Plastic behavior of halite single-crystals at different temperatures and strain rates: New insights from in-situ experiments and full field measures

Rock salt, or halite, is a rock forming mineral with numerous applications. In the laboratory, natural or synthetized, it is an analog material for understanding of the physical properties of rocks and ductile deformation mechanisms of other crystalline classes of materials. It is thus surprising that very few studies have been devoted to the plasticity of NaCl single crystals with well documented experimental conditions. In the present study, we deform at several temperatures NaCl single crystals of selected initial orientations by uniaxial compression. The new contribution of this work resides in the multi-scale investigations, with the combination of mechanical tests and observations by optical microscopy and scanning electron microscopy. The use of digital image correlation (DIC) at these different scales allows the measure of displacements and the computation of global or full-field strains as well as very local ones during the loading history. The optical set-up provides images of two orthogonal surfaces of the samples, so that the slip lines and their orientations can be observed on two surfaces resulting in a better identification of the active slip systems. We show that for NaCl, temperature is a key parameter for the activation of slip systems. At high temperature (0.6Tf), we present the variation of the yield stress with strain rates, in the range 2×10−6 to 2×10−5s−1. The initial critical shear stress values and the hardening behavior that we have experimentally determined are essential for the implementation of crystal plasticity finite element models that will simulate the plastic behavior of polycrystalline halite.