3D Dislocation Density–Based Crystal Plasticity Model for Rock Salt under Different Temperatures and Strain Rates

Abstract

Rock salt is a sedimentary rock found in nature as bedded or domal deposits due to evaporating inland seas or any enclosed bodies of saline water. Rock salt hosts caverns within the underground deposits that can potentially serve as a long-term and safe repository for carbon dioxide, radioactive nuclear waste, and the waste of oil drilling operations. The accuracy of simulating the constitutive response of rock salt hinges on the fidelity of both the engineering model and the geometrical representation of the cracked material. The main constituent of rock salt is the halite mineral, which has a building block of sodium chloride (NaCl), forming a cubic crystal system with a constitutive response that is dependent on strain rate and deforming temperature. The constitutive behavior of rock salt has so far been simulated using phenomenological creep models that lack the representation of its microscale crystal structure. Accordingly, this paper seeks to develop a three-dimensional (3D) dislocation density–based crystal plasticity model that can enhance the current numerical representation of crack mechanisms and growth in rock salt. The model was introduced and then validated using literature experiments on single-crystal specimens of artificial rock salt tested in triaxial extension against different crystal orientations, a wide range of strain rates, and various temperatures. When implementing the model to predict the response of natural single-crystal rock salt specimens tested in unconfined one-dimensional (1D) compression, the model parameters needed fine recalibration via a genetic optimization procedure due to the existence of cleavage planes in the natural rock salt material. The viscoplastic nature of the calibrated model was also evaluated to accurately replicate the ratcheting plastic deformations in natural rock salt specimens when tested in cyclic unconfined 1D compression. Overall, the proposed dislocation density–based crystal plasticity model form is able, through reasonable parameter adjustment, to simulate both the monotonic and cyclic response of high-purity artificial and natural single-crystal rock salt.