Surgénérateurs ; l'état des matériaux aux hautes irradiations, hautes puissances locales et températures, leurs gradients et propriétés mécaniques adaptées aux contraintes qui en résultent

The motivations to realize nuclear breeder reactors are developed in the present context of a strong growth in electronuclear power stations in many countries, using mostly moderated and water cooled reactors.The past studies can be of a substantial profit in France and, to a lesser degree, in other countries of the EU. However, to use fully the 238 uranium isotope, the materials for these breeders must withstand much harder radiation than those for water reactors. The power densities and thermal gradients will also be much more intense. The mechanical stresses, both static and dynamic, will be large and will act on materials with altered mechanical properties. Fuel elements will have to be produced with materials already irradiated several times and therefore showing such alterations.A field of studies concerning materials and their mechanical behavior in new and severe conditions is sketched here, both in construction and working conditions, together with proposed necessary instrumentation and research orientations.     

Rigidité à la torsion d'un cylindre présentant une double périodicité

The objective of the present Note is to estimate the equivalent torsion rigidity modulus for a cylinder whose cross-section Σ exhibits a periodical distribution of porous zones Σ_P. Taking into account a second, finer, periodical distribution of pores in Σ_P, we have to use the homogenization method in a biperiodical context. However, the contrast of scales at the interfaces between Σ_P and the compact part Σ_C of Σ, requires some subtle fitting up of this method. Finally, we point out the existence of boundary layers around the interfaces ∂Σ_P and we estimate the weakening of the torque rigidness. To cite this article: M'B. Taghite et al., C. R. Mecanique 334 (2006).     

Analyse numérique du comportement d''une solution presque périodique d''une équation différentielle périodique par une méthode des sections

After having reminded the reader of the cross section method used by Jean (Int. J. Non-Linear Mech. 15, 367–376, 1980) to localise almost periodic solutions to a T-periodic ordinary differential equation, we give a numerical approximation of the said method. Numerical results are then presented together with evidence of successive bifurcations of the initial torus of solutions into double, quadruple, etc.     

Etude de la direction des véhicules articulés à chenille (l analyse théorique et expérimentale)

This paper presents theoretical and experimental analysis of steering performance of articulated tracked vehicles on level ground. A mathematical model for predicting the steerability of articulated units has been developed and computerized for numerical application. The accuracy of the analog has been verified by scale model tests.From the results of the simulation and scale model tests it was found that steerability was significantly improved and required sprocket torques for steering and track slippage were considerably decreased in articulated tracked vehicles when compared with a single and coupled tracked vehicles.     

Mécanique de la rupture fragile en présence de plasticité : modélisation de la fissure par une entaille

Some issues are met in elastic-plastic fracture mechanics if the crack is modelled by a sharp tipped crack. They may be overcome with a notch model. An energy release rate can be defined using the Francfort and Marigo theory and Continuum Damage Mechanics. In particular, the paradox of Rice and some spurious scale effects are removed with this approach. The results obtained in the case of the analysis of the shallow crack effect are in good agreement with the experimental results. To cite this article: Y. Wadier, E. Lorentz, C. R. Mecanique 332 (2004).     

Homogénéisation de problèmes d''évolution dans une structure renforcée de fibresHomogenization of evolution problems in a fiber reinforced structure

We study the homogenization of evolution equations such as:

where the coefficient a is -periodic and takes very high values on a subset TΩ (fibered structure) of very small measure. We find a non-local effective equation deduced from a homogenized system of several equations. To cite this article: M. Bellieud, C. R. Mecanique 330 (2002) 843–848.     

Vérification expérimentale de la relation de réciprocité d'Onsager pour l'électro-osmose et l'électro-filtration dans une argile naturelleExperimental verification of the Onsager's reciprocal relations for electro-osmosis and electro-filtration phenomena on a saturated clay

This Note is devoted to the experimental verification of the Onsager's reciprocal relations in the particular case of electro-osmosis and electro-filtration. A special set up has been designed to carry out the measurements of both the electro-osmotic permeability and the streaming potential. This has been performed by using a natural material i.e., saturated kaolinite. To cite this article: K. Beddiar et al., C. R. Mecanique 330 (2002) 893–898.     

Résumé and remarks on the open boundary condition minisymposium

The incompressible Navier-Stokes equations—and their thermal convection and stratified flow analogue, the Boussinesq equations—possess solutions in bounded domains only when appropriate/legitimate boundary conditions (BCs) are appended at all points on the domain boundary. When the boundary—or, more commonly, a portion of it—is not endowed with a Dirichlet BC, we are faced with selecting what are called open boundary conditions (OBCs), because the fluid may presumably enter or leave the domain through such boundaries. The two minisymposia on OBCs that are summarized in this paper had the objective of finding the best OBCs for a small subset of two-dimensional test problems. This objective, which of course is not really well-defined, was not met (we believe), but the contributions obtained probably raised many more questions/issues than were resolved—notable among them being the advent of a new class of OBCs that we call FBCs (fuzzy boundary conditions).     

Composites graphite/sel pour le stockage d'énergie à haute température : étude des effets du graphite et de la microstructure des composites sur les propriétés de changement de phase des sels

Thermal energy storage at high temperature is an efficient way for energy saving in the industrial sector, as well as a key component for power generation based on renewable energy resources. Thermal energy storage technology based on phase change materials (mainly salts) has been identified to meet the requirements of investment costs and compactness. However, the low thermal conductivity of salts (1 W/m/K) could be a limiting factor concerning power. To overcome such a drawback, new materials combining salts with graphite have been developed. Nevertheless, it is important to verify that no degradation of the salts storage properties is induced by their thermal conductivity enhancement. In this Note, the effects of the graphite and the composites graphite/salt microstructure on the phase change properties of salts are analysed. To cite this article: J. Lopez et al., C. R. Mecanique 336 (2008).     

Modèles discrets de structures tissées : Analyse de stabilité et de drapéDiscrete models of woven structures: stability and draping analysis

A discrete model of a woven fabric structure is established, whereby nodes endowed with a mass and a rotational rigidity are connected by rigid bars to form a two-dimensional truss. The set of four bars that delineate a quadrilateral area is further endowed with a torsion deformation mode. The kinematics of the truss reproduces the large rotations and displacements encountered for real tissues. The equilibrium shape of such a structure is obtained as the minimum of its total potential energy versus the whole set of kinematic translational and rotational variables, accounting for eventual kinematic constraints due to contact with a rigid surface by the Lagrange multipliers method. A stability analysis is conducted, and the potentiality of the model is illustrated by fabric draping simulations. To cite this article: B. Ben Boubaker et al., C. R. Mecanique 330 (2002) 871–877.     

Une nouvelle technique de détection des endommagements dans les composites basée sur l'utilisation des micro-ondes et des circuits microrubans résonants

In this article, we present an innovative non-destructive method of detecting damage in composite materials. The method is based on the observation and analysis of the modifications in a material's dielectric properties that result from damage. The originality of this method comes from the fact that the diagnostic is obtained by using a microstrip resonator submitted to a microwave electromagnetic field. In this Note, the method's feasibility is demonstrated by the detection of fibre ruptures in a unidirectional composite submitted to flexural loading. To cite this article: J. Rossignol, A. Thionnet, C. R. Mecanique 334 (2006).