A true triaxial experimental study on porous Vosges sandstone: from strain localization precursors to failure using full-field measurements
Résumé
This study systematically investigates the effect of deviatoric loading paths on diffuse and localized deformation developing during the mechanical loading of a high porosity (20%) Vosges sandstone (Eastern France). Laboratory scale experiments are performed using a high pressure true triaxial apparatus, designed to provide access to full-field surface kinematics at high spatial and temporal resolutions during the loading phase. The true triaxial experiments, with independent control of the three principal stress, are conducted at two constant mean stresses, in the brittle-ductile transition regime, and at five prescribed Lode angles, from axisymmetric compression (ASC) to axisymmetric extension (ASE). First, the transition from diffuse towards localized deformation is analyzed in different loading increments and shows an intermediate step of early strain localization, characterized by a large number of early deformation bands developing well before the stress peak and with a predominantly dilatant behavior. Secondly, the evolution of the mechanical behavior and localization patterns, such as deformation band angles and localized dilatancy, indicate a transition from the brittle regime to the ductile regime that is not only dependent on an increase in the mean stress, but also on a decrease in the Lode angle. The analysis of fullfield measurements also provides insights into the emergence and evolution of local strains, as deformation structures coalesce or relocate and different failure modes develop depending on the prescribed stress paths.
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