Essai et simulation du comportement d'une structure sandwich entaillée jusqu'à rupture

International audienceUn nouvel essai sur une éprouvette sandwich entaillée de grande dimension et soumise à un chargement statique de flexion/torsion est proposé. L'éprouvette entaillée, constitué de plis tissés en verre/époxy et de mousse, ressemble à une pièce représentative d’une structure aéronautique présentant une fissure. L'objectif de l'essai est de générer l'initiation et la propagation stable d'une fissure au bord de l'entaille dans le cas d'un chargement complexe caractéristique d'une structure réelle. Cet essai est suivi par un système de corrélation d'image numérique 3D. Le résultat de l'essai est utilisé pour démontrer la validité d'un modèle basé sur la mécanique de l'endommagement et un critère non local. La très bonne corrélation entre la simulation et l'expérience au niveau des champs et de l'effort à rupture montre l’efficience de la méthode proposée

Climate change projections using the IPSL-CM5 Earth System Model: from CMIP3 to CMIP5

We present the global general circulation model IPSL-CM5 developed to study the long-term response of the climate system to natural and anthropogenic forcings as part of the 5th Phase of the Coupled Model Intercomparison Project (CMIP5). This model includes an interactive carbon cycle, a representation of tropospheric and stratospheric chemistry, and a comprehensive representation of aerosols. As it represents the principal dynamical, physical, and bio-geochemical processes relevant to the climate system, it may be referred to as an Earth System Model. However, the IPSL-CM5 model may be used in a multitude of configurations associated with different boundary conditions and with a range of complexities in terms of processes and interactions. This paper presents an overview of the different model components and explains how they were coupled and used to simulate historical climate changes over the past 150 years and different scenarios of future climate change. A single version of the IPSL-CM5 model (IPSL-CM5A-LR) was used to provide climate projections associated with different socio-economic scenarios, including the different Representative Concentration Pathways considered by CMIP5 and several scenarios from the Special Report on Emission Scenarios considered by CMIP3. Results suggest that the magnitude of global warming projections primarily depends on the socio-economic scenario considered, that there is potential for an aggressive mitigation policy to limit global warming to about two degrees, and that the behavior of some components of the climate system such as the Arctic sea ice and the Atlantic Meridional Overturning Circulation may change drastically by the end of the twenty-first century in the case of a no climate policy scenario. Although the magnitude of regional temperature and precipitation changes depends fairly linearly on the magnitude of the projected global warming (and thus on the scenario considered), the geographical pattern of these changes is strikingly similar for the different scenarios. The representation of atmospheric physical processes in the model is shown to strongly influence the simulated climate variability and both the magnitude and pattern of the projected climate changes

A ply scale non local fibre criterion for CFRP women ply laminates structures

Non renseign

Micromechanical modelling of matrix cracks effect on shear and transverse response for unidirectional composites with a full field approach

International audienceModelling the damage of composite materials is not an easy task because different modes of ruins coexist: Fiber matrix decohesion,matrix cracks, delami-nation, and fiber cracks. In the case of laminated composites, the matrix cracks have the particularity to remain parallel to the fibers. As a consequence of the orientation of this crack network, only shear and transverse moduli in the plane of the ply are degraded in proportion to the increase of the crack density. The main point of this work is to characterize the relation linking transverse and shear damage with respect to the crack density. Following this objective, full field calculations are run using CraFT, a software developed at the LMA. The modeling is done in two steps: first the undamaged composite is homogenized, then, as a second step, the damaged behavior is determined by introducing cracks into the healthy composite. The behavior is calculated from an optimal size of RVE (Representative Volume Element) in order to determine numerically the relation between transverse and shear moduli variables

DAMAGE EVOLUTION UNDER LONG-TERM, HIGH AND CONSTANT LOADING OF A CARBON/EPOXY LAMINATE

International audienceWhen a composite material of carbon fiber and epoxy resin is subjected to mechanical loading, different phenomena can lead to changes in its properties or even irreversible damage (propagation of cracks, debonding between folds, fiber breakage). The objective of this work is to study, under high loads and long periods, the propagation of transverse microcracks (diffuse damage) until the fracture of the laminate under matrix modes (instability). Since long term tests are necessary to characterize the damage evolution as well as the creep and stress relaxation phenomena, a testing machine was carried out. Optimal orientations ([45°,-45°]ns and [60°,-60°]ns) and specimen shape have been defined to study this phenomena. Experimental results are presented here and it is observed an evolution of the matrix damage under constant loads. This evolution is compared to the evolution of the matrix damage in the case of cyclic loads (fatigue) which in this latter case is faster

Multiscale simulation and experimental analysis of damping in CFRP structures containing rubber

International audienceThis paper gives an intuitive numerical multi-scale method to estimate damping in anisotropic viscoelastic hybrid composite structures using finite element analysis. Different CFRP-R (CFRP with Rubber) architectures, both microstructural and macrostructural, are studied and compared in order to maximize damping but also to minimize rigidity loss. Homogenization by virtual DMA in frequency domain is performed on representative volume elements (RVE) to obtain the effective viscoelastic behaviour of every hybrid microstructure. The effective behaviours are used to define mechanical behaviour of laminates on which vibratory simulations are performed. Interesting and advanced simulations are discussed regarding materials parameters and geometrical aspects and are compared to experimental results

Composite sandwich structure with a notch in bending/torsion: test and simulation up to rupture

International audienceIt is proposed a new test on a large sandwich notched specimen loaded in static bending/torsion and consisting of woven fabric GFRP laminates and foam material. The aim of this test is to generate crack initiation and propagation around the notch. This test is used to validate a model based on continuum damage mechanics and a nonlocal criterion developed since several years. Numerical results compared to DIC and the force at failure show the efficiency of the proposed approach

Test and simulation of composite sandwich structure with a notch up to failure

International audienceIt is proposed a new test on a large sandwich notched specimen loaded in static bending/torsion and consisting of woven fabric GFRP laminates and foam material. The aim of this test is to generate crack initiation and propagation around the notch. This test is used to validate a model based on continuum damage mechanics and a nonlocal criterion developed since several years. Numerical results compared to DIC and the force at failure show the efficiency of the proposed approach

Estimation des contraintes résiduelles dans des pièces composites imprimées 3D HT-FDM. Estimation of residual stresses in printed composite (SPC) parts

peer reviewedCe travail, résultat d’une thèse doctorale en collaboration de l’université d’Aix-Marseille et l’Université du Luxembourg, possède la finalité d’utiliser les outils de la mécanique des solides et la mécanique computationnelle dans la prédiction des contraintes internes dans les pièces composites obtenus par une procédure d’impression HT-FDM (High Temperature Fused Deposition Modeling). Le travail considère le problème multiéchelle par une procédure d’homogénéisation à deux étapes ; en combinant des techniques d’homogénéisation en champ moyen à description probabiliste des paramètres microstructuraux, avec des approches par champ complet pour l’estimation du comportement macroscopique, tout en gardant une représentation mathématique du matériau qui est fidèle au comportement réel du polymère, en conclusion, on cherche une prédiction du comportement thermo-viscoélastique effective d’une pièce imprimé avec une représentation mathématique qui est sensible aux variations dans la cinétique des charges mécaniques et thermiques. Et en fin en présentant un scénario fiable et plausible du prototypage virtuel en impression 3D