Radiation effects in concentrated alloys and compounds: equilibrium and kinetics of driven systems

What organization of condensed matter does resist irradiation, as a function of irradiation conditions? How to characterize the latter? We survey the advances in the field during the past three decades, when irradiation effects reduce to nuclear collisions. While in simple cases (structure defined by a scalar order parameter) one may define a stochastic potential, which yields the stationary states of the compounds under irradiation and their respective stability, in more general cases, we are left with brute force atomistic simulations to explore materials' behaviour as a function of irradiation conditions. Special attention is given to the kinetics of concentration fields under irradiation, a question with several practical implications. We conclude that irradiation conditions are best defined by three parameters: the cascade features (number of displacements and replacements, length of replacement sequences, …), the frequency of cascade occurrence, and the cumulated dose. We suggest cascade features be named ‘(elementary) dose’ and the cascade occurrence frequency ‘dose rate’. To cite this article: G. Martin, P. Bellon, C. R. Physique 9 (2008).     

Approche micromécanique du couplage perméabilité–endommagementMicromechanical approach to the coupling between permeability and damage

A self-consistent scheme is used in order to determine the permeability of a cracked porous medium. For weak values of the permeability of the uncracked porous matrix, it is found that the order of magnitude of the permeability increases beyond a critical threshold of the crack density parameter. In the framework of a micromechanical model, it is shown that both the evolution of crack opening and the crack propagation are controlled by Terzaghi's effective stress which therefore captures the coupling between permeability and mechanical loading. To cite this article: L. Dormieux, D. Kondo, C. R. Mecanique 332 (2004).     

A micromechanical analysis of damage propagation in fluid-saturated cracked mediaUne analyse micromécanique de la propagation de l'endommagement d'une fissure sous pression de fluide

We first revisit the well known framework of Linear Elastic Fracture Mechanics (LEFM) in the case of a fluid-saturated crack. We next consider a r.e.v. of cracked medium comprising a family of cracks characterized by the corresponding crack density parameter ε. Generalizing the classical energy approach of LEFM, the proposed damage criterion is written on the thermodynamic force associated with ε, which is estimated by means of standard homogenization schemes. This criterion proves to involve a macroscopic effective strain tensor, or alternatively the Terzaghi effective stress tensor. The stability of damage propagation is discussed for various homogenization schemes. A comparison with experimental results is presented in the case of a uniaxial tensile test on concrete. To cite this article: L. Dormieux et al., C. R. Mecanique 334 (2006).     

Une condition de déviation des fissures dans les CMC et les multicouches

A crack deflection criterion is proposed on the basis of the Cook and Gordon mechanism. The stress state induced by a crack was computed in an elementary cell of bimaterial using the finite element method. An interface failure criterion was established in terms of strengths and elastic moduli of constituents. A master curve was produced. It allows matrix crack deflection to be predicted with respect to constituents properties and interface strength. The model can be used also to evaluate the strength of interfaces and interphases in ceramic matrix composites and in multilayers. To cite this article: S. Pompidou, J. Lamon, C. R. Mecanique 333 (2005).     

On the non-conservativeness of a class of anisotropic damage models with unilateral effectsSur le caractère non-conservatif de quelques modèles d'endommagement anisotrope avec conditions unilatérales

The aim of this Note is to show that a class of anisotropic elastic-damage models including unilateral effects can be considered, for constant damage values, as non-linear and non-conservative elastic. The conservative character of corresponding constitutive models is related to the symmetry of the Hessian tensor. For the models under consideration, it is shown that the condition of conservativeness (existence of the elastic potential energy function) is obtained only when there is coaxiality of the strain and damage tensors. To cite this article: N. Challamel et al., C. R. Mecanique 334 (2006).     

Positivité de la dissipation intrinsèque d'une classe de modèles d'endommagement anisotropes non standardsPositivity of intrinsic dissipation of a class of nonstandard anisotropic damage models

A nonstandard thermodynamics framework ensures the positivity of the dissipation due to degradation mechanisms for damage states represented by a symmetric second order tensor. The proof of the positivity of the intrinsic dissipation is given. An increasing damage, in terms of positive principal values of the damage rate tensor, guaranties this positivity for the considered class of models, extending then to induced anisotropy the isotropic case property of a positive damage rate. This result gives many possibilities of modeling for anisotropic damage. To cite this article: R. Desmorat, C. R. Mecanique 334 (2006).     

Détermination du comportement macroscopique d'un milieu à fissures frottantesDetermination of the macroscopic behavior of a medium with frictional cracks

A micromechanical modeling of closed cracks as flat ellipsoidal inhomogeneities has been recently proposed in [Deudé et al., C. R. Mecanique 330 (2002) 589–599]. The present Note extends this approach to the case of a frictional contact between the crack lips. For von Mises friction, a linear hardening is obtained at the macroscopic scale, the state equation in terms of stress and strain rates being identical to that derived for unfrictional cracks. For Drucker–Prager friction, the micromechanical approach predicts a macroscopic dilatant behavior. To cite this article: J.-F. Barthélémy et al., C. R. Mecanique 331 (2003).     

Pont entre les « micro » et « méso » mécaniques des composites stratifiésRelationships between ‘micro’ and ‘meso’ mechanics of laminated composites

A relatively complete bridge is built between the micromechanics of laminates for which there are numerous theoritical and experimental works and the mesomechanics of laminates introduced and developped in particular at Cachan for more than 15 years. At the ‘meso’ scale, the ply and the interface are homogeneized. To cite this article: P. Ladevèze, G. Lubineau, C. R. Mecanique 331 (2003).