Experimental Characterization of Microstructure Development for Calculating Fabric and Stiffness Tensors in Salt Rock

Abstract

Uniaxial consolidation tests were conducted on reagent-grade granular salt in dry conditions at 150 C. 2Dmicroscopic images, parallel to the axis of consolidation, were obtained at several stages of progressive consolidation from 15% to 3% porosity. Microstructure image analyses were performed to obtain probability density functions (PDFs) of the area, solidity, coordination number, orientation, elongation and roundness of the grains, as well as the PDFs of the branch lengths, branch orientations and solid volume fraction, defined locally over polygons with edges matching grain centroids. It is found that sample deformation is mostly due to grain rearrangement and that upon consolidation, grains become less convex, and elongate in the direction perpendicular to the loading axis. Four fabric tensors were calculated to assess microstructure anisotropy induced by grain orientation, branch length orientation, grain solidity and local solid volume fraction. Fabric tensors were diagonal and orthogonal. Therefore, their product was used to define a global fabric tensor, which was introduced in the expression of the stiffness tensors. The constitutive parameters were calibrated against the consolidation tests. The approach paves the way to enrich continuum damage and healing mechanics model with fabric descriptors that can play the role of internal variables.