Le Dr Anne-Laure FAUCHILLE, Research Associate, School of Materials, University of Manchester, donnera un séminaire le 4 mai 2017 de 10 à 11h à Centrale Nantes sur le sujet suivant:

Mécanismes multi-échelles de déformation et fissuration dans un milieu a microstructure : exemple expérimental des roches argileuses

Mutli-scale mechanisms of deformation and fracturing in microstructural materials: an experimental case of clayrocks subjected to desiccation

Clay rocks have been considered as potential repositories for high-level radioactive wastes at great depth in several industrial countries, because of their mechanical and microstructural properties. Nevertheless, a significant cracking due to a desaturation process of the argillaceous medium is
observed on the gallery walls in several underground research laboratories, such as the experimental platform of Tournemire in France. This desiccation cracking takes part in the so called excavation damaged zone (EDZ). The initiation and extension of the EDZ are governed by different parameters such as the material anisotropy, the initial stress field, the geometry of the gallery, the mineralogy and so on. In the Underground Laboratory of Tournemire, the desiccation cracking at the decimetre scale is organised in a network of sub-horizontal cracks parallel to the bedding planes and spaced out 64 to 100 mm, and a vertical network which shows more complex orientations. The mean crack aperture of these cracks is correlated with the relative humidity in the gallery and partially by the presence of microstructural interfaces at the micrometre scale. At a much lower scale, some desiccation fractures with apertures of 1 μm were observed under environmental scanning electron microscopy on Callovo-Oxfordian clays rocks from Bure laboratory (France). However, these previous observations were all obtained at very different space scales, and the phenomenological links or causal relationships between them are still unclear.

The main objective of this talk is providing new correlations between hydric strains, desiccation crack apertures at state variables (relative humidity and water content) and microstructure at various scales from the μm to the cm, which are rarely compared in the context of clay rocks. A new experimental setup using a quantitative superimposition between digital image correlation and scanning electron microscopy will be presented, to improve the identification of the micromechanisms governing desiccation cracking at various scales.