Influence of strain-induced crystallization on the crack driving force in fracture behavior of rubber

International audienceFatigue crack growth resistance increases with the loading ratio due to strain-induced crystallization, even if the peak stress increases. Recent experiments have allowed determination of the strain-induced crystallization (SIC) distribution around a crack tip during uninterrupted fatigue tests. The purpose of this work is to compare spatial distributions of crystallinity in a cracked sample at different elongations between one experiment and simulation results based on our model

Analyse de stabilité d'une nappe fibrée en compression

National audienceL'objectif de ce travail est de modéliser le flambement de nappes fibrées lorsque les câbles sont soumis à une compression axiale. Nous réalisons une analyse de stabilité multi- échelles basée sur le résultat de [1], qui permet de réduire le problème à une cellule élémentaire 2D et de modéliser les modes propres sous forme d'ondes de Bloch. Nous avons choisi de nous placer dans le cas particulier d'une flexion circulaire, mais la méthode proposée est valable pour des chargement plus généraux

Robust filtering for joint state parameter estimation for distributed mechanical systems

International audienceWe present an effective filtering procedure for jointly estimating state variables and parameters in a distributed mechanical system. This method is based on a robust, low-cost filter related to collocated feedback and used to estimate state variables, and an $H^\infty$ setting is then employed to formulate a joint state-parameter estimation filter. In addition to providing a tractable filtering approach for an infinite-dimensional mechanical system, the $H^\infty$ setting allows to consider measurement errors that cannot be handled by Kalman type filters, e.g. for measurements only available on the boundary. For this estimation strategy a complete error analysis is given, and a detailed numerical assessment - using a test problem inspired from cardiac biomechanics - demonstrates the effectiveness of our approach

O método do Lagrangeano aumentado no estudo de cabos umbilicais

O objetivo deste trabalho é apresentar um modelo numérico para cabos umbilicais hiperelásticos que experimentem grandes deslocamentos e grandes rotacoes. O modelo mecanico resulta num sistema náo-linear, que é resolvido por um método de decomposicáo-coordenacao via Lagrangeano Aumentado. Este tratamento posibilita a descricáo do acoplamento existente entre flexao e torcáo em cabos submetidos A grandes delocamentosPeer Reviewe

Filtering for distributed mechanical systems using position measurements: perspectives in medical imaging

International audienceWe propose an effective filtering methodology designed to perform estimation in a distributed mechanical system using position measurements. As in a previously introduced method, the filter is inspired from robust control feedback, but here we take full advantage of the estimation specificity to choose a feedback law that can act on displacements instead of velocities and still retain the same kind of dissipativity property which guarantees robustness. This is very valuable in many applications for which positions are more readily available than velocities, as in medical imaging. We provide an in-depth analysis of the proposed procedure, as well as detailed numerical assessments using a test problem inspired from cardiac biomechanics, as medical diagnosis assistance is an important perspective for this approach. The method is formulated first for measurements based on Lagrangian displacements, but we then derive a nonlinear extension allowing to instead consider segmented images, which of course is even more relevant in medical applications

Glissement intermateriaux lors de simulations ALE en grandes déformations et grandes vitesses

National audienceLors de simulations de milieux multimatériaux en grandes déformations avec une méthode ALE, l'interface entre les matériaux peut se retrouver à l'intérieur des mailles de calcul. Il faut donc mettre en place une stratégie spécifique dans ces mailles mixtes. La méthode proposée, basée sur les éléments finis enrichis permet d'avoir un champ de vitesse propre à chaque matériau y compris dans les mailles mixtes. La réunion des différents champs de vitesse peut présenter une discontinuité sur l'interface ce qui donne la liberté nécessaire à la simulation du glissement entre les matériaux.See http://hal.archives-ouvertes.fr/docs/00/59/27/08/ANNEX/r_MF58LJ0L.pd

Multiscale thermomechanical modeling of shock-driven dry friction in hydrodynamics

International audienceThe purpose of the present work is to provide new insights in the understanding and computational modeling of shock-induced metal-on-metal dry friction. Based on a multiscale approach, we develop herein a 1D finite difference subgrid model. To adequately describe the physics of dynamic friction under shock-induced conditions, it accounts for frictional contact, elastoplastic yielding and work hardening, heating by friction and plastic work, thermal softening and melting, as well as dynamics effects. Temperature and dynamic elastoplasticity are predicted at a local scale through a nonlinear time implicit numerical solver. Two strategies have been considered for the coupling of the subgrid model to a standard thermoelastoplastic macroscopic model. The first one is velocity driven. Its implementation is rather straightforward, it leads to correct qualitative results but is restricted to sliding situations. To account for stick–slip cases, a second force driven downscaling strategy has been developed

An a posteriori Error Estimate of Hierarchical Type

Projet M3NIn this work we present a new a posteriori parameter free error estimate of hierarchical type and we apply this error estimate to the elasticity equations for linear isotropic heterogeneous materials. This estimate is proved to be optimal, independently of the material heterogeneities. The proof introduces an easy to check fundamental inf-sup condition, which implies the saturation assumption and partition lemma usually assumed in the analysis of hierarchical estimates. Insight on the numerical implementa- tion and various numerical examples are finally presented

Structures en grands déplacements couplées à des fluides en mouvement

Projet M3NLe calcul en configuration Eulérienne d'écoulements visqueux dans des structures fortement défor­mables (écoulements dans des tuyaux collabables, amortisseurs hydrauliques) pose des problèmes difficiles de compatibilité cinématique et d'actualisation de géo­mé­trie. Pour surmonter ces difficultés, on propose de traiter la structure et le fluide comme un milieu continu unique et d'en rapporter le mouvement à la configuration de calcul délimitée par la structure au repos. Le problème obtenu est ensuite séparé en une partie fluide et une partie solide par décomposition de l'espace des vitesses cinématiquement admissibles. Cette séparation conduit ainsi à une modélisation purement lagrangienne de la structure couplée à une formulation ALE du problème fluide. Cette stratégie a trois avantages qui sont développés dans l'article~: - - - elle permet d'introduire des schémas de discrétisation en temps et des algorithmes de couplage simples qui respectent la compatibilité cinématique à l'interface et qui ont les bonnes propriétés énergétiques~; - - - elle autorise l'emploi d'éléments finis indépendants sur la structure et sur le domaine fluide~; - - - elle permet d'utiliser directement les modèles récents de coques hyperélastiques en grands déplacements, et de garantir ainsi la cohérence mathématique et l'objectivité du modèle de structure choisi. Cette méthodologie a été intégrée dans un code de calcul industriel et a été validée sur des problèmes industriels de calcul d'amortisseurs hydrauliques présentés en fin d'article

Solving dynamic contact problems with local refinement in space and time

International audienceFrictional dynamic contact problems with complex geometries are a challenging task from the compu tational as well as from the analytical point of view since they generally involve space and time multi scale aspects. To be able to reduce the complexity of this kind of contact problem, we employ a non conforming domain decomposition method in space, consisting of a coarse global mesh not resolving the local struc ture and an overlapping fine patch for the contact computation. This leads to several benefits: First, we resolve the details of the surface only where it is needed, i.e., in the vicinity of the actual contact zone. Second, the subproblems can be discretized independently of each other which enables us to choose a much finer time scale on the contact zone than on the coarse domain. Here, we propose a set of interface conditions that yield optimal a priori error estimates on the fine meshed subdomain without any artificial dissipation. Further, we develop an efficient iterative solution scheme for the coupled problem that is robust with respect to jumps in the material parameters. Several complex numerical examples illustrate the performance of the new scheme