Quelle approche expographique pour un musée "colonial" ?

Le musée Africain de Namur est installé dans le corps de garde des anciennes casernes militaires Léopold. L’édifice a été construit en 1885, qui est aussi l’année de la Conférence de Berlin au cours de laquelle les puissances coloniales européennes se sont "partagées" l’Afrique. © F. Poncelet Fondé en 1912, dans le cadre de la propagande coloniale belge, le musée Africain de Namur a récemment connu un renouveau important, à tous les niveaux. Une période de mise en conformité (2014-2015) et ..

Utilisation de l'imagerie IR pour l'étude de la fatigue des aciers : Premières observations d'effets de surface

International audienceDe nouvelles méthodes de caractérisation de la tenue à la fatigue des matériaux métalliques par mesure thermique sont développées depuis plusieurs années. Elles donnent accès en quelques dizaines de minutes à une estimation de la limite d'endurance et de la dispersion des résultats de fatigue d'un matériau, là où plusieurs jours sont nécessaires traditionnellement. Un des axes de développement de ces méthodes consiste à caractériser à l'aide de ces techniques les effets de surface sur les propriétés à la fatigue. Pour capter l'information due à l'hétérogénéité locale provoquée par le traitement de surface, il est nécessaire de passer d'une vision moyenne à des mesures de champ. Deux points clefs peuvent être considérés pour ce passage. Le premier concerne la mesure et est traité dans cet article. Le second concerne l'identification du champ de sources locales à partir du champ de température mesurée et n'est pas traité ici. Un protocole expérimental de mesure du champ de température d'une tôle mince avec une précision suffisante (incertitude de l'ordre du milliKelvin) est présenté pour discerner des hétérogénéités de propriété à la fatigue (p. ex. surface vs. cœur). L'article expose les différentes sources d'artefacts rencontrés et les techniques utilisées pour les supprimer

Desiccation crack in lime-treated silty clay: Experimental evaluation and constitutive interpretation

peer reviewedThe present work investigates the desiccation effects on a lime-treated clayey silt. Original experimental techniques have been developed to control suction conditions (with osmotic technique) and to track volume variations and cracks occurrence upon drying. Free and constrained dryings are performed to evaluate the shrinkage potential (for free drying) and the conditions of desiccation crack triggering (upon constrained drying). Also, indirect tensile tests and uniaxial compression tests are carried out to evaluate the strength at various suctions. Those investigations have been performed on natural and lime-treated clayey silt in order to emphasis the role of the lime treatment in the triggering and/or mitigation of the cracking process. At the end, generalized effective stress framework with an effective stress parameter calibrated according to a power law is used to provide a constitutive interpretation of the occurrence of desiccation cracks in relation with the water retention properties, the soil stiffness, the tensile strength and the geometrical constraints of the soil samples. For the used compacted materials, it is demonstrated that the lime treatment postpones the occurrence of desiccation cracks and so, plays a favourable role in the stabilization of soft soils subject to drying

Probabilistic multiscale models and measurements of self-heating under multiaxial high cycle fatigue

WOSInternational audienceDifferent approaches have been proposed to link high cycle fatigue properties to thermal measurements under cyclic loadings, usually referred to as “self-heating tests.” This paper focuses on two models whose parameters are tuned by resorting to self-heating tests and then used to predict high cycle fatigue properties. The first model is based upon a yield surface approach to account for stress multiaxiality at a microscopic scale, whereas the second one relies on a probabilistic modelling of microplasticity at the scale of slip-planes. Both model identifications are cost effective, relying mainly on quickly-obtained temperature data in self-heating tests. They both describe the influence of the stress heterogeneity, the volume effect and the hydrostatic stress on fatigue limits. The thermal effects and mean fatigue limit predictions are in good agreement with experimental results for in and out-of phase tension-torsion loadings. In the case of fatigue under non-proportional loading paths, the mean fatigue limit prediction error of the critical shear stress approach is three times less than with the yield surface approach

Dissipation measurements in steel sheets under cyclic loading by use of infrared microthermography

WOSInternational audienceHeterogeneous dissipation in steel sheets due to cyclic loading is difficult to measure, especially in the transverse direction because of the high conductivity and low thickness of the sheets. The goal of this article is thus to develop an experimental protocol allowing for the dissipation field determination from infra-red thermography. The protocol is based on a specific differential measurement and an asynchronous acquisition. It reduces measurement artefacts due to coating, rigid body motion, convection, and optical deleterious effects. It is eventually applied to different specimens

Rapid multiaxial high cycle fatigue limit predictions using self-heating-based probabilistic multiscale models

Thermal measurements under multiaxial cyclic loadings are used herein to predict multiaxial fatigue properties. Two models describing random microplasticity activation via a Poisson Point Process. The thermal response is interpreted as the “mean” behaviour of the microplastic activity, whereas the fatigue limit relies on the weakest link assumption. The first model is based upon a yield surface approach to account for stress multiaxiality at a microscopic scale. The second one relies on a probabilistic modelling of microplasticity at the scale of slip-planes. Both models are identified on thermal results and a uniaxial mean fatigue limit, and then validated using fatigue limits as well as thermal responses in the case of tension-torsion loadings on tubular specimens made of medium carbon steel. They predict well hydrostatic stress, volume and proportional multiaxial effects. The model with microplasticity described at the scale of slip-planes also offers a good prediction of nonproportional mean fatigue limits (~ 5% error) whereas the other model is less predictive (~ 17% error)

Dialogue essais-modèle pour l'interprétation des liens entre mesure d'auto-échauffement sous chargement cyclique et fatigue polycyclique

WOSInternational audienceUne démarche de développement d'un modèle probabiliste à deux échelles pour la fatigue HCF des aciers est proposée. Elle est basée sur l'utilisation de mesure d'autoéchauffement sous chargements cycliques et est validée sur la base de la prévision des courbes de Wöhler d'un acier dual-phase pour différents rapport de charge

An effective stress constitutive framework for the prediction of desiccation crack in lime-treated soil: Experimental characterization and constitutive prediction

peer reviewedThe present work investigates the desiccation effects on a lime-treated silty clay. Original experimental techniques have been developed to control suction conditions (with osmotic technique), to track volume variations and cracks occurrence upon drying. Free and constrained desiccations are performed to evaluate the shrinkage potential (for free drying) and the conditions of desiccation crack triggering (upon constrained drying). Also, indirect tensile tests and uniaxial compression tests are carried out to evaluate the strength and stiffness at various suctions. Those investigations have been performed on natural and lime-treated compacted silty clay in order to emphasize the benefits of the lime treatment in the triggering and/or mitigation of the cracking process. To simulate the field conditions of compaction and obtain specimens having geomechanical properties as close as possible of the real material on site, the particular kneading compaction process in a CBR mould was used, and the final specimens were cut at required sizes with a milling machine numerically controlled by computer (CNC). At the end, generalized effective stress framework with an effective stress parameter χ calibrated according to a power law is used to provide a constitutive interpretation of the occurrence of desiccation cracks in relation with the water retention properties, the soil stiffness, the tensile strength and the geometrical constraints of the soil specimens. It is observed that the cracks initiate under positive (compressive) effective stress. For the used compacted materials, it is demonstrated that the lime treatment postpones the occurrence of desiccation cracks, that are triggered at higher suctions. So, lime treatment plays a favourable role in the reduction of shrinkage and crack occurrence of soft soils subject to drying

Hybrid Stereocorrelation Using Infrared and Visible Light Cameras

International audience3D kinematic fields are measured using an original stereovision system composed of one infrared (IR) and one visible light camera. Global stereocorrelation (SC) is proposed to register pictures shot by both imaging systems. The stereo rig is calibrated by using a NURBS representation of the 3D target. The projection matrices are determined by an integrated approach. The effect of gray level and distortion corrections is assessed on the projection matrices. SC is performed once the matrices are calibrated to measure 3D displacements. Amplitudes varying from 0 to 800 µm are well captured for in-plane and out-of-plane motions. It is shown that when known rigid body translations are applied to the target, the calibration can be improved when its actual metrology is approximate. Applications are shown for two different setups for which the resolution of the IR camera has been modified

Experimental database of mixed-mode crack propagation tests performed on mortar specimens with a hexapod and full-field measurements. Part II: interactive loading

International audienceThis second paper presents a series of 4 crack propagation tests with the same experimental protocol as in a companion paper, but with some significant loading modifications. The first difference is that the loading is composed of in-plane rotation in addition to tension and shear translations. The second difference is that the loading is manually changed during the tests, depending on the crack tip location. This leads to tests with several bifurcations, and/or different loading ratios during the same test. One of them leads to mode I+II, and then mode I+III crack propagation. Some tests end with instabilities while others are controlled to be stable up to the complete failure of the specimen. In some cases, crack closure and friction between the crack faces occur