Mechanical Behavior and Microstructure Development in Consolidation of Nominally Dry Granular Salt

Abstract

Uniaxial consolidation of granular salt is carried out to study the mechanical behavior and fabric development in a material that deforms by microscopic brittle and intracrystalline-plastic processes. Dry granular salt is sieved to produce well-sorted size fractions. The granular salt is consolidated in a heated cell at axial stresses up to 90 MPa and temperatures of 100 - 200 ˚C to document stress-consolidation relationships and microstructural development. Polished and chemically-etched petrographic sections of salt samples prior to and after deformation at 150˚C are studied using transmitted- and reflected-light optical microscopy. We show that temperature has profound effect on porosity reduction during consolidation. At tested conditions, the dominant deformation mechanism is crystal plasticity; brittle deformation is largely suppressed. Samples consolidated at higher maximum axial stress develop higher overall dislocation densities. The distribution of dislocations, however, is strongly heterogeneous from grain to grain because of the complex grain-scale loading geometries and the distribution of intragranular flaws such as fluid inclusions. Static recrystallization occurs in some highly strained areas, but overall is minor at 150˚C. The experiments help to improve our understanding of consolidation, and serve to guide the fabrication of synthetic rock salt as experimental material, as well as to inform and test constitutive models of deformation of granular salt for engineering needs.