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Comportement du béton sous chargement triaxial sévère : analyse tomographique et modélisation à l'échelle mésoscopique

Abstract : This thesis focuses on the behavior of concrete under severe triaxial loading. The stress levels studied are, more accurately, those caused by a missile impact. The broader context of this study is to improve the understanding of infrastructures under dynamic loading type impact, which can generate mean stresses in the concrete of the order of GPa. Quasi-static tests are needed to characterize the behavior of a material in a homogeneous state of stress. The work presented in this thesis proposes the investigation of damage mechanisms of concrete during triaxial loading tests. For this, two innovative machines are used : a large capacity triaxial press and an X-ray computed tomography instrument. The process of conducting tests is to scan concrete samples in the undamaged state and after each loading cycle (load-unload) performed by mean of the triaxial press. The images from these tomographic examinations allow to assess the evolution of the mesostructure of concrete (scale where aggregates and macropores appear) for different loading paths and loading levels. Two samples were tested according to this process. The first one, at relatively low confinement (50 MPa), shows that the mechanisms leading to failure are very localized and mainly initiated at the microscopic scale. The second one, tested at a very high confinement (650 MPa), has a diffuse damage with also a localized failure mechanism. A mesoscopic discrete element model is also presented in this manuscript. The originality of this approach lies in the predictive model developed on one hand, the behavior of mortar, aggregates or their interaction is identified a priori or from tests on mortar and rock. On the other hand, the method of constructing the discrete element mesh is based on the 3D segmentation of tomographic images what allows a comparison between fracture facies of both experiment and numerical specimens. This model leads to a good prediction of the triaxial behavior of concrete and appears to be a promising tool to study damage mechanisms and the influence of parameters of concrete composition.
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Submitted on : Wednesday, May 11, 2011 - 10:54:15 AM
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Cédric Poinard. Comportement du béton sous chargement triaxial sévère : analyse tomographique et modélisation à l'échelle mésoscopique. Matériaux. Université de Grenoble, 2010. Français. ⟨tel-00592103⟩

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