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

Théories de l’expérience et pratique du journal

Le journal présente l’expérience comme un espace de congruence entre la théorie et la pratique, il est l’outil qui permet au praticien d’être également chercheur en adoptant une posture réflexive. Je suis assistante sociale de formation et exerce toujours cette profession, actuellement dans le champ de la psychiatrie mais pendant plusieurs années dans celui de la grande précarité. Tout en exerçant ce métier, j’ai repris il y a plusieurs années mes études en Sciences de l’Education à l’Univers..

A micromechanical model of elastoplastic and damage behavior of a cohesive geomaterial

AbstractThe present study is devoted to the development and validation of a nonlinear homogenization approach of the mechanical behavior of Callovo-Oxfordian argillites. The material is modeled as an heterogeneous composite composed of an elastoplastic clay matrix and of linear elastic or elastic damage inclusions. The macroscopic constitutive law is obtained by adapting the incremental method proposed by Hill [Hill, R., 1965. Continuum micro-mechanics of elastoplastic polycrystals. J. Mech. Phys. Solids 13, 89–101]. The approach consists in formulating the macroscopic tangent operator of the material by considering the nonlinear local behavior of each phase. Due to the matrix/inclusion morphology of the microstructure of the argillite, a Mori–Tanaka scheme is considered for the localization step. The developed model is first compared to Finite Element calculations and then validated and applied for the prediction of the macroscopic stress–strain responses of argillites

Estudio pre/post de los efectos agudos del procedimiento STENDO sobre el rendimiento de la marcha y la adaptación vascular (NIRS) en pacientes con EPOC.

Objetivos: Determinar si el dispositivo STENDO puede mejorar el rendimiento de la marcha en pacientes sintomáticos con EPOC inmediatamente después de la estimulación.Método: Se trata de un estudio experimental, intervencionista, aleatorizado, controlado con placebo (STENDO placebo-controlled) y unicéntrico. Catorce pacientes con EPOC de 67 ± 10 años se sometieron a una prueba de marcha de seis minutos (TM6) pre/post STENDO durante la cual se midieron el intercambio gaseoso pulmonar, la oxigenación muscular mediante NIRS, la saturación arterial pulmonar y el esfuerzo percibido.Resultados: La información principal recogida durante este estudio sobre STENDO muestra que TM6 no distingue ninguna diferencia significativa entre el grupo Placebo (461,7 ± 100,8 m) y el grupo Intervención (448,5 ± 36,14m). Sin embargo, se observó que el dispositivo STENDO aumentó de forma aguda el flujo sanguíneo al flexor radial del carpo en T5, T35 e inmediatamente después de la parada, en comparación con el grupo placebo (p0,05) sin efecto sobre la disnea en comparación con el grupo.Conclusiones: La comparación entre los grupos Placebo e Intervención no estableció que el dispositivo STENDO el rendimiento de la marcha en pacientes sintomáticos con EPOC inmediatamente después de la estimulación. <br /

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

A Multi-Actor Literature Review on Alternative and Sustainable Food Systems for the Promotion of Cereal Biodiversity

Organic and low-input food systems are emerging worldwide in answer to the sustainability crisis of the conventional agri-food sector. “Alternative” systems are based on local, decentralized approaches to production and processing, regarding quality and health, and short supply-chains for products with strong local identities. Diversity is deeply embedded in these food systems, from the agrobiodiversity grown in farmers’ fields, which improves resilience and adaptation, to diverse approaches, contexts and actors in food manufacturing and marketing. Diversity thus becomes a cross-sectoral issue which acknowledges consumers’ demand for healthy products. In the framework of the European project “CERERE, CEreal REnaissance in Rural Europe: embedding diversity in organic and low-input food systems”, the paper aims at reviewing recent research on alternative and sustainable food systems by adopting an innovative and participatory multi-actor approach; this has involved ten practitioners and twenty-two researchers from across Europe and a variety of technical backgrounds in the paper and analysis stages. The participatory approach is the main innovation and distinctive feature of this literature review. Partners selected indeed what they perceived as most relevant in order to facilitate a transition towards more sustainable and diversity based cereal systems and food chains. This includes issues related to alternative food networks, formal and informal institutional settings, grass root initiatives, consumer involvement and, finally, knowledge exchange and sustainability. The review provides an overview of recent research that is relevant to CERERE partners as well as to anyone interested in alternative and sustainable food systems. The main objective of this paper was indeed to present a narrative of studies, which can form the foundation for future applied research to promote alternative methods of cereal production in Europe.Peer reviewe