Une formulation variationnelle du problème de contact avec frottement de Coulomb

A variational relationship is proposed as the weak form of the large deformation contact problem with Coulomb friction. It is a mixed relationship involving both the displacements and the multipliers; the weighting functions are the virtual displacements and the virtual multipliers. It is shown that the proposed weak form is equivalent to the strong form of the initial/boundary value contact problem and the multipliers are equal to the contact tractions. To cite this article: A. Le van, T.H.T. Nguyen, C. R. Mecanique 336 (2008).     

L'approche variationnelle de la fatigue : des premiers résultats

By using a principle of least energy and a Dugdale surface energy with an irreversibility condition, we build a debonding model of thin films valid both for monotone and cyclic loading. We show that, if the internal length introduced in Dugdale model is small in comparison to the film length, then the growth of the debonding follows Griffith's law under monotone loading and a Paris-type law under cycling loading. To cite this article: A. Jaubert, J.-J. Marigo, C. R. Mecanique 333 (2005).     

Les états de coaction. Aspects spécifiques et influence opérationnelle

Meccanica - Il rapporto si propone di delineare gli aspetti specifici degli equilibri per coazione. A tal fine vengono, in primo luogo, raffrontati gli equilibri da forze e quelli da deformazioni...     

‘Les fleurs du mal’ – an adaptive wavelet method of arbitrary lines I: convection–diffusion problems« Les fleurs du MAL » – une méthode d'ondelettes adaptive de lignes arbitraires I : problèmes de convection–diffusion

Baudelaire's ‘les fleurs du mal’ refers to various new developments (‘les fleurs’) of the method ofarbitrarylines (mal), since it was first published (in C. R. Acad. Sci. Paris, Sér. I, in 1991). Here we revisit the basic mal (semi-discretization) methodology for stationary convection–diffusion problems and develop an adaptive, wavelet-based solver that is capable of capturing the thin layers that arise in such problems. We show the efficacy and high accuracy of the wavelet-mal solver by applying it to a challenging 2D problem involving both boundary and interior layers. To cite this article: X. Ren, L.S. Xanthis, C. R. Mecanique 332 (2004).     

LINEAR ACTIVE STRUCTURES AND MODES （ Ⅰ ） — BASIC CONCEPTS AND PROPERTIES

Some basic concepts about the active structures were firstly explained, and the main subjects to study in the field of active structure dynamics were synthesized. For the linear active structures, the annotations on the modes were done in detail. The physical meanings of the right and left eigenvectors were explained. The right eigenvectors are the modal shapes and the modal responses of an active structure depend on the left ones. The adjoint structure of an active structure was defined and the reciprocity theorem was interpreted. For two active structures, which are adjoint to each other and with the reciprocal gain-matrices, the right and left eigenvector are reciprocal The relationship between an active structure and the corresponding passive structure is expressed with the transfer functions, which is employed to resolve the estimation problems.     

Evolution of fabric tensors in damage mechanics of solids with micro-cracks: Part I – Theory and fundamental concepts

The evolution of fabric tensors based on micro-crack distributions is formulated based on sound thermodynamic principles. In Part I of this work, the exact definition of fabric tensors based on micro-crack distributions is presented. This definition is seen to incorporate both the orientation and length of a micro-crack. In this regard, the micro-crack distribution is assumed to be radially symmetric, i.e. symmetric about a line through the origin.The equations of thermodynamics are employed in order to derive the exact evolution equations of the fabric tensors defined in the first part. In this regard, a thermodynamic force that is associated with the fabric tensor is defined and utilized in the derivation of the evolution equations. The application of the theory to the case of uniaxial tension is derived in Part II (companion paper) of this work.     

Reactive plasticity for clays during dehydration and rehydration. Part 1: concepts and options

A mixture theory framework is adapted to analyze the effects of changes in clay chemistry during dehydration and rehydration on clay mechanical properties. Macroscopic and microscopic evidence points to a possibility of modeling the mineralogical processes of illitization of smectites and re-smectitization of illite as kinetic reactions in closed systems. A version of thermo-chemo-plasticity for rehydrating illite is presented in which a hidden variable of hardening depends on temperature and the reaction progress variable in addition to plastic strain.     

Buckle propagation in pipe-in-pipe systems.: Part I. Experiments

Pipe-in-pipe systems are extensively used in offshore pipeline applications in which thermal insulation of the pipeline is necessary. Typically, the space between the two pipes is either empty or contains insulation material which provide minimal mechanical support to the system. In deepwater applications, the carrier pipe must be designed to resist collapse due to the ambient external pressure while the design of the inner pipe is usually governed by the pressure of the hydrocarbons it carries. The integrity of the two-pipe system in the event of accidental collapse of the carrier pipe is an issue of concern.In Part I of this two-part report, the results of an extensive experimental study of the problem are presented. The experiments were carried out on two-inch diameter carrier tubes with D/t values of 24.1, 21.1 and 16.7 and inner tubes of several diameters and wall thicknesses. In most cases local collapse of the outer tube led to simultaneous collapse of the inner one. Subsequently, the collapse propagated simultaneously collapsing both pipes. The propagation pressure of the two-pipe system (P_P2) has been quantified parametrically. An interesting second mode of collapse propagation was also discovered in which the carrier pipe collapses leaving the inner one intact. Propagation of collapse affecting both pipes is still possible but usually at a higher pressure level. The pressure at which this switch takes place has been found to closely correspond to the propagation pressure of a carrier pipe with a solid rod insert (P_PS) of the same diameter as the inner pipe. The parametric dependence of P_PS has also been established experimentally. Part I finishes with a discussion of how these new critical pressures of pipe-in-pipe systems should influence the design of such pipelines.     

Comportement rheologique de sols d'acide polysilicique. II. Etude de la gélification

Résumé L'analyse du comportement rhéologique de sols d'acide polysilicique en solution aqueuse de concentration supérieure à 7 g 1^–1 de silice en fonction du pH entre 6 et 11 et de la température entre 25 et 45 °C a permis de situer la gélification dans un domaine de pH compris entre 8 et 10. Ce processus prend une intensité maximale à 30°C. Le comportement rhéofluidifiant à bas gradients de cisaillement et antithixotrope donne naissance sur les rhéogrammes à un point d'inversion à pH = 9. L'ionisation des groupes silanols à la surface des particules colloïdales permet la réorganisation du milieu après cisaillement. Un état d'ionisation trop élevé est responsable d'un effet electro-répulsif à pH = 10. L'influence de la concentration et de la température sur ces processus est discutée.

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The rheological behavior of polysilicic acid in aqueous solutions at higher concentrations than 7 g 1^–1 of silice is studied for pH between 6 and 11 with temperature varying from 25° to 45°C. This study indicates that gelification takes place between pH 8 and 10. The process of gel formation attains the highest intensity at 30°C. The shear-thinning behavior at low shear rate gives rise to an inversion point at pH = 9 in shear stress—shear rate curves. The state of ionization at the surface of colloïdal silice particles after shear involve shear thickening observed at pH = 9. A high ionization degree causes an electrostatic repulsion at pH = 10. The concentration and temperature effects upon the organization of network are discussed.