Génie Mécaniques
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Item Caractérisation expérimentale des élastomères magnétorhéologiques anisotropes(Université M'Hamed Bougara Boumerdès : Faculté de Technologie, 2025) Bendjeddou, Walid; Aguib, Salah(Directeur de thèse)Ce travail s'inscrit dans l'étude des élastomères magnétorhéologiques anisotropes, des matériaux intelligents dont les propriétés mécaniques évoluent sous l'effet d'un champ magnétique. Une première phase de recherche bibliographique a permis d'explorer les différentes catégories de matériaux composites jusqu'aux MREs anisotropes, mettant en lumière leur structure et leurs mécanismes d'interaction avec les champs externes. Ensuite, un modèle mathématique a été développé pour exprimer le comportement sous l'effet de plusieurs paramètres, en donnant importance à l'intensité du champ magnétique et de l'orientation des chaînes de particules. Une étude expérimentale a ensuite été menée pour analyser le comportement de ces matériaux sous diverses sollicitations, notamment en fonction du taux de charge et de la fréquence d'excitation. Une caractérisation hors axe a permis d'approfondir l'effet de l'anisotropie en faisant varier l'intensité du champ magnétique et l'angle d'orientation des particules. Enfin, une validation du modèle a été effectuée par comparaison avec les résultats expérimentaux, permettant d'extraire les paramètres du modèle et d'évaluer sa capacité à décrire précisément le comportement des MREs anisotropesItem Rheology of concentrated suspensions of spherefiber fiber mixtures in view of applications to reinforced cementitious materials(Université M'Hamed Bougara : Faculté de Technologie, 2022) Meloussi, Mounir; Khzhr, Pavel(Directeur de thèse); Aguib, Salah(Directeur de thèse)Discontinuous shear thickening (DST) in dense non-Brownian suspensions is a welldocumented phenomenon in scientific research, however its origins and effects are still under discussion nowadays. Not being able to recognize the direct cause of the phenomenon represents a point of weakness in many industrial fields, especially in the field of concrete and fiber reinforced concrete production. In this thesis, we will study experimentally as well as theoretically the DST in a suspension of calcium carbonate microparticles loaded with rigid polyamide and glass fibers. The rheology of this suspension simulates the behavior of fiber-reinforced concrete. We reproduce on a reduced scale different types of flows occurring in the concrete placement process, such as double-helix mixing, pumping through tubes, jet flow at the tube outlet, and we derive fundamental rheological behaviors applicable to any type of "sphere-fiber" mixtures. Using "mixing" type rheometry (double helix tools adapted to the rotational rheometer), we will first show that the addition of fibers shifts the DST transition to lower critical shear rates, which is explained by an increase in the viscosity of the suspension, so that the shear rate to reach the DST onset stress decreases. However, the mixture jams at a fiber volume fraction greater than or equal to 4% vol which is interpreted in terms of the percolation threshold of the fiber network in the shear thickening matrix of calcium carbonate. We will show in a second stage that the rheological behavior in a flow induced by a pressure gradient through a capillary remains quite similar to that in a simple shear but only at low fiber volume fractions ?? ? 1 % vol, and if the Mouney-Rabinowitch correction is correctly applied. Above this volume fraction, the flow ?? curves in the capillary rheometry become very different from those measured in simple shear likely because of microstructural difference in two different flow geometries. The theoretical model based on the homogenization approach allows to reproduce at least semi-quantitatively the flow curves in the " mixing" type and capillary rheometry at low fiber volume fractions but fails to capture microstructural changes at higher volume fractions. Finally, the instabilities of the calcium carbonate suspension jet under gravity with and without polyamide fibers will be studied. This instability is manifested by strong lateral oscillations of the axial symmetry axis of the jet accompanied by a slight undulation of the jet surface. We will perform for the first time a two-dimensional direct Fourier transform (2D DFT) analysis of the spatiotemporal variation of the jet diameter and the lateral deflection of the jet in the DST regime. We will show that the addition of polyamide fibers at different concentrations in the suspension allows for jet stability and promotes jet fractures. A theoretical explanation for the onset of jet lateral instability and the stabilizing effect of the fibers will then be developed based on the evaluations of tensile stresses and the lower and upper thresholds of the DST.