Effect of the long-range van der Waals forces on the motion of an elongated bubble through a shear-thinning fluid

International audienceWe study the influence of the long-range van der Waals forces on the motion of an elongated bubble in a capillary tube filled with a non-Newtonian shear-thinning fluid. Using the lubrication theory we extend the classical Bretherton thin film model to include the Lifshitz form of the disjoining pressure in the context of shear-thinning fluids to investigate how much it impacts on the bubble characteristics in both planar and circular geometries. The fluid rheology is described by the Ellis viscosity model so that both the low-shear-rate Newtonian viscosity and the shear-thinning effects are properly described. Interestingly, the stabilizing effect of the disjoining pressure change the shape of the elongated bubble suppressing the undulations at the rear of the elongated bubble. In addition, thanks to a proper rescaling of the effective viscosity, we propose a generalization of the scaling law for the dimensionless film thickness that applies to both Newtonian and shear-thinning fluids. Such scaling law captures the ultra-low capillary number regime (dominated by the disjoining pressure) where the film thickness assumes a constant value and the low capillary number regime (dominated by surface tension) where the film thickness follows the classical 2/3 scaling law typical of thin-film problems. We also explore the limiting case of a power-law fluid

La mise en œuvre du Green IT : comprendre l’émergence des paradoxes entre transformation numérique et enjeux environnementaux

International audienceUne démarche de transformation numérique dans les organisations ne peut plus échapper à la prise en considération des conséquences environnementales que les Technologies de l’Information et de la Communication (TIC) engendrent. Néanmoins, cet enjeu de transformation numérique conduit à interroger les tensions pouvant émerger entre des injonctions environnementales et économiques qui peuvent être envisagées comme paradoxales. À travers l’articulation du cadre théorique « Technologie, Organisation, Environnement » (TOE) (Depietro et al., 1990) et celui des paradoxes (Lewis, 2000 ; Poole & Van de Ven, 1989 ; Smith & Lewis, 2011), notre recherche, à travers une étude de cas encastrée, contribue à une meilleure compréhension des paradoxes liés au Green IT et de leur émergence. Ces derniers sont liés à la fois à la prise de décision ainsi qu’à l’utilisation des outils numériques qui peuvent émerger au cours du processus de transformation numérique

From surface damage to subsurface evolution: A multiscale microstructural analysis of grease-lubricated bearings under false brinelling

International audienceFew studies dedicated to the service life of thrust bearings have mostly focused on surface wear, without investigating subsurface microstructural changes or establishing any correlation between these evolutions and the underlying wear mechanisms. This study investigates wear mechanisms and microstructural changes in grease-lubricated thrust ball bearings under false brinelling. Perfluorinated grease degradation increases friction and shear, promoting adhesive and oxidative wear. KAM and EBSD analyses reveal plastic deformation localized in martensite, with fragmentation. To enable a finer analysis of subsurface damage, techniques such as TEM and SAED analyses show nanostructuring of martensite near the surface and carbide-matrix interactions without decohesion. Inter-carbide spacing measurements and TEM cross-sections confirm carbide clustering in high shear zones. Reorientation of carbides under false brinelling stresses favors crack propagation. Partial carbide dissolution, identified via TEM, leads to iron and carbon diffusion into the martensite, increasing hardness and brittleness. This promotes crack initiation, flaking, and debris formation, which intensify local stresses. These results highlight the interplay between lubrication efficiency, microstructural evolution, and damage mechanisms

Impact of load shedding on lot sizing problem

International audienc

Réseaux télécom et soutenabilité forte

National audienc

Symbioses Territoriales Andrézieux-Bouthéon

International audienc

Comment aborder les corrélations entre les indicateurs pour éviter les biais dans la prise de décision multicritères?

International audienceL’opérationnalisation de l’économie circulaire repose sur des systèmes complexes avec plusieurs parties prenantes, chaines de valeurs et échelles territoriales. Ces parties prenantes interviennent dans le processus de décision qui implique l’usage d’indicateurs variés.Les indicateurs servent à évaluer les performances, les retombées et les impacts associés à l’implémentation des stratégies de circularité. Leur fonction demeure simple : donner une indication et ainsi guider la décision. Or, derrière cette simplicité se pose la question de l’usage de plusieurs indicateurs corrélés entre eux. Si elle n’est pas maitrisée, cette corrélation entraîne un biais dans la prise de décision par la redondance de l’information. Cette communication détaille une nouvelle méthode pour considérer les corrélations lors de la prise de décision multicritères à une étape de pondération. La méthode se repose sur les préférences des parties prenantes et les informations contenues dans les indicateurs. Trois études de cas permettent la validation de la méthode à l’aide d’un cadre qualitatif d’analyse des changements. Ces études portent sur l’économie circulaire, le développement durable et la productivité agricole au sein de l’Union européenne.Finalement, cette communication détaille la contribution de la méthode au processus de prise de décision. Elle met aussi en lumière des perspectives de recherche, dont des considérations sur la mise en application auprès de parties prenantes

Influence of sewage sludge ashes on the performance of cementitious composites

International audienceParticular attention has been paid to replacing cement with sewage sludge ash (SSA) in order to improve circular economy practices and reduce carbon emissions linked to cement production. This work explored the effect of SSA on the hydration kinetics, phase assemblage and early properties SSA-blended composites. Four SSA were used, originating from a unique sewage sludge incineration process, with limestone injection for toxic gas treatment. The findings showed that SSA contained residual limestone. The lime content varied between SSA, creating a more or less exothermic hydration reaction at early age due to its dissolution. The flue gas desulphurisation by limestone led to the formation of calcium sulfate wich delayed the sulfate depletion peak. The introduction of SSA in cement delayed also the alite peak reaction but the delay in the setting times were <30 min. The mineralogic analyses of 30%SSA-blended cement paste highlighted the formation of monocarbonate due to the residual calcite content brought by SSA. Moreover, SSA insoluble phases (whitlockite, hematite, quartz, biotite, and illite) were still detected and quantified in the pastes. The hydration degree of cement paste with SSA was comparable to that of the reference OPC, showing that SSA did not hinder the hydration reaction. Finally, SSA-blended mortars exhibited a sligth reduction in compressive strength, which increased with the substitution rate but remained below 14% for 30% SSA (58 MPa) compared to the reference mortar (68 MPa)

Le modèle permaindustriel, une stratégie d’anticipation pour le vivant sous le regard des capacités dynamiques

National audienc

An innovative setup to study the breakage of SiO2 agglomerates under shear stress

International audienceGranular materials are involved in many industrial processes such as mixing, compaction, etc. When the granular material is in the form of agglomerates, i.e. an assembly of aggregates, particle fragmentation might occur under shear stress. This can either be a benefit for the process and should be controlled, or an issue which must be avoided. This paper focuses on the study of agglomerate breakage under shear stress, presenting a new experimental set-up designed for industrial contexts. The stress range selected lead to two distinct regimes: at low stresses, agglomerates break into individualized fragments, while high stresses fines agglomeration leads to the formation of flakes. These observations contribute to quantify the breakage stress of initial agglomerates, showing agreement with findings in the existing literature