Le papier concerne l'outil numérique parallèle développé pour l'étude des interactions entre corps rigides ou déformables. Les interactions concernent d'une part la séparation dans le cadre de la rupture dynamique de matériaux hétérogènes et d'autre part le contact entre particules en présence de fluide. La plateforme numérique associée repose sur le couplage du logiciel LMGC90 (Dynamique des Contacts) pour la prise en compte d'interactions complexes entre les corps et la bibliothèque PELICANS pour la résolution des comportements volumiques (Eléments finis ou Volumes Finis) des corps.

Numerous modelling strategies have been used over the last decade to improve the understanding of the physical behaviour of the railway track system thanks to numerical simulation. In this context, discrete element (DE) methods are traditionally used to describe the granular behaviour of the ballast layer of the railway track whereas finite element (FE) methods are used to model the whole track system (soil and ballast) in which ballast is modelled as a continuous medium. If both approaches offer relevant modelling frameworks to study railway track, this work aims at going further by coupling those two approaches in an hybrid FE-DE model, making possible the improvement of the understanding of the global behaviour of the railway track. This paper aims to describe different aspects of the methodologies which are currently in LMGC90 software.

La méthode d'Eigenerosion développée par Pandolfi et Ortiz [ Int. J. Numer. Methods Eng. Wiley 92 (2012) 694-714 ] combine l'approche variationnelle de Francfort et Marigo [ J. Mech. Phys. Solids Elsevier 46 (1998) 1319-1342 ] et une méthode de type ((killing element)) pour permettre une simulation rapide et efficace de la fissuration des matériaux homogènes. Une extension de cette méthode aux matériaux hétérogènes est proposée ici et appliquée à la multi-fissuration d'un béton modèle. Les effets dissociés de la fraction volumique de granulats et de la polydispersité de leur taille sont analysés au travers d 'une étude paramétrique.

In 1921, Griffith introduced the concept of energy release rate in brittle fracture: below a certain amount of energy, no crack extension can occur. A variational formulation of this idea has been proposed by Francfort and Marigo [1] in the late 90's whose a regularization (1) has been recently developed by Schmidt et al. [4].

Sur la base de l'approche variationnelle de la rupture de Francfort et Marigo [2], Pandolfi et Ortiz [6] ont proposé une méthode — d'Eigenerosion — s'apparentant à une méthode de «killing element » et respectant le critère de Griffith. Les travaux proposés ici portent sur la mise en œuvre de la méthode et sur son extension à la dynamique et aux matériaux hétérogènes.

In this chapter we propose a graphic display tool for the results of calculations carried out using a discrete element code: Graphic Interface for Discrete Element Code (GIDE). This is a post-processing application written in C++ based on portable open source libraries, making GIDE compatible with different OS (Windows, Linux, Unix, MacOS, etc.).

In this study a numerical approach to simulate elastic behavior of lightweight concrete, is presented, at mesoscopic level. Concrete is considered as a bi-phasic material, composed of a granular skeleton dispersed in a mortar. Aggregates generation should respect a granular model where a maximum distance between aggregates is imposed. The granular media is also defined by a granular curve and a compacity. A numerical concrete sample is carried out, using three-dimensional finite element mesh. Here lightweight concretes are considered, where Young's modulus of natural sand based mortar is higher than the modulus of the lightweight coarse aggregates. Different concretes are carried out, according to experimental studies from literature, in order to distinguish the influence of Young's modulus contrast, and of the concrete compacity, on mechanical behavior. Then numerical compressive tests are realized until an experimental value of compressive strength, and the local stress and strain distribution around aggregates is studied, still remaining in the elastic domain. According to these results, breaking of this kind of concrete occurs when the maximum strain is reached in the lightweight aggregates surrounded mortar.