Some remarks on the damage unilateral effect modelling for microcracked materials

This study deals with the macroscopic modelling of the mechanical behaviour of microcracked materials and particularly with the unilateral aspect of such damage which leads, at the closure of microcracks, to a partial damage deactivation. By means of a micromechanical analysis, the aim of this article is first to point out the influence of the opening-closure of microdefects on the effective elastic properties of a microcracked medium. According to these considerations, a new elastic moduli recovery condition at damage deactivation is proposed. The introduction of this condition within the anisotropic damage model proposed by Halm and Dragon, 1996 allows to extend its micromechanical background while preserving its main advantages, in particular the continuity of the stress-strain response and the symmetry of the stiffness tensor

A critical review of some damage models with unilateral effect

The concern here is the macroscopic modeling of the brittle damage unilateral effect (due to the opening-closure of microcracks). Several formulations have been proposed in recent years to solve the problems pointed out by Chaboche (Int. J. Damage Mech. 1 (1992) 148). In this paper, we examine precisely two of these new formulations (Int. J. Damage Mech. 2 (1993) 311; Int. J. Damage Mech. 5 (1996) 384) and show that they still exhibit some major inconsistencies

A stress-based macroscopic approach for microcracks unilateral effect

The question of the nonlinear response of brittle materials undergoing elastic damage is investigated here. Owing to the specific nature of microcracking, the macroscopic behaviour of these materials is complex, generally anisotropic owing to the possible preferential orientation of defects and multilinear because of the unilateral effect due to the transition between open and closed state of microcracks. A new three-dimensional macroscopic model outlined by Welemane and Cormery [1] has been proposed to account simultaneously for these both aspects. This paper intends to present in details the principles of such approach and to demonstrate its applicability to a stress-based framework. Based on a fabric tensor representation of the damage density distribution, the model provides a continuum and rigorous description of the contribution of defaults which avoids classical spectral decompositions and related inconsistencies. The model is also strongly micromechanically motivated, especially to handle the elastic moduli recovery that occurs at the closure of microcracks. The macroscopic theoretical framework proposed constitutes a general approach that leads in particular to predictions of a class of micromechanical models. The capacities of the approach are illustrated and discussed on various cases of damage configurations and opening 13closure states, with a special attention to the differences with the strain-based framework and to the influence of the damage variables order

An alternative 3D model for damage induced anisotropy and unilateral effect in microcracked materials

A three-dimensional model of damage by microcrack growth is proposed to account for the mechanical behavior of quasi brittle materials (especially for concrete and rocks). The emphasis is put on the induced anisotropy and on the elastic moduli dependence on the opening and closure of microcracks (unilateral effect). This formulation is based first on a damage characterization throught the microcracked density distribution, and secondly avoids the use of spectral decompositions generally adopted in literature and which induce some major inconsistencies

Basic concepts and models in continuum damage mechanics

In this paper, we present some basic elements of macroscopic modelling of damage. We then recall the general approach of continuum damage based on the thermodynamics of irreversible processes and its application to isotropic damage modelling. The study of damage induced anisotropy is treated by considering a second order tensorial damage variable. Finally, we present an original macroscopic approach through which is addressed the question of unilateral effects due to the microcracks closure

Modélisation micro-macro du comportement élastoplastique endommageable de l'argilite du Callovo Oxfordien

Cette étude est consacrée au développement et à la validation d'une approche d'homogénéisation non linéaire appliquée au comportement mécanique de l'argilite du Callovo-Oxfordien. Le matériau est modélisé comme un composite à trois phases constitué d'une matrice élastoplastique et d'inclusions élastiques linéaires et élastiques endommageables. La loi constitutive macroscopique est obtenue à l'aide d'une adaptation de la méthode incrémentale de Hill (1965). Cette approche aboutit à la construction de l'opérateur tangent macroscopique du matériau qui dépend du comportement local non linéaire des phases. Compte tenu de la morphologie matrice/inclusion de la microstruture de l'argilite du Callovo-Oxfordien, un schéma d'homogénéisation de type Mori-Tanaka est utilisé pour la résolution du problème de localisation. Le modèle ainsi développé est appliqué à la prédiction des réponses macroscopiques contrainte-déformation de l'argilite du Callovo-Oxfordien sous différents trajets de chargement

Une modélisation de l'endommagement et du glissement avec frottement dans les matériaux quasi-fragiles

Sous chargement, les matériaux dits quasi-fragiles tels que les bétons et de nombreuses roches présentent souvent une perte de rigidité progressive, ainsi qu un comportement anisotrope, asymétrique et hystérétique. Il est maintenant largement admis que ce comportement, fortement non linéaire et complexe, est lié principalement à la création, au développement et au jeu d ouverture et fermeture des réseaux de microfissures accompagnés de glissement et de frottement entre lèvres de microdéfauts en contact.Dans l optique d une utilisation industrielle sérieuse, la construction d un modèle d endommagement simple, fiable sur le plan mathématique et thermodynamique et offrant une réponse pertinente pour les matériaux quasi-fragiles jusqu à l apparition d une localisation de l endommagement, constitue à l heure actuelle un enjeu important. Il représente en effet une étape indispensable avant de pouvoir espérer modéliser de manière satisfaisante le comportement jusqu à la ruine de nombreux ouvrages du génie civil.L objectif du travail de thèse est d améliorer les capacités prédictives d un modèle simple d endommagement par microfissuration existant qui prend en compte les effets unilatéraux liés à l ouverture-fermeture des microfissures. La nouvelle approche proposée est basée sur l introduction d un second phénomène dissipatif susceptible d être induit lors de la fermeture des microdéfauts : le glissement avec frottement des lèvres en contact. La modélisation de ce nouveau mécanisme dissipatif s effectue à l échelle macroscopique en ne faisant référence à l échelle inférieure ou aux résultats de la micromécanique des milieux microfissurés que pour interpréter ou justifier certaines hypothèses. Une attention particulière est accordée à la continue différentiabilité du potentiel thermodynamique proposé. L étude et la simulation de différents essais permettent d illustrer la pertinence des choix retenus.LILLE1-Bib. Electronique (590099901) / SudocSudocFranceF

Synthesis of numerical methods for the design of segmental tunnel lining

International audienceThis paper presents a numerical study that aims to compare the behavior of the segmental tunnel lining using the direct, indirect and experimental methods. This model is based on a practical case applied in university of Tongji: a project of water conveyance tunnel. A reduction in the bending moment and increasing of the displacement in the tunnel lining is showed in numerical results, when taking into account the effect of the joints. It has been shown that the number of joints in the tunnel-lining structure highly affects the results in terms internal forces and displacements. Furthermore, the internal forces obtained by the continuous method are high compared to the other methods when the effects on segmental joints on tunnel lining behaviour are usually considered. Additionally, the bending moment of the direct method with behaviour of rotation spring linear and experimental method is comparable

Contributions à la modélisation micromécanique du comportement non linéaire de l'argilite du Callovo-Oxfordien

LILLE1-BU (590092102) / SudocSudocFranceF

Micromechanics based modeling of the Callovo-Oxfordian argillite mechanical behavior

The present study is devoted to the development and validation of a non-linear homogenization approach of the mechanical behavior of Callovo-Oxfordian argillites. The material is modelled as an heterogeneous one composed of an elastoplastic clay matrix and of linear elastic or elastic damage inclusions. The macroscopic constitutive law is obtained by adapting the Hill-type incremental method [1]. The approach consists in formulating the macroscopic tangent operator of the material from the non-linear local behavior of its phases. Due to the matrix/inclusion morphology of the microstructure of the argillites, a Mori-Tanaka scheme is considered for the localization step. The developed model is first compared to Finite-Elements calculations and then validated and applied for the prediction of the macroscopic stress-strain responses of argillites