NC. It communicates with a custom software application that processes the position data and generates corrected signals according to a geometric model based on the rigid body assumption. The NC is then induced to perform volumetric error correction based on its default programming. The compensation methods are compared based on their ability to bring out or correct imposed geometric errors. The highlighted solution shows performances comparable to the G-code modification by correcting more than 96% of the imposed geometric errors without affecting the numerical chain from the program generation to its execution on the machine. It is also independent of the NC or the motors control cards
Amélioration de la prédiction des limites de ductilité des matériaux polycristallins en utilisant des schémas multi-échelles pertinents
No full textThe main objective of this PhD thesis is to improve the capabilities of the developed numerical methods and tools in the prediction of the ductility limits of polycrystalline metal sheets using the Crystal Plasticity Finite Element Method (CPFEM). This method uses a polycrystalline Representative Volume Element (RVE) to accurately capture the mechanical characteristics of metal sheets. The periodic homogenization multiscale scheme is adopted to ensure the transition between the RVE and single crystal scales. At the single crystal scale, the constitutive framework follows a finite strain rate-independent formulation, with the plastic flow governed by the Schmid law. To improve the predictive capabilities of the developed computational approach, the effects of kinematic hardening, dislocation density-based hardening, grain size, and damage within the framework of Continuum Damage Mechanics (CDM) are incorporated into the single crystal constitutive modeling. Furthermore, the effects of microstructural parameters (e.g., morphological and crystallographic textures) are investigated. At the macroscopic scale, the ductility limits are predicted under the plane-stress assumption using the Rice bifurcation theory. The findings of this thesis demonstrate that these advanced multiscale approaches provide a robust and reliable tool for accurately predicting the ductility limits of polycrystalline metal sheets.L’objectif principal de cette thèse de doctorat est d’améliorer les capacités des méthodes et outils numériques développés dans la prédiction des limites de ductilité des tôles métalliques polycristallines à l’aide de la méthode des éléments finis en plasticité cristalline (CPFEM). Cette méthode utilise un Volume Elémentaire Représentatif (VER) polycristallin pour capter avec précision les caractéristiques mécaniques des tôles étudiées. La technique d’homogénéisation périodique est adoptée pour assurer la transition entre l’échelle du VER et celle du monocristal. À l’échelle du monocristal, le comportement mécanique suit une formulation élastoplastique en grandes déformations, avec un écoulement plastique régi par la loi de Schmid. Pour améliorer les capacités prédictives de l’approche numérique développée, les effets de l’écrouissage cinématique, l’écrouissage isotrope basé sur la densité des dislocations, la taille de grains et l’endommagement microscopique sont intégrés dans le modèle constitutif du monocristal. De plus, les effets des paramètres microstructuraux (e.g., textures morphologiques et cristallographiques) sont étudiés. À l’échelle macroscopique, les limites de ductilité sont prédites sous l’hypothèse de contraintes planes en utilisant le critère de bifurcation de Rice. Les résultats de cette thèse démontrent que ces approches multi-échelles avancées fournissent un outil robuste et fiable pour prédire avec précision les limites de ductilité des tôles métalliques polycristallines
Optimizing social interactions in VR
No full textInternational audienceTechnological developments have made Virtual Reality (VR) technologies accessible, and have democratized its use for industrial, cultural or entertainment purposes. VR can be seen as a unique medium: while being immersed together in a virtual environment (VE), people can feel the presence of each other as if they were in the same physical space even if they are far apart in reality. This phenomenon is known as co-presence. The VR medium introduces specific factors influencing on the dynamics of the social interaction. This PhD project aims at understanding that dynamics through the study of co-presence