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Influence de la morphologie tridimensionnelle des phases sur le comportement mécanique de réfractaires électrofondus

Abstract : Demand of new high quality glass compositions requires a better knowledge of the design and an optimization of glass furnaces concept. Fused-cast refractories are the best candidates for this challenge. Their manufacturing process, similar to that used in metallurgical foundry,
leads to an original microstructure, very different from the ones obtained by conventional techniques (sintering).

This work aims to study the macroscopic mechanical behaviour of fused-cast refractories from the knowledge of the microstructure topology and the properties of the elementary constituents. A numerical micro-macro approach is used. Finite element modeling which
introduces explicitly the original microstructure morphology of the actual material, including phase distribution, is performed.

3D representations of the material have been characterized using high energy X-ray microtomography
at the European Synchrotron Radiation Facility (ESRF, Grenoble, France) with one of the highest resolution (0.7 microns) available on the ID19 beamline that has been used at ESRF. At first, the exploitation of these images allowed to demonstrate that both phases in the material are interconnected, contrary to sintered materials constituted of isolated grains.
The sharp imbrication of the dendrites (interlocking) creates a continuous skeleton of zirconia responsible of the high creep resistance observed at high temperature. Subsequently, the roles played by the phases at high temperature (1400°C were quantified from 3D observations of
the microstructure, using X-ray micro-tomography at room temperature, of crept samples at different strain levels. Results confirm that, at high temperature, deformation is controlled by zirconia, whereas the glassy phase does not play any structural role.

In parallel, finite element simulations have been performed to simulate some of the phenomena occuring during the stage of refractories cooling : creep at high temperature and damage at low temperature. 3D grids were built from the stack of segmented images :
(i) first a triangulated closed surface domain is obtained using the marching cube algorithm from 3D voxels, (ii) then an unstructured tetrahedral mesh is built on the basis of the surface triangulation using advancing front method. The creep law of the zirconia skeleton is identified by an inverse method at 1400C, from its 3D real morphology. Numerical creep tests were performed and compared with experiments. A good agreement is revealed. Afterwards, the objective was to simulate the end of cooling (thermo-elastoviscoplastic simulations). The large size of the volumes implies grids with a high number of nodes, that require the use of a large number of parallel processors in order to perform finite element calculations. In our case, 12 bi-processors have been used (time of calculation : 36 hours). Predictions allow to quantify the level of stresses in the material caused by the differences in thermal expansion between the constituents. The large stress values calculated explain the observed microcracking of the glassy phase or of the interfaces during cooling. To quantify the risk of damage in the glassy phase, an uncoupled damage model based on the maximum positive eigen stress criterion has
been formulated.
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Kamel Madi. Influence de la morphologie tridimensionnelle des phases sur le comportement mécanique de réfractaires électrofondus. Mécanique [physics.med-ph]. École Nationale Supérieure des Mines de Paris, 2006. Français. ⟨tel-00147059⟩

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