Experimental characterization of a cohesive zone model using Digital Image Correlation

International audienceIn recent years, cohesive-zone models have been formulated and used to numerically simulate the fracture of solid materials. Cohesive-zone models presented in the literature involve a 'jump' in the displacement field describing crack onset within a predefined interface network corresponding to interfaces between elements of the finite element (FE) mesh. The introduction of a virtual displacement jump is convenient to numerically manage micro-crack or void initiation, growth and coalescence. Until now, the forms of interface laws were mainly chosen in connection with the overall responses of specimens when subjected to standard loadings. In this study, a cohesive-zone model identification method is proposed based on the local material behaviour derived from kinematical measurements obtained by digital image correlation (DIC). A series of tensile loadings were performed for several damageable elastic-plastic materials on standard tensile specimens. Kinematical data analysis enabled early detection and tracking of the zone where the crack occurs. The results of this study highlight the potential of DIC to quantify damage and show how damage assessments can be inserted in cohesive-zone model identification

Etude expérimentale et numérique de la diffusion de la chaleur dans la peau : influence de la circulation sanguine

Agir rapidement sur des brûlures corporelles, pour éviter la propagation des lésions due à la diffusion de la chaleur est un des objectifs à long terme de cette étude. L'article présente une expérimentation et propose un modèle numérique de la peau de l'avant-bras. L'évolution de la chaleur est mesurée avec une caméra infrarouge et les résultats ont montré une très nette influence de la circulation sanguine sur la diffusion de la température

Mise en évidence et quantification des couplages thermomécaniques réversibles et irréversibles dans les bétons sains et endommagés par des cycles gel-dégel

International audienceShowing and measuring of reversible or not thermomechanical couplings in undamaged and freezing/thawing damaged concrete We study thermal phenomena which occur during compressive loading tests on some damaged or not concrete. Two calorific effects are shown through an experimental study using infrared thermography. The first, intrinsically reversible, is due to the thermoelastic coupling. The second is due to damage concrete state.À partir de l'observation fine par thermographie infrarouge des phénomènes thermiques mis en jeu lors de sollicitations de compression quasi-statiques, sont identifiées et quantifiées l'incidence de l'effet thermoélastique et celle de la dissipation intrinsèque associée à l'état d'endommagement d'un béton ayant subi des cycles gel-dégel

Comportement thermomécanique d'un béton ordinaire en compression cyclée : expérience et modélisation

International audienceLes faibles phénomènes thermiques apparaissant lors d’essais de compression sur un bétonordinaire ont pu être observés par thermographie infrarouge. Pour leur modélisation etleur interprétation, il est proposé une extension thermomécanique du modèle élastiqueendommageable de M. Frémond et B. Nedjar. Elle permet un dialogue intéressant entreles résultats expérimentaux et ceux obtenus par simulation numérique.Infrared thermography observations permit to show thermal phenomena occurring on aplain concrete during a compressive test. A modelling of the thermomechanical behaviourof this materials is proposed as an extension of M. Frémond and B. Nedjar’s model. Itpermits an interesting dialog between the experimental results and those obtained bya numerical simulation of a simple compressive test

Mise en évidence par granularité en lumière blanche de phénomènes de multilocalisation de la déformation pour les bétons de poudres réactivessollicités en traction

International audienceShowing of multilocalisation strain phenomena occurring in reactive powders concrete during tensile tests by digital speckle images correlation in lighting white mode From kinematic observations by granularity in whiting light mode based on a technique of digital speckle images correlation, the behaviour in tension of a reactive powders concrete is studied. The measures show several localisation areas of the deformation fields and the role of the fibres in the transmission of the stresses in the neighbourhood of a damaged area.Le comportement en traction d'un béton de poudres réactives est étudié à partir d'obser-vations cinématiques par granularité en lumière blanche fondées sur une technique d'inter-corrélation d'images. Les mesures mettent en évidence pour des BPR suffisamment fibrés, à la différence des bétons ordinaires, l'apparition systématique de plusieurs zones de loca-lisation de la déformation et le rôle des fibres dans la redistribution des efforts au voisinage d'une zone fissurée

Poutre de grande portée en pierre précontrainte

National audienc

Grey and harbour seals in France : distribution at sea, connectivity and trends in abundance at haulout sites

Grey (Halichoerus grypus) and harbour seals (Phoca vitulina) are sympatric seal species, but they display distinct strategies of habitat use and connectivity between haulout sites. The distribution patterns and variations in relative abundance of both species were investigated along the French coast of the English Channel, at the southern limit of their range where seal numbers are increasing. Regular censuses conducted at all main haulout sites in mainland France showed significant seasonal variations at most sites, with more harbour seals counted during summer (breeding and moulting seasons), and more grey seals during summer only in the eastern English Channel. Trends in maximum haulout numbers at haulout sites showed a significant increase over the last five years, ranging from 9.7 to 30.9% per year for harbour seals, and from 5.8% (in the western English Channel) to 49.2% (in the eastern English Channel) per year for grey seals. These rates of increase in grey seal numbers are not linked to local pup production and most probably result from seal movements from the southwest British Isles and the North Sea, respectively. Aerial surveys conducted across the English Channel showed that most seal observations at sea were concentrated in the north-eastern English Channel. Telemetry showed that the 28 harbour seals tracked remained highly coastal, within a radius of 100 km from their haulout sites, and did not move to other known colonies. Grey seals moved much greater distances, reaching up to 1200 km from their capture site. More than half of the 45 grey seals tracked crossed the English Channel, especially during the breeding season, moving to known colonies in the southwest British Isles and the North Sea. Combining individual tracks and long-term surveys of the seal populations allowed a better understanding of the dynamics of these populations and their connectivity at a larger regional scale. The findings provide direct information for the management of grey and harbour seals within the frame of the Marine Strategy Framework Directive, and highlight focus areas where potential interactions between the two species should be monitored.PostprintPeer reviewe

Une étude expérimentale et une première modélisation du comportement thermomécanique endommageable de quelques bétons

MONTPELLIER-BU Sciences (341722106) / SudocSudocFranceF

Combined model of human skin - heat transfer in the vein and tissue: experimental and numerical study

International audienceThe aim of this study is to propose a combined model of heat transfer in the vein and tissue of human skin. It allows to better understand the thermomechanical behavior of the skin and its direct environment when exposed to strong thermal variations. The work is based on experimental and numerical investigations. The first experimental step consists in placing a cooled cylindrical steel bar on the skin of a human forearm and measuring the temperature change using an infrared camera. Blood circulation in the veins was seen to clearly influence heat diffusion. The second experimental step consists in measuring geometrical properties of the veins and blood velocity using an echo-Doppler probe. These experimental measurements provide a numerical model of the skin and its direct vicinity. The three-dimensional multilayer model uses Pennes equation to model biological tissue and the convective heat transport equation, to model blood. The properties of the biological materials obtained from the literature are validated by our experimentation. The numerical model is able to simulate the experimental observations, but also to estimate blood temperature and velocity in the veins